factor out some shared code

irc/client.go

@@ -488,40 +488,19 @@ func (client *Client) lookupHostname(session *Session, overwrite bool) {
 	if session.proxiedIP != nil {
 		ip = session.proxiedIP
 	}
-	ipString := ip.String()
 
-	var hostname, candidate string
+	var hostname string
+	lookupSuccessful := false
 	if config.Server.lookupHostnames {
 		session.Notice("*** Looking up your hostname...")
-
-		names, err := net.LookupAddr(ipString)
-		if err == nil && 0 < len(names) {
-			candidate = strings.TrimSuffix(names[0], ".")
-		}
-		if utils.IsHostname(candidate) {
-			if config.Server.ForwardConfirmHostnames {
-				addrs, err := net.LookupHost(candidate)
-				if err == nil {
-					for _, addr := range addrs {
-						if addr == ipString {
-							hostname = candidate // successful forward confirmation
-							break
-						}
-					}
-				}
-			} else {
-				hostname = candidate
-			}
-		}
-	}
-
-	if hostname != "" {
-		session.Notice("*** Found your hostname")
-	} else {
-		if config.Server.lookupHostnames {
+		hostname, lookupSuccessful = utils.LookupHostname(ip, config.Server.ForwardConfirmHostnames)
+		if lookupSuccessful {
+			session.Notice("*** Found your hostname")
+		} else {
 			session.Notice("*** Couldn't look up your hostname")
 		}
-		hostname = utils.IPStringToHostname(ipString)
+	} else {
+		hostname = utils.IPStringToHostname(ip.String())
 	}
 
 	session.rawHostname = hostname

irc/histserv.go

@@ -7,7 +7,6 @@ import (
 	"bufio"
 	"fmt"
 	"os"
-	"runtime/debug"
 	"strconv"
 	"time"
 
@@ -156,12 +155,7 @@ func histservExportHandler(service *ircService, server *Server, client *Client,
 }
 
 func histservExportAndNotify(service *ircService, server *Server, cfAccount string, outfile *os.File, filename, alertNick string) {
-	defer func() {
-		if r := recover(); r != nil {
-			server.logger.Error("history",
-				fmt.Sprintf("Panic in history export routine: %v\n%s", r, debug.Stack()))
-		}
-	}()
+	defer server.HandlePanic()
 
 	defer outfile.Close()
 	writer := bufio.NewWriter(outfile)

irc/panic.go

@@ -0,0 +1,19 @@
+// Copyright (c) 2021 Shivaram Lingamneni
+// released under the MIT license
+
+package irc
+
+import (
+	"fmt"
+	"runtime/debug"
+)
+
+// HandlePanic is a general-purpose panic handler for ad-hoc goroutines.
+// Because of the semantics of `recover`, it must be called directly
+// from the routine on whose call stack the panic would occur, with `defer`,
+// e.g. `defer server.HandlePanic()`
+func (server *Server) HandlePanic() {
+	if r := recover(); r != nil {
+		server.logger.Error("internal", fmt.Sprintf("Panic encountered: %v\n%s", r, debug.Stack()))
+	}
+}

irc/server.go

@@ -12,7 +12,6 @@ import (
 	_ "net/http/pprof"
 	"os"
 	"os/signal"
-	"runtime/debug"
 	"strconv"
 	"strings"
 	"sync"
@@ -245,14 +244,12 @@ func (server *Server) checkTorLimits() (banned bool, message string) {
 
 func (server *Server) handleAlwaysOnExpirations() {
 	defer func() {
-		if r := recover(); r != nil {
-			server.logger.Error("internal",
-				fmt.Sprintf("Panic in always-on cleanup: %v\n%s", r, debug.Stack()))
-		}
-		// either way, reschedule
+		// reschedule whether or not there was a panic
 		time.AfterFunc(alwaysOnExpirationPollPeriod, server.handleAlwaysOnExpirations)
 	}()
 
+	defer server.HandlePanic()
+
 	config := server.Config()
 	deadline := time.Duration(config.Accounts.Multiclient.AlwaysOnExpiration)
 	if deadline == 0 {
@@ -514,16 +511,7 @@ func (client *Client) getWhoisOf(target *Client, hasPrivs bool, rb *ResponseBuff
 // rehash reloads the config and applies the changes from the config file.
 func (server *Server) rehash() error {
 	// #1570; this needs its own panic handling because it can be invoked via SIGHUP
-	defer func() {
-		if r := recover(); r != nil {
-			if server.Config().Debug.recoverFromErrors {
-				server.logger.Error("internal",
-					fmt.Sprintf("Panic during rehash: %v\n%s", r, debug.Stack()))
-			} else {
-				panic(r)
-			}
-		}
-	}()
+	defer server.HandlePanic()
 
 	server.logger.Info("server", "Attempting rehash")
 

irc/utils/net.go

@@ -193,3 +193,37 @@ func HandleXForwardedFor(remoteAddr string, xForwardedFor string, whitelist []ne
 	// or nil:
 	return
 }
+
+// LookupHostname does an (optionally reverse-confirmed) hostname lookup
+// suitable for use as an IRC hostname. It falls back to a string
+// representation of the IP address (again suitable for use as an IRC
+// hostname).
+func LookupHostname(ip net.IP, forwardConfirm bool) (hostname string, lookupSuccessful bool) {
+	ipString := ip.String()
+	var candidate string
+	names, err := net.LookupAddr(ipString)
+	if err == nil && 0 < len(names) {
+		candidate = strings.TrimSuffix(names[0], ".")
+	}
+	if IsHostname(candidate) {
+		if forwardConfirm {
+			addrs, err := net.LookupHost(candidate)
+			if err == nil {
+				for _, addr := range addrs {
+					if forwardIP := net.ParseIP(addr); ip.Equal(forwardIP) {
+						hostname = candidate // successful forward confirmation
+						break
+					}
+				}
+			}
+		} else {
+			hostname = candidate
+		}
+	}
+
+	if hostname != "" {
+		return hostname, true
+	} else {
+		return IPStringToHostname(ipString), false
+	}
+}