Java 客户端和 C++ 服务器通过 TCP 套接字发送和接收
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Java client and a C++ server send and receive via TCP Socket
提问by MartinO.
I have a C++ server and two clients (ruby and java). Everything is running on a 64-bit linux-machine (java 1.7.0_17) The ruby client is fully working, but the java version makes problems.
我有一个 C++ 服务器和两个客户端（ruby 和 java）。一切都在 64 位 linux 机器 (java 1.7.0_17) 上运行 ruby 客户端完全正常工作，但 java 版本会出现问题。
In Java I tried to send a String from the client to the server. Actually the Server received the entire String, but the server thinks there is still something more to receive.
在 Java 中，我尝试从客户端向服务器发送一个字符串。实际上服务器收到了整个字符串，但服务器认为还有更多的东西要接收。
The ruby client looks a little bit like this:
ruby 客户端看起来有点像这样：
socket = TCPSocket.open(@options[:host],@options[:port])
test = "Hello, World"
socket.puts test
socket.shutdown 1
response = socket.gets
Everything here is working fine. The ruby client sends a string. The server receives that string and sends a reply.
这里一切正常。ruby 客户端发送一个字符串。服务器接收该字符串并发送回复。
The Java Version looks like:
Java 版本如下所示：
String ip = "127.0.0.1";
int port = 6686;
java.net.Socket socket = new java.net.Socket(ip,port);
OutputStreamWriter out = new OutputStreamWriter(socket.getOutputStream());
InputStreamReader in = new InputStreamReader(socket.getInputStream());
String msg = "Hello, world!";
//send
PrintWriter pw = new PrintWriter(out, true);
pw.print(msg);
pw.flush();
// I also tried: out.write(msg); out.flush(); nothing changed
//receive the reply
BufferedReader br = new BufferedReader(in);
char[] buffer = new char[300];
int count = br.read(buffer, 0, 300);
String reply = new String(buffer, 0, count);
System.out.println(reply);
socket.close();
On the other side there is a C++ Server:
在另一边有一个 C++ 服务器：
string receive(int SocketFD) {
char buffer[SOCKET_BUFFER_SIZE];
int recv_count;
// empty messagestring
string message = "";
// empty buffer
memset(buffer, 0, sizeof(buffer));
while ((recv_count = recv(SocketFD, buffer, sizeof(buffer) - 1, 0)) > 0) {
/*if (recv_count == -1) {
cout << "failed." << endl;
break;
}*/
cout << recv_count << endl;
if (ECHO_SOCKETS) cout << "received: " << buffer << endl;
message.append(buffer);
memset(buffer, 0, sizeof(buffer));
if (ECHO_SOCKETS) cout << "message is now: " << message << endl;
}
return message;
}
The server output from the Java-message is:
Java 消息的服务器输出是：
13
received: Hello, world!
message is now: Hello, world!
and then nothing happens. The problem is that:
然后什么也没有发生。问题在于：
recv(SocketFD, buffer, sizeof(buffer) - 1, 0)
is catched in an endless loop (or something like that). If I kill the Java-client process or I type something like:
陷入无限循环（或类似的东西）。如果我终止 Java 客户端进程或键入以下内容：
pw.print(msg);
out.close();
the output on the server side is:
服务器端的输出是：
_sending reply: "Request unrecognized/invalid" request="Hello, world!"
send reply success
now close connection
This output is right (except "send reply success"), but in case of adding:
此输出是正确的（“发送回复成功”除外），但在添加的情况下：
out.close();
the client can't receive the reply of the server. Because the Socket is closed.
客户端收不到服务器的回复。因为 Socket 是关闭的。
java.net.SocketException: Socket is closed
at java.net.Socket.getInputStream(Socket.java:864)
at MyServer.writeMessage(MyServer.java:56)
at MyServer.test(MyServer.java:42)
at MyServer.main(MyServer.java:30)
Edit
编辑
I tried to call pw.flush(); and different delimiters like "\n", "\r", "\r\n" and "\n\r" but the server still thinks there is still something to read. I also tried to use DatagramSockets:
我试图调用 pw.flush(); 和不同的分隔符，如“\n”、“\r”、“\r\n”和“\n\r”，但服务器仍然认为还有一些东西要读。我也尝试使用 DatagramSockets：
java.net.DatagramSocket dSocket = new java.net.DatagramSocket();
InetAddress address = InetAddress.getByName("localhost");
String msg = "Hello, world!";
byte[] buf = msg.getBytes();
java.net.DatagramPacket packet = new DatagramPacket(buf, buf.length, address, 6686);
But the server can't accept the packet.
但是服务器不能接受数据包。
Solution
解决方案
The ruby-client does something like a socket.shutdownOutput(); (ruby: socket.shutdown 1) after the call of puts. I changed the java-client-code:
ruby-client 做一些类似于 socket.shutdownOutput(); 的事情。(ruby: socket.shutdown 1) 在调用 puts 之后。我更改了 java-client-code：
out.write(msg);
socket.shutdownOutput();
and it works!
它有效！
As @Charly said: I have to define a "protocol". In my case I'm not allowed to change any communication related code (in the server and the ruby-client) because this functionality is used by a another group of researchers. So I've to modify my java-client in that way, that it does the exactsame things at the exactsame time as the ruby-client (something like a protocol).
正如@Charly 所说：我必须定义一个“协议”。就我而言，我不允许更改任何与通信相关的代码（在服务器和 ruby 客户端中），因为该功能被另一组研究人员使用。所以我修改这样我的Java客户端，它确实的确切同样的事情在精确的同时红宝石客户端（如协议的东西）。
采纳答案by Charly
PrintWriter buffer (when autoflush is true) is only flushed by calling println or printf. Calling print may not flush the buffer (Javadoc). Try calling println or use a OutputStreamWriter directly and flush(). Be aware of using the right charset (You can set it up in OutputStreamWriter constructor).
PrintWriter 缓冲区（当 autoflush 为真时）只能通过调用 println 或 printf 来刷新。调用 print 可能不会刷新缓冲区 ( Javadoc)。尝试调用 println 或直接使用 OutputStreamWriter 并flush()。请注意使用正确的字符集（您可以在 OutputStreamWriter 构造函数中进行设置）。
回答by Jan Piel
Close the stream respectively flush it in a way like this:
关闭流以如下方式分别冲洗它：
DataOutputStream dataOut = new DataOutputStream(socket.getOutputStream());
dataOut.writeUTF(s);
dataOut.flush();
回答by user207421
while ((recv_count = recv(SocketFD, buffer, sizeof(buffer) - 1, 0)) > 0) {
if (recv_count == -1) {
I don't know what your problem is but this code is certainly nonsense. It is impossible for the inner test ever to succeed.
我不知道你的问题是什么，但这段代码肯定是无稽之谈。内测永远不可能成功。
