Add a comment. Active Oldest Votes. Great answer rsaw! Besides very instructive, it also explains why Python sometimes is a preferred programming language. Thank you for this. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog. Refer to the tutorial Socket in Linux before learning this tutorial. You always open the Google page in your web browser but do you know how our web browser accesses the Google page form www.
When you type www. Server always listens to the request from different hosts. When server receives and accepts the request it sends response back to the host i. Local PC. After establishment of connection, server will send the Google page to our web browser. This tutorial assumes you know about socket in Linux and are aware with C programming language. Socket programming is a way of connecting two nodes on a network to communicate with each other.
One socket node listens on a particular port at an IP, while other socket reaches out to the other to form a connection. Server forms the listener socket while client reaches out to the server. This is the same number which appears on protocol field in the IP header of a packet.
This is completely optional, but it helps in reuse of address and port. Listen: int listen int sockfd, int backlog ; It puts the server socket in a passive mode, where it waits for the client to approach the server to make a connection. Server processes are always alert and ready to serve incoming requests. Note that the client needs to know the address of the server, but the server does not need to know the address or even the existence of the client prior to the connection being established.
Once a connection is established, both sides can send and receive information. This type of architecture may have some security holes and performance problems.
Internet Explorer and Web Server work on two-tier architecture. Middleware are used to perform all the security checks and load balancing in case of heavy load. A middleware takes all requests from the client and after performing the required authentication, it passes that request to the server.
Then the server does the required processing and sends the response back to the middleware and finally the middleware passes this response back to the client. If you want to implement a 3-tier architecture, then you can keep any middleware like Web Logic or WebSphere software in between your Web Server and Web Browser.
Meanwhile, another client keeps waiting. The simplest way to write a concurrent server under Unix is to fork a child process to handle each client separately. The system calls for establishing a connection are somewhat different for the client and the server, but both involve the basic construct of a socket.
Both the processes establish their own sockets. Send and receive data. There are a number of ways to do this, but the simplest way is to use the read and write system calls.
Bind the socket to an address using the bind system call. For a server socket on the Internet, an address consists of a port number on the host machine. Accept a connection with the accept system call. This call typically blocks the connection until a client connects with the server. Various structures are used in Unix Socket Programming to hold information about the address and port, and other information.
Most socket functions require a pointer to a socket address structure as an argument. Structures defined in this chapter are related to Internet Protocol Family. This is a generic socket address structure, which will be passed in most of the socket function calls.
Socket address structures are an integral part of every network program. We allocate them, fill them in, and pass pointers to them to various socket functions.
Sometimes we pass a pointer to one of these structures to a socket function and it fills in the contents. We always pass these structures by reference i. When a socket function fills in a structure, the length is also passed by reference, so that its value can be updated by the function. We call these value-result arguments. Always, set the structure variables to NULL i. When a client process wants to a connect a server, the client must have a way of identifying the server that it wants to connect.
If the client knows the bit Internet address of the host on which the server resides, it can contact that host. But how does the client identify the particular server process running on that host?
To resolve the problem of identifying a particular server process running on a host, both TCP and UDP have defined a group of well-known ports. For our purpose, a port will be defined as an integer number between and This is because all port numbers smaller than are considered well-known -- for example, telnet uses port 23, http uses 80, ftp uses 21, and so on.
If you are writing your own server then care must be taken to assign a port to your server. You should make sure that this port should not be assigned to any other server. Normally it is a practice to assign any port number more than But there are many organizations who have written servers having port numbers more than Here is a small list of services and associated ports.
Unfortunately, not all computers store the bytes that comprise a multibyte value in the same order. Consider a bit internet that is made up of 2 bytes. There are two ways to store this value.
To allow machines with different byte order conventions communicate with each other, the Internet protocols specify a canonical byte order convention for data transmitted over the network.
This is known as Network Byte Order. These functions are macros and result in the insertion of conversion source code into the calling program. On little-endian machines, the code will change the values around to network byte order.
0コメント