为自定义TCP协议实现客户端

Question

I have to implement a client for communication with the server by custom protocol based on XML format. This is an application layer protocol, based on TCP . So, my client sends a request XML message and receives a response, also XML message. Now, I consider how to be ensured that I received whole mesage before I start parsing it.

I see two aproaches:

1. Receiving bytes to the some magic number that means end of message. It is the best approch (for my eye), yes?

2. But, it is possible that there is no magic number and size of message is not known. What about that case? I saw some clients for other protocols and I see something like that.

    while(true){ r = socket.read(buffer, offset, 1024); if(r < 1024) break; offset += r; } // parse buffer 

and I am not sure whether it is ok. It assumes that if we read less than 1024 bytes then the messae is completed. Is it ok?

What is a recommend way to solve it?

Answer 1

In your custom protocol you need to include the steps below :

Client

1. Calculate number of 1024 byte chunks of the XML contents ie ceiling(XML content bytes /1024)
2. Send the number of step 1 to the server through the socket
3. Transmit the contents in chunks of a defined buffer size eg 1024 bytes

Server

1. Read number of chunks to receive from client

2. Inside a for loop of size equal to the number read at step 1, start receiving contents in the predifined buffer size.

This way the server knows how many bytes the actual content is before it starts receiving the XML contents.