go socket close那些事

溫故而知新吞杭，可以為師矣

基于目前socket在編程中的重要地位争剿，我打算仔細(xì)琢磨一下go的socket編程羽利。打造一個屬于自己的方便調(diào)用的go socket框架捻勉。因為畢竟自己有c的socket經(jīng)驗，所以我覺得應(yīng)該沒什么難度虹茶。

一路下來也確實沒有碰到什么問題逝薪，在此就大致記錄下編碼過程以及新體會吧。

編寫go客戶端：

獲取服務(wù)器ip地址

    ip, err := net.ResolveIPAddr("", "127.0.0.1")
    if err != nil {
      Log("err1=%v\n", err.Error())  
      return
    }

建立連接

    ipStr := fmt.Sprintf("%s:20003", ip.IP.String())
    conn, err := net.Dial("tcp", ipStr)
    if err != nil {
        Log("err2=%v\n", err.Error())
        return
    }

數(shù)據(jù)處理

    defer func() {
        err := conn.Close()
        if err != nil {
            Log("err3=%v\n", err.Error())
            return
        }
    }()

    Log("connected ...\n")
    hello := "Hi,here is glp"
    n, err := conn.Write([]byte(hello))
    if err != nil {
        Log("err4=%v\n", err.Error())
        return
    }
    Log("send server [%d]=%s\n", n, hello)

    <-time.After(time.Second)

編寫go服務(wù)端：

首先獲取到一個監(jiān)聽的IP地址：

//獲取服務(wù)器監(jiān)聽ip地址
    ip, err := net.ResolveTCPAddr("", ":20003")
    if err != nil {
        Log("err1=%v\n", err.Error())
        return
    }

創(chuàng)建監(jiān)聽的socket

//創(chuàng)建一個監(jiān)聽的socket
conn, err := net.ListenTCP("tcp", ip)
if err != nil {
    Log("err2=%v\n", err.Error())
    return
}

服務(wù)器邏輯主循環(huán)

clientConn, err := conn.Accept()
if err != nil {
    Log("err3=%v\n", err.Error())
    return
}
Log("new client conn=%v,ip=%v\n", clientConn, clientConn.RemoteAddr())
go handlerClient(&StatusConn{clientConn, StatusNormal})

對客戶端socket的處理邏輯主要片段

buffer := make([]byte, 1024)
err := conn.SetReadDeadline(time.Now().Add(time.Second * 10))
if err != nil {
    Log("handlerClient err2=%v\n", err.Error())
    conn.Status = StatusError
    return
}
n, err := conn.Read(buffer)
if err != nil {
    Log("handlerClient err3=%v\n", err.Error())
    if err == io.EOF {
        conn.Status = StatusClosed
    } else {
        conn.Status = StatusError
    }
    return
}

clientBytes := buffer[:n]
Log("read client [%d]=%s\n", n, string(clientBytes))
hello := fmt.Sprintf("from server back【go】:%s", string(clientBytes))

n, err = conn.Write([]byte(hello))
Log("send client [%d]=%s\n", n, hello)
if err != nil {
    Log("handlerClient err4=%v\n", err.Error())
}

實驗

直接啟動服務(wù)器跟客戶端蝴罪，發(fā)現(xiàn)打印如下：
客戶端：

2019/05/30 16:35:44.255:connected ...
2019/05/30 16:35:44.269:send server [14]=Hi,here is glp

服務(wù)端：

2019/05/30 16:35:39.543:cur goos=windows
2019/05/30 16:35:39.560:server wait...
2019/05/30 16:35:44.255:new client conn=&{{0xc0000862c0}},ip=127.0.0.1:56795
2019/05/30 16:35:44.269:read client [14]=Hi,here is glp
2019/05/30 16:35:44.269:send client [39]=from server back【go】:Hi,here is glp
2019/05/30 16:35:45.269:handlerClient err3=read tcp 127.0.0.1:20003->127.0.0.1:56795: wsarecv: An existing connection was forcibly closed by the remote host.
2019/05/30 16:35:45.269:handlerClient Status=3

是這個報錯內(nèi)容：An existing connection was forcibly closed by the remote host.
意思應(yīng)該是連接被遠(yuǎn)端強(qiáng)制關(guān)閉董济，誒。要门。這個跟io.EOF到底有什么區(qū)別呢虏肾。我記得我在編寫c++ socket的時候好像沒碰到這個。印象中強(qiáng)制關(guān)閉的判斷應(yīng)該就是判斷recv(...)==0欢搜。帶著這個好奇封豪，我于是編寫了c++ socket服務(wù)器。

c++服務(wù)器主要邏輯代碼：

服務(wù)器主循環(huán)

int main() {
    Env env = Env();

    SOCKET listenFd = -1;
    listenFd = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);//socket 描述符
    if (INVALID_SOCKET == listenFd)
    {
        Printf("create socket error %d\n", errno);
        return -1;
    }
    Printf("服務(wù)器創(chuàng)建網(wǎng)絡(luò)描述符 fd=%d\n", listenFd);

    if (setAddrReuse(listenFd) != 0) {
        Printf("setAddrReuse error %d\n", errno);
        return -1;
    }
    Printf("服務(wù)器設(shè)置地址重用成功\n");

    struct sockaddr_in ipAddr = { 0 };
    ipAddr.sin_family = AF_INET;
    ipAddr.sin_port = htons(20003);
    ipAddr.sin_addr.s_addr = htonl(INADDR_ANY);

    if (0 != bind(listenFd, (struct sockaddr*) & ipAddr, sizeof(ipAddr)))
    {
        Printf("socket bind error %d\n", errno);
        return -1;
    }
    Printf("服務(wù)器綁定地址成功\n");

    if (::listen(listenFd, SOMAXCONN) != 0) {
        Printf("socket listen error %d\n", errno);
        return -1;
    }
    Printf("服務(wù)器監(jiān)聽成功\n");

    sockaddr addr;
#ifdef WIN32
    int len = sizeof(addr);
#else
    socklen_t len = sizeof(addr);
#endif
    while (true) {
        SOCKET clientSocket = accept(listenFd, &addr, &len);
        if (clientSocket == INVALID_SOCKET) {
            Printf("socket accept error %d\n", errno);
            return -1;
        }

        Printf("客戶端新連接:接入 fd = %d,ip = %s\n", clientSocket, GetPeerIp(clientSocket));
        auto clientThread = std::thread(handlerClient, clientSocket);
        clientThread.detach();
    }
}

客戶端連接處理片段

        char buf[65535] = { 0 };
        int len = (int) ::recv(fd, buf, sizeof(buf), 0);//接收網(wǎng)絡(luò)數(shù)據(jù)
        if (len == 0) {
            Printf("客戶端連接被主動關(guān)閉\n");
            return;
        }

        if (len == SOCKET_ERROR) {
            int errorcode;
#ifdef WIN32
            errorcode = GetLastError();//這里的錯誤碼炒瘟，必須用windows的GetLastError獲取吹埠。
            if (errorcode != WSAEWOULDBLOCK) {
#else//Linux
            errorcode = errno;
            if (errorcode != EAGAIN) {
#endif
                Printf("client[%d] recv err=%d\n", fd, errorcode);
                return;
            }
            continue;
        }

        Printf("client[%d] recv[%d]=%s\n", fd, len, buf);
        char hello[65535] = { 0 };
        sprintf(hello, "from server back[c++]:%s", buf);
        Printf("send to client[%d]=%s\n", fd, hello);
        ::send(fd, hello, strlen(hello), 0);

實驗2，用go客戶端連接這個c++服務(wù)器看打印結(jié)果

客戶端打印

2019/05/30 16:30:30.380:connected ...
2019/05/30 16:30:30.393:send server [14]=Hi,here is glp

c++服務(wù)器打印

2019-05-30 16:30:20.499：服務(wù)器創(chuàng)建網(wǎng)絡(luò)描述符 fd=636
2019-05-30 16:30:20.499：服務(wù)器設(shè)置地址重用成功
2019-05-30 16:30:20.499：服務(wù)器綁定地址成功
2019-05-30 16:30:20.499：服務(wù)器監(jiān)聽成功
2019-05-30 16:30:30.381：客戶端新連接:接入 fd = 640,ip = 127.0.0.1
2019-05-30 16:30:30.393：client[640] recv[14]=Hi,here is glp
2019-05-30 16:30:30.393：send to client[640]=from server back[c++]:Hi,here is glp
2019-05-30 16:30:31.393：client[640] recv err=10054

特地去查了下10054：

//
// MessageId: WSAECONNRESET
//
// MessageText:
//
// An existing connection was forcibly closed by the remote host.
//
#define WSAECONNRESET                    10054L

發(fā)現(xiàn)跟go服務(wù)器打印的錯誤信息一致疮装。缘琅。。
c++的recv函數(shù)在這里也確實返回了-1廓推，看來并不是所有的客戶端socket close刷袍，都可以讓服務(wù)器的recv得到0》梗看來是我自己以前沒怎么關(guān)注這塊只顧寫邏輯去了呻纹。。go的底層socket代碼應(yīng)該是跟c++保持一致的专缠。

實驗3 linux服務(wù)器

上面的服務(wù)器我都是在本地windows運行的雷酪，現(xiàn)在嘗試在linux上看看。
我把編寫的go服務(wù)器代碼編譯發(fā)布到服務(wù)器上再看服務(wù)器打印日志：

2019/05/30 16:45:00.012:cur goos=linux
2019/05/30 16:45:00.012:server wait...
2019/05/30 16:46:36.104:new client conn=&{{0xc00009a080}},ip=115.192.79.216:56919
2019/05/30 16:46:36.132:read client [14]=Hi,here is glp
2019/05/30 16:46:36.132:send client [39]=from server back【go】:Hi,here is glp
2019/05/30 16:46:37.133:handlerClient err3=read tcp 172.16.200.43:20003->115.192.79.216:56919: read: connection reset by peer
2019/05/30 16:46:37.133:handlerClient Status=3

到了linux這邊就變成了connection reset by peer.
可以看到windows和linux返回的錯誤提示是不同的藤肢。不過他們想表達(dá)的意思應(yīng)該是一致的太闺。

實驗4 嘗試讀取服務(wù)器發(fā)來的數(shù)據(jù)再關(guān)閉socket

上面的go客戶端是沒有讀取服務(wù)器返回的數(shù)據(jù)，自己等待一秒鐘就關(guān)閉了∴胰Γ現(xiàn)在把客戶端邏輯改成：

    Log("connected ...\n")
    hello := "Hi,here is glp"
    n, err := conn.Write([]byte(hello))
    if err != nil {
        Log("err4=%v\n", err.Error())
        return
    }
    Log("send server [%d]=%s\n", n, hello)
//新增讀取服務(wù)器數(shù)據(jù)代碼 begin
    buffer := make([]byte, 1024)
    n, err = conn.Read(buffer)
    if err != nil {
        Log("err5=%v\n", err.Error())
        return
    }
    Log("read server [%d]=%s\n", n, string(buffer))
//新增讀取服務(wù)器數(shù)據(jù)代碼 end

    <-time.After(time.Second)

再去請求go服務(wù)器和c++服務(wù)器
go服務(wù)器打印(linux)：

2019/05/30 17:02:28.809:cur goos=linux
2019/05/30 17:02:28.809:server wait...
2019/05/30 17:02:43.239:new client conn=&{{0xc00009a080}},ip=115.192.79.216:57079
2019/05/30 17:02:43.253:read client [14]=Hi,here is glp
2019/05/30 17:02:43.253:send client [39]=from server back【go】:Hi,here is glp
2019/05/30 17:02:44.259:handlerClient err3=EOF
2019/05/30 17:02:44.259:handlerClient Status=1

go服務(wù)器打印(windows)：

2019/05/30 17:03:21.963:cur goos=windows
2019/05/30 17:03:21.976:server wait...
2019/05/30 17:03:31.903:new client conn=&{{0xc00008c2c0}},ip=127.0.0.1:57090
2019/05/30 17:03:31.922:read client [14]=Hi,here is glp
2019/05/30 17:03:31.922:send client [39]=from server back【go】:Hi,here is glp
2019/05/30 17:03:32.923:handlerClient err3=EOF
2019/05/30 17:03:32.923:handlerClient Status=1

c++服務(wù)器打印(windows)：

2019-05-30 17:06:08.737：服務(wù)器創(chuàng)建網(wǎng)絡(luò)描述符 fd=644
2019-05-30 17:06:08.737：服務(wù)器設(shè)置地址重用成功
2019-05-30 17:06:08.737：服務(wù)器綁定地址成功
2019-05-30 17:06:08.737：服務(wù)器監(jiān)聽成功
2019-05-30 17:06:29.437：客戶端新連接:接入 fd = 604,ip = 127.0.0.1
2019-05-30 17:06:29.449：client[604] recv[14]=Hi,here is glp
2019-05-30 17:06:29.450：send to client[604]=from server back[c++]:Hi,here is glp
2019-05-30 17:06:30.451：客戶端連接被主動關(guān)閉

經(jīng)過這步實驗證明確實是因為客戶端沒有讀取服務(wù)器發(fā)來的數(shù)據(jù)就關(guān)閉導(dǎo)致服務(wù)器的read或者recv報錯了省骂。

經(jīng)過調(diào)試我發(fā)現(xiàn)我可以通過如下步驟找到對應(yīng)的error

if err1, ok := err.(*net.OpError); ok {
    if err2, ok := err1.Err.(*os.SyscallError); ok {
        if err3, ok := err2.Err.(syscall.Errno); ok {
            if err3 == syscall.WSAECONNRESET {
                Log("err3 == syscall.WSAECONNRESET True\n")
            }
        }
    }
}

go定義的Errno

但是syscall.WSAECONNRESET不能用于linux蟀淮，在編譯linux的時候會報錯：

src\study\testServer.go:68:18: undefined: syscall.WSAECONNRESET

如果想要把沒有讀取數(shù)據(jù)的強(qiáng)制關(guān)閉也要歸結(jié)為close而不是error的時候，用上面的辦法只能用于windows钞澳。而我需要跨平臺解決方案怠惶。
在提出最后的解決方案之前，我們還有一個實驗需要做一下就是：

socket 10053

實驗5 socket出現(xiàn)10053的原因

改寫我們的go客戶端：

Log("connected ...\n")
hello := "Hi,here is glp"
n, err := conn.Write([]byte(hello))
if err != nil {
    Log("err4=%v\n", err.Error())
    return
}
Log("send server [%d]=%s\n", n, hello)

//buffer := make([]byte, 1024)
//n, err = conn.Read(buffer)
//if err != nil {
//  Log("err5=%v\n", err.Error())
//  return
//}
//Log("read server [%d]=%s\n", n, string(buffer))
//
//<-time.After(time.Second)

把讀取和等待的代碼都注釋了轧粟，查看服務(wù)器打硬咧巍：
go服務(wù)器打印(linux)：

2019/05/30 17:26:09.186:cur goos=linux
2019/05/30 17:26:09.187:server wait...
2019/05/30 17:26:12.750:new client conn=&{{0xc0000b4080}},ip=115.192.79.216:57420
2019/05/30 17:26:12.760:read client [14]=Hi,here is glp
2019/05/30 17:26:12.760:send client [39]=from server back【go】:Hi,here is glp
2019/05/30 17:26:12.760:handlerClient err3=EOF
2019/05/30 17:26:12.760:handlerClient Status=1