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% The SWI-Prolog documentation system
\subsection{library(http/http_open): HTTP client library}
\label{sec:httpopen}
\begin{tags}
\mtag{See also}- \predref{load_html}{3} and \predref{xpath}{3} can be used to parse and navigate HTML
documents. \\- \predref{http_get}{3} and \predref{http_post}{4} provide an alternative interface that
convert the reply depending on the \verb$Content-Type$ header.
\end{tags}
This library defines \predref{http_open}{3}, which opens an URL as a Prolog stream.
The functionality of the library can be extended by loading two
additional modules that act as plugins:
\begin{description}
\termitem{library}{http/http_ssl_plugin}
Loading this library causes \predref{http_open}{3} to handle HTTPS connections.
Relevant options for SSL certificate handling are handed to
\predref{ssl_context}{3}. This plugin is loaded automatically if the scheme
\const{https} is requested using a default SSL context. See the plugin for
additional information regarding security.
\termitem{library}{zlib}
Loading this library supports the \const{gzip} transfer encoding. This
plugin is lazily loaded if a connection is opened that claims this
transfer encoding.
\termitem{library}{http/http_cookie}
Loading this library adds tracking cookies to \predref{http_open}{3}. Returned
cookies are collected in the Prolog database and supplied for
subsequent requests.
\termitem{library}{http/http_stream}
This library adds support for \textit{chunked} encoding. It is lazily
loaded if the server sends a \verb$Transfer-encoding: chunked$ header.
\end{description}
Here is a simple example to fetch a web-page:
\begin{code}
?- http_open('http://www.google.com/search?q=prolog', In, []),
copy_stream_data(In, user_output),
close(In).
prolog - Google Search