MM-14575 - Automatically serve static files for plugins (#10476)

* MM-14575 - Automatically serve static files for plugins
* Added static handler for plugin public files
* Added StaticFilesPath method to Environment for use by MainRouter
* Added "static_files" property to Manifest Server
* Added unit tests for these changes

* MM-14575: Adding comment for cache control value

* MM-14575: Moved Static Plugin Request handler to plugin_requests
* Updated testing

* MM-14575: Removing the StaticFiles from Manifest Server

* MM-14575: Removing static files from test

* MM-14575: Updating static files test

* MM14575: Removing cache directive from plugin static files

* MM14575: Moving plugin public directory to root

* MM-14575: Updating tests for changed public directory

* MM-14575: Moved compileGo to a common utils package for tests

* MM-14575: Moving plugins initialization to InitPlugins find in tests

* Update utils/test_files_compiler.go

Adding Copyright header

Co-Authored-By: happygaijin <happygaijin@users.noreply.github.com>

* MM-14575: Consistent usage of static vs public name

* Removing spurious newline

* Comment typo

Co-Authored-By: happygaijin <happygaijin@users.noreply.github.com>

* Removing spurious new line

Co-Authored-By: happygaijin <happygaijin@users.noreply.github.com>

* MM14575: Adding a test to make sure only public files can be requested

* MM-14575 Adding a test for redirects on public files

app/plugin_requests.go

@@ -4,8 +4,10 @@
 package app
 
 import (
+	"fmt"
 	"net/http"
 	"path"
+	"path/filepath"
 	"strings"
 
 	"bytes"
@@ -40,6 +42,34 @@ func (a *App) ServePluginRequest(w http.ResponseWriter, r *http.Request) {
 	a.servePluginRequest(w, r, hooks.ServeHTTP)
 }
 
+// ServePluginPublicRequest serves public plugin files
+// at the URL http(s)://$SITE_URL/plugins/$PLUGIN_ID/public/{anything}
+func (a *App) ServePluginPublicRequest(w http.ResponseWriter, r *http.Request) {
+	if strings.HasSuffix(r.URL.Path, "/") {
+		http.NotFound(w, r)
+		return
+	}
+
+	// Should be in the form of /$PLUGIN_ID/public/{anything} by the time we get here
+	vars := mux.Vars(r)
+	pluginID := vars["plugin_id"]
+
+	publicFilesPath, err := a.GetPluginsEnvironment().PublicFilesPath(pluginID)
+	if err != nil {
+		http.NotFound(w, r)
+		return
+	}
+
+	publicFilePath := path.Clean(r.URL.Path)
+	prefix := fmt.Sprintf("/plugins/%s/public/", pluginID)
+	if !strings.HasPrefix(publicFilePath, prefix) {
+		http.NotFound(w, r)
+		return
+	}
+	publicFile := filepath.Join(publicFilesPath, strings.TrimPrefix(publicFilePath, prefix))
+	http.ServeFile(w, r, publicFile)
+}
+
 func (a *App) servePluginRequest(w http.ResponseWriter, r *http.Request, handler func(*plugin.Context, http.ResponseWriter, *http.Request)) {
 	token := ""
 	context := &plugin.Context{