fix(desktop): match WSAEADDRINUSE on Windows and repair the Go test build

CHANGELOG.md

@@ -19,6 +19,7 @@
 - 手机截图写到专家自己的工作区。只改定时任务文案时，间隔任务不再重新计时
 - 浏览器工作台恢复中文输入。主动关怀等对话安静后再发
 - 向导密码随数据目录迁移。Linux 桌面无边框窗口可以拖边缘调整大小
+- 桌面端（Windows）配置端口被占用时不会顺延到下一个空闲端口：端口探测误用 Windows 上恒不成立的 `syscall.EADDRINUSE`，现按平台匹配 `WSAEADDRINUSE`；同时修复 desktop Go 测试包因重复声明 `err` 而无法编译（Fixes #1905）
 
 ### 变更
 - 云端协同默认打码对端地址和账号。共享来的资源在头像上做标记

desktop/src/filedrop_test.go

@@ -88,7 +88,6 @@ func TestDropServerServesOnlyPublishedFiles(t *testing.T) {
 		t.Fatal(err)
 	}
 	var resp *http.Response
-	var err error
 	for attempt := 0; attempt < 20; attempt++ {
 		resp, err = http.Get(base + "/0")
 		if err == nil {

desktop/src/process.go

@@ -2,7 +2,6 @@ package main
 
 import (
 	"encoding/json"
-	"errors"
 	"fmt"
 	"io"
 	"net"
@@ -13,7 +12,6 @@ import (
 	"runtime"
 	"strconv"
 	"strings"
-	"syscall"
 	"time"
 )
 
@@ -219,7 +217,7 @@ func listenProbe(host string, port int) (bool, error) {
 		_ = ln.Close()
 		return false, nil
 	}
-	if errors.Is(err, syscall.EADDRINUSE) {
+	if addrInUse(err) {
 		return true, nil
 	}
 	return false, err

desktop/src/process_test.go

@@ -127,6 +127,25 @@ func TestChooseFreePortStopsWhenHostCannotBind(t *testing.T) {
 	}
 }
 
+func TestChooseFreePortSkipsALiveListener(t *testing.T) {
+	ln, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer ln.Close()
+	busy := ln.Addr().(*net.TCPAddr).Port
+	if busy > 65535-freePortScanLimit {
+		t.Skipf("ephemeral port %d leaves no room for a scan window", busy)
+	}
+	got, err := chooseFreePort("127.0.0.1", busy)
+	if err != nil {
+		t.Fatalf("chooseFreePort(%d) = %v", busy, err)
+	}
+	if got == busy {
+		t.Fatalf("chooseFreePort returned the busy port %d", busy)
+	}
+}
+
 func TestListenProbeSeesOpenListener(t *testing.T) {
 	ln, err := net.Listen("tcp", "127.0.0.1:0")
 	if err != nil {

desktop/src/process_unix.go

@@ -3,6 +3,7 @@
 package main
 
 import (
+	"errors"
 	"os/exec"
 	"syscall"
 )
@@ -15,3 +16,7 @@ func killProcessTree(cmd *exec.Cmd) {
 	_ = syscall.Kill(-cmd.Process.Pid, syscall.SIGTERM)
 	_ = cmd.Wait()
 }
+
+func addrInUse(err error) bool {
+	return errors.Is(err, syscall.EADDRINUSE)
+}

desktop/src/process_windows.go

@@ -3,6 +3,7 @@
 package main
 
 import (
+	"errors"
 	"io"
 	"os/exec"
 	"strconv"
@@ -29,3 +30,7 @@ func killProcessTree(cmd *exec.Cmd) {
 	hideConsole(kill)
 	_ = kill.Run()
 }
+
+func addrInUse(err error) bool {
+	return errors.Is(err, windows.WSAEADDRINUSE)
+}