From 7b65d7c508cbe0f7f0ae971ab5c9ac0c7a7eb69e Mon Sep 17 00:00:00 2001
From: eldritch horrors <pennae@lix.systems>
Date: Mon, 16 Jun 2025 18:51:59 +0200
Subject: [PATCH] libutil: add buffered async streams

these will let us share async stream io buffers with sync sinks and sources.

Change-Id: If3149803a9e1fda62391399177da62f7522a811b
---
 lix/libutil/async-io.cc | 50 +++++++++++++++++++++++++++++++++++++++++
 lix/libutil/async-io.hh | 47 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 97 insertions(+)

diff --git a/lix/libutil/async-io.cc b/lix/libutil/async-io.cc
index eaa6786c6..22d943437 100644
--- a/lix/libutil/async-io.cc
+++ b/lix/libutil/async-io.cc
@@ -83,4 +83,54 @@ try {
 } catch (...) {
     return {result::current_exception()};
 }
+
+kj::Promise<Result<size_t>> AsyncBufferedInputStream::read(void * data, size_t size)
+try {
+    while (buffer->used() == 0) {
+        const auto space = buffer->getWriteBuffer();
+        const auto got = TRY_AWAIT(inner.read(space.data(), space.size()));
+        if (got == 0) {
+            co_return 0;
+        }
+        buffer->added(got);
+    }
+
+    const auto available = buffer->getReadBuffer();
+    const auto n = std::min(size, available.size());
+    memcpy(data, available.data(), n);
+    buffer->consumed(n);
+    co_return result::success(n);
+} catch (...) {
+    co_return result::current_exception();
+}
+
+kj::Promise<Result<size_t>> AsyncBufferedOutputStream::write(const void * src, size_t size)
+try {
+    if (size > buffer->size()) {
+        TRY_AWAIT(flush());
+        co_return TRY_AWAIT(inner.write(src, size));
+    }
+
+    if (size > buffer->getWriteBuffer().size()) {
+        TRY_AWAIT(flush());
+    }
+
+    const auto into = buffer->getWriteBuffer();
+    memcpy(into.data(), src, size);
+    buffer->added(size);
+    co_return size;
+} catch (...) {
+    co_return result::current_exception();
+}
+
+kj::Promise<Result<void>> AsyncBufferedOutputStream::flush()
+try {
+    if (auto unsent = buffer->getReadBuffer(); !unsent.empty()) {
+        TRY_AWAIT(inner.writeFull(unsent.data(), unsent.size()));
+        buffer->consumed(unsent.size());
+    }
+    co_return result::success();
+} catch (...) {
+    co_return result::current_exception();
+}
 }
diff --git a/lix/libutil/async-io.hh b/lix/libutil/async-io.hh
index 6f54c97e2..d71b043b0 100644
--- a/lix/libutil/async-io.hh
+++ b/lix/libutil/async-io.hh
@@ -3,6 +3,8 @@
 
 #include "lix/libutil/async.hh"
 #include "lix/libutil/box_ptr.hh"
+#include "lix/libutil/io-buffer.hh"
+#include "lix/libutil/ref.hh"
 #include "lix/libutil/result.hh"
 #include "lix/libutil/serialise.hh"
 #include <kj/async.h>
@@ -81,6 +83,28 @@ public:
     kj::Promise<Result<size_t>> read(void * data, size_t len) override;
 };
 
+class AsyncBufferedInputStream : public AsyncInputStream
+{
+    AsyncInputStream & inner;
+    ref<IoBuffer> buffer;
+
+public:
+    AsyncBufferedInputStream(AsyncInputStream & inner, ref<IoBuffer> buffer)
+        : inner(inner)
+        , buffer(buffer)
+    {
+    }
+
+    AsyncBufferedInputStream(AsyncInputStream & inner, size_t bufSize = 32 * 1024)
+        : AsyncBufferedInputStream(inner, make_ref<IoBuffer>(bufSize))
+    {
+    }
+
+    KJ_DISALLOW_COPY_AND_MOVE(AsyncBufferedInputStream);
+
+    kj::Promise<Result<size_t>> read(void * data, size_t size) override;
+};
+
 class AsyncOutputStream : private kj::AsyncObject
 {
 public:
@@ -105,4 +129,27 @@ public:
         );
     }
 };
+
+class AsyncBufferedOutputStream : public AsyncOutputStream
+{
+    AsyncOutputStream & inner;
+    ref<IoBuffer> buffer;
+
+public:
+    AsyncBufferedOutputStream(AsyncOutputStream & inner, ref<IoBuffer> buffer)
+        : inner(inner)
+        , buffer(buffer)
+    {
+    }
+
+    AsyncBufferedOutputStream(AsyncOutputStream & inner, size_t bufSize = 32 * 1024)
+        : AsyncBufferedOutputStream(inner, make_ref<IoBuffer>(bufSize))
+    {
+    }
+
+    KJ_DISALLOW_COPY_AND_MOVE(AsyncBufferedOutputStream);
+
+    kj::Promise<Result<size_t>> write(const void * src, size_t size) override;
+    kj::Promise<Result<void>> flush();
+};
 }