Tuesday, January 4, 2011

pipe, stream, pesudo file, tcp-socket

* Java has a family of IO classes;
* c++ has a family of stream classes derived from class ios;
* unix has various file-like things.

"pipe" and "stream" are 2 general terminologies for an input/output destination with sequential[1] access. A file is one subtype of stream. Therefore java and c++ access files using their family of classes above.

[1] c++ gives each sequential stream a get-ptr and a put-ptr.
A named pipe is an entity in the file system....

TCP (not UDP) socket is a stream-oriented protocol. Sockets, either unix domain or TCP (not udp), is also like a pipe/stream. In fact, Unix treats any socket as a file so you can read and write to a it like a file. Perl liberally "confuses" file handles and sockets, just as C uses the same type of file-descriptor-number for files and sockets.

TCP (not UDP) is ordered -- if two messages are sent over a connection in sequence, the first message will reach the receiving application first. When data segments arrive in the wrong order, TCP buffers the out-of-order data until all data can be properly re-ordered and delivered to the application.

Python wraps the socket descriptor number in a socket object, but you can still get the underlying descriptor number by mySocket.fileno()--

import socket
mySocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
print mySocket.fileno()

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