socket

【socket】

socket.socket([family[, type[, proto]]])

The address family should be AF_INET (the default), AF_INET6 or AF_UNIX.

The socket type should be SOCK_STREAM (the default), SOCK_DGRAM or perhaps one of the other SOCK_ constants.

The protocol number is usually zero and may be omitted in that case.（通常忽略） 

socket.getaddrinfo(host, port[, family[, socktype[, proto[, flags]]]])

　　Translate the host/port argument into a sequence of 5-tuples that contain all the necessary arguments for creating a socket connected to that service.

　　Host is a domain name, a string representation of an IPv4/v6 address or None.

　　Port is a string service name such as 'http', a numeric port number or None.

　　The family, socktype and proto arguments can be optionally specified in order to narrow the list of addresses returned. By default, their value is 0, meaning that the full range of results is selected.

　　The flags argument can be one or several of the AI_* constants, and will influence how results are computed and returned. Its default value is 0. For example, AI_NUMERICHOST will disable domain name resolution and will raise an error if host is a domain name.

　　The function returns a list of 5-tuples with the following structure:

　　(family, socktype, proto, canonname, sockaddr)

　　In these tuples, family, socktype, proto are all integers and are meant to be passed to the socket() function. canonname will be a string representing the canonical name of the host if 　　AI_CANONNAME is part of the flags argument; else canonname will be empty. sockaddr is a tuple describing a socket address, whose format depends on the returned family (a (address, port) 2-tuple for AF_INET, a (address, port, flow info, scope id) 4-tuple for AF_INET6), and is meant to be passed to the socket.connect() method.

Example：

　　

 【bind】

　　

　　A couple things to notice: we used socket.gethostname() so that the socket would be visible to the outside world. If we had used s.bind(('localhost', 80)) or s.bind(('127.0.0.1', 80)) we would still have a “server” socket, but one that was only visible within the same machine. s.bind(('', 80)) specifies that the socket is reachable by any address the machine happens to have.

【flush】

　　There are two sets of verbs to use for communication. You can use send and recv, or you can transform your client socket into a file-like beast and use read and write. The latter is the way Java presents its sockets. I’m not going to talk about it here, except to warn you that you need to use flush on sockets. These are buffered “files”, and a common mistake is to write something, and then read for a reply. Without a flush in there, you may wait forever for the reply, because the request may still be in your output buffer.

 【send & recv】

　　Now we come to the major stumbling block of sockets - send and recv operate on the network buffers. They do not necessarily handle all the bytes you hand them (or expect from them), because their major focus is handling the network buffers. In general, they return when the associated network buffers have been filled (send) or emptied (recv). They then tell you how many bytes they handled. It is your responsibility to call them again until your message has been completely dealt with.

　　When a recv returns 0 bytes, it means the other side has closed (or is in the process of closing) the connection. You will not receive any more data on this connection. Ever. You may be able to send data successfully.

　　A protocol like HTTP uses a socket for only one transfer. The client sends a request, then reads a reply. That’s it. The socket is discarded. This means that a client can detect the end of the reply by receiving 0 bytes.