luasocket/doc/http.html

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<!-- http +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<h2 id="http">HTTP</h2>

<p>
HTTP (Hyper Text  Transfer Protocol) is the protocol  used to exchange
information  between  web-browsers and  servers.  The  <tt>http</tt>
namespace offers  full support for the client  side of the HTTP
protocol (i.e.,
the facilities that would be  used by a web-browser implementation). The
implementation    conforms     to    the    HTTP/1.1     standard,
<a href="http://www.ietf.org/rfc/rfc2616.txt">RFC 2616</a>.
</p>

<p>
The module exports functions that provide HTTP functionality in different
levels of abstraction. From the simple
string oriented requests, through generic
<a href="http://lua-users.org/wiki/FiltersSourcesAndSinks">LTN12</a> based, down to even lower-level if you bother to look through the source code.
</p>

<p>
To obtain the <tt>http</tt> namespace, run:
</p>

<pre class="example">
-- loads the HTTP module and any libraries it requires
local http = require("socket.http")
</pre>

<p>
URLs must conform to
<a href="http://www.ietf.org/rfc/rfc1738.txt">RFC 1738</a>,
that is, an URL is a string in the form:
</p>

<blockquote>
<pre>
[http://][&lt;user&gt;[:&lt;password&gt;]@]&lt;host&gt;[:&lt;port&gt;][/&lt;path&gt;]
</pre>
</blockquote>

<p>
MIME headers are represented as a Lua table in the form:
</p>

<blockquote>
<table summary="MIME headers in Lua table">
<tr><td><tt>
headers = {<br>
&nbsp;&nbsp;field-1-name = <i>field-1-value</i>,<br>
&nbsp;&nbsp;field-2-name = <i>field-2-value</i>,<br>
&nbsp;&nbsp;field-3-name = <i>field-3-value</i>,<br>
&nbsp;&nbsp;...<br>
&nbsp;&nbsp;field-n-name = <i>field-n-value</i><br>
}
</tt></td></tr>
</table>
</blockquote>

<p>
Field names are case insensitive (as specified by the standard) and all
functions work with lowercase field names (but see
<a href="socket.html#headers.canonic"><tt>socket.headers.canonic</tt></a>).
Field values are left unmodified.
</p>

<p class="note">
Note: MIME headers are independent of order. Therefore, there is no problem
in representing them in a Lua table.
</p>

<p>
The following constants can be set to control the default behavior of
the HTTP module:
</p>

<ul>
<li> <tt>PROXY</tt>: default proxy used for connections;</li>
<li> <tt>TIMEOUT</tt>: sets the timeout for all I/O operations;</li>
<li> <tt>USERAGENT</tt>: default user agent reported to server.</li>
</ul>

<p class="note">
Note: These constants are global. Changing them will also
change the behavior other code that might be using LuaSocket.
</p>

<!-- http.request ++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class="name" id="request">
http.<b>request(</b>url [, body]<b>)</b><br>
http.<b>request{</b><br>
&nbsp;&nbsp;url = <i>string</i>,<br>
&nbsp;&nbsp;[sink = <i>LTN12 sink</i>,]<br>
&nbsp;&nbsp;[method = <i>string</i>,]<br>
&nbsp;&nbsp;[headers = <i>header-table</i>,]<br>
&nbsp;&nbsp;[source = <i>LTN12 source</i>],<br>
&nbsp;&nbsp;[step = <i>LTN12 pump step</i>,]<br>
&nbsp;&nbsp;[proxy = <i>string</i>,]<br>
&nbsp;&nbsp;[redirect = <i>boolean</i>,]<br>
&nbsp;&nbsp;[create = <i>function</i>,]<br>
&nbsp;&nbsp;[maxredirects = <i>number</i>]<br>
<b>}</b>
</p>

<p class="description">
The request function has two forms. The simple form downloads
a URL using the <tt>GET</tt> or <tt>POST</tt> method and is based
on strings. The generic form performs any HTTP method and is
<a href="http://lua-users.org/wiki/FiltersSourcesAndSinks">LTN12</a> based.
</p>

<p class="parameters">
If the first argument of the <tt>request</tt> function is a string, it
should be an <tt>url</tt>. In that case, if a <tt>body</tt>
is provided as a string, the function will perform a <tt>POST</tt> method
in the <tt>url</tt>. Otherwise, it performs a <tt>GET</tt> in the
<tt>url</tt>
</p>

<p class="parameters">
If the first argument is instead a table, the most important fields are
the <tt>url</tt> and the <em>simple</em>
<a href="http://lua-users.org/wiki/FiltersSourcesAndSinks">LTN12</a>
<tt>sink</tt> that will receive the downloaded content.
Any part of the <tt>url</tt> can be overridden by including
the appropriate field in the request table.
If authentication information is provided, the function
uses the  Basic Authentication Scheme (see  <a href="#authentication">note</a>)
to retrieve  the document. If <tt>sink</tt> is <tt><b>nil</b></tt>, the
function discards the downloaded data. The optional parameters are the
following:
</p>
<ul>
<li><tt>method</tt>: The HTTP request method. Defaults to "GET";</li>
<li><tt>headers</tt>: Any additional HTTP headers to send with the request;</li>
<li><tt>source</tt>: <em>simple</em>
<a href="http://lua-users.org/wiki/FiltersSourcesAndSinks">LTN12</a>
source to provide the request body. If there
is a body, you need to provide an appropriate "<tt>content-length</tt>"
request header field, or the function will attempt to send the body as
"<tt>chunked</tt>" (something few servers support). Defaults to the empty source;</li>
<li><tt>step</tt>:
<a href="http://lua-users.org/wiki/FiltersSourcesAndSinks">LTN12</a>
pump step function used to move data.
Defaults to the LTN12 <tt>pump.step</tt> function.</li>
<li><tt>proxy</tt>: The URL of a proxy server to use. Defaults to no proxy;</li>
<li><tt>redirect</tt>: Set to <tt><b>false</b></tt> to prevent the
function from  automatically following 301 or 302 server redirect messages;</li>
<li><tt>create</tt>: An optional function to be used instead of
<a href="tcp.html#socket.tcp"><tt>socket.tcp</tt></a> when the communications socket is created.</li>
<li><tt>maxredirects</tt>: An optional number specifying the maximum number of
    redirects to follow.  Defaults to <tt>5</tt> if not specified. A boolean
    <tt>false</tt> value means no maximum (unlimited).</li>
</ul>

<p class="return">
In case of failure, the function returns <tt><b>nil</b></tt> followed by an
error message. If successful, the simple form returns the response
body as a string, followed by the response status code, the response
headers and the response status line. The generic function returns the same
information, except the first return value is just the number 1 (the body
goes to the <tt>sink</tt>).
</p>

<p class="return">
Even  when the server fails to provide the contents of the requested URL (URL not  found, for  example),
it usually returns a message body (a web page informing the
URL  was  not found  or  some  other useless  page).  To  make sure  the
operation was successful, check  the returned status <tt>code</tt>. For
a  list  of  the  possible  values  and  their  meanings,  refer  to  <a
href="http://www.ietf.org/rfc/rfc2616.txt">RFC 2616</a>.
</p>

<p class="description">
Here are a few examples with the simple interface:
</p>

<pre class="example">
-- load the http module
local io = require("io")
local http = require("socket.http")
local ltn12 = require("ltn12")

-- connect to server "www.cs.princeton.edu" and retrieves this manual
-- file from "~diego/professional/luasocket/http.html" and print it to stdout
http.request{
    url = "http://www.cs.princeton.edu/~diego/professional/luasocket/http.html",
    sink = ltn12.sink.file(io.stdout)
}

-- connect to server "www.example.com" and tries to retrieve
-- "/private/index.html". Fails because authentication is needed.
b, c, h = http.request("http://www.example.com/private/index.html")
-- b returns some useless page telling about the denied access,
-- h returns authentication information
-- and c returns with value 401 (Authentication Required)

-- tries to connect to server "wrong.host" to retrieve "/"
-- and fails because the host does not exist.
r, e = http.request("http://wrong.host/")
-- r is nil, and e returns with value "host not found"
</pre>

<p class="description">
And here is an example using the generic interface:
</p>

<pre class="example">
-- load the http module
http = require("socket.http")

-- Requests information about a document, without downloading it.
-- Useful, for example, if you want to display a download gauge and need
-- to know the size of the document in advance
r, c, h = http.request {
  method = "HEAD",
  url = "http://www.tecgraf.puc-rio.br/~diego"
}
-- r is 1, c is 200, and h would return the following headers:
-- h = {
--   date = "Tue, 18 Sep 2001 20:42:21 GMT",
--   server = "Apache/1.3.12 (Unix)  (Red Hat/Linux)",
--   ["last-modified"] = "Wed, 05 Sep 2001 06:11:20 GMT",
--   ["content-length"] = 15652,
--   ["connection"] = "close",
--   ["content-Type"] = "text/html"
-- }
</pre>

<p class="note" id="post">
Note: When sending a POST request, simple interface adds a
"<tt>Content-type: application/x-www-form-urlencoded</tt>"
header to the request. This is the type used by
HTML forms. If you need another type, use the generic
interface.
</p>

<p class="note" id="authentication">
Note: Some URLs are protected by their
servers from anonymous download. For those URLs, the server must receive
some  sort of  authentication along  with the  request or  it will  deny
download and return status "401&nbsp;Authentication Required".
</p>

<p class="note">
The  HTTP/1.1 standard  defines  two authentication  methods: the  Basic
Authentication  Scheme  and  the   Digest  Authentication  Scheme,  both
explained in detail in
<a href="http://www.ietf.org/rfc/rfc2068.txt">RFC 2068</a>.
</p>

<p class="note">The Basic  Authentication   Scheme  sends
<tt>&lt;user&gt;</tt>  and
<tt>&lt;password&gt;</tt>  unencrypted to  the server  and is  therefore
considered unsafe.  Unfortunately, by  the time of  this implementation,
the wide majority of servers and browsers support the Basic Scheme only.
Therefore,   this  is   the  method   used  by   the  toolkit   whenever
authentication is required.
</p>

<pre class="example">
-- load required modules
http = require("socket.http")
mime = require("mime")

-- Connect to server "www.example.com" and tries to retrieve
-- "/private/index.html", using the provided name and password to
-- authenticate the request
b, c, h = http.request("http://fulano:silva@www.example.com/private/index.html")

-- Alternatively, one could fill the appropriate header and authenticate
-- the request directly.
r, c = http.request {
  url = "http://www.example.com/private/index.html",
  headers = { authorization = "Basic " .. (mime.b64("fulano:silva")) }
}
</pre>

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Last modified by Eric Westbrook on <br>
Sat Feb 23 19:09:42 UTC 2019
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