Module http_server
:- use_module(library(http/http_server)).This library provides an starting point to build HTTP server based applications. It is based on Warp, which allows for HTTP/1.0, HTTP/1.1 and HTTP/2. However, some advanced features that Warp provides are still not accesible.
Usage
The main predicate of the library is http_listen/2, which needs a port number (usually 80) and a list of handlers. A handler is a compound term with the functor as one HTTP method (in lowercase) and followed by a Route Match and a predicate which will handle the call.
text_handler(Request, Response) :-
http_status_code(Response, 200),
http_body(Response, text("Welcome to Scryer Prolog!")).
parameter_handler(User, Request, Response) :-
http_body(Response, text(User)).
http_listen(7890, [
get(echo, text_handler), % GET /echo
post(user/User, parameter_handler(User)) % POST /user/<User>
]).Every handler predicate will have at least 2-arity, with Request and Response. Although you can work directly with http_request and http_response terms, it is recommeded to use the helper predicates, which are easier to understand and cleaner:
http_headers(Response/Request, Headers)http_status_code(Responde, StatusCode)http_body(Response/Request, text(Body))http_body(Response/Request, binary(Body))http_body(Request, form(Form))http_body(Response, file(Filename))http_redirect(Response, Url)http_query(Request, QueryName, QueryValue)
Some things that are still missing:
http_listen(+Port, +Handlers).
Equivalent to http_listen(Port, Handlers, []).
http_listen(+Port, +Handlers, +Options).
Listens for HTTP connections on port Port. Each handler on the list Handlers should be of the form: HttpVerb(PathUnification, Predicate). For example: get(user/User, get_info(User)) will match an HTTP request that is a GET, the path unifies with /user/User (where User is a variable) and it will call get_info with three arguments: an http_request term, an http_response term and User.
The following options are supported:
tls_key(+Key)- a TLS key for HTTPS (string)tls_cert(+Cert)- a TLS cert for HTTPS (string)content_length_limit(+Limit)- maximum length (in bytes) for the incoming bodies. By default, 32KB.
In order to have a HTTPS server (instead of plain HTTP), both tls_key and tls_cert options must be provided.
http_headers(?Request_Response, ?Headers).
True iff Request_Response is a request or response with headers Headers. Can be used both to get headers (usually in from a request) and to add headers (usually in a response).
http_body(?Request_Response, ?Body).
True iff Body is the body of the request or response. A body can be of the following types:
bytes(Bytes)for both requests and responses, interprets the body as bytestext(Bytes)for both requests and responses, interprets the body as textform(Form)only for requests, interprets the body as anapplication/x-www-form-urlencodedform.file(File)only for responses, interprets the body as the content of a file (useful to send static files).
http_status_code(?Response, ?StatusCode).
True iff the status code of the response Response unifies with StatusCode.
http_redirect(-Response, +Uri).
True iff Response is a response that redirects the user to the uri Uri.
http_query(+Request, ?Key, ?Value).
True iff there's a query in request Request with key Key and value Value.
http_basic_auth(+LoginPredicate, +Handler, +Request, -Response)
Metapredicate that wraps an existing Handler with an HTTP Basic Auth flow. Checks if a given user + password is authorized to execute that handler, returning 401 if it's not satisfied.
LoginPredicate must be a predicate of arity 2 that takes a User and a Password. Handler will have, in addition to the Request and Response arguments, a User argument containing the User given in the authentication.
Example:
main :-
http_listen(8800,[get('/', http_basic_auth(login, inside_handler("data")))]).
login(User, Pass) :-
User = "aarroyoc",
Pass = "123456".
inside_handler(Data, User, Request, Response) :-
http_body(Response, text(User)).