Parse Webhook payload into actual event

Closes #427.

Change-Id: I67faac8df63e0d55fcce4ca5f9ab50e26c04d6b3

github/messages.go

@@ -14,6 +14,7 @@ import (
 	"crypto/sha256"
 	"crypto/sha512"
 	"encoding/hex"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"hash"
@@ -30,6 +31,35 @@ const (
 	sha512Prefix = "sha512"
 	// signatureHeader is the GitHub header key used to pass the HMAC hexdigest.
 	signatureHeader = "X-Hub-Signature"
+	// eventTypeHeader is the Github header key used to pass the event type.
+	eventTypeHeader = "X-Github-Event"
+)
+
+var (
+	// eventTypeMapping maps webhooks types to their corresponding go-github struct types.
+	eventTypeMapping = map[string]string{
+		"commit_comment":              "CommitCommentEvent",
+		"create":                      "CreateEvent",
+		"delete":                      "DeleteEvent",
+		"deployment":                  "DeploymentEvent",
+		"deployment_status":           "DeploymentStatusEvent",
+		"fork":                        "ForkEvent",
+		"gollum":                      "GollumEvent",
+		"issue_comment":               "IssueCommentEvent",
+		"issues":                      "IssuesEvent",
+		"member":                      "MemberEvent",
+		"membership":                  "MembershipEvent",
+		"page_build":                  "PageBuildEvent",
+		"public":                      "PublicEvent",
+		"pull_request_review_comment": "PullRequestReviewCommentEvent",
+		"pull_request":                "PullRequestEvent",
+		"push":                        "PushEvent",
+		"repository":                  "RepositoryEvent",
+		"release":                     "ReleaseEvent",
+		"status":                      "StatusEvent",
+		"team_add":                    "TeamAddEvent",
+		"watch":                       "WatchEvent",
+	}
 )
 
 // genMAC generates the HMAC signature for a message provided the secret key
@@ -117,3 +147,42 @@ func validateSignature(signature string, payload, secretKey []byte) error {
 	}
 	return nil
 }
+
+// WebHookType returns the event type of webhook request r.
+func WebHookType(r *http.Request) string {
+	return r.Header.Get(eventTypeHeader)
+}
+
+// ParseWebHook parses the event payload. For recognized event types, a
+// value of the corresponding struct type will be returned (as returned
+// by Event.Payload()). An error will be returned for unrecognized event
+// types.
+//
+// Example usage:
+//
+//     func (s *GitHubEventMonitor) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+//       payload, err := github.ValidatePayload(r, s.webhookSecretKey)
+//       if err != nil { ... }
+//       event, err := github.ParseWebHook(github.WebHookType(r), payload)
+//       if err != nil { ... }
+//       switch event := event.(type) {
+//       case CommitCommentEvent:
+//           processCommitCommentEvent(event)
+//       case CreateEvent:
+//           processCreateEvent(event)
+//       ...
+//       }
+//     }
+//
+func ParseWebHook(messageType string, payload []byte) (interface{}, error) {
+	eventType, ok := eventTypeMapping[messageType]
+	if !ok {
+		return nil, fmt.Errorf("unknown X-Github-Event in message: %v", messageType)
+	}
+
+	event := Event{
+		Type:       &eventType,
+		RawPayload: (*json.RawMessage)(&payload),
+	}
+	return event.Payload(), nil
+}

github/messages_test.go

@@ -7,7 +7,9 @@ package github
 
 import (
 	"bytes"
+	"encoding/json"
 	"net/http"
+	"reflect"
 	"testing"
 )
 
@@ -79,3 +81,110 @@ func TestValidatePayload(t *testing.T) {
 		}
 	}
 }
+
+func TestParseWebHook(t *testing.T) {
+	tests := []struct {
+		payload     interface{}
+		messageType string
+	}{
+		{
+			payload:     &CommitCommentEvent{},
+			messageType: "commit_comment",
+		},
+		{
+			payload:     &CreateEvent{},
+			messageType: "create",
+		},
+		{
+			payload:     &DeleteEvent{},
+			messageType: "delete",
+		},
+		{
+			payload:     &DeploymentEvent{},
+			messageType: "deployment",
+		},
+
+		{
+			payload:     &DeploymentStatusEvent{},
+			messageType: "deployment_status",
+		},
+		{
+			payload:     &ForkEvent{},
+			messageType: "fork",
+		},
+		{
+			payload:     &GollumEvent{},
+			messageType: "gollum",
+		},
+		{
+			payload:     &IssueCommentEvent{},
+			messageType: "issue_comment",
+		},
+		{
+			payload:     &IssuesEvent{},
+			messageType: "issues",
+		},
+		{
+			payload:     &MemberEvent{},
+			messageType: "member",
+		},
+		{
+			payload:     &MembershipEvent{},
+			messageType: "membership",
+		},
+		{
+			payload:     &PageBuildEvent{},
+			messageType: "page_build",
+		},
+		{
+			payload:     &PublicEvent{},
+			messageType: "public",
+		},
+		{
+			payload:     &PullRequestEvent{},
+			messageType: "pull_request",
+		},
+		{
+			payload:     &PullRequestReviewCommentEvent{},
+			messageType: "pull_request_review_comment",
+		},
+		{
+			payload:     &PushEvent{},
+			messageType: "push",
+		},
+		{
+			payload:     &ReleaseEvent{},
+			messageType: "release",
+		},
+		{
+			payload:     &RepositoryEvent{},
+			messageType: "repository",
+		},
+		{
+			payload:     &StatusEvent{},
+			messageType: "status",
+		},
+		{
+			payload:     &TeamAddEvent{},
+			messageType: "team_add",
+		},
+		{
+			payload:     &WatchEvent{},
+			messageType: "watch",
+		},
+	}
+
+	for _, test := range tests {
+		p, err := json.Marshal(test.payload)
+		if err != nil {
+			t.Fatalf("Marshal(%#v): %v", test.payload, err)
+		}
+		got, err := ParseWebHook(test.messageType, p)
+		if err != nil {
+			t.Fatalf("ParseWebHook: %v", err)
+		}
+		if want := test.payload; !reflect.DeepEqual(got, want) {
+			t.Errorf("ParseWebHook(%#v, %#v) = %#v, want %#v", test.messageType, p, got, want)
+		}
+	}
+}