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</pre><pre class="rust"><code><span class="kw">use</span> <span class="ident">std::io::Write</span>;

<span class="kw">use</span> <span class="ident">anyhow</span>::{<span class="ident">Context</span>, <span class="prelude-ty">Result</span>};
<span class="kw">use</span> <span class="ident">futures_channel::mpsc</span>;

<span class="kw">use</span> <span class="ident">abstutil::prettyprint_usize</span>;

<span class="doccomment">/// Downloads bytes from a URL. This must be called with a tokio runtime somewhere. The caller</span>
<span class="doccomment">/// creates an mpsc channel pair and provides the sender. Progress will be described through it.</span>
<span class="kw">pub</span> <span class="kw">async</span> <span class="kw">fn</span> <span class="ident">download_bytes</span><span class="op">&lt;</span><span class="ident">I</span>: <span class="ident">AsRef</span><span class="op">&lt;</span><span class="ident">str</span><span class="op">&gt;</span><span class="op">&gt;</span>(
    <span class="ident">url</span>: <span class="ident">I</span>,
    <span class="ident">post_body</span>: <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="ident">String</span><span class="op">&gt;</span>,
    <span class="ident">progress</span>: <span class="kw-2">&amp;mut</span> <span class="ident">mpsc::Sender</span><span class="op">&lt;</span><span class="ident">String</span><span class="op">&gt;</span>,
) -&gt; <span class="prelude-ty">Result</span><span class="op">&lt;</span><span class="ident">Vec</span><span class="op">&lt;</span><span class="ident">u8</span><span class="op">&gt;</span><span class="op">&gt;</span> {
    <span class="kw">let</span> <span class="ident">url</span> <span class="op">=</span> <span class="ident">url</span>.<span class="ident">as_ref</span>();
    <span class="macro">info!</span>(<span class="string">&quot;Downloading {}&quot;</span>, <span class="ident">url</span>);
    <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">resp</span> <span class="op">=</span> <span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="ident">body</span>) <span class="op">=</span> <span class="ident">post_body</span> {
        <span class="ident">reqwest::Client::new</span>()
            .<span class="ident">post</span>(<span class="ident">url</span>)
            .<span class="ident">body</span>(<span class="ident">body</span>)
            .<span class="ident">send</span>()
            .<span class="kw">await</span>
            .<span class="ident">unwrap</span>()
    } <span class="kw">else</span> {
        <span class="ident">reqwest::get</span>(<span class="ident">url</span>).<span class="kw">await</span>.<span class="ident">unwrap</span>()
    };
    <span class="ident">resp</span>.<span class="ident">error_for_status_ref</span>()
        .<span class="ident">with_context</span>(<span class="op">|</span><span class="op">|</span> <span class="ident">url</span>.<span class="ident">to_string</span>())<span class="question-mark">?</span>;

    <span class="kw">let</span> <span class="ident">total_size</span> <span class="op">=</span> <span class="ident">resp</span>.<span class="ident">content_length</span>().<span class="ident">map</span>(<span class="op">|</span><span class="ident">x</span><span class="op">|</span> <span class="ident">x</span> <span class="kw">as</span> <span class="ident">usize</span>);
    <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">bytes</span> <span class="op">=</span> <span class="ident">Vec::new</span>();
    <span class="kw">while</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="ident">chunk</span>) <span class="op">=</span> <span class="ident">resp</span>.<span class="ident">chunk</span>().<span class="kw">await</span>.<span class="ident">unwrap</span>() {
        <span class="comment">// TODO Throttle?</span>
        <span class="kw">let</span> <span class="ident">msg</span> <span class="op">=</span> <span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="ident">n</span>) <span class="op">=</span> <span class="ident">total_size</span> {
            <span class="macro">format!</span>(
                <span class="string">&quot;{:.2}% ({} / {} bytes)&quot;</span>,
                (<span class="ident">bytes</span>.<span class="ident">len</span>() <span class="kw">as</span> <span class="ident">f64</span>) <span class="op">/</span> (<span class="ident">n</span> <span class="kw">as</span> <span class="ident">f64</span>) <span class="op">*</span> <span class="number">100.0</span>,
                <span class="ident">prettyprint_usize</span>(<span class="ident">bytes</span>.<span class="ident">len</span>()),
                <span class="ident">prettyprint_usize</span>(<span class="ident">n</span>)
            )
        } <span class="kw">else</span> {
            <span class="comment">// One example where the HTTP response won&#39;t say the response size is the Overpass API</span>
            <span class="macro">format!</span>(
                <span class="string">&quot;{} bytes (unknown total size)&quot;</span>,
                <span class="ident">prettyprint_usize</span>(<span class="ident">bytes</span>.<span class="ident">len</span>())
            )
        };
        <span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Err</span>(<span class="ident">err</span>) <span class="op">=</span> <span class="ident">progress</span>.<span class="ident">try_send</span>(<span class="ident">msg</span>) {
            <span class="macro">warn!</span>(<span class="string">&quot;Couldn&#39;t send download progress message: {}&quot;</span>, <span class="ident">err</span>);
        }

        <span class="ident">bytes</span>.<span class="ident">write_all</span>(<span class="kw-2">&amp;</span><span class="ident">chunk</span>).<span class="ident">unwrap</span>();
    }
    <span class="macro">println!</span>();
    <span class="prelude-val">Ok</span>(<span class="ident">bytes</span>)
}

<span class="doccomment">/// Download a file from a URL. This must be called with a tokio runtime somewhere. Progress will</span>
<span class="doccomment">/// be printed to STDOUT.</span>
<span class="kw">pub</span> <span class="kw">async</span> <span class="kw">fn</span> <span class="ident">download_to_file</span><span class="op">&lt;</span><span class="ident">I1</span>: <span class="ident">AsRef</span><span class="op">&lt;</span><span class="ident">str</span><span class="op">&gt;</span>, <span class="ident">I2</span>: <span class="ident">AsRef</span><span class="op">&lt;</span><span class="ident">str</span><span class="op">&gt;</span><span class="op">&gt;</span>(
    <span class="ident">url</span>: <span class="ident">I1</span>,
    <span class="ident">post_body</span>: <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="ident">String</span><span class="op">&gt;</span>,
    <span class="ident">path</span>: <span class="ident">I2</span>,
) -&gt; <span class="prelude-ty">Result</span><span class="op">&lt;</span>()<span class="op">&gt;</span> {
    <span class="kw">let</span> (<span class="kw-2">mut</span> <span class="ident">tx</span>, <span class="ident">rx</span>) <span class="op">=</span> <span class="ident">futures_channel::mpsc::channel</span>(<span class="number">1000</span>);
    <span class="ident">print_download_progress</span>(<span class="ident">rx</span>);
    <span class="kw">let</span> <span class="ident">bytes</span> <span class="op">=</span> <span class="ident">download_bytes</span>(<span class="ident">url</span>, <span class="ident">post_body</span>, <span class="kw-2">&amp;mut</span> <span class="ident">tx</span>).<span class="kw">await</span><span class="question-mark">?</span>;
    <span class="kw">let</span> <span class="ident">path</span> <span class="op">=</span> <span class="ident">path</span>.<span class="ident">as_ref</span>();
    <span class="op">|</span><span class="op">|</span> -&gt; <span class="prelude-ty">Result</span><span class="op">&lt;</span>()<span class="op">&gt;</span> {
        <span class="ident">fs_err::create_dir_all</span>(<span class="ident">std::path::Path::new</span>(<span class="ident">path</span>).<span class="ident">parent</span>().<span class="ident">unwrap</span>())<span class="question-mark">?</span>;
        <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">file</span> <span class="op">=</span> <span class="ident">fs_err::File::create</span>(<span class="ident">path</span>)<span class="question-mark">?</span>;
        <span class="ident">file</span>.<span class="ident">write_all</span>(<span class="kw-2">&amp;</span><span class="ident">bytes</span>)<span class="question-mark">?</span>;
        <span class="prelude-val">Ok</span>(())
    }()
    .<span class="ident">with_context</span>(<span class="op">|</span><span class="op">|</span> <span class="ident">path</span>.<span class="ident">to_string</span>())
}

<span class="doccomment">/// Print download progress to STDOUT. Pass this the receiver, then call download_to_file or</span>
<span class="doccomment">/// download_bytes with the sender.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">print_download_progress</span>(<span class="kw-2">mut</span> <span class="ident">progress</span>: <span class="ident">mpsc::Receiver</span><span class="op">&lt;</span><span class="ident">String</span><span class="op">&gt;</span>) {
    <span class="ident">tokio::task::spawn_blocking</span>(<span class="kw">move</span> <span class="op">|</span><span class="op">|</span> <span class="kw">loop</span> {
        <span class="kw">match</span> <span class="ident">progress</span>.<span class="ident">try_next</span>() {
            <span class="prelude-val">Ok</span>(<span class="prelude-val">Some</span>(<span class="ident">msg</span>)) =&gt; {
                <span class="ident">abstutil::clear_current_line</span>();
                <span class="macro">print!</span>(<span class="string">&quot;{}&quot;</span>, <span class="ident">msg</span>);
                <span class="ident">std::io::stdout</span>().<span class="ident">flush</span>().<span class="ident">unwrap</span>();
            }
            <span class="prelude-val">Ok</span>(<span class="prelude-val">None</span>) =&gt; <span class="kw">break</span>,
            <span class="comment">// Per</span>
            <span class="comment">// https://docs.rs/futures-channel/0.3.14/futures_channel/mpsc/struct.Receiver.html#method.try_next,</span>
            <span class="comment">// this means no messages are available yet</span>
            <span class="prelude-val">Err</span>(<span class="kw">_</span>) =&gt; {}
        }
    });
}
</code></pre></div>
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