Squashed 'vendor/github.com/golang/groupcache/' content from commit 604ed57

git-subtree-dir: vendor/github.com/golang/groupcache
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.gitignore

@@ -0,0 +1 @@
+*~

LICENSE

@@ -0,0 +1,191 @@
+Apache License
+Version 2.0, January 2004
+http://www.apache.org/licenses/
+
+TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
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+   Licensed under the Apache License, Version 2.0 (the "License");
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+     http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.

README.md

@@ -0,0 +1,73 @@
+# groupcache
+
+## Summary
+
+groupcache is a caching and cache-filling library, intended as a
+replacement for memcached in many cases.
+
+For API docs and examples, see http://godoc.org/github.com/golang/groupcache
+
+## Comparison to memcached
+
+### **Like memcached**, groupcache:
+
+ * shards by key to select which peer is responsible for that key
+
+### **Unlike memcached**, groupcache:
+
+ * does not require running a separate set of servers, thus massively
+   reducing deployment/configuration pain.  groupcache is a client
+   library as well as a server.  It connects to its own peers.
+
+ * comes with a cache filling mechanism.  Whereas memcached just says
+   "Sorry, cache miss", often resulting in a thundering herd of
+   database (or whatever) loads from an unbounded number of clients
+   (which has resulted in several fun outages), groupcache coordinates
+   cache fills such that only one load in one process of an entire
+   replicated set of processes populates the cache, then multiplexes
+   the loaded value to all callers.
+
+ * does not support versioned values.  If key "foo" is value "bar",
+   key "foo" must always be "bar".  There are neither cache expiration
+   times, nor explicit cache evictions.  Thus there is also no CAS,
+   nor Increment/Decrement.  This also means that groupcache....
+
+ * ... supports automatic mirroring of super-hot items to multiple
+   processes.  This prevents memcached hot spotting where a machine's
+   CPU and/or NIC are overloaded by very popular keys/values.
+
+ * is currently only available for Go.  It's very unlikely that I
+   (bradfitz@) will port the code to any other language.
+
+## Loading process
+
+In a nutshell, a groupcache lookup of **Get("foo")** looks like:
+
+(On machine #5 of a set of N machines running the same code)
+
+ 1. Is the value of "foo" in local memory because it's super hot?  If so, use it.
+
+ 2. Is the value of "foo" in local memory because peer #5 (the current
+    peer) is the owner of it?  If so, use it.
+
+ 3. Amongst all the peers in my set of N, am I the owner of the key
+    "foo"?  (e.g. does it consistent hash to 5?)  If so, load it.  If
+    other callers come in, via the same process or via RPC requests
+    from peers, they block waiting for the load to finish and get the
+    same answer.  If not, RPC to the peer that's the owner and get
+    the answer.  If the RPC fails, just load it locally (still with
+    local dup suppression).
+
+## Users
+
+groupcache is in production use by dl.google.com (its original user),
+parts of Blogger, parts of Google Code, parts of Google Fiber, parts
+of Google production monitoring systems, etc.
+
+## Presentations
+
+See http://talks.golang.org/2013/oscon-dl.slide
+
+## Help
+
+Use the golang-nuts mailing list for any discussion or questions.

byteview.go

@@ -0,0 +1,160 @@
+/*
+Copyright 2012 Google Inc.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package groupcache
+
+import (
+	"bytes"
+	"errors"
+	"io"
+	"strings"
+)
+
+// A ByteView holds an immutable view of bytes.
+// Internally it wraps either a []byte or a string,
+// but that detail is invisible to callers.
+//
+// A ByteView is meant to be used as a value type, not
+// a pointer (like a time.Time).
+type ByteView struct {
+	// If b is non-nil, b is used, else s is used.
+	b []byte
+	s string
+}
+
+// Len returns the view's length.
+func (v ByteView) Len() int {
+	if v.b != nil {
+		return len(v.b)
+	}
+	return len(v.s)
+}
+
+// ByteSlice returns a copy of the data as a byte slice.
+func (v ByteView) ByteSlice() []byte {
+	if v.b != nil {
+		return cloneBytes(v.b)
+	}
+	return []byte(v.s)
+}
+
+// String returns the data as a string, making a copy if necessary.
+func (v ByteView) String() string {
+	if v.b != nil {
+		return string(v.b)
+	}
+	return v.s
+}
+
+// At returns the byte at index i.
+func (v ByteView) At(i int) byte {
+	if v.b != nil {
+		return v.b[i]
+	}
+	return v.s[i]
+}
+
+// Slice slices the view between the provided from and to indices.
+func (v ByteView) Slice(from, to int) ByteView {
+	if v.b != nil {
+		return ByteView{b: v.b[from:to]}
+	}
+	return ByteView{s: v.s[from:to]}
+}
+
+// SliceFrom slices the view from the provided index until the end.
+func (v ByteView) SliceFrom(from int) ByteView {
+	if v.b != nil {
+		return ByteView{b: v.b[from:]}
+	}
+	return ByteView{s: v.s[from:]}
+}
+
+// Copy copies b into dest and returns the number of bytes copied.
+func (v ByteView) Copy(dest []byte) int {
+	if v.b != nil {
+		return copy(dest, v.b)
+	}
+	return copy(dest, v.s)
+}
+
+// Equal returns whether the bytes in b are the same as the bytes in
+// b2.
+func (v ByteView) Equal(b2 ByteView) bool {
+	if b2.b == nil {
+		return v.EqualString(b2.s)
+	}
+	return v.EqualBytes(b2.b)
+}
+
+// EqualString returns whether the bytes in b are the same as the bytes
+// in s.
+func (v ByteView) EqualString(s string) bool {
+	if v.b == nil {
+		return v.s == s
+	}
+	l := v.Len()
+	if len(s) != l {
+		return false
+	}
+	for i, bi := range v.b {
+		if bi != s[i] {
+			return false
+		}
+	}
+	return true
+}
+
+// EqualBytes returns whether the bytes in b are the same as the bytes
+// in b2.
+func (v ByteView) EqualBytes(b2 []byte) bool {
+	if v.b != nil {
+		return bytes.Equal(v.b, b2)
+	}
+	l := v.Len()
+	if len(b2) != l {
+		return false
+	}
+	for i, bi := range b2 {
+		if bi != v.s[i] {
+			return false
+		}
+	}
+	return true
+}
+
+// Reader returns an io.ReadSeeker for the bytes in v.
+func (v ByteView) Reader() io.ReadSeeker {
+	if v.b != nil {
+		return bytes.NewReader(v.b)
+	}
+	return strings.NewReader(v.s)
+}
+
+// ReadAt implements io.ReaderAt on the bytes in v.
+func (v ByteView) ReadAt(p []byte, off int64) (n int, err error) {
+	if off < 0 {
+		return 0, errors.New("view: invalid offset")
+	}
+	if off >= int64(v.Len()) {
+		return 0, io.EOF
+	}
+	n = v.SliceFrom(int(off)).Copy(p)
+	if n < len(p) {
+		err = io.EOF
+	}
+	return
+}

byteview_test.go

@@ -0,0 +1,142 @@
+/*
+Copyright 2012 Google Inc.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package groupcache
+
+import (
+	"fmt"
+	"io"
+	"io/ioutil"
+	"testing"
+)
+
+func TestByteView(t *testing.T) {
+	for _, s := range []string{"", "x", "yy"} {
+		for _, v := range []ByteView{of([]byte(s)), of(s)} {
+			name := fmt.Sprintf("string %q, view %+v", s, v)
+			if v.Len() != len(s) {
+				t.Errorf("%s: Len = %d; want %d", name, v.Len(), len(s))
+			}
+			if v.String() != s {
+				t.Errorf("%s: String = %q; want %q", name, v.String(), s)
+			}
+			var longDest [3]byte
+			if n := v.Copy(longDest[:]); n != len(s) {
+				t.Errorf("%s: long Copy = %d; want %d", name, n, len(s))
+			}
+			var shortDest [1]byte
+			if n := v.Copy(shortDest[:]); n != min(len(s), 1) {
+				t.Errorf("%s: short Copy = %d; want %d", name, n, min(len(s), 1))
+			}
+			if got, err := ioutil.ReadAll(v.Reader()); err != nil || string(got) != s {
+				t.Errorf("%s: Reader = %q, %v; want %q", name, got, err, s)
+			}
+			if got, err := ioutil.ReadAll(io.NewSectionReader(v, 0, int64(len(s)))); err != nil || string(got) != s {
+				t.Errorf("%s: SectionReader of ReaderAt = %q, %v; want %q", name, got, err, s)
+			}
+		}
+	}
+}
+
+// of returns a byte view of the []byte or string in x.
+func of(x interface{}) ByteView {
+	if bytes, ok := x.([]byte); ok {
+		return ByteView{b: bytes}
+	}
+	return ByteView{s: x.(string)}
+}
+
+func TestByteViewEqual(t *testing.T) {
+	tests := []struct {
+		a    interface{} // string or []byte
+		b    interface{} // string or []byte
+		want bool
+	}{
+		{"x", "x", true},
+		{"x", "y", false},
+		{"x", "yy", false},
+		{[]byte("x"), []byte("x"), true},
+		{[]byte("x"), []byte("y"), false},
+		{[]byte("x"), []byte("yy"), false},
+		{[]byte("x"), "x", true},
+		{[]byte("x"), "y", false},
+		{[]byte("x"), "yy", false},
+		{"x", []byte("x"), true},
+		{"x", []byte("y"), false},
+		{"x", []byte("yy"), false},
+	}
+	for i, tt := range tests {
+		va := of(tt.a)
+		if bytes, ok := tt.b.([]byte); ok {
+			if got := va.EqualBytes(bytes); got != tt.want {
+				t.Errorf("%d. EqualBytes = %v; want %v", i, got, tt.want)
+			}
+		} else {
+			if got := va.EqualString(tt.b.(string)); got != tt.want {
+				t.Errorf("%d. EqualString = %v; want %v", i, got, tt.want)
+			}
+		}
+		if got := va.Equal(of(tt.b)); got != tt.want {
+			t.Errorf("%d. Equal = %v; want %v", i, got, tt.want)
+		}
+	}
+}
+
+func TestByteViewSlice(t *testing.T) {
+	tests := []struct {
+		in   string
+		from int
+		to   interface{} // nil to mean the end (SliceFrom); else int
+		want string
+	}{
+		{
+			in:   "abc",
+			from: 1,
+			to:   2,
+			want: "b",
+		},
+		{
+			in:   "abc",
+			from: 1,
+			want: "bc",
+		},
+		{
+			in:   "abc",
+			to:   2,
+			want: "ab",
+		},
+	}
+	for i, tt := range tests {
+		for _, v := range []ByteView{of([]byte(tt.in)), of(tt.in)} {
+			name := fmt.Sprintf("test %d, view %+v", i, v)
+			if tt.to != nil {
+				v = v.Slice(tt.from, tt.to.(int))
+			} else {
+				v = v.SliceFrom(tt.from)
+			}
+			if v.String() != tt.want {
+				t.Errorf("%s: got %q; want %q", name, v.String(), tt.want)
+			}
+		}
+	}
+}
+
+func min(a, b int) int {
+	if a < b {
+		return a
+	}
+	return b
+}

consistenthash/consistenthash.go

@@ -0,0 +1,81 @@
+/*
+Copyright 2013 Google Inc.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// Package consistenthash provides an implementation of a ring hash.
+package consistenthash
+
+import (
+	"hash/crc32"
+	"sort"
+	"strconv"
+)
+
+type Hash func(data []byte) uint32
+
+type Map struct {
+	hash     Hash
+	replicas int
+	keys     []int // Sorted
+	hashMap  map[int]string
+}
+
+func New(replicas int, fn Hash) *Map {
+	m := &Map{
+		replicas: replicas,
+		hash:     fn,
+		hashMap:  make(map[int]string),
+	}
+	if m.hash == nil {
+		m.hash = crc32.ChecksumIEEE
+	}
+	return m
+}
+
+// Returns true if there are no items available.
+func (m *Map) IsEmpty() bool {
+	return len(m.keys) == 0
+}
+
+// Adds some keys to the hash.
+func (m *Map) Add(keys ...string) {
+	for _, key := range keys {
+		for i := 0; i < m.replicas; i++ {
+			hash := int(m.hash([]byte(strconv.Itoa(i) + key)))
+			m.keys = append(m.keys, hash)
+			m.hashMap[hash] = key
+		}
+	}
+	sort.Ints(m.keys)
+}
+
+// Gets the closest item in the hash to the provided key.
+func (m *Map) Get(key string) string {
+	if m.IsEmpty() {
+		return ""
+	}
+
+	hash := int(m.hash([]byte(key)))
+
+	// Binary search for appropriate replica.
+	idx := sort.Search(len(m.keys), func(i int) bool { return m.keys[i] >= hash })
+
+	// Means we have cycled back to the first replica.
+	if idx == len(m.keys) {
+		idx = 0
+	}
+
+	return m.hashMap[m.keys[idx]]
+}

consistenthash/consistenthash_test.go

@@ -0,0 +1,110 @@
+/*
+Copyright 2013 Google Inc.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package consistenthash
+
+import (
+	"fmt"
+	"strconv"
+	"testing"
+)
+
+func TestHashing(t *testing.T) {
+
+	// Override the hash function to return easier to reason about values. Assumes
+	// the keys can be converted to an integer.
+	hash := New(3, func(key []byte) uint32 {
+		i, err := strconv.Atoi(string(key))
+		if err != nil {
+			panic(err)
+		}
+		return uint32(i)
+	})
+
+	// Given the above hash function, this will give replicas with "hashes":
+	// 2, 4, 6, 12, 14, 16, 22, 24, 26
+	hash.Add("6", "4", "2")
+
+	testCases := map[string]string{
+		"2":  "2",
+		"11": "2",
+		"23": "4",
+		"27": "2",
+	}
+
+	for k, v := range testCases {
+		if hash.Get(k) != v {
+			t.Errorf("Asking for %s, should have yielded %s", k, v)
+		}
+	}
+
+	// Adds 8, 18, 28
+	hash.Add("8")
+
+	// 27 should now map to 8.
+	testCases["27"] = "8"
+
+	for k, v := range testCases {
+		if hash.Get(k) != v {
+			t.Errorf("Asking for %s, should have yielded %s", k, v)
+		}
+	}
+
+}
+
+func TestConsistency(t *testing.T) {
+	hash1 := New(1, nil)
+	hash2 := New(1, nil)
+
+	hash1.Add("Bill", "Bob", "Bonny")
+	hash2.Add("Bob", "Bonny", "Bill")
+
+	if hash1.Get("Ben") != hash2.Get("Ben") {
+		t.Errorf("Fetching 'Ben' from both hashes should be the same")
+	}
+
+	hash2.Add("Becky", "Ben", "Bobby")
+
+	if hash1.Get("Ben") != hash2.Get("Ben") ||
+		hash1.Get("Bob") != hash2.Get("Bob") ||
+		hash1.Get("Bonny") != hash2.Get("Bonny") {
+		t.Errorf("Direct matches should always return the same entry")
+	}
+
+}
+
+func BenchmarkGet8(b *testing.B)   { benchmarkGet(b, 8) }
+func BenchmarkGet32(b *testing.B)  { benchmarkGet(b, 32) }
+func BenchmarkGet128(b *testing.B) { benchmarkGet(b, 128) }
+func BenchmarkGet512(b *testing.B) { benchmarkGet(b, 512) }
+
+func benchmarkGet(b *testing.B, shards int) {
+
+	hash := New(50, nil)
+
+	var buckets []string
+	for i := 0; i < shards; i++ {
+		buckets = append(buckets, fmt.Sprintf("shard-%d", i))
+	}
+
+	hash.Add(buckets...)
+
+	b.ResetTimer()
+
+	for i := 0; i < b.N; i++ {
+		hash.Get(buckets[i&(shards-1)])
+	}
+}

groupcache.go

@@ -0,0 +1,455 @@
+/*
+Copyright 2012 Google Inc.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// Package groupcache provides a data loading mechanism with caching
+// and de-duplication that works across a set of peer processes.
+//
+// Each data Get first consults its local cache, otherwise delegates
+// to the requested key's canonical owner, which then checks its cache
+// or finally gets the data.  In the common case, many concurrent
+// cache misses across a set of peers for the same key result in just
+// one cache fill.
+package groupcache
+
+import (
+	"errors"
+	"math/rand"
+	"strconv"
+	"sync"
+	"sync/atomic"
+
+	pb "github.com/golang/groupcache/groupcachepb"
+	"github.com/golang/groupcache/lru"
+	"github.com/golang/groupcache/singleflight"
+)
+
+// A Getter loads data for a key.
+type Getter interface {
+	// Get returns the value identified by key, populating dest.
+	//
+	// The returned data must be unversioned. That is, key must
+	// uniquely describe the loaded data, without an implicit
+	// current time, and without relying on cache expiration
+	// mechanisms.
+	Get(ctx Context, key string, dest Sink) error
+}
+
+// A GetterFunc implements Getter with a function.
+type GetterFunc func(ctx Context, key string, dest Sink) error
+
+func (f GetterFunc) Get(ctx Context, key string, dest Sink) error {
+	return f(ctx, key, dest)
+}
+
+var (
+	mu     sync.RWMutex
+	groups = make(map[string]*Group)
+
+	initPeerServerOnce sync.Once
+	initPeerServer     func()
+)
+
+// GetGroup returns the named group previously created with NewGroup, or
+// nil if there's no such group.
+func GetGroup(name string) *Group {
+	mu.RLock()
+	g := groups[name]
+	mu.RUnlock()
+	return g
+}
+
+// NewGroup creates a coordinated group-aware Getter from a Getter.
+//
+// The returned Getter tries (but does not guarantee) to run only one
+// Get call at once for a given key across an entire set of peer
+// processes. Concurrent callers both in the local process and in
+// other processes receive copies of the answer once the original Get
+// completes.
+//
+// The group name must be unique for each getter.
+func NewGroup(name string, cacheBytes int64, getter Getter) *Group {
+	return newGroup(name, cacheBytes, getter, nil)
+}
+
+// If peers is nil, the peerPicker is called via a sync.Once to initialize it.
+func newGroup(name string, cacheBytes int64, getter Getter, peers PeerPicker) *Group {
+	if getter == nil {
+		panic("nil Getter")
+	}
+	mu.Lock()
+	defer mu.Unlock()
+	initPeerServerOnce.Do(callInitPeerServer)
+	if _, dup := groups[name]; dup {
+		panic("duplicate registration of group " + name)
+	}
+	g := &Group{
+		name:       name,
+		getter:     getter,
+		peers:      peers,
+		cacheBytes: cacheBytes,
+	}
+	if fn := newGroupHook; fn != nil {
+		fn(g)
+	}
+	groups[name] = g
+	return g
+}
+
+// newGroupHook, if non-nil, is called right after a new group is created.
+var newGroupHook func(*Group)
+
+// RegisterNewGroupHook registers a hook that is run each time
+// a group is created.
+func RegisterNewGroupHook(fn func(*Group)) {
+	if newGroupHook != nil {
+		panic("RegisterNewGroupHook called more than once")
+	}
+	newGroupHook = fn
+}
+
+// RegisterServerStart registers a hook that is run when the first
+// group is created.
+func RegisterServerStart(fn func()) {
+	if initPeerServer != nil {
+		panic("RegisterServerStart called more than once")
+	}
+	initPeerServer = fn
+}
+
+func callInitPeerServer() {
+	if initPeerServer != nil {
+		initPeerServer()
+	}
+}
+
+// A Group is a cache namespace and associated data loaded spread over
+// a group of 1 or more machines.
+type Group struct {
+	name       string
+	getter     Getter
+	peersOnce  sync.Once
+	peers      PeerPicker
+	cacheBytes int64 // limit for sum of mainCache and hotCache size
+
+	// mainCache is a cache of the keys for which this process
+	// (amongst its peers) is authorative. That is, this cache
+	// contains keys which consistent hash on to this process's
+	// peer number.
+	mainCache cache
+
+	// hotCache contains keys/values for which this peer is not
+	// authorative (otherwise they would be in mainCache), but
+	// are popular enough to warrant mirroring in this process to
+	// avoid going over the network to fetch from a peer.  Having
+	// a hotCache avoids network hotspotting, where a peer's
+	// network card could become the bottleneck on a popular key.
+	// This cache is used sparingly to maximize the total number
+	// of key/value pairs that can be stored globally.
+	hotCache cache
+
+	// loadGroup ensures that each key is only fetched once
+	// (either locally or remotely), regardless of the number of
+	// concurrent callers.
+	loadGroup singleflight.Group
+
+	// Stats are statistics on the group.
+	Stats Stats
+}
+
+// Stats are per-group statistics.
+type Stats struct {
+	Gets           AtomicInt // any Get request, including from peers
+	CacheHits      AtomicInt // either cache was good
+	PeerLoads      AtomicInt // either remote load or remote cache hit (not an error)
+	PeerErrors     AtomicInt
+	Loads          AtomicInt // (gets - cacheHits)
+	LoadsDeduped   AtomicInt // after singleflight
+	LocalLoads     AtomicInt // total good local loads
+	LocalLoadErrs  AtomicInt // total bad local loads
+	ServerRequests AtomicInt // gets that came over the network from peers
+}
+
+// Name returns the name of the group.
+func (g *Group) Name() string {
+	return g.name
+}
+
+func (g *Group) initPeers() {
+	if g.peers == nil {
+		g.peers = getPeers()
+	}
+}
+
+func (g *Group) Get(ctx Context, key string, dest Sink) error {
+	g.peersOnce.Do(g.initPeers)
+	g.Stats.Gets.Add(1)
+	if dest == nil {
+		return errors.New("groupcache: nil dest Sink")
+	}
+	value, cacheHit := g.lookupCache(key)
+
+	if cacheHit {
+		g.Stats.CacheHits.Add(1)
+		return setSinkView(dest, value)
+	}
+
+	// Optimization to avoid double unmarshalling or copying: keep
+	// track of whether the dest was already populated. One caller
+	// (if local) will set this; the losers will not. The common
+	// case will likely be one caller.
+	destPopulated := false
+	value, destPopulated, err := g.load(ctx, key, dest)
+	if err != nil {
+		return err
+	}
+	if destPopulated {
+		return nil
+	}
+	return setSinkView(dest, value)
+}
+
+// load loads key either by invoking the getter locally or by sending it to another machine.
+func (g *Group) load(ctx Context, key string, dest Sink) (value ByteView, destPopulated bool, err error) {
+	g.Stats.Loads.Add(1)
+	viewi, err := g.loadGroup.Do(key, func() (interface{}, error) {
+		g.Stats.LoadsDeduped.Add(1)
+		var value ByteView
+		var err error
+		if peer, ok := g.peers.PickPeer(key); ok {
+			value, err = g.getFromPeer(ctx, peer, key)
+			if err == nil {
+				g.Stats.PeerLoads.Add(1)
+				return value, nil
+			}
+			g.Stats.PeerErrors.Add(1)
+			// TODO(bradfitz): log the peer's error? keep
+			// log of the past few for /groupcachez?  It's
+			// probably boring (normal task movement), so not
+			// worth logging I imagine.
+		}
+		value, err = g.getLocally(ctx, key, dest)
+		if err != nil {
+			g.Stats.LocalLoadErrs.Add(1)
+			return nil, err
+		}
+		g.Stats.LocalLoads.Add(1)
+		destPopulated = true // only one caller of load gets this return value
+		g.populateCache(key, value, &g.mainCache)
+		return value, nil
+	})
+	if err == nil {
+		value = viewi.(ByteView)
+	}
+	return
+}
+
+func (g *Group) getLocally(ctx Context, key string, dest Sink) (ByteView, error) {
+	err := g.getter.Get(ctx, key, dest)
+	if err != nil {
+		return ByteView{}, err
+	}
+	return dest.view()
+}
+
+func (g *Group) getFromPeer(ctx Context, peer ProtoGetter, key string) (ByteView, error) {
+	req := &pb.GetRequest{
+		Group: &g.name,
+		Key:   &key,
+	}
+	res := &pb.GetResponse{}
+	err := peer.Get(ctx, req, res)
+	if err != nil {
+		return ByteView{}, err
+	}
+	value := ByteView{b: res.Value}
+	// TODO(bradfitz): use res.MinuteQps or something smart to
+	// conditionally populate hotCache.  For now just do it some
+	// percentage of the time.
+	if rand.Intn(10) == 0 {
+		g.populateCache(key, value, &g.hotCache)
+	}
+	return value, nil
+}
+
+func (g *Group) lookupCache(key string) (value ByteView, ok bool) {
+	if g.cacheBytes <= 0 {
+		return
+	}
+	value, ok = g.mainCache.get(key)
+	if ok {
+		return
+	}
+	value, ok = g.hotCache.get(key)
+	return
+}
+
+func (g *Group) populateCache(key string, value ByteView, cache *cache) {
+	if g.cacheBytes <= 0 {
+		return
+	}
+	cache.add(key, value)
+
+	// Evict items from cache(s) if necessary.
+	for {
+		mainBytes := g.mainCache.bytes()
+		hotBytes := g.hotCache.bytes()
+		if mainBytes+hotBytes <= g.cacheBytes {
+			return
+		}
+
+		// TODO(bradfitz): this is good-enough-for-now logic.
+		// It should be something based on measurements and/or
+		// respecting the costs of different resources.
+		victim := &g.mainCache
+		if hotBytes > mainBytes/8 {
+			victim = &g.hotCache
+		}
+		victim.removeOldest()
+	}
+}
+
+// CacheType represents a type of cache.
+type CacheType int
+
+const (
+	// The MainCache is the cache for items that this peer is the
+	// owner for.
+	MainCache CacheType = iota + 1
+
+	// The HotCache is the cache for items that seem popular
+	// enough to replicate to this node, even though it's not the
+	// owner.
+	HotCache
+)
+
+// CacheStats returns stats about the provided cache within the group.
+func (g *Group) CacheStats(which CacheType) CacheStats {
+	switch which {
+	case MainCache:
+		return g.mainCache.stats()
+	case HotCache:
+		return g.hotCache.stats()
+	default:
+		return CacheStats{}
+	}
+}
+
+// cache is a wrapper around an *lru.Cache that adds synchronization,
+// makes values always be ByteView, and counts the size of all keys and
+// values.
+type cache struct {
+	mu         sync.RWMutex
+	nbytes     int64 // of all keys and values
+	lru        *lru.Cache
+	nhit, nget int64
+	nevict     int64 // number of evictions
+}
+
+func (c *cache) stats() CacheStats {
+	c.mu.RLock()
+	defer c.mu.RUnlock()
+	return CacheStats{
+		Bytes:     c.nbytes,
+		Items:     c.itemsLocked(),
+		Gets:      c.nget,
+		Hits:      c.nhit,
+		Evictions: c.nevict,
+	}
+}
+
+func (c *cache) add(key string, value ByteView) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if c.lru == nil {
+		c.lru = &lru.Cache{
+			OnEvicted: func(key lru.Key, value interface{}) {
+				val := value.(ByteView)
+				c.nbytes -= int64(len(key.(string))) + int64(val.Len())
+				c.nevict++
+			},
+		}
+	}
+	c.lru.Add(key, value)
+	c.nbytes += int64(len(key)) + int64(value.Len())
+}
+
+func (c *cache) get(key string) (value ByteView, ok bool) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	c.nget++
+	if c.lru == nil {
+		return
+	}
+	vi, ok := c.lru.Get(key)
+	if !ok {
+		return
+	}
+	c.nhit++
+	return vi.(ByteView), true
+}
+
+func (c *cache) removeOldest() {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if c.lru != nil {
+		c.lru.RemoveOldest()
+	}
+}
+
+func (c *cache) bytes() int64 {
+	c.mu.RLock()
+	defer c.mu.RUnlock()
+	return c.nbytes
+}
+
+func (c *cache) items() int64 {
+	c.mu.RLock()
+	defer c.mu.RUnlock()
+	return c.itemsLocked()
+}
+
+func (c *cache) itemsLocked() int64 {
+	if c.lru == nil {
+		return 0
+	}
+	return int64(c.lru.Len())
+}
+
+// An AtomicInt is an int64 to be accessed atomically.
+type AtomicInt int64
+
+// Add atomically adds n to i.
+func (i *AtomicInt) Add(n int64) {
+	atomic.AddInt64((*int64)(i), n)
+}
+
+// Get atomically gets the value of i.
+func (i *AtomicInt) Get() int64 {
+	return atomic.LoadInt64((*int64)(i))
+}
+
+func (i *AtomicInt) String() string {
+	return strconv.FormatInt(i.Get(), 10)
+}
+
+// CacheStats are returned by stats accessors on Group.
+type CacheStats struct {
+	Bytes     int64
+	Items     int64
+	Gets      int64
+	Hits      int64
+	Evictions int64
+}

groupcache_test.go

@@ -0,0 +1,367 @@
+/*
+Copyright 2012 Google Inc.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// Tests for groupcache.
+
+package groupcache
+
+import (
+	"errors"
+	"fmt"
+	"hash/crc32"
+	"math/rand"
+	"reflect"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/golang/protobuf/proto"
+
+	pb "github.com/golang/groupcache/groupcachepb"
+	testpb "github.com/golang/groupcache/testpb"
+)
+
+var (
+	once                    sync.Once
+	stringGroup, protoGroup Getter
+
+	stringc = make(chan string)
+
+	dummyCtx Context
+
+	// cacheFills is the number of times stringGroup or
+	// protoGroup's Getter have been called. Read using the
+	// cacheFills function.
+	cacheFills AtomicInt
+)
+
+const (
+	stringGroupName = "string-group"
+	protoGroupName  = "proto-group"
+	testMessageType = "google3/net/groupcache/go/test_proto.TestMessage"
+	fromChan        = "from-chan"
+	cacheSize       = 1 << 20
+)
+
+func testSetup() {
+	stringGroup = NewGroup(stringGroupName, cacheSize, GetterFunc(func(_ Context, key string, dest Sink) error {
+		if key == fromChan {
+			key = <-stringc
+		}
+		cacheFills.Add(1)
+		return dest.SetString("ECHO:" + key)
+	}))
+
+	protoGroup = NewGroup(protoGroupName, cacheSize, GetterFunc(func(_ Context, key string, dest Sink) error {
+		if key == fromChan {
+			key = <-stringc
+		}
+		cacheFills.Add(1)
+		return dest.SetProto(&testpb.TestMessage{
+			Name: proto.String("ECHO:" + key),
+			City: proto.String("SOME-CITY"),
+		})
+	}))
+}
+
+// tests that a Getter's Get method is only called once with two
+// outstanding callers.  This is the string variant.
+func TestGetDupSuppressString(t *testing.T) {
+	once.Do(testSetup)
+	// Start two getters. The first should block (waiting reading
+	// from stringc) and the second should latch on to the first
+	// one.
+	resc := make(chan string, 2)
+	for i := 0; i < 2; i++ {
+		go func() {
+			var s string
+			if err := stringGroup.Get(dummyCtx, fromChan, StringSink(&s)); err != nil {
+				resc <- "ERROR:" + err.Error()
+				return
+			}
+			resc <- s
+		}()
+	}
+
+	// Wait a bit so both goroutines get merged together via
+	// singleflight.
+	// TODO(bradfitz): decide whether there are any non-offensive
+	// debug/test hooks that could be added to singleflight to
+	// make a sleep here unnecessary.
+	time.Sleep(250 * time.Millisecond)
+
+	// Unblock the first getter, which should unblock the second
+	// as well.
+	stringc <- "foo"
+
+	for i := 0; i < 2; i++ {
+		select {
+		case v := <-resc:
+			if v != "ECHO:foo" {
+				t.Errorf("got %q; want %q", v, "ECHO:foo")
+			}
+		case <-time.After(5 * time.Second):
+			t.Errorf("timeout waiting on getter #%d of 2", i+1)
+		}
+	}
+}
+
+// tests that a Getter's Get method is only called once with two
+// outstanding callers.  This is the proto variant.
+func TestGetDupSuppressProto(t *testing.T) {
+	once.Do(testSetup)
+	// Start two getters. The first should block (waiting reading
+	// from stringc) and the second should latch on to the first
+	// one.
+	resc := make(chan *testpb.TestMessage, 2)
+	for i := 0; i < 2; i++ {
+		go func() {
+			tm := new(testpb.TestMessage)
+			if err := protoGroup.Get(dummyCtx, fromChan, ProtoSink(tm)); err != nil {
+				tm.Name = proto.String("ERROR:" + err.Error())
+			}
+			resc <- tm
+		}()
+	}
+
+	// Wait a bit so both goroutines get merged together via
+	// singleflight.
+	// TODO(bradfitz): decide whether there are any non-offensive
+	// debug/test hooks that could be added to singleflight to
+	// make a sleep here unnecessary.
+	time.Sleep(250 * time.Millisecond)
+
+	// Unblock the first getter, which should unblock the second
+	// as well.
+	stringc <- "Fluffy"
+	want := &testpb.TestMessage{
+		Name: proto.String("ECHO:Fluffy"),
+		City: proto.String("SOME-CITY"),
+	}
+	for i := 0; i < 2; i++ {
+		select {
+		case v := <-resc:
+			if !reflect.DeepEqual(v, want) {
+				t.Errorf(" Got: %v\nWant: %v", proto.CompactTextString(v), proto.CompactTextString(want))
+			}
+		case <-time.After(5 * time.Second):
+			t.Errorf("timeout waiting on getter #%d of 2", i+1)
+		}
+	}
+}
+
+func countFills(f func()) int64 {
+	fills0 := cacheFills.Get()
+	f()
+	return cacheFills.Get() - fills0
+}
+
+func TestCaching(t *testing.T) {
+	once.Do(testSetup)
+	fills := countFills(func() {
+		for i := 0; i < 10; i++ {
+			var s string
+			if err := stringGroup.Get(dummyCtx, "TestCaching-key", StringSink(&s)); err != nil {
+				t.Fatal(err)
+			}
+		}
+	})
+	if fills != 1 {
+		t.Errorf("expected 1 cache fill; got %d", fills)
+	}
+}
+
+func TestCacheEviction(t *testing.T) {
+	once.Do(testSetup)
+	testKey := "TestCacheEviction-key"
+	getTestKey := func() {
+		var res string
+		for i := 0; i < 10; i++ {
+			if err := stringGroup.Get(dummyCtx, testKey, StringSink(&res)); err != nil {
+				t.Fatal(err)
+			}
+		}
+	}
+	fills := countFills(getTestKey)
+	if fills != 1 {
+		t.Fatalf("expected 1 cache fill; got %d", fills)
+	}
+
+	g := stringGroup.(*Group)
+	evict0 := g.mainCache.nevict
+
+	// Trash the cache with other keys.
+	var bytesFlooded int64
+	// cacheSize/len(testKey) is approximate
+	for bytesFlooded < cacheSize+1024 {
+		var res string
+		key := fmt.Sprintf("dummy-key-%d", bytesFlooded)
+		stringGroup.Get(dummyCtx, key, StringSink(&res))
+		bytesFlooded += int64(len(key) + len(res))
+	}
+	evicts := g.mainCache.nevict - evict0
+	if evicts <= 0 {
+		t.Errorf("evicts = %v; want more than 0", evicts)
+	}
+
+	// Test that the key is gone.
+	fills = countFills(getTestKey)
+	if fills != 1 {
+		t.Fatalf("expected 1 cache fill after cache trashing; got %d", fills)
+	}
+}
+
+type fakePeer struct {
+	hits int
+	fail bool
+}
+
+func (p *fakePeer) Get(_ Context, in *pb.GetRequest, out *pb.GetResponse) error {
+	p.hits++
+	if p.fail {
+		return errors.New("simulated error from peer")
+	}
+	out.Value = []byte("got:" + in.GetKey())
+	return nil
+}
+
+type fakePeers []ProtoGetter
+
+func (p fakePeers) PickPeer(key string) (peer ProtoGetter, ok bool) {
+	if len(p) == 0 {
+		return
+	}
+	n := crc32.Checksum([]byte(key), crc32.IEEETable) % uint32(len(p))
+	return p[n], p[n] != nil
+}
+
+// tests that peers (virtual, in-process) are hit, and how much.
+func TestPeers(t *testing.T) {
+	once.Do(testSetup)
+	rand.Seed(123)
+	peer0 := &fakePeer{}
+	peer1 := &fakePeer{}
+	peer2 := &fakePeer{}
+	peerList := fakePeers([]ProtoGetter{peer0, peer1, peer2, nil})
+	const cacheSize = 0 // disabled
+	localHits := 0
+	getter := func(_ Context, key string, dest Sink) error {
+		localHits++
+		return dest.SetString("got:" + key)
+	}
+	testGroup := newGroup("TestPeers-group", cacheSize, GetterFunc(getter), peerList)
+	run := func(name string, n int, wantSummary string) {
+		// Reset counters
+		localHits = 0
+		for _, p := range []*fakePeer{peer0, peer1, peer2} {
+			p.hits = 0
+		}
+
+		for i := 0; i < n; i++ {
+			key := fmt.Sprintf("key-%d", i)
+			want := "got:" + key
+			var got string
+			err := testGroup.Get(dummyCtx, key, StringSink(&got))
+			if err != nil {
+				t.Errorf("%s: error on key %q: %v", name, key, err)
+				continue
+			}
+			if got != want {
+				t.Errorf("%s: for key %q, got %q; want %q", name, key, got, want)
+			}
+		}
+		summary := func() string {
+			return fmt.Sprintf("localHits = %d, peers = %d %d %d", localHits, peer0.hits, peer1.hits, peer2.hits)
+		}
+		if got := summary(); got != wantSummary {
+			t.Errorf("%s: got %q; want %q", name, got, wantSummary)
+		}
+	}
+	resetCacheSize := func(maxBytes int64) {
+		g := testGroup
+		g.cacheBytes = maxBytes
+		g.mainCache = cache{}
+		g.hotCache = cache{}
+	}
+
+	// Base case; peers all up, with no problems.
+	resetCacheSize(1 << 20)
+	run("base", 200, "localHits = 49, peers = 51 49 51")
+
+	// Verify cache was hit.  All localHits are gone, and some of
+	// the peer hits (the ones randomly selected to be maybe hot)
+	run("cached_base", 200, "localHits = 0, peers = 49 47 48")
+	resetCacheSize(0)
+
+	// With one of the peers being down.
+	// TODO(bradfitz): on a peer number being unavailable, the
+	// consistent hashing should maybe keep trying others to
+	// spread the load out. Currently it fails back to local
+	// execution if the first consistent-hash slot is unavailable.
+	peerList[0] = nil
+	run("one_peer_down", 200, "localHits = 100, peers = 0 49 51")
+
+	// Failing peer
+	peerList[0] = peer0
+	peer0.fail = true
+	run("peer0_failing", 200, "localHits = 100, peers = 51 49 51")
+}
+
+func TestTruncatingByteSliceTarget(t *testing.T) {
+	var buf [100]byte
+	s := buf[:]
+	if err := stringGroup.Get(dummyCtx, "short", TruncatingByteSliceSink(&s)); err != nil {
+		t.Fatal(err)
+	}
+	if want := "ECHO:short"; string(s) != want {
+		t.Errorf("short key got %q; want %q", s, want)
+	}
+
+	s = buf[:6]
+	if err := stringGroup.Get(dummyCtx, "truncated", TruncatingByteSliceSink(&s)); err != nil {
+		t.Fatal(err)
+	}
+	if want := "ECHO:t"; string(s) != want {
+		t.Errorf("truncated key got %q; want %q", s, want)
+	}
+}
+
+func TestAllocatingByteSliceTarget(t *testing.T) {
+	var dst []byte
+	sink := AllocatingByteSliceSink(&dst)
+
+	inBytes := []byte("some bytes")
+	sink.SetBytes(inBytes)
+	if want := "some bytes"; string(dst) != want {
+		t.Errorf("SetBytes resulted in %q; want %q", dst, want)
+	}
+	v, err := sink.view()
+	if err != nil {
+		t.Fatalf("view after SetBytes failed: %v", err)
+	}
+	if &inBytes[0] == &dst[0] {
+		t.Error("inBytes and dst share memory")
+	}
+	if &inBytes[0] == &v.b[0] {
+		t.Error("inBytes and view share memory")
+	}
+	if &dst[0] == &v.b[0] {
+		t.Error("dst and view share memory")
+	}
+}
+
+// TODO(bradfitz): port the Google-internal full integration test into here,
+// using HTTP requests instead of our RPC system.

groupcachepb/groupcache.pb.go

@@ -0,0 +1,65 @@
+// Code generated by protoc-gen-go.
+// source: groupcache.proto
+// DO NOT EDIT!
+
+package groupcachepb
+
+import proto "github.com/golang/protobuf/proto"
+import json "encoding/json"
+import math "math"
+
+// Reference proto, json, and math imports to suppress error if they are not otherwise used.
+var _ = proto.Marshal
+var _ = &json.SyntaxError{}
+var _ = math.Inf
+
+type GetRequest struct {
+	Group            *string `protobuf:"bytes,1,req,name=group" json:"group,omitempty"`
+	Key              *string `protobuf:"bytes,2,req,name=key" json:"key,omitempty"`
+	XXX_unrecognized []byte  `json:"-"`
+}
+
+func (m *GetRequest) Reset()         { *m = GetRequest{} }
+func (m *GetRequest) String() string { return proto.CompactTextString(m) }
+func (*GetRequest) ProtoMessage()    {}
+
+func (m *GetRequest) GetGroup() string {
+	if m != nil && m.Group != nil {
+		return *m.Group
+	}
+	return ""
+}
+
+func (m *GetRequest) GetKey() string {
+	if m != nil && m.Key != nil {
+		return *m.Key
+	}
+	return ""
+}
+
+type GetResponse struct {
+	Value            []byte   `protobuf:"bytes,1,opt,name=value" json:"value,omitempty"`
+	MinuteQps        *float64 `protobuf:"fixed64,2,opt,name=minute_qps" json:"minute_qps,omitempty"`
+	XXX_unrecognized []byte   `json:"-"`
+}
+
+func (m *GetResponse) Reset()         { *m = GetResponse{} }
+func (m *GetResponse) String() string { return proto.CompactTextString(m) }
+func (*GetResponse) ProtoMessage()    {}
+
+func (m *GetResponse) GetValue() []byte {
+	if m != nil {
+		return m.Value
+	}
+	return nil
+}
+
+func (m *GetResponse) GetMinuteQps() float64 {
+	if m != nil && m.MinuteQps != nil {
+		return *m.MinuteQps
+	}
+	return 0
+}
+
+func init() {
+}

groupcachepb/groupcache.proto

@@ -0,0 +1,32 @@
+/*
+Copyright 2012 Google Inc.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package groupcachepb;
+
+message GetRequest {
+  required string group = 1;
+  required string key = 2; // not actually required/guaranteed to be UTF-8
+}
+
+message GetResponse {
+  optional bytes value = 1;
+  optional double minute_qps = 2;
+}
+
+service GroupCache {
+  rpc Get(GetRequest) returns (GetResponse) {
+  };
+}

http.go

@@ -0,0 +1,229 @@
+/*
+Copyright 2013 Google Inc.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package groupcache
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"strings"
+	"sync"
+
+	"github.com/golang/groupcache/consistenthash"
+	pb "github.com/golang/groupcache/groupcachepb"
+	"github.com/golang/protobuf/proto"
+)
+
+const defaultBasePath = "/_groupcache/"
+
+const defaultReplicas = 50
+
+// HTTPPool implements PeerPicker for a pool of HTTP peers.
+type HTTPPool struct {
+	// Context optionally specifies a context for the server to use when it
+	// receives a request.
+	// If nil, the server uses a nil Context.
+	Context func(*http.Request) Context
+
+	// Transport optionally specifies an http.RoundTripper for the client
+	// to use when it makes a request.
+	// If nil, the client uses http.DefaultTransport.
+	Transport func(Context) http.RoundTripper
+
+	// base path including leading and trailing slash, e.g. "/_groupcache/"
+	basePath string
+
+	// this peer's base URL, e.g. "https://example.net:8000"
+	self string
+
+	mu          sync.Mutex // guards peers and httpGetters
+	peers       *consistenthash.Map
+	httpGetters map[string]*httpGetter // keyed by e.g. "http://10.0.0.2:8008"
+}
+
+// HTTPPoolOptions are the configurations of a HTTPPool.
+type HTTPPoolOptions struct {
+	// BasePath specifies the HTTP path that will serve groupcache requests.
+	// If blank, it defaults to "/_groupcache/".
+	BasePath string
+
+	// Replicas specifies the number of key replicas on the consistent hash.
+	// If blank, it defaults to 50.
+	Replicas int
+
+	// HashFn specifies the hash function of the consistent hash.
+	// If blank, it defaults to crc32.ChecksumIEEE.
+	HashFn consistenthash.Hash
+}
+
+// NewHTTPPool initializes an HTTP pool of peers, and registers itself as a PeerPicker.
+// For convenience, it also registers itself as an http.Handler with http.DefaultServeMux.
+// The self argument be a valid base URL that points to the current server,
+// for example "http://example.net:8000".
+func NewHTTPPool(self string) *HTTPPool {
+	p := NewHTTPPoolOpts(self, nil)
+	http.Handle(p.basePath, p)
+	return p
+}
+
+var httpPoolMade bool
+
+// NewHTTPPoolOpts initializes an HTTP pool of peers with the given options.
+// Unlike NewHTTPPool, this function does not register the created pool as an HTTP handler.
+// The returned *HTTPPool implements http.Handler and must be registered using http.Handle.
+func NewHTTPPoolOpts(self string, o *HTTPPoolOptions) *HTTPPool {
+	if httpPoolMade {
+		panic("groupcache: NewHTTPPool must be called only once")
+	}
+	httpPoolMade = true
+
+	opts := HTTPPoolOptions{}
+	if o != nil {
+		opts = *o
+	}
+	if opts.BasePath == "" {
+		opts.BasePath = defaultBasePath
+	}
+	if opts.Replicas == 0 {
+		opts.Replicas = defaultReplicas
+	}
+
+	p := &HTTPPool{
+		basePath:    opts.BasePath,
+		self:        self,
+		peers:       consistenthash.New(opts.Replicas, opts.HashFn),
+		httpGetters: make(map[string]*httpGetter),
+	}
+	RegisterPeerPicker(func() PeerPicker { return p })
+	return p
+}
+
+// Set updates the pool's list of peers.
+// Each peer value should be a valid base URL,
+// for example "http://example.net:8000".
+func (p *HTTPPool) Set(peers ...string) {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+	p.peers = consistenthash.New(defaultReplicas, nil)
+	p.peers.Add(peers...)
+	p.httpGetters = make(map[string]*httpGetter, len(peers))
+	for _, peer := range peers {
+		p.httpGetters[peer] = &httpGetter{transport: p.Transport, baseURL: peer + p.basePath}
+	}
+}
+
+func (p *HTTPPool) PickPeer(key string) (ProtoGetter, bool) {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+	if p.peers.IsEmpty() {
+		return nil, false
+	}
+	if peer := p.peers.Get(key); peer != p.self {
+		return p.httpGetters[peer], true
+	}
+	return nil, false
+}
+
+func (p *HTTPPool) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	// Parse request.
+	if !strings.HasPrefix(r.URL.Path, p.basePath) {
+		panic("HTTPPool serving unexpected path: " + r.URL.Path)
+	}
+	parts := strings.SplitN(r.URL.Path[len(p.basePath):], "/", 2)
+	if len(parts) != 2 {
+		http.Error(w, "bad request", http.StatusBadRequest)
+		return
+	}
+	groupName := parts[0]
+	key := parts[1]
+
+	// Fetch the value for this group/key.
+	group := GetGroup(groupName)
+	if group == nil {
+		http.Error(w, "no such group: "+groupName, http.StatusNotFound)
+		return
+	}
+	var ctx Context
+	if p.Context != nil {
+		ctx = p.Context(r)
+	}
+
+	group.Stats.ServerRequests.Add(1)
+	var value []byte
+	err := group.Get(ctx, key, AllocatingByteSliceSink(&value))
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+
+	// Write the value to the response body as a proto message.
+	body, err := proto.Marshal(&pb.GetResponse{Value: value})
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+	w.Header().Set("Content-Type", "application/x-protobuf")
+	w.Write(body)
+}
+
+type httpGetter struct {
+	transport func(Context) http.RoundTripper
+	baseURL   string
+}
+
+var bufferPool = sync.Pool{
+	New: func() interface{} { return new(bytes.Buffer) },
+}
+
+func (h *httpGetter) Get(context Context, in *pb.GetRequest, out *pb.GetResponse) error {
+	u := fmt.Sprintf(
+		"%v%v/%v",
+		h.baseURL,
+		url.QueryEscape(in.GetGroup()),
+		url.QueryEscape(in.GetKey()),
+	)
+	req, err := http.NewRequest("GET", u, nil)
+	if err != nil {
+		return err
+	}
+	tr := http.DefaultTransport
+	if h.transport != nil {
+		tr = h.transport(context)
+	}
+	res, err := tr.RoundTrip(req)
+	if err != nil {
+		return err
+	}
+	defer res.Body.Close()
+	if res.StatusCode != http.StatusOK {
+		return fmt.Errorf("server returned: %v", res.Status)
+	}
+	b := bufferPool.Get().(*bytes.Buffer)
+	b.Reset()
+	defer bufferPool.Put(b)
+	_, err = io.Copy(b, res.Body)
+	if err != nil {
+		return fmt.Errorf("reading response body: %v", err)
+	}
+	err = proto.Unmarshal(b.Bytes(), out)
+	if err != nil {
+		return fmt.Errorf("decoding response body: %v", err)
+	}
+	return nil
+}

http_test.go

@@ -0,0 +1,166 @@
+/*
+Copyright 2013 Google Inc.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package groupcache
+
+import (
+	"errors"
+	"flag"
+	"log"
+	"net"
+	"net/http"
+	"os"
+	"os/exec"
+	"strconv"
+	"strings"
+	"sync"
+	"testing"
+	"time"
+)
+
+var (
+	peerAddrs = flag.String("test_peer_addrs", "", "Comma-separated list of peer addresses; used by TestHTTPPool")
+	peerIndex = flag.Int("test_peer_index", -1, "Index of which peer this child is; used by TestHTTPPool")
+	peerChild = flag.Bool("test_peer_child", false, "True if running as a child process; used by TestHTTPPool")
+)
+
+func TestHTTPPool(t *testing.T) {
+	if *peerChild {
+		beChildForTestHTTPPool()
+		os.Exit(0)
+	}
+
+	const (
+		nChild = 4
+		nGets  = 100
+	)
+
+	var childAddr []string
+	for i := 0; i < nChild; i++ {
+		childAddr = append(childAddr, pickFreeAddr(t))
+	}
+
+	var cmds []*exec.Cmd
+	var wg sync.WaitGroup
+	for i := 0; i < nChild; i++ {
+		cmd := exec.Command(os.Args[0],
+			"--test.run=TestHTTPPool",
+			"--test_peer_child",
+			"--test_peer_addrs="+strings.Join(childAddr, ","),
+			"--test_peer_index="+strconv.Itoa(i),
+		)
+		cmds = append(cmds, cmd)
+		wg.Add(1)
+		if err := cmd.Start(); err != nil {
+			t.Fatal("failed to start child process: ", err)
+		}
+		go awaitAddrReady(t, childAddr[i], &wg)
+	}
+	defer func() {
+		for i := 0; i < nChild; i++ {
+			if cmds[i].Process != nil {
+				cmds[i].Process.Kill()
+			}
+		}
+	}()
+	wg.Wait()
+
+	// Use a dummy self address so that we don't handle gets in-process.
+	p := NewHTTPPool("should-be-ignored")
+	p.Set(addrToURL(childAddr)...)
+
+	// Dummy getter function. Gets should go to children only.
+	// The only time this process will handle a get is when the
+	// children can't be contacted for some reason.
+	getter := GetterFunc(func(ctx Context, key string, dest Sink) error {
+		return errors.New("parent getter called; something's wrong")
+	})
+	g := NewGroup("httpPoolTest", 1<<20, getter)
+
+	for _, key := range testKeys(nGets) {
+		var value string
+		if err := g.Get(nil, key, StringSink(&value)); err != nil {
+			t.Fatal(err)
+		}
+		if suffix := ":" + key; !strings.HasSuffix(value, suffix) {
+			t.Errorf("Get(%q) = %q, want value ending in %q", key, value, suffix)
+		}
+		t.Logf("Get key=%q, value=%q (peer:key)", key, value)
+	}
+}
+
+func testKeys(n int) (keys []string) {
+	keys = make([]string, n)
+	for i := range keys {
+		keys[i] = strconv.Itoa(i)
+	}
+	return
+}
+
+func beChildForTestHTTPPool() {
+	addrs := strings.Split(*peerAddrs, ",")
+
+	p := NewHTTPPool("http://" + addrs[*peerIndex])
+	p.Set(addrToURL(addrs)...)
+
+	getter := GetterFunc(func(ctx Context, key string, dest Sink) error {
+		dest.SetString(strconv.Itoa(*peerIndex) + ":" + key)
+		return nil
+	})
+	NewGroup("httpPoolTest", 1<<20, getter)
+
+	log.Fatal(http.ListenAndServe(addrs[*peerIndex], p))
+}
+
+// This is racy. Another process could swoop in and steal the port between the
+// call to this function and the next listen call. Should be okay though.
+// The proper way would be to pass the l.File() as ExtraFiles to the child
+// process, and then close your copy once the child starts.
+func pickFreeAddr(t *testing.T) string {
+	l, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer l.Close()
+	return l.Addr().String()
+}
+
+func addrToURL(addr []string) []string {
+	url := make([]string, len(addr))
+	for i := range addr {
+		url[i] = "http://" + addr[i]
+	}
+	return url
+}
+
+func awaitAddrReady(t *testing.T, addr string, wg *sync.WaitGroup) {
+	defer wg.Done()
+	const max = 1 * time.Second
+	tries := 0
+	for {
+		tries++
+		c, err := net.Dial("tcp", addr)
+		if err == nil {
+			c.Close()
+			return
+		}
+		delay := time.Duration(tries) * 25 * time.Millisecond
+		if delay > max {
+			delay = max
+		}
+		time.Sleep(delay)
+	}
+}

lru/lru.go

@@ -0,0 +1,121 @@
+/*
+Copyright 2013 Google Inc.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// Package lru implements an LRU cache.
+package lru
+
+import "container/list"
+
+// Cache is an LRU cache. It is not safe for concurrent access.
+type Cache struct {
+	// MaxEntries is the maximum number of cache entries before
+	// an item is evicted. Zero means no limit.
+	MaxEntries int
+
+	// OnEvicted optionally specificies a callback function to be
+	// executed when an entry is purged from the cache.
+	OnEvicted func(key Key, value interface{})
+
+	ll    *list.List
+	cache map[interface{}]*list.Element
+}
+
+// A Key may be any value that is comparable. See http://golang.org/ref/spec#Comparison_operators
+type Key interface{}
+
+type entry struct {
+	key   Key
+	value interface{}
+}
+
+// New creates a new Cache.
+// If maxEntries is zero, the cache has no limit and it's assumed
+// that eviction is done by the caller.
+func New(maxEntries int) *Cache {
+	return &Cache{
+		MaxEntries: maxEntries,
+		ll:         list.New(),
+		cache:      make(map[interface{}]*list.Element),
+	}
+}
+
+// Add adds a value to the cache.
+func (c *Cache) Add(key Key, value interface{}) {
+	if c.cache == nil {
+		c.cache = make(map[interface{}]*list.Element)
+		c.ll = list.New()
+	}
+	if ee, ok := c.cache[key]; ok {
+		c.ll.MoveToFront(ee)
+		ee.Value.(*entry).value = value
+		return
+	}
+	ele := c.ll.PushFront(&entry{key, value})
+	c.cache[key] = ele
+	if c.MaxEntries != 0 && c.ll.Len() > c.MaxEntries {
+		c.RemoveOldest()
+	}
+}
+
+// Get looks up a key's value from the cache.
+func (c *Cache) Get(key Key) (value interface{}, ok bool) {
+	if c.cache == nil {
+		return
+	}
+	if ele, hit := c.cache[key]; hit {
+		c.ll.MoveToFront(ele)
+		return ele.Value.(*entry).value, true
+	}
+	return
+}
+
+// Remove removes the provided key from the cache.
+func (c *Cache) Remove(key Key) {
+	if c.cache == nil {
+		return
+	}
+	if ele, hit := c.cache[key]; hit {
+		c.removeElement(ele)
+	}
+}
+
+// RemoveOldest removes the oldest item from the cache.
+func (c *Cache) RemoveOldest() {
+	if c.cache == nil {
+		return
+	}
+	ele := c.ll.Back()
+	if ele != nil {
+		c.removeElement(ele)
+	}
+}
+
+func (c *Cache) removeElement(e *list.Element) {
+	c.ll.Remove(e)
+	kv := e.Value.(*entry)
+	delete(c.cache, kv.key)
+	if c.OnEvicted != nil {
+		c.OnEvicted(kv.key, kv.value)
+	}
+}
+
+// Len returns the number of items in the cache.
+func (c *Cache) Len() int {
+	if c.cache == nil {
+		return 0
+	}
+	return c.ll.Len()
+}

lru/lru_test.go

@@ -0,0 +1,73 @@
+/*
+Copyright 2013 Google Inc.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package lru
+
+import (
+	"testing"
+)
+
+type simpleStruct struct {
+	int
+	string
+}
+
+type complexStruct struct {
+	int
+	simpleStruct
+}
+
+var getTests = []struct {
+	name       string
+	keyToAdd   interface{}
+	keyToGet   interface{}
+	expectedOk bool
+}{
+	{"string_hit", "myKey", "myKey", true},
+	{"string_miss", "myKey", "nonsense", false},
+	{"simple_struct_hit", simpleStruct{1, "two"}, simpleStruct{1, "two"}, true},
+	{"simeple_struct_miss", simpleStruct{1, "two"}, simpleStruct{0, "noway"}, false},
+	{"complex_struct_hit", complexStruct{1, simpleStruct{2, "three"}},
+		complexStruct{1, simpleStruct{2, "three"}}, true},
+}
+
+func TestGet(t *testing.T) {
+	for _, tt := range getTests {
+		lru := New(0)
+		lru.Add(tt.keyToAdd, 1234)
+		val, ok := lru.Get(tt.keyToGet)
+		if ok != tt.expectedOk {
+			t.Fatalf("%s: cache hit = %v; want %v", tt.name, ok, !ok)
+		} else if ok && val != 1234 {
+			t.Fatalf("%s expected get to return 1234 but got %v", tt.name, val)
+		}
+	}
+}
+
+func TestRemove(t *testing.T) {
+	lru := New(0)
+	lru.Add("myKey", 1234)
+	if val, ok := lru.Get("myKey"); !ok {
+		t.Fatal("TestRemove returned no match")
+	} else if val != 1234 {
+		t.Fatalf("TestRemove failed.  Expected %d, got %v", 1234, val)
+	}
+
+	lru.Remove("myKey")
+	if _, ok := lru.Get("myKey"); ok {
+		t.Fatal("TestRemove returned a removed entry")
+	}
+}

peers.go

@@ -0,0 +1,71 @@
+/*
+Copyright 2012 Google Inc.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// peers.go defines how processes find and communicate with their peers.
+
+package groupcache
+
+import (
+	pb "github.com/golang/groupcache/groupcachepb"
+)
+
+// Context is an opaque value passed through calls to the
+// ProtoGetter. It may be nil if your ProtoGetter implementation does
+// not require a context.
+type Context interface{}
+
+// ProtoGetter is the interface that must be implemented by a peer.
+type ProtoGetter interface {
+	Get(context Context, in *pb.GetRequest, out *pb.GetResponse) error
+}
+
+// PeerPicker is the interface that must be implemented to locate
+// the peer that owns a specific key.
+type PeerPicker interface {
+	// PickPeer returns the peer that owns the specific key
+	// and true to indicate that a remote peer was nominated.
+	// It returns nil, false if the key owner is the current peer.
+	PickPeer(key string) (peer ProtoGetter, ok bool)
+}
+
+// NoPeers is an implementation of PeerPicker that never finds a peer.
+type NoPeers struct{}
+
+func (NoPeers) PickPeer(key string) (peer ProtoGetter, ok bool) { return }
+
+var (
+	portPicker func() PeerPicker
+)
+
+// RegisterPeerPicker registers the peer initialization function.
+// It is called once, when the first group is created.
+func RegisterPeerPicker(fn func() PeerPicker) {
+	if portPicker != nil {
+		panic("RegisterPeerPicker called more than once")
+	}
+	portPicker = fn
+}
+
+func getPeers() PeerPicker {
+	if portPicker == nil {
+		return NoPeers{}
+	}
+	pk := portPicker()
+	if pk == nil {
+		pk = NoPeers{}
+	}
+	return pk
+}

singleflight/singleflight.go

@@ -0,0 +1,64 @@
+/*
+Copyright 2012 Google Inc.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// Package singleflight provides a duplicate function call suppression
+// mechanism.
+package singleflight
+
+import "sync"
+
+// call is an in-flight or completed Do call
+type call struct {
+	wg  sync.WaitGroup
+	val interface{}
+	err error
+}
+
+// Group represents a class of work and forms a namespace in which
+// units of work can be executed with duplicate suppression.
+type Group struct {
+	mu sync.Mutex       // protects m
+	m  map[string]*call // lazily initialized
+}
+
+// Do executes and returns the results of the given function, making
+// sure that only one execution is in-flight for a given key at a
+// time. If a duplicate comes in, the duplicate caller waits for the
+// original to complete and receives the same results.
+func (g *Group) Do(key string, fn func() (interface{}, error)) (interface{}, error) {
+	g.mu.Lock()
+	if g.m == nil {
+		g.m = make(map[string]*call)
+	}
+	if c, ok := g.m[key]; ok {
+		g.mu.Unlock()
+		c.wg.Wait()
+		return c.val, c.err
+	}
+	c := new(call)
+	c.wg.Add(1)
+	g.m[key] = c
+	g.mu.Unlock()
+
+	c.val, c.err = fn()
+	c.wg.Done()
+
+	g.mu.Lock()
+	delete(g.m, key)
+	g.mu.Unlock()
+
+	return c.val, c.err
+}

singleflight/singleflight_test.go

@@ -0,0 +1,85 @@
+/*
+Copyright 2012 Google Inc.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package singleflight
+
+import (
+	"errors"
+	"fmt"
+	"sync"
+	"sync/atomic"
+	"testing"
+	"time"
+)
+
+func TestDo(t *testing.T) {
+	var g Group
+	v, err := g.Do("key", func() (interface{}, error) {
+		return "bar", nil
+	})
+	if got, want := fmt.Sprintf("%v (%T)", v, v), "bar (string)"; got != want {
+		t.Errorf("Do = %v; want %v", got, want)
+	}
+	if err != nil {
+		t.Errorf("Do error = %v", err)
+	}
+}
+
+func TestDoErr(t *testing.T) {
+	var g Group
+	someErr := errors.New("Some error")
+	v, err := g.Do("key", func() (interface{}, error) {
+		return nil, someErr
+	})
+	if err != someErr {
+		t.Errorf("Do error = %v; want someErr", err)
+	}
+	if v != nil {
+		t.Errorf("unexpected non-nil value %#v", v)
+	}
+}
+
+func TestDoDupSuppress(t *testing.T) {
+	var g Group
+	c := make(chan string)
+	var calls int32
+	fn := func() (interface{}, error) {
+		atomic.AddInt32(&calls, 1)
+		return <-c, nil
+	}
+
+	const n = 10
+	var wg sync.WaitGroup
+	for i := 0; i < n; i++ {
+		wg.Add(1)
+		go func() {
+			v, err := g.Do("key", fn)
+			if err != nil {
+				t.Errorf("Do error: %v", err)
+			}
+			if v.(string) != "bar" {
+				t.Errorf("got %q; want %q", v, "bar")
+			}
+			wg.Done()
+		}()
+	}
+	time.Sleep(100 * time.Millisecond) // let goroutines above block
+	c <- "bar"
+	wg.Wait()
+	if got := atomic.LoadInt32(&calls); got != 1 {
+		t.Errorf("number of calls = %d; want 1", got)
+	}
+}

sinks.go

@@ -0,0 +1,322 @@
+/*
+Copyright 2012 Google Inc.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package groupcache
+
+import (
+	"errors"
+
+	"github.com/golang/protobuf/proto"
+)
+
+// A Sink receives data from a Get call.
+//
+// Implementation of Getter must call exactly one of the Set methods
+// on success.
+type Sink interface {
+	// SetString sets the value to s.
+	SetString(s string) error
+
+	// SetBytes sets the value to the contents of v.
+	// The caller retains ownership of v.
+	SetBytes(v []byte) error
+
+	// SetProto sets the value to the encoded version of m.
+	// The caller retains ownership of m.
+	SetProto(m proto.Message) error
+
+	// view returns a frozen view of the bytes for caching.
+	view() (ByteView, error)
+}
+
+func cloneBytes(b []byte) []byte {
+	c := make([]byte, len(b))
+	copy(c, b)
+	return c
+}
+
+func setSinkView(s Sink, v ByteView) error {
+	// A viewSetter is a Sink that can also receive its value from
+	// a ByteView. This is a fast path to minimize copies when the
+	// item was already cached locally in memory (where it's
+	// cached as a ByteView)
+	type viewSetter interface {
+		setView(v ByteView) error
+	}
+	if vs, ok := s.(viewSetter); ok {
+		return vs.setView(v)
+	}
+	if v.b != nil {
+		return s.SetBytes(v.b)
+	}
+	return s.SetString(v.s)
+}
+
+// StringSink returns a Sink that populates the provided string pointer.
+func StringSink(sp *string) Sink {
+	return &stringSink{sp: sp}
+}
+
+type stringSink struct {
+	sp *string
+	v  ByteView
+	// TODO(bradfitz): track whether any Sets were called.
+}
+
+func (s *stringSink) view() (ByteView, error) {
+	// TODO(bradfitz): return an error if no Set was called
+	return s.v, nil
+}
+
+func (s *stringSink) SetString(v string) error {
+	s.v.b = nil
+	s.v.s = v
+	*s.sp = v
+	return nil
+}
+
+func (s *stringSink) SetBytes(v []byte) error {
+	return s.SetString(string(v))
+}
+
+func (s *stringSink) SetProto(m proto.Message) error {
+	b, err := proto.Marshal(m)
+	if err != nil {
+		return err
+	}
+	s.v.b = b
+	*s.sp = string(b)
+	return nil
+}
+
+// ByteViewSink returns a Sink that populates a ByteView.
+func ByteViewSink(dst *ByteView) Sink {
+	if dst == nil {
+		panic("nil dst")
+	}
+	return &byteViewSink{dst: dst}
+}
+
+type byteViewSink struct {
+	dst *ByteView
+
+	// if this code ever ends up tracking that at least one set*
+	// method was called, don't make it an error to call set
+	// methods multiple times. Lorry's payload.go does that, and
+	// it makes sense. The comment at the top of this file about
+	// "exactly one of the Set methods" is overly strict. We
+	// really care about at least once (in a handler), but if
+	// multiple handlers fail (or multiple functions in a program
+	// using a Sink), it's okay to re-use the same one.
+}
+
+func (s *byteViewSink) setView(v ByteView) error {
+	*s.dst = v
+	return nil
+}
+
+func (s *byteViewSink) view() (ByteView, error) {
+	return *s.dst, nil
+}
+
+func (s *byteViewSink) SetProto(m proto.Message) error {
+	b, err := proto.Marshal(m)
+	if err != nil {
+		return err
+	}
+	*s.dst = ByteView{b: b}
+	return nil
+}
+
+func (s *byteViewSink) SetBytes(b []byte) error {
+	*s.dst = ByteView{b: cloneBytes(b)}
+	return nil
+}
+
+func (s *byteViewSink) SetString(v string) error {
+	*s.dst = ByteView{s: v}
+	return nil
+}
+
+// ProtoSink returns a sink that unmarshals binary proto values into m.
+func ProtoSink(m proto.Message) Sink {
+	return &protoSink{
+		dst: m,
+	}
+}
+
+type protoSink struct {
+	dst proto.Message // authorative value
+	typ string
+
+	v ByteView // encoded
+}
+
+func (s *protoSink) view() (ByteView, error) {
+	return s.v, nil
+}
+
+func (s *protoSink) SetBytes(b []byte) error {
+	err := proto.Unmarshal(b, s.dst)
+	if err != nil {
+		return err
+	}
+	s.v.b = cloneBytes(b)
+	s.v.s = ""
+	return nil
+}
+
+func (s *protoSink) SetString(v string) error {
+	b := []byte(v)
+	err := proto.Unmarshal(b, s.dst)
+	if err != nil {
+		return err
+	}
+	s.v.b = b
+	s.v.s = ""
+	return nil
+}
+
+func (s *protoSink) SetProto(m proto.Message) error {
+	b, err := proto.Marshal(m)
+	if err != nil {
+		return err
+	}
+	// TODO(bradfitz): optimize for same-task case more and write
+	// right through? would need to document ownership rules at
+	// the same time. but then we could just assign *dst = *m
+	// here. This works for now:
+	err = proto.Unmarshal(b, s.dst)
+	if err != nil {
+		return err
+	}
+	s.v.b = b
+	s.v.s = ""
+	return nil
+}
+
+// AllocatingByteSliceSink returns a Sink that allocates
+// a byte slice to hold the received value and assigns
+// it to *dst. The memory is not retained by groupcache.
+func AllocatingByteSliceSink(dst *[]byte) Sink {
+	return &allocBytesSink{dst: dst}
+}
+
+type allocBytesSink struct {
+	dst *[]byte
+	v   ByteView
+}
+
+func (s *allocBytesSink) view() (ByteView, error) {
+	return s.v, nil
+}
+
+func (s *allocBytesSink) setView(v ByteView) error {
+	if v.b != nil {
+		*s.dst = cloneBytes(v.b)
+	} else {
+		*s.dst = []byte(v.s)
+	}
+	s.v = v
+	return nil
+}
+
+func (s *allocBytesSink) SetProto(m proto.Message) error {
+	b, err := proto.Marshal(m)
+	if err != nil {
+		return err
+	}
+	return s.setBytesOwned(b)
+}
+
+func (s *allocBytesSink) SetBytes(b []byte) error {
+	return s.setBytesOwned(cloneBytes(b))
+}
+
+func (s *allocBytesSink) setBytesOwned(b []byte) error {
+	if s.dst == nil {
+		return errors.New("nil AllocatingByteSliceSink *[]byte dst")
+	}
+	*s.dst = cloneBytes(b) // another copy, protecting the read-only s.v.b view
+	s.v.b = b
+	s.v.s = ""
+	return nil
+}
+
+func (s *allocBytesSink) SetString(v string) error {
+	if s.dst == nil {
+		return errors.New("nil AllocatingByteSliceSink *[]byte dst")
+	}
+	*s.dst = []byte(v)
+	s.v.b = nil
+	s.v.s = v
+	return nil
+}
+
+// TruncatingByteSliceSink returns a Sink that writes up to len(*dst)
+// bytes to *dst. If more bytes are available, they're silently
+// truncated. If fewer bytes are available than len(*dst), *dst
+// is shrunk to fit the number of bytes available.
+func TruncatingByteSliceSink(dst *[]byte) Sink {
+	return &truncBytesSink{dst: dst}
+}
+
+type truncBytesSink struct {
+	dst *[]byte
+	v   ByteView
+}
+
+func (s *truncBytesSink) view() (ByteView, error) {
+	return s.v, nil
+}
+
+func (s *truncBytesSink) SetProto(m proto.Message) error {
+	b, err := proto.Marshal(m)
+	if err != nil {
+		return err
+	}
+	return s.setBytesOwned(b)
+}
+
+func (s *truncBytesSink) SetBytes(b []byte) error {
+	return s.setBytesOwned(cloneBytes(b))
+}
+
+func (s *truncBytesSink) setBytesOwned(b []byte) error {
+	if s.dst == nil {
+		return errors.New("nil TruncatingByteSliceSink *[]byte dst")
+	}
+	n := copy(*s.dst, b)
+	if n < len(*s.dst) {
+		*s.dst = (*s.dst)[:n]
+	}
+	s.v.b = b
+	s.v.s = ""
+	return nil
+}
+
+func (s *truncBytesSink) SetString(v string) error {
+	if s.dst == nil {
+		return errors.New("nil TruncatingByteSliceSink *[]byte dst")
+	}
+	n := copy(*s.dst, v)
+	if n < len(*s.dst) {
+		*s.dst = (*s.dst)[:n]
+	}
+	s.v.b = nil
+	s.v.s = v
+	return nil
+}

testpb/test.pb.go

@@ -0,0 +1,235 @@
+// Code generated by protoc-gen-go.
+// source: test.proto
+// DO NOT EDIT!
+
+package testpb
+
+import proto "github.com/golang/protobuf/proto"
+import json "encoding/json"
+import math "math"
+
+// Reference proto, json, and math imports to suppress error if they are not otherwise used.
+var _ = proto.Marshal
+var _ = &json.SyntaxError{}
+var _ = math.Inf
+
+type TestMessage struct {
+	Name             *string `protobuf:"bytes,1,opt,name=name" json:"name,omitempty"`
+	City             *string `protobuf:"bytes,2,opt,name=city" json:"city,omitempty"`
+	XXX_unrecognized []byte  `json:"-"`
+}
+
+func (m *TestMessage) Reset()         { *m = TestMessage{} }
+func (m *TestMessage) String() string { return proto.CompactTextString(m) }
+func (*TestMessage) ProtoMessage()    {}
+
+func (m *TestMessage) GetName() string {
+	if m != nil && m.Name != nil {
+		return *m.Name
+	}
+	return ""
+}
+
+func (m *TestMessage) GetCity() string {
+	if m != nil && m.City != nil {
+		return *m.City
+	}
+	return ""
+}
+
+type TestRequest struct {
+	Lower            *string `protobuf:"bytes,1,req,name=lower" json:"lower,omitempty"`
+	RepeatCount      *int32  `protobuf:"varint,2,opt,name=repeat_count,def=1" json:"repeat_count,omitempty"`
+	XXX_unrecognized []byte  `json:"-"`
+}
+
+func (m *TestRequest) Reset()         { *m = TestRequest{} }
+func (m *TestRequest) String() string { return proto.CompactTextString(m) }
+func (*TestRequest) ProtoMessage()    {}
+
+const Default_TestRequest_RepeatCount int32 = 1
+
+func (m *TestRequest) GetLower() string {
+	if m != nil && m.Lower != nil {
+		return *m.Lower
+	}
+	return ""
+}
+
+func (m *TestRequest) GetRepeatCount() int32 {
+	if m != nil && m.RepeatCount != nil {
+		return *m.RepeatCount
+	}
+	return Default_TestRequest_RepeatCount
+}
+
+type TestResponse struct {
+	Value            *string `protobuf:"bytes,1,opt,name=value" json:"value,omitempty"`
+	XXX_unrecognized []byte  `json:"-"`
+}
+
+func (m *TestResponse) Reset()         { *m = TestResponse{} }
+func (m *TestResponse) String() string { return proto.CompactTextString(m) }
+func (*TestResponse) ProtoMessage()    {}
+
+func (m *TestResponse) GetValue() string {
+	if m != nil && m.Value != nil {
+		return *m.Value
+	}
+	return ""
+}
+
+type CacheStats struct {
+	Items            *int64 `protobuf:"varint,1,opt,name=items" json:"items,omitempty"`
+	Bytes            *int64 `protobuf:"varint,2,opt,name=bytes" json:"bytes,omitempty"`
+	Gets             *int64 `protobuf:"varint,3,opt,name=gets" json:"gets,omitempty"`
+	Hits             *int64 `protobuf:"varint,4,opt,name=hits" json:"hits,omitempty"`
+	Evicts           *int64 `protobuf:"varint,5,opt,name=evicts" json:"evicts,omitempty"`
+	XXX_unrecognized []byte `json:"-"`
+}
+
+func (m *CacheStats) Reset()         { *m = CacheStats{} }
+func (m *CacheStats) String() string { return proto.CompactTextString(m) }
+func (*CacheStats) ProtoMessage()    {}
+
+func (m *CacheStats) GetItems() int64 {
+	if m != nil && m.Items != nil {
+		return *m.Items
+	}
+	return 0
+}
+
+func (m *CacheStats) GetBytes() int64 {
+	if m != nil && m.Bytes != nil {
+		return *m.Bytes
+	}
+	return 0
+}
+
+func (m *CacheStats) GetGets() int64 {
+	if m != nil && m.Gets != nil {
+		return *m.Gets
+	}
+	return 0
+}
+
+func (m *CacheStats) GetHits() int64 {
+	if m != nil && m.Hits != nil {
+		return *m.Hits
+	}
+	return 0
+}
+
+func (m *CacheStats) GetEvicts() int64 {
+	if m != nil && m.Evicts != nil {
+		return *m.Evicts
+	}
+	return 0
+}
+
+type StatsResponse struct {
+	Gets             *int64      `protobuf:"varint,1,opt,name=gets" json:"gets,omitempty"`
+	CacheHits        *int64      `protobuf:"varint,12,opt,name=cache_hits" json:"cache_hits,omitempty"`
+	Fills            *int64      `protobuf:"varint,2,opt,name=fills" json:"fills,omitempty"`
+	TotalAlloc       *uint64     `protobuf:"varint,3,opt,name=total_alloc" json:"total_alloc,omitempty"`
+	MainCache        *CacheStats `protobuf:"bytes,4,opt,name=main_cache" json:"main_cache,omitempty"`
+	HotCache         *CacheStats `protobuf:"bytes,5,opt,name=hot_cache" json:"hot_cache,omitempty"`
+	ServerIn         *int64      `protobuf:"varint,6,opt,name=server_in" json:"server_in,omitempty"`
+	Loads            *int64      `protobuf:"varint,8,opt,name=loads" json:"loads,omitempty"`
+	PeerLoads        *int64      `protobuf:"varint,9,opt,name=peer_loads" json:"peer_loads,omitempty"`
+	PeerErrors       *int64      `protobuf:"varint,10,opt,name=peer_errors" json:"peer_errors,omitempty"`
+	LocalLoads       *int64      `protobuf:"varint,11,opt,name=local_loads" json:"local_loads,omitempty"`
+	XXX_unrecognized []byte      `json:"-"`
+}
+
+func (m *StatsResponse) Reset()         { *m = StatsResponse{} }
+func (m *StatsResponse) String() string { return proto.CompactTextString(m) }
+func (*StatsResponse) ProtoMessage()    {}
+
+func (m *StatsResponse) GetGets() int64 {
+	if m != nil && m.Gets != nil {
+		return *m.Gets
+	}
+	return 0
+}
+
+func (m *StatsResponse) GetCacheHits() int64 {
+	if m != nil && m.CacheHits != nil {
+		return *m.CacheHits
+	}
+	return 0
+}
+
+func (m *StatsResponse) GetFills() int64 {
+	if m != nil && m.Fills != nil {
+		return *m.Fills
+	}
+	return 0
+}
+
+func (m *StatsResponse) GetTotalAlloc() uint64 {
+	if m != nil && m.TotalAlloc != nil {
+		return *m.TotalAlloc
+	}
+	return 0
+}
+
+func (m *StatsResponse) GetMainCache() *CacheStats {
+	if m != nil {
+		return m.MainCache
+	}
+	return nil
+}
+
+func (m *StatsResponse) GetHotCache() *CacheStats {
+	if m != nil {
+		return m.HotCache
+	}
+	return nil
+}
+
+func (m *StatsResponse) GetServerIn() int64 {
+	if m != nil && m.ServerIn != nil {
+		return *m.ServerIn
+	}
+	return 0
+}
+
+func (m *StatsResponse) GetLoads() int64 {
+	if m != nil && m.Loads != nil {
+		return *m.Loads
+	}
+	return 0
+}
+
+func (m *StatsResponse) GetPeerLoads() int64 {
+	if m != nil && m.PeerLoads != nil {
+		return *m.PeerLoads
+	}
+	return 0
+}
+
+func (m *StatsResponse) GetPeerErrors() int64 {
+	if m != nil && m.PeerErrors != nil {
+		return *m.PeerErrors
+	}
+	return 0
+}
+
+func (m *StatsResponse) GetLocalLoads() int64 {
+	if m != nil && m.LocalLoads != nil {
+		return *m.LocalLoads
+	}
+	return 0
+}
+
+type Empty struct {
+	XXX_unrecognized []byte `json:"-"`
+}
+
+func (m *Empty) Reset()         { *m = Empty{} }
+func (m *Empty) String() string { return proto.CompactTextString(m) }
+func (*Empty) ProtoMessage()    {}
+
+func init() {
+}

testpb/test.proto

@@ -0,0 +1,61 @@
+/*
+Copyright 2012 Google Inc.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package testpb;
+
+message TestMessage {
+  optional string name = 1;
+  optional string city = 2;
+}
+
+message TestRequest {
+  required string lower = 1; // to be returned upper case
+  optional int32 repeat_count = 2 [default = 1]; // .. this many times
+}
+
+message TestResponse {
+  optional string value = 1;
+}
+
+message CacheStats {
+  optional int64 items = 1;
+  optional int64 bytes = 2;
+  optional int64 gets = 3;
+  optional int64 hits = 4;
+  optional int64 evicts = 5;
+}
+
+message StatsResponse {
+  optional int64 gets = 1;
+  optional int64 cache_hits = 12;
+  optional int64 fills = 2;
+  optional uint64 total_alloc = 3;
+  optional CacheStats main_cache = 4;
+  optional CacheStats hot_cache = 5;
+  optional int64 server_in = 6;
+  optional int64 loads = 8;
+  optional int64 peer_loads = 9;
+  optional int64 peer_errors = 10;
+  optional int64 local_loads = 11;
+}
+
+message Empty {}
+
+service GroupCacheTest {
+  rpc InitPeers(Empty) returns (Empty) {};
+  rpc Get(TestRequest) returns (TestResponse) {};
+  rpc GetStats(Empty) returns (StatsResponse) {};
+}