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                <ol class="chapter"><li class="chapter-item expanded "><a href="../networking-introduction.html"><strong aria-hidden="true">1.</strong> Networking introduction</a></li><li class="chapter-item expanded "><a href="../quinn.html"><strong aria-hidden="true">2.</strong> Quinn introduction</a></li><li class="chapter-item expanded "><a href="../quinn.html"><strong aria-hidden="true">3.</strong> QUINN Introduction</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../quinn/certificate.html"><strong aria-hidden="true">3.1.</strong> Certificate Configuration</a></li><li class="chapter-item expanded "><a href="../quinn/set-up-connection.html"><strong aria-hidden="true">3.2.</strong> Connection Setup</a></li><li class="chapter-item expanded "><a href="../quinn/data-transfer.html" class="active"><strong aria-hidden="true">3.3.</strong> Data Transfer</a></li></ol></li><li class="chapter-item expanded "><a href="../quic.html"><strong aria-hidden="true">4.</strong> The QUIC protocol</a></li></ol>
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                        <h1 id="data-transfer"><a class="header" href="#data-transfer">Data Transfer</a></h1>
<p>The <a href="set-up-connection.html">previous chapter</a> explained how to set up an <a href="https://docs.rs/quinn/latest/quinn/generic/struct.Endpoint.html">Endpoint</a>
and then get access to a <a href="https://docs.rs/quinn/latest/quinn/generic/struct.NewConnection.html">NewConnection</a> instance.
This chapter continues with the subject of sending data over this connection.</p>
<h2 id="multiplexing"><a class="header" href="#multiplexing">Multiplexing</a></h2>
<p>Multiplexing is the act of combining data from multiple streams into a single stream. 
This can have a significant positive effect on the performance of the application. 
With QUIC, the programmer is in full control over the stream allocation.</p>
<h2 id="stream-types"><a class="header" href="#stream-types">Stream Types</a></h2>
<p>QUIC provides support for both stream and message-based communication.
Streams and messages can be initiated both on the client and server.</p>
<table><thead><tr><th align="left">Type</th><th align="left">Description</th><th align="left">Reference</th></tr></thead><tbody>
<tr><td align="left"><strong>Bidirectional Stream</strong></td><td align="left">two way stream communication.</td><td align="left">see <a href="https://docs.rs/quinn/latest/quinn/generic/struct.Connection.html#method.open_bi">open_bi</a></td></tr>
<tr><td align="left"><strong>Unidirectional Stream</strong></td><td align="left">one way stream communication.</td><td align="left">see <a href="https://docs.rs/quinn/latest/quinn/generic/struct.Connection.html#method.open_uni">open_uni</a></td></tr>
<tr><td align="left"><strong>Unreliable Messaging (extension)</strong></td><td align="left">message based unreliable communication.</td><td align="left">see <a href="https://docs.rs/quinn/latest/quinn/generic/struct.Connection.html#method.send_datagram">send_datagram</a></td></tr>
</tbody></table>
<h2 id="how-to-use"><a class="header" href="#how-to-use">How to Use</a></h2>
<p>New streams can be created with <a href="https://docs.rs/quinn/latest/quinn/generic/struct.Connection.html#method.open_bi">open_bi()</a>, <a href="https://docs.rs/quinn/latest/quinn/generic/struct.Connection.html#method.open_uni">open_uni()</a> from type <a href="https://docs.rs/quinn/latest/quinn/generic/struct.NewConnection.html#structfield.connection">Connection</a>.
An instance of this type, together with existing streams, can be found in the <a href="https://docs.rs/quinn/latest/quinn/generic/struct.NewConnection.html#structfield.connection">connection</a> field of <a href="https://docs.rs/quinn/latest/quinn/generic/struct.NewConnection.html">NewConnection</a>.</p>
<h2 id="bidirectional-streams"><a class="header" href="#bidirectional-streams">Bidirectional Streams</a></h2>
<p>With bidirectional streams, data can be sent in both directions. 
For example, from the connection initiator to the peer and the other way around.</p>
<p><em>open bidirectional stream</em></p>
<pre><pre class="playground"><code class="language-rust">
<span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>async fn open_bidirectional_stream(connection: Connection) -&gt; anyhow::Result&lt;()&gt; {
    let (mut send, recv) = connection.
        open_bi()
        .await?;

    send.write_all(b&quot;test&quot;).await?;
    send.finish().await?;
    
    let received = recv.read_to_end(10).await?;

    Ok(())
}
<span class="boring">}
</span></code></pre></pre>
<p><em>iterate incoming bidirectional stream(s)</em></p>
<pre><pre class="playground"><code class="language-rust">
<span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>async fn receive_bidirectional_stream(mut connection: NewConnection) -&gt; anyhow::Result&lt;()&gt; {
    while let Some(Ok((send, recv))) = connection.bi_streams.next().await {
        // Because it is a bidirectional stream, we can both send and recieve.
        println!(&quot;request: {:?}&quot;, recv.read_to_end(50).await?);

        send.write_all(b&quot;response&quot;).await?;
        send.finish().await?;
    }

    Ok(())
}
<span class="boring">}
</span></code></pre></pre>
<h2 id="unidirectional-streams"><a class="header" href="#unidirectional-streams">Unidirectional Streams</a></h2>
<p>With unidirectional streams, you can carry data only in one direction: from the initiator of the stream to its peer.
It is possible to get reliability without ordering (so no head-of-line blocking) by opening a new stream for each packet.</p>
<p><em>open unidirectional stream</em></p>
<pre><pre class="playground"><code class="language-rust">
<span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>async fn open_unidirectional_stream(connection: Connection)-&gt; anyhow::Result&lt;()&gt; {
    let mut send = connection.
        open_uni()
        .await?;

    send.write_all(b&quot;test&quot;).await.unwrap();
    send.finish().await?;

    Ok(())
}
<span class="boring">}
</span></code></pre></pre>
<p><em>iterating incoming unidirectional stream(s)</em></p>
<pre><pre class="playground"><code class="language-rust">
<span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>async fn receive_unidirectional_stream(mut connection: NewConnection) -&gt; anyhow::Result&lt;()&gt; {
    while let Some(Ok(recv)) = connection.uni_streams.next().await {
        // Because it is a unidirectional stream, we can only receive not send back.
        println!(&quot;{:?}&quot;, recv.read_to_end(50).await?);
    }

    Ok(())
}
<span class="boring">}
</span></code></pre></pre>
<h2 id="unreliable-messaging"><a class="header" href="#unreliable-messaging">Unreliable Messaging</a></h2>
<p>With unreliable messaging, you can transfer data without reliability. 
This could be useful if data arrival isn't essential or when high throughput is important.</p>
<p><em>send datagram</em></p>
<pre><pre class="playground"><code class="language-rust">
<span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>async fn send_unreliable(connection: Connection)-&gt; anyhow::Result&lt;()&gt; {
    connection
        .send_datagram(b&quot;test&quot;.into())
        .await?;

    Ok(())
}
<span class="boring">}
</span></code></pre></pre>
<p><em>iterating datagram stream(s)</em></p>
<pre><pre class="playground"><code class="language-rust">
<span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>async fn receive_datagram(mut connection: NewConnection) -&gt; anyhow::Result&lt;()&gt; {
    while let Some(Ok(received_bytes)) = connection.datagrams.next().await {
        // Because it is a unidirectional stream, we can only receive not send back.
        println!(&quot;request: {:?}&quot;, received);
    }

    Ok(())
}
<span class="boring">}
</span></code></pre></pre>

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