rpc: avoid use of cgo by hard-coding maxPathSize (#27447)

Package rpc uses cgo to find the maximum UNIX domain socket path 
length. If exceeded, a warning is printed. This is the only use of cgo in this
package. It seems excessive to depend on cgo just for this warning, so
we now hard-code the usual limit for Linux instead.

---------
Co-authored-by: Felix Lange <fjl@twurst.com>

rpc/constants_unix.go

-// Copyright 2019 The go-ethereum Authors
-// This file is part of the go-ethereum library.
-//
-// The go-ethereum library is free software: you can redistribute it and/or modify
-// it under the terms of the GNU Lesser General Public License as published by
-// the Free Software Foundation, either version 3 of the License, or
-// (at your option) any later version.
-//
-// The go-ethereum library is distributed in the hope that it will be useful,
-// but WITHOUT ANY WARRANTY; without even the implied warranty of
-// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
-// GNU Lesser General Public License for more details.
-//
-// You should have received a copy of the GNU Lesser General Public License
-// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
-
-//go:build darwin || dragonfly || freebsd || linux || nacl || netbsd || openbsd || solaris
-// +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris
-
-package rpc
-
-/*
-#include <sys/un.h>
-
-int max_socket_path_size() {
-struct sockaddr_un s;
-return sizeof(s.sun_path);
-}
-*/
-import "C"
-
-var (
-	max_path_size = C.max_socket_path_size()
-)

rpc/constants_unix_nocgo.go

-// Copyright 2019 The go-ethereum Authors
-// This file is part of the go-ethereum library.
-//
-// The go-ethereum library is free software: you can redistribute it and/or modify
-// it under the terms of the GNU Lesser General Public License as published by
-// the Free Software Foundation, either version 3 of the License, or
-// (at your option) any later version.
-//
-// The go-ethereum library is distributed in the hope that it will be useful,
-// but WITHOUT ANY WARRANTY; without even the implied warranty of
-// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
-// GNU Lesser General Public License for more details.
-//
-// You should have received a copy of the GNU Lesser General Public License
-// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
-
-//go:build !cgo && !windows
-// +build !cgo,!windows
-
-package rpc
-
-var (
-	//  On Linux, sun_path is 108 bytes in size
-	// see http://man7.org/linux/man-pages/man7/unix.7.html
-	max_path_size = 108
-)

rpc/ipc_unix.go

@@ -29,11 +29,17 @@ import (
 	"github.com/ethereum/go-ethereum/log"
 )
 
+const (
+	// On Linux, sun_path is 108 bytes in size
+	// see http://man7.org/linux/man-pages/man7/unix.7.html
+	maxPathSize = int(108)
+)
+
 // ipcListen will create a Unix socket on the given endpoint.
 func ipcListen(endpoint string) (net.Listener, error) {
 	// account for null-terminator too
-	if len(endpoint)+1 > int(max_path_size) {
-		log.Warn(fmt.Sprintf("The ipc endpoint is longer than %d characters. ", max_path_size-1),
+	if len(endpoint)+1 > maxPathSize {
+		log.Warn(fmt.Sprintf("The ipc endpoint is longer than %d characters. ", maxPathSize-1),
 			"endpoint", endpoint)
 	}