Sink

Introduction

xpp::io::Sink is a write-discarding async writer. Every call to write() returns len immediately (the data is silently discarded). Useful for benchmarks, /dev/null equivalents, and situations where a writer is expected but the output is not needed.

Satisfies the AsyncWriter concept — composable with io::copy and BufWriter. C++11-compatible (uses xpp::resolve(len)).

Example — .await()

#include <xpp/io/sink.h>

xpp::io::Sink s;
ssize_t n = s.write("hello", 5).await();
// n == 5 (data discarded)

How it works

Sink is a simple struct whose write() returns xpp::resolve(static_cast<ssize_t>(len)) — an immediately-resolved Promise reporting that all bytes were "written". No I/O, no state, no coroutine overhead.

Use the sink() factory function:

auto s = xpp::io::sink();

API Reference

Usage Examples

Benchmark copy throughput — .await()

auto s = xpp::io::sink();
xpp::io::copy(reader, s).await();  // measures pure read throughput

Benchmark copy throughput — co_await (C++20)

xpp::Promise<void> benchmark_copy(xpp::io::AsyncReader auto &reader) {
    auto s = xpp::io::sink();
    co_await xpp::io::copy(reader, s);
}

Discard unwanted output — .await()

char header[4];
conn.read(header, 4).await();

auto s = xpp::io::sink();
xpp::io::copy(conn, s).await();  // read and discard remaining data

Discard unwanted output — co_await (C++20)

xpp::Promise<void> parse_request(xpp::net::TcpStream conn) {
    char header[4];
    co_await conn.read(header, 4);
    auto s = xpp::io::sink();
    co_await xpp::io::copy(conn, s);
}

As default writer parameter

// .await()
auto s = xpp::io::sink();
xpp::io::copy(reader, s).await();

// co_await (C++20)
template <AsyncWriter W>
xpp::Promise<void> log_or_discard(xpp::io::AsyncReader auto &reader, W &writer) {
    co_await xpp::io::copy(reader, writer);
}
auto s = xpp::io::sink();
log_or_discard(reader, s).await();