Saturday, August 6, 2011


The SOCK_STREAM socket type is used when you want to perform stream I/O with a remote socket. A stream in the socket sense is the same concept that applies to a UNIX pipe. Bytes written to one end of the pipe (or socket) are received at the other end as one continuous stream of bytes. There are no dividing lines or boundaries. There is no record length, block size, or concept of a packet at the receiving end. Whatever data is currently available at the receiving end is returned in the caller's buffer.

Properties of a SOCK_STREAM socket:
  • No message boundaries are preserved. The receiving end cannot determine how many write(2) calls were used to send the received data. Nor can it determine where the write(2) calls began or ended in the stream of bytes received.
  • The data bytes received are guaranteed to be in precisely the same order in which they were written.
  • All data written is guaranteed to be received by the remote end without error. If a failure occurs, an error is reported after all reasonable attempts at recovery have been made. Any recovery attempts are automatic and are not directed by your application program.

The last point presented is a new one to this discussion. A stream socket implies that every reasonable effort will be made to deliver data written to one socket, to the socket at the other end. 
If this cannot be done, the error will be made known to the receiving end as well as the writing end. In this respect, SOCK_STREAM socket is a reliable data transport. This feature makes it a very popular socket type. There is one more property of the SOCK_STREAM type of socket. It is

• The data is transported over a pair of connected sockets.

In order to guarantee delivery of data, and to enforce byte ordering, the underlying protocols use a
connected pair of sockets. For the moment, simply know that the SOCK_STREAM type implies that a connection must be established before communications can proceed.

Sample Codes:

  1. using SOCK_STREAM with socketpair
  2. using SOCK_STREAM with socket

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