fix(uds): align request wire format with sra-common LocateRequest

Go server was parsing fid at bytes 0-15 (Go format), but Rust
uds_client sends opcode(1)+pad(3)+request_id(4)+fid(16) per
sra-common::uds_proto::LocateRequest repr(C).

Now Go parses: opcode at byte 0, request_id at bytes 4-7, fid at
bytes 8-23. Matches the Rust wire format exactly.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

weed/server/volume_server_uds.go

@@ -36,10 +36,13 @@ type UdsServer struct {
 }
 
 // LocateRequest represents a UDS locate request
+// Wire format matches sra-common::uds_proto::LocateRequest (repr(C)):
+//   opcode(1) + pad(3) + request_id(4) + fid(16) = 24 bytes
 type LocateRequest struct {
-	Fid     [16]byte // ASCII fid, null-padded
-	Version uint32
-	Flags   uint32
+	Opcode    uint8
+	_pad      [3]byte
+	RequestId uint32
+	Fid       [16]byte // ASCII fid, null-padded
 }
 
 // LocateResponse represents a UDS locate response
@@ -136,11 +139,12 @@ func (u *UdsServer) handleConnection(conn net.Conn) {
 			return
 		}
 
-		// Parse request
+		// Parse request (matches sra-common::uds_proto::LocateRequest repr(C))
+		// opcode(1) + pad(3) + request_id(4) + fid(16) = 24 bytes
 		var req LocateRequest
-		copy(req.Fid[:], reqBuf[0:16])
-		req.Version = binary.LittleEndian.Uint32(reqBuf[16:20])
-		req.Flags = binary.LittleEndian.Uint32(reqBuf[20:24])
+		req.Opcode = reqBuf[0]
+		req.RequestId = binary.LittleEndian.Uint32(reqBuf[4:8])
+		copy(req.Fid[:], reqBuf[8:24])
 
 		// Handle request
 		resp := u.handleLocate(&req)

weed/server/volume_server_uds_test.go

@@ -21,27 +21,28 @@ func TestLocateRequestResponseSize(t *testing.T) {
 }
 
 func TestLocateRequestSerialization(t *testing.T) {
+	// Wire format: opcode(1) + pad(3) + request_id(4) + fid(16) = 24
 	req := LocateRequest{
-		Version: 1,
-		Flags:   0,
+		Opcode:    1, // VolumeOpcode::Locate
+		RequestId: 42,
 	}
 	copy(req.Fid[:], "3,01637037")
 
 	buf := make([]byte, UdsRequestSize)
-	copy(buf[0:16], req.Fid[:])
-	binary.LittleEndian.PutUint32(buf[16:20], req.Version)
-	binary.LittleEndian.PutUint32(buf[20:24], req.Flags)
+	buf[0] = req.Opcode
+	binary.LittleEndian.PutUint32(buf[4:8], req.RequestId)
+	copy(buf[8:24], req.Fid[:])
 
-	// Verify fid is correctly placed
-	fid := string(buf[0:10])
+	// Verify fid is correctly placed at offset 8
+	fid := string(buf[8:18])
 	if fid != "3,01637037" {
 		t.Errorf("Expected fid='3,01637037', got '%s'", fid)
 	}
 
-	// Verify version
-	version := binary.LittleEndian.Uint32(buf[16:20])
-	if version != 1 {
-		t.Errorf("Expected version=1, got %d", version)
+	// Verify request_id
+	requestId := binary.LittleEndian.Uint32(buf[4:8])
+	if requestId != 42 {
+		t.Errorf("Expected request_id=42, got %d", requestId)
 	}
 }
 
@@ -145,10 +146,11 @@ func TestUdsServerProtocol(t *testing.T) {
 	defer conn.Close()
 
 	// Send a request (will fail because vs is nil, but we're testing protocol)
+	// Wire format: opcode(1) + pad(3) + request_id(4) + fid(16)
 	reqBuf := make([]byte, UdsRequestSize)
-	copy(reqBuf[0:16], "3,01637037")
-	binary.LittleEndian.PutUint32(reqBuf[16:20], 1) // version
-	binary.LittleEndian.PutUint32(reqBuf[20:24], 0) // flags
+	reqBuf[0] = 1 // VolumeOpcode::Locate
+	binary.LittleEndian.PutUint32(reqBuf[4:8], 1) // request_id
+	copy(reqBuf[8:24], "3,01637037")              // fid at offset 8
 
 	_, err = conn.Write(reqBuf)
 	if err != nil {
@@ -195,8 +197,8 @@ func TestUdsSocketCleanup(t *testing.T) {
 
 func TestFidParsing(t *testing.T) {
 	tests := []struct {
-		fid    string
-		valid  bool
+		fid   string
+		valid bool
 	}{
 		{"3,01637037", true},
 		{"1,abc123", true},
@@ -221,7 +223,6 @@ func TestFidParsing(t *testing.T) {
 			}
 			fid := string(fidBytes[:fidLen])
 
-			// For empty fid, we expect empty string
 			if tt.fid == "" && fid != "" {
 				t.Errorf("Expected empty fid, got '%s'", fid)
 			}