Add pprof HTTP server

This enables production debugging of the bouncer.

Closes: https://todo.sr.ht/~emersion/soju/155

cmd/soju/main.go

@@ -9,6 +9,7 @@ import (
 	"log"
 	"net"
 	"net/http"
+	_ "net/http/pprof"
 	"net/url"
 	"os"
 	"os/signal"
@@ -286,6 +287,26 @@ func main() {
 					log.Fatalf("serving %q: %v", listen, err)
 				}
 			}()
+		case "http+pprof":
+			// Only allow localhost as listening host for security reasons.
+			// Users can always explicitly setup reverse proxies if desirable.
+			hostname, _, err := net.SplitHostPort(u.Host)
+			if err != nil {
+				log.Fatalf("invalid host in URI %q: %v", listen, err)
+			} else if hostname != "localhost" {
+				log.Fatalf("pprof listening host must be localhost")
+			}
+
+			// net/http/pprof registers its handlers in http.DefaultServeMux
+			httpSrv := http.Server{
+				Addr:    u.Host,
+				Handler: http.DefaultServeMux,
+			}
+			go func() {
+				if err := httpSrv.ListenAndServe(); err != nil {
+					log.Fatalf("serving %q: %v", listen, err)
+				}
+			}()
 		default:
 			log.Fatalf("failed to listen on %q: unsupported scheme", listen)
 		}

doc/soju.1.scd

@@ -100,6 +100,9 @@ The following directives are supported:
 	  port: 113)
 	- _http+prometheus://localhost:<port>_ listens for plain-text HTTP
 	  connections and serves Prometheus metrics (host must be "localhost")
+	- _http+pprof://localhost:<port>_ listens for plain-text HTTP connections
+	  and serves pprof runtime profiling data (host must be "localhost"). For
+	  more information, see: <https://pkg.go.dev/net/http/pprof>.
 
 	If the scheme is omitted, "ircs" is assumed. If multiple *listen*
 	directives are specified, soju will listen on each of them.