Add ability to stream command output as a response

Author: milolav

docs/Hook-Definition.md

@@ -13,6 +13,7 @@ Hooks are defined as JSON objects. Please note that in order to be considered va
  * `http-methods` - a list of allowed HTTP methods, such as `POST` and `GET`
  * `include-command-output-in-response` - boolean whether webhook should wait for the command to finish and return the raw output as a response to the hook initiator. If the command fails to execute or encounters any errors while executing the response will result in 500 Internal Server Error HTTP status code, otherwise the 200 OK status code will be returned.
  * `include-command-output-in-response-on-error` - boolean whether webhook should include command stdout & stderror as a response in failed executions. It only works if `include-command-output-in-response` is set to `true`.
+ * `stream-command-output` - boolean whether webhook should stream command stdout & stderror as a response. If true `include-command-output-in-response` is ignored.
  * `parse-parameters-as-json` - specifies the list of arguments that contain JSON strings. These parameters will be decoded by webhook and you can access them like regular objects in rules and `pass-arguments-to-command`.
  * `pass-arguments-to-command` - specifies the list of arguments that will be passed to the command. Check [Referencing request values page](Referencing-Request-Values.md) to see how to reference the values from the request. If you want to pass a static string value to your command you can specify it as
 `{ "source": "string", "name": "argumentvalue" }`

internal/hook/hook.go

@@ -508,6 +508,7 @@ type Hook struct {
 	ResponseMessage                     string          `json:"response-message,omitempty"`
 	ResponseHeaders                     ResponseHeaders `json:"response-headers,omitempty"`
 	CaptureCommandOutput                bool            `json:"include-command-output-in-response,omitempty"`
+	StreamCommandOutput                 bool            `json:"stream-command-output,omitempty"`
 	CaptureCommandOutputOnError         bool            `json:"include-command-output-in-response-on-error,omitempty"`
 	PassEnvironmentToCommand            []Argument      `json:"pass-environment-to-command,omitempty"`
 	PassArgumentsToCommand              []Argument      `json:"pass-arguments-to-command,omitempty"`

webhook.go

@@ -6,6 +6,7 @@ import (
 	"encoding/json"
 	"flag"
 	"fmt"
+	"io"
 	"io/ioutil"
 	"log"
 	"net"
@@ -66,6 +67,19 @@ var (
 	pidFile *pidfile.PIDFile
 )
 
+type flushWriter struct {
+	f http.Flusher
+	w io.Writer
+}
+
+func (fw *flushWriter) Write(p []byte) (n int, err error) {
+	n, err = fw.w.Write(p)
+	if fw.f != nil {
+		fw.f.Flush()
+	}
+	return
+}
+
 func matchLoadedHook(id string) *hook.Hook {
 	for _, hooks := range loadedHooksFromFiles {
 		if hook := hooks.Match(id); hook != nil {
@@ -514,8 +528,10 @@ func hookHandler(w http.ResponseWriter, r *http.Request) {
 			w.Header().Set(responseHeader.Name, responseHeader.Value)
 		}
 
-		if matchedHook.CaptureCommandOutput {
-			response, err := handleHook(matchedHook, rid, &headers, &query, &payload, &body)
+		if matchedHook.StreamCommandOutput {
+			handleHook(matchedHook, rid, &headers, &query, &payload, &body, w)
+		} else if matchedHook.CaptureCommandOutput {
+			response, err := handleHook(matchedHook, rid, &headers, &query, &payload, &body, nil)
 
 			if err != nil {
 				w.WriteHeader(http.StatusInternalServerError)
@@ -533,7 +549,7 @@ func hookHandler(w http.ResponseWriter, r *http.Request) {
 				fmt.Fprint(w, response)
 			}
 		} else {
-			go handleHook(matchedHook, rid, &headers, &query, &payload, &body)
+			go handleHook(matchedHook, rid, &headers, &query, &payload, &body, nil)
 
 			// Check if a success return code is configured for the hook
 			if matchedHook.SuccessHttpResponseCode != 0 {
@@ -556,7 +572,7 @@ func hookHandler(w http.ResponseWriter, r *http.Request) {
 	fmt.Fprint(w, "Hook rules were not satisfied.")
 }
 
-func handleHook(h *hook.Hook, rid string, headers, query, payload *map[string]interface{}, body *[]byte) (string, error) {
+func handleHook(h *hook.Hook, rid string, headers, query, payload *map[string]interface{}, body *[]byte, w http.ResponseWriter) (string, error) {
 	var errors []error
 
 	// check the command exists
@@ -625,12 +641,31 @@ func handleHook(h *hook.Hook, rid string, headers, query, payload *map[string]in
 
 	log.Printf("[%s] executing %s (%s) with arguments %q and environment %s using %s as cwd\n", rid, h.ExecuteCommand, cmd.Path, cmd.Args, envs, cmd.Dir)
 
-	out, err := cmd.CombinedOutput()
+	var out []byte
 
-	log.Printf("[%s] command output: %s\n", rid, out)
+	if w != nil {
+		log.Printf("[%s] command output will be streamed to response", rid)
 
-	if err != nil {
-		log.Printf("[%s] error occurred: %+v\n", rid, err)
+		// Implementation from https://play.golang.org/p/PpbPyXbtEs
+		// as described in https://stackoverflow.com/questions/19292113/not-buffered-http-responsewritter-in-golang
+		fw := flushWriter{w: w}
+		if f, ok := w.(http.Flusher); ok {
+			fw.f = f
+		}
+		cmd.Stderr = &fw
+		cmd.Stdout = &fw
+
+		if err := cmd.Run(); err != nil {
+			log.Printf("[%s] error occurred: %+v\n", rid, err)
+		}
+	} else {
+		out, err = cmd.CombinedOutput()
+
+		log.Printf("[%s] command output: %s\n", rid, out)
+
+		if err != nil {
+			log.Printf("[%s] error occurred: %+v\n", rid, err)
+		}
 	}
 
 	for i := range files {