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HTTP

HTTP. Introduction. Client-Server communication protocol Request-response Version 1.0 Stateless Version 1.1 added the ability to keep connections open virtual hosting etc. Request/Response. Request - Response Architecture Client makes request Server issues response General Structure

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HTTP

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  1. HTTP

  2. Introduction • Client-Server communication protocol • Request-response • Version 1.0 • Stateless • Version 1.1 added • the ability to keep connections open • virtual hosting • etc

  3. Request/Response • Request - Response Architecture • Client makes request • Server issues response • General Structure • Start_Line<CRLF> • Message Header<CRLF> • <CRLF> • Message Body<CRLF>

  4. More Details • Start_line (Request or Response) • Request • Method<SP>Request-URI<SP>HTTP-Version<CRLF> • Response • HTTP-Version<SP>Status-code<SP>Response-Phrase<CRLF> • Message Header • Field_name:<SP>Field_value, Field_value • Message Body • Binary data

  5. HTTP Request Methods • GET – Retrieve the URL • POST – Give information to server • HEAD – Retrieve the headers for the URL • OPTIONS – Request available options • PUT – Store document at specified URL • DELETE – Delete specified URL • and many others……

  6. Typical Request • Version 1.0 • Version 1.1 GET /path/fiile.html HTTP/1.0 From: someuser@jmarshall.com User-Agent: HTTPTool/1.0 [blank line here] GET /path/fiile.html HTTP/1.1 Host: www.host1.com:80 [blank line here]

  7. The GET Method • Retrieves a URL • General case is very simple • Can send information along with URL • URL?name1=value1&name2=value2 • No Message Body GET /path/file.html?n=v HTTP/1.1 Host: www.host1.com:80 [blank line here]

  8. The POST Method • Sends information in the Message Body • Information is free format POST /path/script.cgi HTTP/1.0 From: frog@jmarshall.com User-Agent: HTTPTool/1.0 Content-Type: application/x-www-form-urlencoded Content-Length: 32 home=Cosby&favorite+flavor=flies

  9. URL Encoding • Convert all “unsafe” characters to %xx • xx is the ascii value of the character in hex • “unsafe” characters: = & % + nonprintables • Change all spaces to + • Use = and & to connect name value pairs • name1=val1&name2=val2&name3=val3 • Example: name is Lucy, neighbors are Fred & Ethel • Name=Lucy&neighbors=Fred+%26+Ethel

  10. The HTTP Response • Status-Line • HTTP-Version Status-Code Response-Phrase • Headers • Header-Name: value • Blank line • Message Body

  11. Typical Response HTTP/1.0 200 OK Date: Fri, 31 Dec 1999 23:59:59 GMT Content-Type: text/html Content-Length: 1354 <html> <body> <h1>Happy New Year!</h1> (more fiile contents) . . . </body> </html>

  12. Status Line • HTTP-Version Status-Code Response-Phrase • The HTTP version is in the format "HTTP/x.y". • The status code is meant to be computer-readable; the reason phrase is meant to be human-readable, and may vary. • The status code is a three-digit integer • 1xy indicates an informational message only • 2xy indicates success of some kind • 3xy redirects the client to another URL • 4xy indicates an error on the client's part • 5xy indicates an error on the server's part

  13. Some Status Codes • 200 OK • The request succeeded, and the resulting resource (e.g. file or script output) is returned in the message body • 404 Not Found • 301 Moved Permanently • 302 Moved Temporarily • 303 See Other(HTTP 1.1 only) • The resource has moved to another URL (given by the Location: response header), and should be automatically retrieved by the client. This is often used by a CGI script to redirect the browser to an existing file. • 500 Server Error

  14. Headers • Name value pairs • Header-Name: Header Value • Header-Name is not case sensitive • Header Value may be case sensitive • Any number of spaces or tabs after : • Lines beginning with space or tab are continuations of previous line

  15. Header Examples • Date: Fri, 31 Dec 1999 23:59:59 GMT • Content-Type: text/html • Content-Length: 1354 • From: snell@cs.byu.edu • Last-Modified: Fri, 31 Dec 1999 23:59:59 GMT • Server: Apache/2.3 • User-Agent: Mozilla/3.0Gold

  16. Message Body • Data sent after header lines • after blank line • Request Message Body • User entered data in POST • None for GET • Response Message Body • requested resource • header lines usually describe the data • Content-Type: text/html Mime types • Content-Length: 1234 size in bytes

  17. HTTP 1.1 • Additional Headers • Sockets stay open • Time-out connection default action, or • Connection: close header • Host: header is required • Host: www.servername.domain • Chunked Data • Transfer-Encoding: chunked • chunks followed by zero<crlf>, footers, blank line • chunks are: size<crlf>data

  18. Chunked Transfer HTTP/1.1 200 OK Date: Fri, 31 Dec 1999 23:59:59 GMT Content-Type: text/plain Transfer-Encoding: chunked 1a; ignore-stuff-here Abcdefghijklmnopqrstuvwxyz 10 1234567890abcdef 0 some-footer: some-value another-footer: another-value [blank line here]

  19. Cookies • A small piece of information stored on the client machine and returned to the server. • http headers • Cookie • Set-Cookie • 4 K bytes per cookie • 20 cookies per server or domain

  20. Set-Cookie (server side) Set-Cookie: name=value - URL encoded text [;EXPIRES=dateValue] - Wdy, DD-Mon-YY HH:MM:SS GMT [;DOMAIN=domainName] - valid domain name [;PATH=pathName] - path to send cookie [;SECURE] - transmitted only if communication is SSL

  21. Cookie (client-side) Cookie: name=value1; name=value2 All cookie name=value pairs that match the current path are sent.

  22. Cookie example • Client requests document and receives • Set-Cookie: cust=W_Coyote; path=/; • Client stores cookie • When client requests another URL below /, client sends • Cookie: cust=W_Coyote; • Server may set multiple cookies with different paths • Client returns all matching cookies

  23. Items to remember • When sending response • Headers first • Blank line • Size should match • From blank line - headers not included • Needs to be a full document • Look at access and error logs for help

  24. HTTP Architectures

  25. Common Gateway Interface (CGI) Web Server Client HTTP stdin stdout CGI Program or Script

  26. CGI • User requests URL • Server recognizes dynamic page • Usually by directory and/or file extension • Server spawns app • Passes arguments/message body via stdin • HTTP headers in environment variables • App passes results back to server via stdout • Server sends results to client

  27. CGI • Advantages • Easy/Simple • Substantial installed base • Can use any language available on server • Many free scripts (www.cgidir.com) • Disadvantages • Spawning overhead • Concurrent hits to page cause multiple copies of app to be launched • Many CGI apps use slow interpreted languages

  28. Optimization Java Servlets and JSP also follow this model Web Server Client HTTP Interpreter Script Apache modules php mod-perl java??

  29. Another Server Configuration Web Server Client HTTP Connector socket Why? Java Web Server

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