Add streaming command support.

Add options
- `stream-stdout-in-response`
- `stream-stdout-in-response-on-error`
- `stream-command-kill-grace-period-seconds`

to allow defining webhooks which dynamically stream large content back to the
requestor. This allows the creation of download endpoints from scripts, i.e.
running a `git archive` command or a database dump from a docker container,
without needing to buffer up the original.

test/hookecho.go

@@ -5,13 +5,58 @@ package main
 import (
 	"fmt"
 	"os"
-	"strconv"
 	"strings"
+	"strconv"
+	"io"
 )
 
+func checkPrefix(prefixMap map[string]struct{}, prefix string, arg string) bool {
+	if _, found := prefixMap[prefix]; found {
+		fmt.Printf("prefix specified more then once: %s", arg)
+		os.Exit(-1)
+	}
+
+	if strings.HasPrefix(arg, prefix) {
+		prefixMap[prefix] = struct{}{}
+		return true
+	}
+
+	return false
+}
+
 func main() {
+	var outputStream io.Writer
+	outputStream = os.Stdout
+	seenPrefixes := make(map[string]struct{})
+	exit_code := 0
+
+	for _, arg := range os.Args[1:] {
+		if checkPrefix(seenPrefixes, "stream=", arg) {
+			switch arg {
+			case "stream=stdout":
+				outputStream = os.Stdout
+			case "stream=stderr":
+				outputStream = os.Stderr
+			case "stream=both":
+				outputStream = io.MultiWriter(os.Stdout, os.Stderr)
+			default:
+				fmt.Printf("unrecognized stream specification: %s", arg)
+				os.Exit(-1)
+			}
+		} else if checkPrefix(seenPrefixes, "exit=", arg) {
+			exit_code_str := arg[5:]
+			var err error
+			exit_code_conv, err := strconv.Atoi(exit_code_str)
+			exit_code = exit_code_conv
+			if err != nil {
+				fmt.Printf("Exit code %s not an int!", exit_code_str)
+				os.Exit(-1)
+			}
+		}
+	}
+
 	if len(os.Args) > 1 {
-		fmt.Printf("arg: %s\n", strings.Join(os.Args[1:], " "))
+		fmt.Fprintf(outputStream, "arg: %s\n", strings.Join(os.Args[1:], " "))
 	}
 
 	var env []string
@@ -22,16 +67,8 @@ func main() {
 	}
 
 	if len(env) > 0 {
-		fmt.Printf("env: %s\n", strings.Join(env, " "))
+		fmt.Fprintf(outputStream, "env: %s\n", strings.Join(env, " "))
 	}
 
-	if (len(os.Args) > 1) && (strings.HasPrefix(os.Args[1], "exit=")) {
-		exit_code_str := os.Args[1][5:]
-		exit_code, err := strconv.Atoi(exit_code_str)
-		if err != nil {
-			fmt.Printf("Exit code %s not an int!", exit_code_str)
-			os.Exit(-1)
-		}
-		os.Exit(exit_code)
-	}
+	os.Exit(exit_code)
 }