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<h1 class="page">Buffer Composition</h1>
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<p>Composing buffer sequences without allocation for scatter/gather I/O.</p>
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<p>Creating buffers from different sources</p>
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<p>Using <code>const_buffer_pair</code> and <code>mutable_buffer_pair</code> for scatter/gather I/O</p>
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<p>Zero-allocation buffer sequence patterns</p>
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<p>Understanding of buffer types from <a href="../5.buffers/5b.types.html" class="xref page">Buffer Types</a></p>
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</div>
|
|
<div class="sect1">
|
|
<h2 id="_source_code"><a class="anchor" href="#_source_code"></a>Source Code</h2>
|
|
<div class="sectionbody">
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlightjs highlight"><code class="language-cpp hljs" data-lang="cpp">#include <boost/capy.hpp>
|
|
#include <iostream>
|
|
#include <string>
|
|
#include <array>
|
|
#include <vector>
|
|
|
|
using namespace boost::capy;
|
|
|
|
void demonstrate_single_buffers()
|
|
{
|
|
std::cout << "=== Single Buffer Examples ===\n\n";
|
|
|
|
// Create buffers from various sources
|
|
std::string str = "Hello, World!";
|
|
char arr[] = "Array data";
|
|
std::vector<char> vec = {'V', 'e', 'c', 't', 'o', 'r'};
|
|
|
|
// make_buffer creates buffer views (no copies)
|
|
auto str_buf = make_buffer(str); // mutable_buffer
|
|
auto arr_buf = make_buffer(arr, sizeof(arr) - 1); // mutable_buffer - Exclude null terminator
|
|
auto vec_buf = make_buffer(vec); // mutable_buffer
|
|
|
|
std::cout << "String buffer: " << str_buf.size() << " bytes\n";
|
|
std::cout << "Array buffer: " << arr_buf.size() << " bytes\n";
|
|
std::cout << "Vector buffer: " << vec_buf.size() << " bytes\n";
|
|
}
|
|
|
|
void demonstrate_buffer_pair()
|
|
{
|
|
std::cout << "\n=== Buffer Pair (Scatter/Gather) ===\n\n";
|
|
|
|
// const_buffer_pair is std::array<const_buffer, 2>
|
|
std::string header = "Content-Type: text/plain\r\n\r\n";
|
|
std::string body = "Hello, World!";
|
|
|
|
const_buffer_pair message = {{
|
|
make_buffer(header),
|
|
make_buffer(body)
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|
}};
|
|
|
|
// Calculate total size
|
|
std::size_t total = buffer_size(message);
|
|
std::cout << "Total message size: " << total << " bytes\n";
|
|
std::cout << "Buffer count: " << buffer_length(message) << "\n";
|
|
|
|
// Iterate through buffers
|
|
std::cout << "\nBuffer contents:\n";
|
|
for (auto const& buf : message) // const_buffer const&
|
|
{
|
|
std::cout << " [" << buf.size() << " bytes]: ";
|
|
std::cout.write(static_cast<char const*>(buf.data()), buf.size());
|
|
std::cout << "\n";
|
|
}
|
|
}
|
|
|
|
void demonstrate_buffer_array()
|
|
{
|
|
std::cout << "\n=== Multi-Buffer Array ===\n\n";
|
|
|
|
// Use std::array for more than 2 buffers
|
|
std::string status = "HTTP/1.1 200 OK\r\n";
|
|
std::string content_type = "Content-Type: application/json\r\n";
|
|
std::string server = "Server: Capy/1.0\r\n";
|
|
std::string empty_line = "\r\n";
|
|
std::string body = R"({"status":"ok"})";
|
|
|
|
std::array<const_buffer, 5> http_response = {{
|
|
make_buffer(status),
|
|
make_buffer(content_type),
|
|
make_buffer(server),
|
|
make_buffer(empty_line),
|
|
make_buffer(body)
|
|
}};
|
|
|
|
std::size_t total = buffer_size(http_response);
|
|
std::cout << "HTTP response size: " << total << " bytes\n";
|
|
std::cout << "Buffer count: " << buffer_length(http_response) << "\n";
|
|
|
|
// In real code with streams:
|
|
// co_await write(stream, http_response);
|
|
// This performs scatter/gather I/O - single syscall for all buffers
|
|
}
|
|
|
|
void demonstrate_mutable_buffers()
|
|
{
|
|
std::cout << "\n=== Mutable Buffer Example ===\n\n";
|
|
|
|
// Mutable buffers for receiving data
|
|
char buf1[64];
|
|
char buf2[64];
|
|
|
|
mutable_buffer_pair recv_buffers = {{
|
|
mutable_buffer(buf1, sizeof(buf1)),
|
|
mutable_buffer(buf2, sizeof(buf2))
|
|
}};
|
|
|
|
std::cout << "Prepared " << buffer_length(recv_buffers)
|
|
<< " buffers with " << buffer_size(recv_buffers)
|
|
<< " bytes total capacity\n";
|
|
|
|
// In real code:
|
|
// auto [ec, n] = co_await stream.read_some(recv_buffers);
|
|
}
|
|
|
|
int main()
|
|
{
|
|
demonstrate_single_buffers();
|
|
demonstrate_buffer_pair();
|
|
demonstrate_buffer_array();
|
|
demonstrate_mutable_buffers();
|
|
|
|
return 0;
|
|
}</code></pre>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
<div class="sect1">
|
|
<h2 id="_build"><a class="anchor" href="#_build"></a>Build</h2>
|
|
<div class="sectionbody">
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlightjs highlight"><code class="language-cmake hljs" data-lang="cmake">add_executable(buffer_composition buffer_composition.cpp)
|
|
target_link_libraries(buffer_composition PRIVATE capy)</code></pre>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
<div class="sect1">
|
|
<h2 id="_walkthrough"><a class="anchor" href="#_walkthrough"></a>Walkthrough</h2>
|
|
<div class="sectionbody">
|
|
<div class="sect2">
|
|
<h3 id="_creating_buffers"><a class="anchor" href="#_creating_buffers"></a>Creating Buffers</h3>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlightjs highlight"><code class="language-cpp hljs" data-lang="cpp">auto str_buf = make_buffer(str); // mutable_buffer
|
|
auto arr_buf = make_buffer(arr, sizeof(arr) - 1); // mutable_buffer</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p><code>make_buffer</code> creates buffer views from various sources. No data is copied—the buffers reference the original storage.</p>
|
|
</div>
|
|
</div>
|
|
<div class="sect2">
|
|
<h3 id="_buffer_pairs"><a class="anchor" href="#_buffer_pairs"></a>Buffer Pairs</h3>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlightjs highlight"><code class="language-cpp hljs" data-lang="cpp">const_buffer_pair message = {{
|
|
make_buffer(header),
|
|
make_buffer(body)
|
|
}};</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p><code>const_buffer_pair</code> is <code>std::array<const_buffer, 2></code> — a fixed-size buffer sequence for scatter/gather I/O. Similarly, <code>mutable_buffer_pair</code> holds two mutable buffers.</p>
|
|
</div>
|
|
</div>
|
|
<div class="sect2">
|
|
<h3 id="_multi_buffer_arrays"><a class="anchor" href="#_multi_buffer_arrays"></a>Multi-Buffer Arrays</h3>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlightjs highlight"><code class="language-cpp hljs" data-lang="cpp">std::array<const_buffer, 5> http_response = {{
|
|
make_buffer(status),
|
|
make_buffer(content_type),
|
|
// ...
|
|
}};</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>For more than two buffers, use <code>std::array</code> directly. Buffer sequences support <code>buffer_size()</code> and <code>buffer_length()</code> for querying total bytes and buffer count.</p>
|
|
</div>
|
|
</div>
|
|
<div class="sect2">
|
|
<h3 id="_scattergather_io"><a class="anchor" href="#_scattergather_io"></a>Scatter/Gather I/O</h3>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlightjs highlight"><code class="language-cpp hljs" data-lang="cpp">co_await write(stream, http_response);</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>When you write a buffer sequence, the OS receives all buffers in a single system call. This is <strong>scatter/gather I/O</strong>:</p>
|
|
</div>
|
|
<div class="ulist">
|
|
<ul>
|
|
<li>
|
|
<p>No intermediate buffer allocation</p>
|
|
</li>
|
|
<li>
|
|
<p>No copying data together</p>
|
|
</li>
|
|
<li>
|
|
<p>Single syscall for multiple buffers</p>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
<div class="sect1">
|
|
<h2 id="_output"><a class="anchor" href="#_output"></a>Output</h2>
|
|
<div class="sectionbody">
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlightjs highlight"><code class="language-asciidoc hljs" data-lang="asciidoc">=== Single Buffer Examples ===
|
|
|
|
String buffer: 13 bytes
|
|
Array buffer: 10 bytes
|
|
Vector buffer: 6 bytes
|
|
|
|
=== Buffer Pair (Scatter/Gather) ===
|
|
|
|
Total message size: 41 bytes
|
|
Buffer count: 2
|
|
|
|
Buffer contents:
|
|
[28 bytes]: Content-Type: text/plain
|
|
|
|
|
|
[13 bytes]: Hello, World!
|
|
|
|
=== Multi-Buffer Array ===
|
|
|
|
HTTP response size: 84 bytes
|
|
Buffer count: 5
|
|
|
|
=== Mutable Buffer Example ===
|
|
|
|
Prepared 2 buffers with 128 bytes total capacity</code></pre>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
<div class="sect1">
|
|
<h2 id="_exercises"><a class="anchor" href="#_exercises"></a>Exercises</h2>
|
|
<div class="sectionbody">
|
|
<div class="olist arabic">
|
|
<ol class="arabic">
|
|
<li>
|
|
<p>Create a function that takes any <code>ConstBufferSequence</code> and prints its contents</p>
|
|
</li>
|
|
<li>
|
|
<p>Measure the difference between copying data into a single buffer vs. using <code>cat()</code></p>
|
|
</li>
|
|
<li>
|
|
<p>Implement a simple message framing protocol using buffer composition</p>
|
|
</li>
|
|
</ol>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
<div class="sect1">
|
|
<h2 id="_next_steps"><a class="anchor" href="#_next_steps"></a>Next Steps</h2>
|
|
<div class="sectionbody">
|
|
<div class="ulist">
|
|
<ul>
|
|
<li>
|
|
<p><a href="7d.mock-stream-testing.html" class="xref page">Mock Stream Testing</a> — Unit testing with mock streams</p>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
<div class="edit-this-page">
|
|
<a href="https://github.com/cppalliance/capy/edit/develop/doc/modules/ROOT/pages/7.examples/7c.buffer-composition.adoc">Edit this Page</a>
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