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// SPDX-FileCopyrightText: V <v@anomalous.eu>
// SPDX-License-Identifier: OSL-3.0
package main // import "go.anomalous.eu/cgiserver"
import (
"context"
"flag"
"fmt"
"log"
"net/http"
"net/http/cgi"
"os"
"os/signal"
"syscall"
"github.com/coreos/go-systemd/v22/activation"
"github.com/gorilla/handlers"
)
func main() {
// The journal already has timestamps, so let's avoid adding our own.
log.SetFlags(0)
// The default usage message isn't very helpful, so we provide our own.
flag.Usage = func() {
fmt.Fprintln(flag.CommandLine.Output(), "Usage: cgiserver /path/to/application.cgi")
}
// We didn't configure any flags, so this just serves to display an error
// if someone tries to pass one. It also automatically handles -h/--help.
flag.Parse()
if flag.NArg() != 1 {
flag.Usage()
os.Exit(1)
}
path := flag.Arg(0)
// Socket activation makes our life very easy...
lns, err := activation.Listeners()
if err != nil {
log.Fatal(err)
}
if len(lns) == 0 {
log.Print("One or more listening sockets must be configured.")
log.Print("See systemd.socket(5) for more information.")
os.Exit(1)
}
var handler http.Handler
// ...and Go's standard library does literally all of the hard work.
handler = &cgi.Handler{
Path: path,
Env: os.Environ(), // Environment variables aren't inherited by default.
}
// We want to resolve X-Forwarded-For, etc.
handler = handlers.ProxyHeaders(handler)
// Additionally, we want to log requests.
handler = handlers.CombinedLoggingHandler(os.Stdout, handler)
// Catch SIGTERM so we can shutdown gracefully.
sig := make(chan os.Signal, 1)
signal.Notify(sig, syscall.SIGTERM, syscall.SIGINT)
// Create a Server so we can call Shutdown() on it later.
srv := &http.Server{Handler: handler}
doom := make(chan error)
for _, ln := range lns {
// Loop variables are unsafe to close over with goroutines,
// so this just shadows it with a fresh binding.
ln := ln
go func() {
// If any one of these return, it's game over.
doom <- srv.Serve(ln)
}()
}
select {
case err = <-doom:
// Only the first error matters, the rest will be ErrServerClosed.
log.Printf("Fatal server error: %v", err)
case <-sig:
log.Print("Caught signal, shutting down")
}
// This will block until all existing connections are handled.
srv.Shutdown(context.Background())
if err != nil {
os.Exit(1)
}
}
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