Implementing GitHub webhook handler

Author: doggydogworld

libs/github/webhook/webhook.go

@@ -0,0 +1,141 @@
+package webhook
+
+import (
+	"fmt"
+	"log/slog"
+	"net/http"
+
+	"github.com/google/go-github/v63/github"
+)
+
+// EventHandlerFunc is a function that handles a webhook event.
+// The function should return an error if the event could not be handled.
+// If the error is not nil, the webhook will respond with a 500 Internal Server Error.
+//
+// It is important that this is non-blocking and does not perform any long-running operations.
+// GitHub will close the connection if the webhook does not respond within 10 seconds.
+//
+// Example usage:
+//
+//	func(event interface{}) error {
+//		switch event := event.(type) {
+//			case *github.CommitCommentEvent:
+//				processCommitCommentEvent(event)
+//			case *github.CreateEvent:
+//				processCreateEvent(event)
+//				...
+//		}
+//		return nil
+//	}
+type EventHandlerFunc func(event interface{}) error
+
+// Handler is an implementation of [http.Handler] that handles GitHub webhook events.
+type Handler struct {
+	eventHandler EventHandlerFunc
+	secretToken  []byte
+	log          *slog.Logger
+}
+
+var _ http.Handler = &Handler{}
+
+type Opt func(*Handler) error
+
+// WithSecretToken sets the secret token for the webhook.
+// The secret token is used to create a hash of the request body, which is sent in the X-Hub-Signature header.
+// If not set, the webhook will not verify the signature of the request.
+//
+// For more information, see: https://docs.github.com/en/webhooks/using-webhooks/validating-webhook-deliveries
+func WithSecretToken(secretToken []byte) Opt {
+	return func(p *Handler) error {
+		p.secretToken = secretToken
+		return nil
+	}
+}
+
+// WithLogger sets the logger for the webhook.
+func WithLogger(log *slog.Logger) Opt {
+	return func(p *Handler) error {
+		p.log = log
+		return nil
+	}
+}
+
+var defaultOpts = []Opt{
+	WithLogger(slog.Default()),
+}
+
+// NewHandler creates a new webhook handler.
+func NewHandler(eventHandler EventHandlerFunc, opts ...Opt) *Handler {
+	h := Handler{
+		eventHandler: eventHandler,
+	}
+	for _, opt := range defaultOpts {
+		opt(&h)
+	}
+
+	for _, opt := range opts {
+		opt(&h)
+	}
+	return &h
+}
+
+// Headers is a list of special headers that are sent with a webhook request.
+// For more information, see: https://docs.github.com/en/webhooks/webhook-events-and-payloads#delivery-headers
+type Headers struct {
+	// GithubHookID is the unique identifier of the webhook.
+	GithubHookID string
+	// GithubEvent is the type of event that triggered the delivery.
+	GithubEvent string
+	// GithubDelivery is a globally unique identifier (GUID) to identify the event
+	GithubDelivery string
+	// GitHubHookInstallationTargetType is the type of resource where the webhook was created.
+	GitHubHookInstallationTargetType string
+	// GitHubHookInstallationTargetID is the unique identifier of the resource where the webhook was created.
+	GitHubHookInstallationTargetID string
+
+	// HubSignature256 is the HMAC hex digest of the response body.
+	// Is generated with the SHA-256 algorithm with a shared secret used as the HMAC key.
+	// This header will be sent if the webhook is configured with a secret.
+	HubSignature256 string
+}
+
+// ServeHTTP handles a webhook request.
+func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	// Parse headers for debugging and audit purposes.
+	var head Headers
+	head.GithubHookID = r.Header.Get("X-GitHub-Hook-ID")
+	head.GithubEvent = r.Header.Get("X-GitHub-Event")
+	head.GithubDelivery = r.Header.Get("X-GitHub-Delivery")
+	head.GitHubHookInstallationTargetType = r.Header.Get("X-GitHub-Hook-Installation-Target-Type")
+	head.GitHubHookInstallationTargetID = r.Header.Get("X-GitHub-Hook-Installation-Target-ID")
+	head.HubSignature256 = r.Header.Get("X-Hub-Signature-256")
+
+	payload, err := github.ValidatePayload(r, h.secretToken) // If secretToken is empty, the signature will not be verified.
+	if err != nil {
+		h.log.Warn("webhook validation failed", "headers", head)
+		http.Error(w, "invalid request", http.StatusBadRequest)
+		return
+	}
+
+	event, err := github.ParseWebHook(head.GithubEvent, payload)
+	if err != nil {
+		h.log.Error("failed to parse webhook event", "error", err)
+		http.Error(w, "invalid request", http.StatusBadRequest)
+		return
+	}
+
+	if err := h.eventHandler(event); err != nil {
+		h.log.Error("failed to handle webhook event", "error", err)
+		http.Error(w, "internal server error", http.StatusInternalServerError)
+		return
+	}
+
+	// Respond to the request.
+	w.WriteHeader(http.StatusOK)
+}
+
+// String returns a string representation of the Headers.
+func (h *Headers) String() string {
+	return fmt.Sprintf("GithubHookID: %s\nGithubEvent: %s\nGithubDelivery: %s\nGitHubHookInstallationTargetType: %s\nGitHubHookInstallationTargetID: %s\nHubSignature256: %s\n",
+		h.GithubHookID, h.GithubEvent, h.GithubDelivery, h.GitHubHookInstallationTargetType, h.GitHubHookInstallationTargetID, h.HubSignature256)
+}

tools/approval-service/cmd/approval-service.go

@@ -1,5 +1,19 @@
 package main
 
+import (
+	"context"
+	"log"
+	"log/slog"
+	"net/http"
+
+	"github.com/google/go-github/v69/github"
+	"github.com/gravitational/shared-workflows/libs/github/webhook"
+	"github.com/gravitational/trace"
+	"golang.org/x/sync/errgroup"
+)
+
+var logger = slog.Default()
+
 // Process:
 // 1. Take in events from CI/CD systems
 // 2. Extract common information
@@ -28,19 +42,22 @@ func main() {
 	eventSources := []EventSource{
 		NewGitHubEventSource(processor),
 	}
-
 	for _, eventSource := range eventSources {
 		_ = eventSource.Setup()
 	}
 
-	done := make(chan struct{}) // TODO replace with error?
+	// 3. Start event sources
+	eg, ctx := errgroup.WithContext(context.Background())
 	for _, eventSource := range eventSources {
-		_ = eventSource.Run(done)
+		eg.Go(func() error {
+			return eventSource.Run(ctx)
+		})
 	}
 
 	// Block until an event source has a fatal error
-	<-done
-	close(done)
+	if err := eg.Wait(); err != nil {
+		log.Fatal(err)
+	}
 }
 
 // This contains information needed to process a request
@@ -99,12 +116,15 @@ type EventSource interface {
 	Setup() error
 
 	// Handle actual requests. This should not block.
-	Run(chan struct{}) error
+	Run(ctx context.Context) error
 }
 
 type GitHubEventSource struct {
 	processor ApprovalProcessor
-	// TODO
+
+	deployReviewChan chan *github.DeploymentReviewEvent
+	addr             string
+	srv              *http.Server
 }
 
 func NewGitHubEventSource(processor ApprovalProcessor) *GitHubEventSource {
@@ -114,43 +134,73 @@ func NewGitHubEventSource(processor ApprovalProcessor) *GitHubEventSource {
 // Setup GH client, webhook secret, etc.
 // https://github.com/go-playground/webhooks may help here
 func (ghes *GitHubEventSource) Setup() error {
-	// TODO
+	deployReviewChan := make(chan *github.DeploymentReviewEvent)
+	ghes.deployReviewChan = deployReviewChan
+
+	mux := http.NewServeMux()
+	eventProcessor := webhook.EventHandlerFunc(func(event interface{}) error {
+		switch event := event.(type) {
+		case *github.DeploymentReviewEvent:
+			deployReviewChan <- event
+			return nil
+		default:
+			return trace.Errorf("unknown event type: %T", event)
+		}
+	})
+	mux.Handle("/webhook", webhook.NewHandler(
+		eventProcessor,
+		webhook.WithSecretToken([]byte("secret-token")), // TODO: get from config
+		webhook.WithLogger(logger),
+	))
+
+	ghes.srv = &http.Server{
+		Addr:    ghes.addr,
+		Handler: mux,
+	}
+
 	return nil
 }
 
 // Take incoming events and respond to them
-func (ghes *GitHubEventSource) Run(done chan struct{}) error {
-	// If anything errors, deny the request. For safety, maybe `defer`
-	// the "response" function?
-	go func() {
-		// Notify the service that the listener is completely done.
-		// Normally this should only be hit if there is a fatal error
-		defer func() { done <- struct{}{} }()
+func (ghes *GitHubEventSource) Run(ctx context.Context) error {
+	errc := make(chan error)
 
-		// Incoming webhook payloads
-		// This should be closed by the webhook listener func
-		payloads := make(chan interface{})
-
-		// Listen for webhook calls
-		go ghes.listenForPayloads(payloads, done)
+	// Start the HTTP server
+	go func() {
+		logger.Info("Listening for GitHub Webhooks", "address", ghes.addr)
+		errc <- ghes.srv.ListenAndServe()
+		close(errc)
+	}()
 
-		for payload := range payloads {
-			go ghes.processWebhookPayload(payload, done)
+	// Process incoming events
+	go func() {
+		defer close(ghes.deployReviewChan)
+		logger.Info("Starting GitHub event processor")
+		for {
+			select {
+			case <-ctx.Done():
+				return
+			case deployReview := <-ghes.deployReviewChan:
+				// Process the event
+				go ghes.processDeploymentReviewEvent(deployReview)
+			}
 		}
 	}()
 
-	return nil
-}
-
-// Listen for incoming webhook events. Register HTTP routes, start server, etc. Long running, blocking.
-func (ghes *GitHubEventSource) listenForPayloads(payloads chan interface{}, done chan struct{}) {
-	// Once a call is received, it should return a 200 response immediately.
+	var err error
+	// This will block until an error occurs or the context is done
+	select {
+	case err = <-errc:
+		ghes.srv.Shutdown(context.Background()) // Ignore error - we're already handling one
+	case <-ctx.Done():
+		err = ghes.srv.Shutdown(context.Background())
+		<-errc // flush the error channel to avoid a goroutine leak
+	}
 
-	// TODO
+	return trace.Wrap(err)
 }
 
-// Given an event, approve or deny it. This is a long running, blocking function.
-func (ghes *GitHubEventSource) processWebhookPayload(payload interface{}, done chan struct{}) {
+func (ghes *GitHubEventSource) processDeploymentReviewEvent(payload *github.DeploymentReviewEvent) error {
 	// Do GitHub-specific checks. Don't approve based off ot this - just deny
 	// if one fails.
 	automatedDenial, err := ghes.performAutomatedChecks(payload)
@@ -170,6 +220,11 @@ func (ghes *GitHubEventSource) processWebhookPayload(payload interface{}, done c
 	}
 
 	_ = ghes.respondToDeployRequest(true, payload)
+	return nil
+}
+
+// Given an event, approve or deny it. This is a long running, blocking function.
+func (ghes *GitHubEventSource) processWebhookPayload(payload interface{}, done chan struct{}) {
 }
 
 // Turns GH-specific information into "common" information for the approver
@@ -183,10 +238,13 @@ func (ghes *GitHubEventSource) convertWebhookPayloadToEvent(payload interface{})
 
 // Performs approval checks that are GH-specific. This should only be used to deny requests,
 // never approve them.
-func (ghes *GitHubEventSource) performAutomatedChecks(payload interface{}) (pass bool, err error) {
+func (ghes *GitHubEventSource) performAutomatedChecks(payload *github.DeploymentReviewEvent) (pass bool, err error) {
 	// Verify request is from Gravitational org repo
 	// Verify request is from Gravitational org member
 	// See RFD for additional examples
+	if *payload.Organization.Login != "gravitational" {
+		return true, nil
+	}
 
 	return false, nil
 }

tools/approval-service/go.mod

@@ -1,3 +1,9 @@
 module github.com/gravitational/shared-workflows/tools/approval-service
 
 go 1.23.5
+
+require (
+	github.com/google/go-github/v63 v63.0.0 // indirect
+	github.com/google/go-github/v69 v69.1.0 // indirect
+	github.com/google/go-querystring v1.1.0 // indirect
+)

tools/approval-service/go.sum

@@ -0,0 +1,8 @@
+github.com/google/go-cmp v0.5.2/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
+github.com/google/go-github/v63 v63.0.0 h1:13xwK/wk9alSokujB9lJkuzdmQuVn2QCPeck76wR3nE=
+github.com/google/go-github/v63 v63.0.0/go.mod h1:IqbcrgUmIcEaioWrGYei/09o+ge5vhffGOcxrO0AfmA=
+github.com/google/go-github/v69 v69.1.0 h1:ljzwzEsHsc4qUqyHEJCNA1dMqvoTK3YX2NAaK6iprDg=
+github.com/google/go-github/v69 v69.1.0/go.mod h1:xne4jymxLR6Uj9b7J7PyTpkMYstEMMwGZa0Aehh1azM=
+github.com/google/go-querystring v1.1.0 h1:AnCroh3fv4ZBgVIf1Iwtovgjaw/GiKJo8M8yD/fhyJ8=
+github.com/google/go-querystring v1.1.0/go.mod h1:Kcdr2DB4koayq7X8pmAG4sNG59So17icRSOU623lUBU=
+golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=