Config: Support abstract unix sockets in remote loader (#6111)

Replaces https://github.com/XTLS/Xray-core/pull/5200

common/utils/unixsocket.go

@@ -0,0 +1,55 @@
+package utils
+
+import (
+	"path/filepath"
+	"runtime"
+	"strings"
+	"syscall"
+)
+
+// ResolveSocketPath applies platform-specific transformations to a Unix
+// socket path, matching the listen-side behaviour in
+// transport/internet/system_listener.go.
+//
+// For abstract sockets (prefix @) on Linux/Android:
+//   - single @ — used as-is (lock-free abstract socket)
+//   - double @@ — stripped to single @ and padded to
+//     syscall.RawSockaddrUnix{}.Path length (HAProxy compat)
+//
+// Filesystem paths and abstract sockets on other platforms are returned
+// unchanged.
+func ResolveSocketPath(path string) string {
+    if len(path) == 0 || path[0] != '@' {
+        return path
+    }
+    if runtime.GOOS != "linux" && runtime.GOOS != "android" {
+        return path
+    }
+    if len(path) > 1 && path[1] == '@' {
+        fullAddr := make([]byte, len(syscall.RawSockaddrUnix{}.Path))
+        copy(fullAddr, path[1:])
+        return string(fullAddr)
+    }
+    return path
+}
+
+// SplitHTTPUnixURL splits a target into an HTTP URL and an optional Unix
+// socket path. For regular http(s) URLs the input is returned unchanged
+// with an empty socketPath. For Unix sockets the format is:
+//
+//	/path/to/socket.sock[:/http/path]
+//	@abstract[:/http/path]
+//	@@padded[:/http/path]
+//
+// The :/ separator delimits the socket path from the HTTP request path.
+// If omitted, "/" is used.
+func SplitHTTPUnixURL(raw string) (httpURL, socketPath string) {
+    if len(raw) == 0 || (!filepath.IsAbs(raw) && raw[0] != '@') {
+        return raw, ""
+    }
+    if idx := strings.Index(raw, ":/"); idx >= 0 {
+        return "http://localhost" + raw[idx+1:], raw[:idx]
+    }
+    return "http://localhost/", raw
+}
+