HTTP

The package consist of the following modules:

• http_server - a simple web server where pages can be registered
• http - interface to access HTTP requests and respond to them
• webfile - a simple file server

Using the HTTP server

• set_default_port(?Port) - sets the port to use for the web server. This must be set before the server is started. An uninstantiated variable means any free port.
• register_page(+Page,+Handler) - registers a page and its HTTP handler. The handler will be called for each HTTP request accessing a path starting with the specified path.
• unregister_page(+Page,+Handler) - unregisters the specified page

HTTP handler

• http_request(+HttpRequest,+HttpResponse) - called whenever a HTTP request is made to the page registered with the handler and is responsible to respond to the request.

The module http

• method(+HttpRequest,-Method) - retrieves the method of the request (GET,POST,HEAD,etc)
• page(+HttpRequest,-Page) - retrieves the page of the request i.e. the first part of the request path
• path(+HttpRequest,-Path) - retrieves the extra path of the request i.e. the path following the page in the request path
• header(+HttpRequest,+Name,-Value) - retrieves the value of the specified header. Fails if no such header was specified in the request.
• query(+HttpRequest,-Query) - retrieves the query of the request. Fails if no query was specified in the request.
• parameter(+HttpRequest,+Name,-Value) - retrieves the value of the specified parameter. Fails if no such parameter was specified in the request.
• authorization(+HttpRequest,-AuthScheme,-Authorization) - retrieves the authorization credentials. Fails if no authorization was specified in the request.

• send_header(+HttpResponse,+Code) - sends a HTTP header with the specified HTTP code
• send_header(+HttpResponse,+Code,+Fields) - sends a HTTP header with the specified HTTP code and response fields
• send_error(+HttpResponse,+ErrorCode) - sends a HTTP header with the specified HTTP error code and a suitable error message
• send_error(+HttpResponse,+ErrorCode,+Fields) - sends a HTTP header with the specified HTTP error code, fields, and a suitable error message

  These two methods are used to send data back to the HTTP requester. A HTTP header is sent automatically with content type set to text/html if no header has yet been sent.

• send(+HttpResponse,+Text) - sends the specified text
• send(+HttpResponse,+Format,+Args) - formats and sends the specified text using same formatting as user:format/2

HTTP Authentication

1. Extract authorization information from the request:
   http:authorization(HttpRequest,basic,BasicCookie)
2. Decode the base64 encoded cookie:
   base64:b64decode(BasicCookie,UserInfo)
3. Extract the user and password from the user information:
   lists:append(User,[0':|Password],UserInfo)
4. Check that the user name and password are correct

If any of the above steps fails, the user is not authenticated and a challenge must be sent:
AuthField = field('WWW-Authenticate',"Basic realm=\"Test Authentication\""),
http:send_error(HttpResponse,unauthorized,[AuthField])

Note that basic authentication transmitts any passwords over Internet in plain text.

Webfile

• add_page(+Page,+Directory) - adds a directory from which files are served whenever a HTTP request is made with a path starting with the specified page.
• remove_page(+Page) - removes the specified page and its directory

Example

The code of a simple web server example can be found here: webserver.pl