csc123_W8.pdf

CSC123 (INTRO TO PROGRAMMING II) Usman Aslam | Computer Science RECAP A client process seeks the service of a server process. The connects to the server, sends request and receives response java.net.Socket class acts as a client and is used to open network connections to remote servers Once connecte...

CSC123 (INTRO TO PROGRAMMING II) Usman Aslam | Computer Science RECAP A client process seeks the service of a server process. The connects to the server, sends request and receives response java.net.Socket class acts as a client and is used to open network connections to remote servers Once connected the client communicates with the server using a preagreed protocol e.g. HTTP HTTP protocol defines how the client should send a request and how the response is structured HTTP URL URL is short for Universal Resource Locator An HTTP URL has three parts: 1. Protocol: Name of the protocol being used followed by a colon and two forward slash characters e.g. http:// 2. Host: IP address or domain name e.g. www.google.com 3. Resource: The actual resource (text, images, videos) e.g. /videos/myvideo.mp4 Example: http://www.google.com/mypage/page.html COMMON HTTP HEADERS Header Type Description User-Agent Request Client sends this information to tell server what type of web browser it is Host Request Client sends this to server with the “host” part of the URL Content-Type Response Server returns this to client to explain the type of content being returned Set-Cookie Response Server returns this to client to store the contained information as a cookie Server Response Server returns this information to explain what type of server software it is running COMMON HTTP HEADERS Code Name Description 200 OK 301 Permanently moved The requested resource has moved to a new location (location is provided) 302 Temporarily moved The requested resource has moved to a new location (location is provided) 400 Bad Request Server does not understand client’s request, request is not according to protocol 401 Unauthorized The client needs to login and provide credentials 403 Forbidden The client has no access rights to the requested resource 404 Not Found The requested resource was not found on the server 500 Internal Server Error There was some error, and the server was not able to complete the request 503 Service Unavailable The server is not ready to service client’s request The server successfully processed request and has returned the output https://developer.mozilla.org/en-US/docs/Web/HTTP/Status SERVER PROCESS A Server process provides a service to clients. It is always “listening” on a pre-defined network port waiting for client connections. The server process: Attaches itself to a specific network port and starts listening Accepts client connection and establishes a two-way communication channel Receives client requests and processes it Sends the response to the client Closes connection when done (Connection closure can be initiated by the client or the server, depending on the protocol) java.net.ServerSocket class represents a server socket SERVER PROCESS ServerSocket server = new ServerSocket(1200); Socket client=server.accept(); // Blocks until client connection is made InputStream in=client.getInputStream(); OutputStream out=client.getOutputStream(); LAB EXERCISES Two lab exercises have been uploaded. One for a Java Client and the other one for a Java Server