Support for receiving webhooks

README.md

     	if specified, requests for / will be redirected to this url
   -repo string
     	the repository to redirect releases for, in user/repo format [required]
+  -webhook string
+    	full path to receive release webhooks from GitHub on
 ```
 
 ## Notes
 
+### Root redirecting
+
 If the `-redirect` option is specified, then requests to the root (i.e. `/`)
 will be redirected to that URL, and no further processing will be done for
 that request.
 
+### Polling and webhooks
+
 Releases are refreshed at startup and then, by default, once an hour. You can
 customise this duration with the `-poll` option; setting the poll time to `0`
 will disable polling entirely other than at startup.
 
+As an alternative to polling, you can configure a webhook URL with the
+`-webhook` argument. This must be the full URL that GitHub will call
+when a release is made, and it is advisable to include a secret in the
+URL to avoid any client on the Internet being able to trigger a refresh.
+
+For example if you run with `-webhook /webhook/gjrCBVy7`, you
+should configure GitHub to send pull requests to
+`https://yourserver.example.com/webook/gjrCBVy7`. You should configure
+the WebHook to only send individual events, and select only the
+`Releases` option.
+
+The contents of the webhook are not used; it is merely used as a signal
+to start a refresh using the GitHub API.
+
+When running with the `-webhook` option it is recommended to also disable
+polling with `-poll 0`, or set the polling time to a much larger value.
+
+### Asset matching
+
 Assets are matched on their name, so an asset attached to the latest release
 named "myproject-installer-1.2.3.exe" will be available at the URL
 `/myproject-installer-1.2.3.exe`.
 if there is no latest release available all requests will respond with 500
 internal server error.
 
+### HTTPS
+
 The service listens only on HTTP, not HTTPS. For production use it should
 be placed behind an SSL-terminating proxy such as Traefik, Nginx or HAProxy.
 
+## Contributing/further work
+
+This performs the job I wrote it to do, so it's unlikely I'll be developing
+any further features. If you're using this and would like to send a pull
+request for a feature I'd be happy to review and merge.
+
+In particular I'd welcome the following:
+
+- [ ] HTTPS support (specifying certs/keys/etc)
+- [ ] Support for GitHub's secret digests, instead of using a secret URL
+- [ ] Parsing of the WebHook content to avoid refreshing needlessly
+
 ## Licence
 
 This software is released under the MIT licence. See the LICENCE file for

main.go

 	owner string
 	repo string
 	redirect *string
+	webhookPath *string
 	ctx context.Context
 	client *github.Client
 	release *github.RepositoryRelease
 	w.WriteHeader(http.StatusTemporaryRedirect)
 }
 
-func serve(w http.ResponseWriter, request *http.Request) {
+func serveStaticPaths(w http.ResponseWriter, request *http.Request) bool {
 	if "/" == request.RequestURI && len(*redirect) > 0 {
 		temporaryRedirect(w, *redirect)
-		return
+		return true
 	}
 
+	if *webhookPath == request.RequestURI {
+		log.Println("Received webhook, starting a refresh")
+		go func() {
+			fetchLatest()
+		}()
+		w.WriteHeader(http.StatusOK)
+		return true
+	}
+
+	return false
+}
+
+func serveAssets(w http.ResponseWriter, request *http.Request) bool {
 	if release == nil {
 		w.WriteHeader(http.StatusInternalServerError)
 		_, _ = fmt.Fprint(w, "Unknown release")
-		return
+		return true
 	}
 
 	for _, asset := range release.Assets {
 		if "/" + *asset.Name == request.RequestURI {
 			temporaryRedirect(w, *asset.BrowserDownloadURL)
-			return
+			return true
 		}
 	}
 
-	w.WriteHeader(http.StatusNotFound)
-	_, _ = fmt.Fprint(w, "Asset not found in release ", *release.Name)
+	return false
+}
+
+func serve(w http.ResponseWriter, request *http.Request) {
+	if !serveStaticPaths(w, request) && !serveAssets(w, request) {
+		w.WriteHeader(http.StatusNotFound)
+		_, _ = fmt.Fprint(w, "Asset not found in release ", *release.Name)
+	}
 }
 
 func parseRepo(fullRepo *string) error {
 
 func main() {
 	redirect = flag.String("redirect", "", "if specified, requests for / will be redirected to this url")
+	webhookPath = flag.String("webhook", "", "full path to receive release webhooks from GitHub on")
 	var fullRepo = flag.String("repo", "", "the repository to redirect releases for, in user/repo format [required]")
 	var port = flag.Int("port", 8080, "the port to listen on for HTTP requests")
 	var poll = flag.Int("poll", 3600, "the amount of time to wait between polling for releases; 0 to disable polling")