usbip: modernize loops and drop unused test helpers

Address `golangci-lint` modernize and unused warnings:
- replace map copy loops with `maps.Copy`
- collapse `if x > y { x = y }` clamps to `min`/`max`
- switch `for i := 0; i < n; i++` to `for i := range n`
- use `t.Context()` in the relay handoff test
- delete the unused `removeOnce` field and `openBinaryDevice` helper

service/usbip/client_assignment.go

@@ -3,6 +3,7 @@
 package usbip
 
 import (
+	"maps"
 	"sync"
 
 	"github.com/sagernet/sing-box/option"
@@ -131,9 +132,7 @@ func (a *clientAssignment) matchedKeysForAssignmentLocked(entries []DeviceEntry,
 		return nil
 	}
 	assignmentKeys := make(map[string]DeviceKey, len(a.matchedKnownKeys)+len(entries)+len(knownKeys))
-	for busid, key := range a.matchedKnownKeys {
-		assignmentKeys[busid] = key
-	}
+	maps.Copy(assignmentKeys, a.matchedKnownKeys)
 	for i := range entries {
 		key := entryDeviceKey(entries[i])
 		if key.BusID == "" {

service/usbip/client_darwin.go

@@ -542,10 +542,7 @@ func (c *darwinVirtualController) completeSubmitInTransfer(ptr unsafe.Pointer, r
 		c.requestClose()
 		return -int32(unix.EOVERFLOW), 0
 	}
-	copyLength := actualLength
-	if copyLength > len(response.Buffer) {
-		copyLength = len(response.Buffer)
-	}
+	copyLength := min(actualLength, len(response.Buffer))
 	if copyLength > 0 && ptr != nil {
 		if len(response.IsoPackets) > 0 {
 			dst := unsafe.Slice((*byte)(ptr), requestLength)
@@ -575,10 +572,7 @@ func scatterIsoInResponseBuffer(dst []byte, payload []byte, packets []IsoPacketD
 			cursor += length
 			continue
 		}
-		end := offset + length
-		if end > len(dst) {
-			end = len(dst)
-		}
+		end := min(offset+length, len(dst))
 		copy(dst[offset:end], payload[cursor:cursor+(end-offset)])
 		cursor += length
 	}

service/usbip/data_protocol.go

@@ -126,10 +126,7 @@ func ReadSubmitResponseBody(r io.Reader, header DataHeader, payloadDirection uin
 		ErrorCount:      int32(binary.BigEndian.Uint32(raw[16:20])),
 	}
 	copy(response.Setup[:], raw[20:28])
-	bufferLength := response.ActualLength
-	if bufferLength < 0 {
-		bufferLength = 0
-	}
+	bufferLength := max(response.ActualLength, 0)
 	buffer, isoPackets, err := readUSBIPPayload(r, payloadDirection, bufferLength, response.NumberOfPackets, false)
 	if err != nil {
 		return SubmitResponse{}, err

service/usbip/host_darwin.go

@@ -7,6 +7,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"maps"
 	"net"
 	"slices"
 	"sync"
@@ -119,9 +120,7 @@ func (h *darwinExportHost) Reconcile(ctx context.Context, isBusy func(busid stri
 
 	h.access.Lock()
 	current := make(map[string]*darwinExport, len(h.exports))
-	for busid, exp := range h.exports {
-		current[busid] = exp
-	}
+	maps.Copy(current, h.exports)
 	h.access.Unlock()
 
 	var (

service/usbip/host_linux.go

@@ -6,6 +6,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"maps"
 	"net"
 	"os"
 	"path/filepath"
@@ -197,9 +198,7 @@ func (h *linuxExportHost) Reconcile(ctx context.Context, isBusy func(busid strin
 
 	h.access.Lock()
 	current := make(map[string]*linuxExport, len(h.exports))
-	for busid, exp := range h.exports {
-		current[busid] = exp
-	}
+	maps.Copy(current, h.exports)
 	h.access.Unlock()
 
 	for busid, device := range desired {
@@ -258,7 +257,7 @@ func (h *linuxExportHost) bindOne(d *sysfsDevice) (*linuxExport, error) {
 		exp *linuxExport
 		err error
 	)
-	for attempt := 0; attempt < 2; attempt++ {
+	for attempt := range 2 {
 		exp, err = h.bindOneOnce(d)
 		if err == nil {
 			return exp, nil

service/usbip/linux_interop_test.go

@@ -67,14 +67,13 @@ type testVirtualFunction struct {
 }
 
 type testVirtualGadget struct {
-	path       string
-	serial     string
-	busid      string
-	functions  []testVirtualFunction
-	nodes      map[string]string
-	closeOnce  sync.Once
-	removeOnce sync.Once
-	udcName    string
+	path      string
+	serial    string
+	busid     string
+	functions []testVirtualFunction
+	nodes     map[string]string
+	closeOnce sync.Once
+	udcName   string
 }
 
 type testACMGadget struct {
@@ -726,14 +725,6 @@ func (r *rawFile) Close() {
 	_ = r.file.Close()
 }
 
-func openBinaryDevice(t *testing.T, path string) *os.File {
-	t.Helper()
-
-	file, err := os.OpenFile(path, os.O_RDWR, 0)
-	require.NoError(t, err)
-	return file
-}
-
 func newTestVirtualGadget(t *testing.T, productID uint16, productName string, functions []testVirtualFunction) *testVirtualGadget {
 	t.Helper()
 	requireRoot(t)

service/usbip/linux_test.go

@@ -299,9 +299,7 @@ func TestUSBIPConnHandoffRelaySocketpairCopies(t *testing.T) {
 
 	left, right := net.Pipe()
 	defer right.Close()
-	ctx, cancel := context.WithCancel(context.Background())
-	defer cancel()
-	handoff, err := newKernelHandoffSession(ctx, opaqueConn{Conn: left}, newTestLogger(t), "test", "relay")
+	handoff, err := newKernelHandoffSession(t.Context(), opaqueConn{Conn: left}, newTestLogger(t), "test", "relay")
 	require.NoError(t, err)
 	defer handoff.Close()
 	require.NotNil(t, handoff.relayConn)

service/usbip/sysfs_linux.go

@@ -139,7 +139,7 @@ func readInterfaces(devicePath, busid string, configValue uint8, count int) []De
 		return nil
 	}
 	interfaces := make([]DeviceInterface, count)
-	for i := 0; i < count; i++ {
+	for i := range count {
 		name := fmt.Sprintf("%s:%d.%d", busid, configValue, i)
 		ipath := filepath.Join(filepath.Dir(devicePath), name)
 		class, _ := readHexU8(ipath, "bInterfaceClass")

service/usbip/usbhost_darwin.go

@@ -485,10 +485,7 @@ func darwinDeviceInfoFromC(info *C.box_usbhost_device_info_t) darwinUSBHostDevic
 	}
 	copy(entry.Info.BusID[:], busid)
 	encodePathField(&entry.Info.Path, path, serial)
-	interfaceCount := int(info.interface_count)
-	if interfaceCount > C.BOX_USBHOST_MAX_INTERFACES {
-		interfaceCount = C.BOX_USBHOST_MAX_INTERFACES
-	}
+	interfaceCount := min(int(info.interface_count), C.BOX_USBHOST_MAX_INTERFACES)
 	if interfaceCount > 0 {
 		rawInterfaces := unsafe.Slice(&info.interfaces[0], interfaceCount)
 		entry.Interfaces = make([]DeviceInterface, interfaceCount)