From a5324bf66e8f565ea9dcd09c90cfff8fa64bee14 Mon Sep 17 00:00:00 2001
From: "Alex Ellis (OpenFaaS Ltd)" <alexellis2@gmail.com>
Date: Wed, 31 May 2023 10:02:37 +0100
Subject: [PATCH] Stream stderr to logs for streaming fork mode

This mode is not expected to be used by any customers in
production, however we received a message from a customer who
had decided to use this mode.

They reported not being able to log to stderr, I was able to
reproduce the problem and have added bindLoggingPipe to
stderr as per the other modes in the of-watchdog.

After testing with a simple Python program, the logging is
now available.

We only recommend HTTP mode for production use.

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <alexellis2@gmail.com>
---
 executor/logging.go                 | 1 -
 executor/serializing_fork_runner.go | 9 +++++++--
 main.go                             | 5 +++--
 3 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/executor/logging.go b/executor/logging.go
index eb9575d1..b6d435a1 100644
--- a/executor/logging.go
+++ b/executor/logging.go
@@ -10,7 +10,6 @@ import (
 )
 
 // bindLoggingPipe spawns a goroutine for passing through logging of the given output pipe.
-//
 func bindLoggingPipe(name string, pipe io.Reader, output io.Writer, logPrefix bool, maxBufferSize int) {
 	log.Printf("Started logging: %s from function.", name)
 
diff --git a/executor/serializing_fork_runner.go b/executor/serializing_fork_runner.go
index ed96f29b..92c07d77 100644
--- a/executor/serializing_fork_runner.go
+++ b/executor/serializing_fork_runner.go
@@ -8,6 +8,7 @@ import (
 	"fmt"
 	"io"
 	"io/ioutil"
+	"os"
 
 	units "github.com/docker/go-units"
 
@@ -21,8 +22,9 @@ import (
 
 // SerializingForkFunctionRunner forks a process for each invocation
 type SerializingForkFunctionRunner struct {
-	ExecTimeout time.Duration
-	LogPrefix   bool
+	ExecTimeout   time.Duration
+	LogPrefix     bool
+	LogBufferSize int
 }
 
 // Run run a fork for each invocation
@@ -99,11 +101,14 @@ func serializeFunction(req FunctionRequest, f *SerializingForkFunctionRunner) (*
 
 	stdout, _ := cmd.StdoutPipe()
 	stdin, _ := cmd.StdinPipe()
+	stderr, _ := cmd.StderrPipe()
 
 	if err := cmd.Start(); err != nil {
 		return nil, err
 	}
 
+	bindLoggingPipe("stderr", stderr, os.Stderr, f.LogPrefix, f.LogBufferSize)
+
 	functionRes, errors := pipeToProcess(stdin, stdout, &data)
 	if len(errors) > 0 {
 		return nil, errors[0]
diff --git a/main.go b/main.go
index 0e8602e8..279db892 100644
--- a/main.go
+++ b/main.go
@@ -233,8 +233,9 @@ func createLockFile() (string, error) {
 
 func makeSerializingForkRequestHandler(watchdogConfig config.WatchdogConfig, logPrefix bool) func(http.ResponseWriter, *http.Request) {
 	functionInvoker := executor.SerializingForkFunctionRunner{
-		ExecTimeout: watchdogConfig.ExecTimeout,
-		LogPrefix:   logPrefix,
+		ExecTimeout:   watchdogConfig.ExecTimeout,
+		LogPrefix:     logPrefix,
+		LogBufferSize: watchdogConfig.LogBufferSize,
 	}
 
 	return func(w http.ResponseWriter, r *http.Request) {