main.go

//go:build linux

package main

import (
	"io"
	"log"
	"os"
	"os/exec"
	"syscall"
)

func main() {
	const fifoPath = "/tmp/access_fifo"
	const logPath = "/var/log/nginx/access.log"
	const capturedLogPath = "/tmp/access_captured.log"
	const procFd1Path = "/proc/1/fd/1"

	// Step 1: Create named pipe
	if err := syscall.Mkfifo(fifoPath, 0666); err != nil {
		log.Fatalf("Failed to create FIFO: %v", err)
	}

	// Step 2: Move FIFO to log location
	if err := os.Rename(fifoPath, logPath); err != nil {
		log.Fatalf("Failed to move FIFO: %v", err)
	}

	// Step 2.5: Reload nginx to pick up the new pipe (before opening FIFO for reading)
	cmd := exec.Command("nginx", "-s", "reload")
	output, err := cmd.CombinedOutput()
	if err != nil {
		log.Fatalf("Failed to reload nginx: %v\nOutput: %s", err, string(output))
	} else {
		log.Printf("nginx reload output: %s", string(output))
	}

	// Step 3: Open the FIFO for reading
	logPipe, err := os.OpenFile(logPath, os.O_RDONLY, 0)
	if err != nil {
		log.Fatalf("Failed to open log FIFO: %v", err)
	}
	defer logPipe.Close()

	// Open captured log for writing
	capturedLog, err := os.OpenFile(capturedLogPath, os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0644)
	if err != nil {
		log.Fatalf("Failed to open captured log: %v", err)
	}
	defer capturedLog.Close()

	// Open /proc/1/fd/1 for writing (stdout of NGINX on PID 1)
	procFd1, err := os.OpenFile(procFd1Path, os.O_WRONLY|os.O_APPEND, 0)
	if err != nil {
		log.Fatalf("Failed to open /proc/1/fd/1: %v", err)
	}
	defer procFd1.Close()

	// Step 4: Read from logFile, write to both capturedLog and procFd1
	multiWriter := io.MultiWriter(capturedLog, procFd1)
	buf := make([]byte, 4096)
	for {
		n, err := logPipe.Read(buf)
		if n > 0 {
			if _, werr := multiWriter.Write(buf[:n]); werr != nil {
				log.Printf("Write error: %v", werr)
			}
		}
		if err != nil {
			if err == io.EOF {
				break
			}
			log.Fatalf("Read error: %v", err)
		}
	}

}