從gin的啟動開始看socket是如何在伺服器中建立的：
gin -> net/http -> net -> internal/syscall -> syscall -> runtime
通過上面的呼叫流程，可以看出，http是對net的封裝，方便開發者呼叫，實際建立Socket的還是net庫，底層已經是到了go的syscall和runtime庫了。
最終呼叫的還是作業系統提供的socket介面。這就是socket建立的流程。

具體流程涉及的檔案以及程式碼：
router.go

r := gin.New()
r.Run(address) // host:port

github.com\gin-gonic\[email protected]\gin.go

err = http.ListenAndServe(address, engine)

Go\src\net\http\server.go

// Go net/http包
return server.ListenAndServe()
ln, err := net.Listen("tcp", addr) // http也是對net的封裝
if err != nil {
return err
}

Go\src\net\dial.go

return lc.Listen(context.Background(), network, address)
l, err = sl.listenTCP(ctx, la)
 

Go\src\net\tcpsock_posix.go

fd, err := internetSocket(ctx, sl.network, laddr, nil, syscall.SOCK_STREAM, 0, "listen", sl.ListenConfig.Control)

Go\src\net\ipsock_posix.go

return socket(ctx, net, family, sotype, proto, ipv6only, laddr, raddr, ctrlFn) // 出現socket函數了

Go\src\net\sock_posix.go

// socket returns a network file descriptor that is ready for
// asynchronous I/O using the network poller.

s, err := sysSocket(family, sotype, proto)

Go\src\net\sock_windows.go

s, err := wsaSocketFunc(int32(family), int32(sotype), int32(proto),nil, 0, windows.WSA_FLAG_OVERLAPPED|windows.WSA_FLAG_NO_HANDLE_INHERIT)

Go\src\net\hook_windows.go

wsaSocketFunc func(int32, int32, int32, *syscall.WSAProtocolInfo, uint32, uint32) (syscall.Handle, error) = windows.WSASocket // windows.WSASocket就是返回的socket

Go\src\internal\syscall\windows\zsyscall_windows.go

// 可以看到檔案已經跳轉到internal資料夾下的系統相關呼叫目錄
func WSASocket(af int32, typ int32, protocol int32, protoInfo *WSAProtocolInfo, group uint32, flags uint32) (handle Handle, err error) {
　　r0, _, e1 := syscall.Syscall6(procWSASocketW.Addr(), 6, uintptr(af), uintptr(typ), uintptr(protocol), uintptr(unsafe.Pointer(protoInfo)), uintptr(group), uintptr(flags))
　　handle = Handle(r0)
　　if handle == InvalidHandle {
　　　　err = errnoErr(e1)
　　}
　　return
}

=== r0 start ===
C:\Program Files\Go\src\syscall\dll_windows.go

// 可以看到檔案已經跳轉到syscall系統呼叫目錄，dll_windows名稱也可看出該檔案底層呼叫的是windos系統提供的介面。
// Implemented in ../runtime/syscall_windows.go.
// 註釋中是說繼承於../runtime/syscall_windows.go檔案中的Syscall6，這個寫法比較特殊，是go1.14剛出的，go:linkname，有興趣的可以繼續深入這個寫法，這裡不做贅述。
func Syscall6(trap, nargs, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err Errno)

C:\Program Files\Go\src\runtime\syscall_windows.go

//go:linkname syscall_Syscall6 syscall.Syscall6
//go:nosplit
//go:cgo_unsafe_args
func syscall_Syscall6(fn, nargs, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2, err uintptr) {
　　lockOSThread()
　　defer unlockOSThread()
　　c := &getg().m.syscall
　　c.fn = fn
　　c.n = nargs
　　c.args = uintptr(noescape(unsafe.Pointer(&a1)))
　　cgocall(asmstdcallAddr, unsafe.Pointer(c))
　　return c.r1, c.r2, c.err
}

=== r0 end ===