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<h3><a href="../contents.html">Table of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">Streams</a><ul>
<li><a class="reference internal" href="#streamreader">StreamReader</a></li>
<li><a class="reference internal" href="#streamwriter">StreamWriter</a></li>
<li><a class="reference internal" href="#examples">Examples</a><ul>
<li><a class="reference internal" href="#tcp-echo-client-using-streams">TCP echo client using streams</a></li>
<li><a class="reference internal" href="#tcp-echo-server-using-streams">TCP echo server using streams</a></li>
<li><a class="reference internal" href="#get-http-headers">Get HTTP headers</a></li>
<li><a class="reference internal" href="#register-an-open-socket-to-wait-for-data-using-streams">Register an open socket to wait for data using streams</a></li>
</ul>
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<section id="streams">
<span id="asyncio-streams"></span><h1>Streams<a class="headerlink" href="#streams" title="Permalink to this headline">¶</a></h1>
<p><strong>Source code:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.10/Lib/asyncio/streams.py">Lib/asyncio/streams.py</a></p>
<hr class="docutils" />
<p>Streams are high-level async/await-ready primitives to work with
network connections. Streams allow sending and receiving data without
using callbacks or low-level protocols and transports.</p>
<p id="asyncio-example-stream">Here is an example of a TCP echo client written using asyncio
streams:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">asyncio</span>
<span class="k">async</span> <span class="k">def</span> <span class="nf">tcp_echo_client</span><span class="p">(</span><span class="n">message</span><span class="p">):</span>
<span class="n">reader</span><span class="p">,</span> <span class="n">writer</span> <span class="o">=</span> <span class="k">await</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">open_connection</span><span class="p">(</span>
<span class="s1">'127.0.0.1'</span><span class="p">,</span> <span class="mi">8888</span><span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s1">'Send: </span><span class="si">{</span><span class="n">message</span><span class="si">!r}</span><span class="s1">'</span><span class="p">)</span>
<span class="n">writer</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="n">message</span><span class="o">.</span><span class="n">encode</span><span class="p">())</span>
<span class="k">await</span> <span class="n">writer</span><span class="o">.</span><span class="n">drain</span><span class="p">()</span>
<span class="n">data</span> <span class="o">=</span> <span class="k">await</span> <span class="n">reader</span><span class="o">.</span><span class="n">read</span><span class="p">(</span><span class="mi">100</span><span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s1">'Received: </span><span class="si">{</span><span class="n">data</span><span class="o">.</span><span class="n">decode</span><span class="p">()</span><span class="si">!r}</span><span class="s1">'</span><span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="s1">'Close the connection'</span><span class="p">)</span>
<span class="n">writer</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
<span class="k">await</span> <span class="n">writer</span><span class="o">.</span><span class="n">wait_closed</span><span class="p">()</span>
<span class="n">asyncio</span><span class="o">.</span><span class="n">run</span><span class="p">(</span><span class="n">tcp_echo_client</span><span class="p">(</span><span class="s1">'Hello World!'</span><span class="p">))</span>
</pre></div>
</div>
<p>See also the <a class="reference internal" href="#examples">Examples</a> section below.</p>
<p class="rubric">Stream Functions</p>
<p>The following top-level asyncio functions can be used to create
and work with streams:</p>
<dl class="py function">
<dt class="sig sig-object py" id="asyncio.open_connection">
<em class="property"><span class="pre">coroutine</span> </em><span class="sig-prename descclassname"><span class="pre">asyncio.</span></span><span class="sig-name descname"><span class="pre">open_connection</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">host</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">port</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="o"><span class="pre">*</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">limit</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">ssl</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">family</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">0</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">proto</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">0</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">flags</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">0</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">sock</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">local_addr</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">server_hostname</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">ssl_handshake_timeout</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">happy_eyeballs_delay</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">interleave</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.open_connection" title="Permalink to this definition">¶</a></dt>
<dd><p>Establish a network connection and return a pair of
<code class="docutils literal notranslate"><span class="pre">(reader,</span> <span class="pre">writer)</span></code> objects.</p>
<p>The returned <em>reader</em> and <em>writer</em> objects are instances of
<a class="reference internal" href="#asyncio.StreamReader" title="asyncio.StreamReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code></a> and <a class="reference internal" href="#asyncio.StreamWriter" title="asyncio.StreamWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamWriter</span></code></a> classes.</p>
<p><em>limit</em> determines the buffer size limit used by the
returned <a class="reference internal" href="#asyncio.StreamReader" title="asyncio.StreamReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code></a> instance. By default the <em>limit</em>
is set to 64 KiB.</p>
<p>The rest of the arguments are passed directly to
<a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.create_connection" title="asyncio.loop.create_connection"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.create_connection()</span></code></a>.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>The <em>sock</em> argument transfers ownership of the socket to the
<a class="reference internal" href="#asyncio.StreamWriter" title="asyncio.StreamWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamWriter</span></code></a> created. To close the socket, call its
<a class="reference internal" href="#asyncio.StreamWriter.close" title="asyncio.StreamWriter.close"><code class="xref py py-meth docutils literal notranslate"><span class="pre">close()</span></code></a> method.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.7: </span>Added the <em>ssl_handshake_timeout</em> parameter.</p>
</div>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.8: </span>Added <em>happy_eyeballs_delay</em> and <em>interleave</em> parameters.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.10: </span>Removed the <em>loop</em> parameter.</p>
</div>
</dd></dl>
<dl class="py function">
<dt class="sig sig-object py" id="asyncio.start_server">
<em class="property"><span class="pre">coroutine</span> </em><span class="sig-prename descclassname"><span class="pre">asyncio.</span></span><span class="sig-name descname"><span class="pre">start_server</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">client_connected_cb</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">host</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">port</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="o"><span class="pre">*</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">limit</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">family</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">socket.AF_UNSPEC</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">flags</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">socket.AI_PASSIVE</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">sock</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">backlog</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">100</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">ssl</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">reuse_address</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">reuse_port</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">ssl_handshake_timeout</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">start_serving</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">True</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.start_server" title="Permalink to this definition">¶</a></dt>
<dd><p>Start a socket server.</p>
<p>The <em>client_connected_cb</em> callback is called whenever a new client
connection is established. It receives a <code class="docutils literal notranslate"><span class="pre">(reader,</span> <span class="pre">writer)</span></code> pair
as two arguments, instances of the <a class="reference internal" href="#asyncio.StreamReader" title="asyncio.StreamReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code></a> and
<a class="reference internal" href="#asyncio.StreamWriter" title="asyncio.StreamWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamWriter</span></code></a> classes.</p>
<p><em>client_connected_cb</em> can be a plain callable or a
<a class="reference internal" href="asyncio-task.html#coroutine"><span class="std std-ref">coroutine function</span></a>; if it is a coroutine function,
it will be automatically scheduled as a <a class="reference internal" href="asyncio-task.html#asyncio.Task" title="asyncio.Task"><code class="xref py py-class docutils literal notranslate"><span class="pre">Task</span></code></a>.</p>
<p><em>limit</em> determines the buffer size limit used by the
returned <a class="reference internal" href="#asyncio.StreamReader" title="asyncio.StreamReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code></a> instance. By default the <em>limit</em>
is set to 64 KiB.</p>
<p>The rest of the arguments are passed directly to
<a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.create_server" title="asyncio.loop.create_server"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.create_server()</span></code></a>.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>The <em>sock</em> argument transfers ownership of the socket to the
server created. To close the socket, call the server’s
<a class="reference internal" href="asyncio-eventloop.html#asyncio.Server.close" title="asyncio.Server.close"><code class="xref py py-meth docutils literal notranslate"><span class="pre">close()</span></code></a> method.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.7: </span>Added the <em>ssl_handshake_timeout</em> and <em>start_serving</em> parameters.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.10: </span>Removed the <em>loop</em> parameter.</p>
</div>
</dd></dl>
<p class="rubric">Unix Sockets</p>
<dl class="py function">
<dt class="sig sig-object py" id="asyncio.open_unix_connection">
<em class="property"><span class="pre">coroutine</span> </em><span class="sig-prename descclassname"><span class="pre">asyncio.</span></span><span class="sig-name descname"><span class="pre">open_unix_connection</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">path</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="o"><span class="pre">*</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">limit</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">ssl</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">sock</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">server_hostname</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">ssl_handshake_timeout</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.open_unix_connection" title="Permalink to this definition">¶</a></dt>
<dd><p>Establish a Unix socket connection and return a pair of
<code class="docutils literal notranslate"><span class="pre">(reader,</span> <span class="pre">writer)</span></code>.</p>
<p>Similar to <a class="reference internal" href="#asyncio.open_connection" title="asyncio.open_connection"><code class="xref py py-func docutils literal notranslate"><span class="pre">open_connection()</span></code></a> but operates on Unix sockets.</p>
<p>See also the documentation of <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.create_unix_connection" title="asyncio.loop.create_unix_connection"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.create_unix_connection()</span></code></a>.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>The <em>sock</em> argument transfers ownership of the socket to the
<a class="reference internal" href="#asyncio.StreamWriter" title="asyncio.StreamWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamWriter</span></code></a> created. To close the socket, call its
<a class="reference internal" href="#asyncio.StreamWriter.close" title="asyncio.StreamWriter.close"><code class="xref py py-meth docutils literal notranslate"><span class="pre">close()</span></code></a> method.</p>
</div>
<p class="availability"><a class="reference internal" href="intro.html#availability"><span class="std std-ref">Availability</span></a>: Unix.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.7: </span>Added the <em>ssl_handshake_timeout</em> parameter.
The <em>path</em> parameter can now be a <a class="reference internal" href="../glossary.html#term-path-like-object"><span class="xref std std-term">path-like object</span></a></p>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.10: </span>Removed the <em>loop</em> parameter.</p>
</div>
</dd></dl>
<dl class="py function">
<dt class="sig sig-object py" id="asyncio.start_unix_server">
<em class="property"><span class="pre">coroutine</span> </em><span class="sig-prename descclassname"><span class="pre">asyncio.</span></span><span class="sig-name descname"><span class="pre">start_unix_server</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">client_connected_cb</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">path</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="o"><span class="pre">*</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">limit</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">sock</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">backlog</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">100</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">ssl</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">ssl_handshake_timeout</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">start_serving</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">True</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.start_unix_server" title="Permalink to this definition">¶</a></dt>
<dd><p>Start a Unix socket server.</p>
<p>Similar to <a class="reference internal" href="#asyncio.start_server" title="asyncio.start_server"><code class="xref py py-func docutils literal notranslate"><span class="pre">start_server()</span></code></a> but works with Unix sockets.</p>
<p>See also the documentation of <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.create_unix_server" title="asyncio.loop.create_unix_server"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.create_unix_server()</span></code></a>.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>The <em>sock</em> argument transfers ownership of the socket to the
server created. To close the socket, call the server’s
<a class="reference internal" href="asyncio-eventloop.html#asyncio.Server.close" title="asyncio.Server.close"><code class="xref py py-meth docutils literal notranslate"><span class="pre">close()</span></code></a> method.</p>
</div>
<p class="availability"><a class="reference internal" href="intro.html#availability"><span class="std std-ref">Availability</span></a>: Unix.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.7: </span>Added the <em>ssl_handshake_timeout</em> and <em>start_serving</em> parameters.
The <em>path</em> parameter can now be a <a class="reference internal" href="../glossary.html#term-path-like-object"><span class="xref std std-term">path-like object</span></a>.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.10: </span>Removed the <em>loop</em> parameter.</p>
</div>
</dd></dl>
<section id="streamreader">
<h2>StreamReader<a class="headerlink" href="#streamreader" title="Permalink to this headline">¶</a></h2>
<dl class="py class">
<dt class="sig sig-object py" id="asyncio.StreamReader">
<em class="property"><span class="pre">class</span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">asyncio.</span></span><span class="sig-name descname"><span class="pre">StreamReader</span></span><a class="headerlink" href="#asyncio.StreamReader" title="Permalink to this definition">¶</a></dt>
<dd><p>Represents a reader object that provides APIs to read data
from the IO stream. As an <a class="reference internal" href="../glossary.html#term-asynchronous-iterable"><span class="xref std std-term">asynchronous iterable</span></a>, the
object supports the <a class="reference internal" href="../reference/compound_stmts.html#async-for"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">async</span> <span class="pre">for</span></code></a> statement.</p>
<p>It is not recommended to instantiate <em>StreamReader</em> objects
directly; use <a class="reference internal" href="#asyncio.open_connection" title="asyncio.open_connection"><code class="xref py py-func docutils literal notranslate"><span class="pre">open_connection()</span></code></a> and <a class="reference internal" href="#asyncio.start_server" title="asyncio.start_server"><code class="xref py py-func docutils literal notranslate"><span class="pre">start_server()</span></code></a>
instead.</p>
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.StreamReader.read">
<em class="property"><span class="pre">coroutine</span> </em><span class="sig-name descname"><span class="pre">read</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">n</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">-</span> <span class="pre">1</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.StreamReader.read" title="Permalink to this definition">¶</a></dt>
<dd><p>Read up to <em>n</em> bytes from the stream.</p>
<p>If <em>n</em> is not provided or set to <code class="docutils literal notranslate"><span class="pre">-1</span></code>,
read until EOF, then return all read <a class="reference internal" href="stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a>.
If EOF was received and the internal buffer is empty,
return an empty <code class="docutils literal notranslate"><span class="pre">bytes</span></code> object.</p>
<p>If <em>n</em> is <code class="docutils literal notranslate"><span class="pre">0</span></code>, return an empty <code class="docutils literal notranslate"><span class="pre">bytes</span></code> object immediately.</p>
<p>If <em>n</em> is positive, return at most <em>n</em> available <code class="docutils literal notranslate"><span class="pre">bytes</span></code>
as soon as at least 1 byte is available in the internal buffer.
If EOF is received before any byte is read, return an empty
<code class="docutils literal notranslate"><span class="pre">bytes</span></code> object.</p>
</dd></dl>
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.StreamReader.readline">
<em class="property"><span class="pre">coroutine</span> </em><span class="sig-name descname"><span class="pre">readline</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.StreamReader.readline" title="Permalink to this definition">¶</a></dt>
<dd><p>Read one line, where “line” is a sequence of bytes
ending with <code class="docutils literal notranslate"><span class="pre">\n</span></code>.</p>
<p>If EOF is received and <code class="docutils literal notranslate"><span class="pre">\n</span></code> was not found, the method
returns partially read data.</p>
<p>If EOF is received and the internal buffer is empty,
return an empty <code class="docutils literal notranslate"><span class="pre">bytes</span></code> object.</p>
</dd></dl>
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.StreamReader.readexactly">
<em class="property"><span class="pre">coroutine</span> </em><span class="sig-name descname"><span class="pre">readexactly</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">n</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.StreamReader.readexactly" title="Permalink to this definition">¶</a></dt>
<dd><p>Read exactly <em>n</em> bytes.</p>
<p>Raise an <a class="reference internal" href="asyncio-exceptions.html#asyncio.IncompleteReadError" title="asyncio.IncompleteReadError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">IncompleteReadError</span></code></a> if EOF is reached before <em>n</em>
can be read. Use the <a class="reference internal" href="asyncio-exceptions.html#asyncio.IncompleteReadError.partial" title="asyncio.IncompleteReadError.partial"><code class="xref py py-attr docutils literal notranslate"><span class="pre">IncompleteReadError.partial</span></code></a>
attribute to get the partially read data.</p>
</dd></dl>
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.StreamReader.readuntil">
<em class="property"><span class="pre">coroutine</span> </em><span class="sig-name descname"><span class="pre">readuntil</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">separator</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">b'\n'</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.StreamReader.readuntil" title="Permalink to this definition">¶</a></dt>
<dd><p>Read data from the stream until <em>separator</em> is found.</p>
<p>On success, the data and separator will be removed from the
internal buffer (consumed). Returned data will include the
separator at the end.</p>
<p>If the amount of data read exceeds the configured stream limit, a
<a class="reference internal" href="asyncio-exceptions.html#asyncio.LimitOverrunError" title="asyncio.LimitOverrunError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">LimitOverrunError</span></code></a> exception is raised, and the data
is left in the internal buffer and can be read again.</p>
<p>If EOF is reached before the complete separator is found,
an <a class="reference internal" href="asyncio-exceptions.html#asyncio.IncompleteReadError" title="asyncio.IncompleteReadError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">IncompleteReadError</span></code></a> exception is raised, and the internal
buffer is reset. The <a class="reference internal" href="asyncio-exceptions.html#asyncio.IncompleteReadError.partial" title="asyncio.IncompleteReadError.partial"><code class="xref py py-attr docutils literal notranslate"><span class="pre">IncompleteReadError.partial</span></code></a> attribute
may contain a portion of the separator.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.5.2.</span></p>
</div>
</dd></dl>
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.StreamReader.at_eof">
<span class="sig-name descname"><span class="pre">at_eof</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.StreamReader.at_eof" title="Permalink to this definition">¶</a></dt>
<dd><p>Return <code class="docutils literal notranslate"><span class="pre">True</span></code> if the buffer is empty and <code class="xref py py-meth docutils literal notranslate"><span class="pre">feed_eof()</span></code>
was called.</p>
</dd></dl>
</dd></dl>
</section>
<section id="streamwriter">
<h2>StreamWriter<a class="headerlink" href="#streamwriter" title="Permalink to this headline">¶</a></h2>
<dl class="py class">
<dt class="sig sig-object py" id="asyncio.StreamWriter">
<em class="property"><span class="pre">class</span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">asyncio.</span></span><span class="sig-name descname"><span class="pre">StreamWriter</span></span><a class="headerlink" href="#asyncio.StreamWriter" title="Permalink to this definition">¶</a></dt>
<dd><p>Represents a writer object that provides APIs to write data
to the IO stream.</p>
<p>It is not recommended to instantiate <em>StreamWriter</em> objects
directly; use <a class="reference internal" href="#asyncio.open_connection" title="asyncio.open_connection"><code class="xref py py-func docutils literal notranslate"><span class="pre">open_connection()</span></code></a> and <a class="reference internal" href="#asyncio.start_server" title="asyncio.start_server"><code class="xref py py-func docutils literal notranslate"><span class="pre">start_server()</span></code></a>
instead.</p>
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.StreamWriter.write">
<span class="sig-name descname"><span class="pre">write</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">data</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.StreamWriter.write" title="Permalink to this definition">¶</a></dt>
<dd><p>The method attempts to write the <em>data</em> to the underlying socket immediately.
If that fails, the data is queued in an internal write buffer until it can be
sent.</p>
<p>The method should be used along with the <code class="docutils literal notranslate"><span class="pre">drain()</span></code> method:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">stream</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="n">data</span><span class="p">)</span>
<span class="k">await</span> <span class="n">stream</span><span class="o">.</span><span class="n">drain</span><span class="p">()</span>
</pre></div>
</div>
</dd></dl>
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.StreamWriter.writelines">
<span class="sig-name descname"><span class="pre">writelines</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">data</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.StreamWriter.writelines" title="Permalink to this definition">¶</a></dt>
<dd><p>The method writes a list (or any iterable) of bytes to the underlying socket
immediately.
If that fails, the data is queued in an internal write buffer until it can be
sent.</p>
<p>The method should be used along with the <code class="docutils literal notranslate"><span class="pre">drain()</span></code> method:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">stream</span><span class="o">.</span><span class="n">writelines</span><span class="p">(</span><span class="n">lines</span><span class="p">)</span>
<span class="k">await</span> <span class="n">stream</span><span class="o">.</span><span class="n">drain</span><span class="p">()</span>
</pre></div>
</div>
</dd></dl>
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.StreamWriter.close">
<span class="sig-name descname"><span class="pre">close</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.StreamWriter.close" title="Permalink to this definition">¶</a></dt>
<dd><p>The method closes the stream and the underlying socket.</p>
<p>The method should be used, though not mandatory,
along with the <code class="docutils literal notranslate"><span class="pre">wait_closed()</span></code> method:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">stream</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
<span class="k">await</span> <span class="n">stream</span><span class="o">.</span><span class="n">wait_closed</span><span class="p">()</span>
</pre></div>
</div>
</dd></dl>
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.StreamWriter.can_write_eof">
<span class="sig-name descname"><span class="pre">can_write_eof</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.StreamWriter.can_write_eof" title="Permalink to this definition">¶</a></dt>
<dd><p>Return <code class="docutils literal notranslate"><span class="pre">True</span></code> if the underlying transport supports
the <a class="reference internal" href="#asyncio.StreamWriter.write_eof" title="asyncio.StreamWriter.write_eof"><code class="xref py py-meth docutils literal notranslate"><span class="pre">write_eof()</span></code></a> method, <code class="docutils literal notranslate"><span class="pre">False</span></code> otherwise.</p>
</dd></dl>
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.StreamWriter.write_eof">
<span class="sig-name descname"><span class="pre">write_eof</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.StreamWriter.write_eof" title="Permalink to this definition">¶</a></dt>
<dd><p>Close the write end of the stream after the buffered write
data is flushed.</p>
</dd></dl>
<dl class="py attribute">
<dt class="sig sig-object py" id="asyncio.StreamWriter.transport">
<span class="sig-name descname"><span class="pre">transport</span></span><a class="headerlink" href="#asyncio.StreamWriter.transport" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the underlying asyncio transport.</p>
</dd></dl>
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.StreamWriter.get_extra_info">
<span class="sig-name descname"><span class="pre">get_extra_info</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">name</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">default</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.StreamWriter.get_extra_info" title="Permalink to this definition">¶</a></dt>
<dd><p>Access optional transport information; see
<a class="reference internal" href="asyncio-protocol.html#asyncio.BaseTransport.get_extra_info" title="asyncio.BaseTransport.get_extra_info"><code class="xref py py-meth docutils literal notranslate"><span class="pre">BaseTransport.get_extra_info()</span></code></a> for details.</p>
</dd></dl>
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.StreamWriter.drain">
<em class="property"><span class="pre">coroutine</span> </em><span class="sig-name descname"><span class="pre">drain</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.StreamWriter.drain" title="Permalink to this definition">¶</a></dt>
<dd><p>Wait until it is appropriate to resume writing to the stream.
Example:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">writer</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="n">data</span><span class="p">)</span>
<span class="k">await</span> <span class="n">writer</span><span class="o">.</span><span class="n">drain</span><span class="p">()</span>
</pre></div>
</div>
<p>This is a flow control method that interacts with the underlying
IO write buffer. When the size of the buffer reaches
the high watermark, <em>drain()</em> blocks until the size of the
buffer is drained down to the low watermark and writing can
be resumed. When there is nothing to wait for, the <a class="reference internal" href="#asyncio.StreamWriter.drain" title="asyncio.StreamWriter.drain"><code class="xref py py-meth docutils literal notranslate"><span class="pre">drain()</span></code></a>
returns immediately.</p>
</dd></dl>
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.StreamWriter.is_closing">
<span class="sig-name descname"><span class="pre">is_closing</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.StreamWriter.is_closing" title="Permalink to this definition">¶</a></dt>
<dd><p>Return <code class="docutils literal notranslate"><span class="pre">True</span></code> if the stream is closed or in the process of
being closed.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.7.</span></p>
</div>
</dd></dl>
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.StreamWriter.wait_closed">
<em class="property"><span class="pre">coroutine</span> </em><span class="sig-name descname"><span class="pre">wait_closed</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.StreamWriter.wait_closed" title="Permalink to this definition">¶</a></dt>
<dd><p>Wait until the stream is closed.</p>
<p>Should be called after <a class="reference internal" href="#asyncio.StreamWriter.close" title="asyncio.StreamWriter.close"><code class="xref py py-meth docutils literal notranslate"><span class="pre">close()</span></code></a> to wait until the underlying
connection is closed, ensuring that all data has been flushed
before e.g. exiting the program.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.7.</span></p>
</div>
</dd></dl>
</dd></dl>
</section>
<section id="examples">
<h2>Examples<a class="headerlink" href="#examples" title="Permalink to this headline">¶</a></h2>
<section id="tcp-echo-client-using-streams">
<span id="asyncio-tcp-echo-client-streams"></span><h3>TCP echo client using streams<a class="headerlink" href="#tcp-echo-client-using-streams" title="Permalink to this headline">¶</a></h3>
<p>TCP echo client using the <a class="reference internal" href="#asyncio.open_connection" title="asyncio.open_connection"><code class="xref py py-func docutils literal notranslate"><span class="pre">asyncio.open_connection()</span></code></a> function:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">asyncio</span>
<span class="k">async</span> <span class="k">def</span> <span class="nf">tcp_echo_client</span><span class="p">(</span><span class="n">message</span><span class="p">):</span>
<span class="n">reader</span><span class="p">,</span> <span class="n">writer</span> <span class="o">=</span> <span class="k">await</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">open_connection</span><span class="p">(</span>
<span class="s1">'127.0.0.1'</span><span class="p">,</span> <span class="mi">8888</span><span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s1">'Send: </span><span class="si">{</span><span class="n">message</span><span class="si">!r}</span><span class="s1">'</span><span class="p">)</span>
<span class="n">writer</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="n">message</span><span class="o">.</span><span class="n">encode</span><span class="p">())</span>
<span class="n">data</span> <span class="o">=</span> <span class="k">await</span> <span class="n">reader</span><span class="o">.</span><span class="n">read</span><span class="p">(</span><span class="mi">100</span><span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s1">'Received: </span><span class="si">{</span><span class="n">data</span><span class="o">.</span><span class="n">decode</span><span class="p">()</span><span class="si">!r}</span><span class="s1">'</span><span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="s1">'Close the connection'</span><span class="p">)</span>
<span class="n">writer</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
<span class="k">await</span> <span class="n">writer</span><span class="o">.</span><span class="n">wait_closed</span><span class="p">()</span>
<span class="n">asyncio</span><span class="o">.</span><span class="n">run</span><span class="p">(</span><span class="n">tcp_echo_client</span><span class="p">(</span><span class="s1">'Hello World!'</span><span class="p">))</span>
</pre></div>
</div>
<div class="admonition seealso">
<p class="admonition-title">See also</p>
<p>The <a class="reference internal" href="asyncio-protocol.html#asyncio-example-tcp-echo-client-protocol"><span class="std std-ref">TCP echo client protocol</span></a>
example uses the low-level <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.create_connection" title="asyncio.loop.create_connection"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.create_connection()</span></code></a> method.</p>
</div>
</section>
<section id="tcp-echo-server-using-streams">
<span id="asyncio-tcp-echo-server-streams"></span><h3>TCP echo server using streams<a class="headerlink" href="#tcp-echo-server-using-streams" title="Permalink to this headline">¶</a></h3>
<p>TCP echo server using the <a class="reference internal" href="#asyncio.start_server" title="asyncio.start_server"><code class="xref py py-func docutils literal notranslate"><span class="pre">asyncio.start_server()</span></code></a> function:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">asyncio</span>
<span class="k">async</span> <span class="k">def</span> <span class="nf">handle_echo</span><span class="p">(</span><span class="n">reader</span><span class="p">,</span> <span class="n">writer</span><span class="p">):</span>
<span class="n">data</span> <span class="o">=</span> <span class="k">await</span> <span class="n">reader</span><span class="o">.</span><span class="n">read</span><span class="p">(</span><span class="mi">100</span><span class="p">)</span>
<span class="n">message</span> <span class="o">=</span> <span class="n">data</span><span class="o">.</span><span class="n">decode</span><span class="p">()</span>
<span class="n">addr</span> <span class="o">=</span> <span class="n">writer</span><span class="o">.</span><span class="n">get_extra_info</span><span class="p">(</span><span class="s1">'peername'</span><span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s2">"Received </span><span class="si">{</span><span class="n">message</span><span class="si">!r}</span><span class="s2"> from </span><span class="si">{</span><span class="n">addr</span><span class="si">!r}</span><span class="s2">"</span><span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s2">"Send: </span><span class="si">{</span><span class="n">message</span><span class="si">!r}</span><span class="s2">"</span><span class="p">)</span>
<span class="n">writer</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="n">data</span><span class="p">)</span>
<span class="k">await</span> <span class="n">writer</span><span class="o">.</span><span class="n">drain</span><span class="p">()</span>
<span class="nb">print</span><span class="p">(</span><span class="s2">"Close the connection"</span><span class="p">)</span>
<span class="n">writer</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
<span class="k">await</span> <span class="n">writer</span><span class="o">.</span><span class="n">wait_closed</span><span class="p">()</span>
<span class="k">async</span> <span class="k">def</span> <span class="nf">main</span><span class="p">():</span>
<span class="n">server</span> <span class="o">=</span> <span class="k">await</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">start_server</span><span class="p">(</span>
<span class="n">handle_echo</span><span class="p">,</span> <span class="s1">'127.0.0.1'</span><span class="p">,</span> <span class="mi">8888</span><span class="p">)</span>
<span class="n">addrs</span> <span class="o">=</span> <span class="s1">', '</span><span class="o">.</span><span class="n">join</span><span class="p">(</span><span class="nb">str</span><span class="p">(</span><span class="n">sock</span><span class="o">.</span><span class="n">getsockname</span><span class="p">())</span> <span class="k">for</span> <span class="n">sock</span> <span class="ow">in</span> <span class="n">server</span><span class="o">.</span><span class="n">sockets</span><span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s1">'Serving on </span><span class="si">{</span><span class="n">addrs</span><span class="si">}</span><span class="s1">'</span><span class="p">)</span>
<span class="k">async</span> <span class="k">with</span> <span class="n">server</span><span class="p">:</span>
<span class="k">await</span> <span class="n">server</span><span class="o">.</span><span class="n">serve_forever</span><span class="p">()</span>
<span class="n">asyncio</span><span class="o">.</span><span class="n">run</span><span class="p">(</span><span class="n">main</span><span class="p">())</span>
</pre></div>
</div>
<div class="admonition seealso">
<p class="admonition-title">See also</p>
<p>The <a class="reference internal" href="asyncio-protocol.html#asyncio-example-tcp-echo-server-protocol"><span class="std std-ref">TCP echo server protocol</span></a>
example uses the <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.create_server" title="asyncio.loop.create_server"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.create_server()</span></code></a> method.</p>
</div>
</section>
<section id="get-http-headers">
<h3>Get HTTP headers<a class="headerlink" href="#get-http-headers" title="Permalink to this headline">¶</a></h3>
<p>Simple example querying HTTP headers of the URL passed on the command line:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">asyncio</span>
<span class="kn">import</span> <span class="nn">urllib.parse</span>
<span class="kn">import</span> <span class="nn">sys</span>
<span class="k">async</span> <span class="k">def</span> <span class="nf">print_http_headers</span><span class="p">(</span><span class="n">url</span><span class="p">):</span>
<span class="n">url</span> <span class="o">=</span> <span class="n">urllib</span><span class="o">.</span><span class="n">parse</span><span class="o">.</span><span class="n">urlsplit</span><span class="p">(</span><span class="n">url</span><span class="p">)</span>
<span class="k">if</span> <span class="n">url</span><span class="o">.</span><span class="n">scheme</span> <span class="o">==</span> <span class="s1">'https'</span><span class="p">:</span>
<span class="n">reader</span><span class="p">,</span> <span class="n">writer</span> <span class="o">=</span> <span class="k">await</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">open_connection</span><span class="p">(</span>
<span class="n">url</span><span class="o">.</span><span class="n">hostname</span><span class="p">,</span> <span class="mi">443</span><span class="p">,</span> <span class="n">ssl</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span>
<span class="k">else</span><span class="p">:</span>
<span class="n">reader</span><span class="p">,</span> <span class="n">writer</span> <span class="o">=</span> <span class="k">await</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">open_connection</span><span class="p">(</span>
<span class="n">url</span><span class="o">.</span><span class="n">hostname</span><span class="p">,</span> <span class="mi">80</span><span class="p">)</span>
<span class="n">query</span> <span class="o">=</span> <span class="p">(</span>
<span class="sa">f</span><span class="s2">"HEAD </span><span class="si">{</span><span class="n">url</span><span class="o">.</span><span class="n">path</span> <span class="ow">or</span> <span class="s1">'/'</span><span class="si">}</span><span class="s2"> HTTP/1.0</span><span class="se">\r\n</span><span class="s2">"</span>
<span class="sa">f</span><span class="s2">"Host: </span><span class="si">{</span><span class="n">url</span><span class="o">.</span><span class="n">hostname</span><span class="si">}</span><span class="se">\r\n</span><span class="s2">"</span>
<span class="sa">f</span><span class="s2">"</span><span class="se">\r\n</span><span class="s2">"</span>
<span class="p">)</span>
<span class="n">writer</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="n">query</span><span class="o">.</span><span class="n">encode</span><span class="p">(</span><span class="s1">'latin-1'</span><span class="p">))</span>
<span class="k">while</span> <span class="kc">True</span><span class="p">:</span>
<span class="n">line</span> <span class="o">=</span> <span class="k">await</span> <span class="n">reader</span><span class="o">.</span><span class="n">readline</span><span class="p">()</span>
<span class="k">if</span> <span class="ow">not</span> <span class="n">line</span><span class="p">:</span>
<span class="k">break</span>
<span class="n">line</span> <span class="o">=</span> <span class="n">line</span><span class="o">.</span><span class="n">decode</span><span class="p">(</span><span class="s1">'latin1'</span><span class="p">)</span><span class="o">.</span><span class="n">rstrip</span><span class="p">()</span>
<span class="k">if</span> <span class="n">line</span><span class="p">:</span>
<span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s1">'HTTP header> </span><span class="si">{</span><span class="n">line</span><span class="si">}</span><span class="s1">'</span><span class="p">)</span>
<span class="c1"># Ignore the body, close the socket</span>
<span class="n">writer</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
<span class="k">await</span> <span class="n">writer</span><span class="o">.</span><span class="n">wait_closed</span><span class="p">()</span>
<span class="n">url</span> <span class="o">=</span> <span class="n">sys</span><span class="o">.</span><span class="n">argv</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span>
<span class="n">asyncio</span><span class="o">.</span><span class="n">run</span><span class="p">(</span><span class="n">print_http_headers</span><span class="p">(</span><span class="n">url</span><span class="p">))</span>
</pre></div>
</div>
<p>Usage:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">python</span> <span class="n">example</span><span class="o">.</span><span class="n">py</span> <span class="n">http</span><span class="p">:</span><span class="o">//</span><span class="n">example</span><span class="o">.</span><span class="n">com</span><span class="o">/</span><span class="n">path</span><span class="o">/</span><span class="n">page</span><span class="o">.</span><span class="n">html</span>
</pre></div>
</div>
<p>or with HTTPS:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">python</span> <span class="n">example</span><span class="o">.</span><span class="n">py</span> <span class="n">https</span><span class="p">:</span><span class="o">//</span><span class="n">example</span><span class="o">.</span><span class="n">com</span><span class="o">/</span><span class="n">path</span><span class="o">/</span><span class="n">page</span><span class="o">.</span><span class="n">html</span>
</pre></div>
</div>
</section>
<section id="register-an-open-socket-to-wait-for-data-using-streams">
<span id="asyncio-example-create-connection-streams"></span><h3>Register an open socket to wait for data using streams<a class="headerlink" href="#register-an-open-socket-to-wait-for-data-using-streams" title="Permalink to this headline">¶</a></h3>
<p>Coroutine waiting until a socket receives data using the
<a class="reference internal" href="#asyncio.open_connection" title="asyncio.open_connection"><code class="xref py py-func docutils literal notranslate"><span class="pre">open_connection()</span></code></a> function:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">asyncio</span>
<span class="kn">import</span> <span class="nn">socket</span>
<span class="k">async</span> <span class="k">def</span> <span class="nf">wait_for_data</span><span class="p">():</span>
<span class="c1"># Get a reference to the current event loop because</span>
<span class="c1"># we want to access low-level APIs.</span>
<span class="n">loop</span> <span class="o">=</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">get_running_loop</span><span class="p">()</span>
<span class="c1"># Create a pair of connected sockets.</span>
<span class="n">rsock</span><span class="p">,</span> <span class="n">wsock</span> <span class="o">=</span> <span class="n">socket</span><span class="o">.</span><span class="n">socketpair</span><span class="p">()</span>
<span class="c1"># Register the open socket to wait for data.</span>
<span class="n">reader</span><span class="p">,</span> <span class="n">writer</span> <span class="o">=</span> <span class="k">await</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">open_connection</span><span class="p">(</span><span class="n">sock</span><span class="o">=</span><span class="n">rsock</span><span class="p">)</span>
<span class="c1"># Simulate the reception of data from the network</span>
<span class="n">loop</span><span class="o">.</span><span class="n">call_soon</span><span class="p">(</span><span class="n">wsock</span><span class="o">.</span><span class="n">send</span><span class="p">,</span> <span class="s1">'abc'</span><span class="o">.</span><span class="n">encode</span><span class="p">())</span>
<span class="c1"># Wait for data</span>
<span class="n">data</span> <span class="o">=</span> <span class="k">await</span> <span class="n">reader</span><span class="o">.</span><span class="n">read</span><span class="p">(</span><span class="mi">100</span><span class="p">)</span>
<span class="c1"># Got data, we are done: close the socket</span>
<span class="nb">print</span><span class="p">(</span><span class="s2">"Received:"</span><span class="p">,</span> <span class="n">data</span><span class="o">.</span><span class="n">decode</span><span class="p">())</span>
<span class="n">writer</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
<span class="k">await</span> <span class="n">writer</span><span class="o">.</span><span class="n">wait_closed</span><span class="p">()</span>
<span class="c1"># Close the second socket</span>
<span class="n">wsock</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
<span class="n">asyncio</span><span class="o">.</span><span class="n">run</span><span class="p">(</span><span class="n">wait_for_data</span><span class="p">())</span>
</pre></div>
</div>
<div class="admonition seealso">
<p class="admonition-title">See also</p>
<p>The <a class="reference internal" href="asyncio-protocol.html#asyncio-example-create-connection"><span class="std std-ref">register an open socket to wait for data using a protocol</span></a> example uses a low-level protocol and
the <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.create_connection" title="asyncio.loop.create_connection"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.create_connection()</span></code></a> method.</p>
<p>The <a class="reference internal" href="asyncio-eventloop.html#asyncio-example-watch-fd"><span class="std std-ref">watch a file descriptor for read events</span></a> example uses the low-level
<a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.add_reader" title="asyncio.loop.add_reader"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.add_reader()</span></code></a> method to watch a file descriptor.</p>
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<h3><a href="../contents.html">Table of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">Streams</a><ul>
<li><a class="reference internal" href="#streamreader">StreamReader</a></li>
<li><a class="reference internal" href="#streamwriter">StreamWriter</a></li>
<li><a class="reference internal" href="#examples">Examples</a><ul>
<li><a class="reference internal" href="#tcp-echo-client-using-streams">TCP echo client using streams</a></li>
<li><a class="reference internal" href="#tcp-echo-server-using-streams">TCP echo server using streams</a></li>
<li><a class="reference internal" href="#get-http-headers">Get HTTP headers</a></li>
<li><a class="reference internal" href="#register-an-open-socket-to-wait-for-data-using-streams">Register an open socket to wait for data using streams</a></li>
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