AK: Expose AllocatingMemoryStream::CHUNK_SIZE

This allows the tests to use that information confidently.

AK/MemoryStream.cpp

@@ -199,8 +199,8 @@ ErrorOr<Optional<size_t>> AllocatingMemoryStream::offset_of(ReadonlyBytes needle
         return Optional<size_t> {};
 
     // Ensure that we don't have to trim away more than one block.
-    VERIFY(m_read_offset < chunk_size);
+    VERIFY(m_read_offset < CHUNK_SIZE);
-    VERIFY(m_chunks.size() * chunk_size - m_write_offset < chunk_size);
+    VERIFY(m_chunks.size() * CHUNK_SIZE - m_write_offset < CHUNK_SIZE);
 
     auto chunk_count = m_chunks.size();
     auto search_spans = TRY(FixedArray<ReadonlyBytes>::create(chunk_count));
@@ -210,7 +210,7 @@ ErrorOr<Optional<size_t>> AllocatingMemoryStream::offset_of(ReadonlyBytes needle
     }
 
     // Trimming is done first to ensure that we don't unintentionally shift around if the first and last chunks are the same.
-    search_spans[chunk_count - 1] = search_spans[chunk_count - 1].trim(m_write_offset % chunk_size);
+    search_spans[chunk_count - 1] = search_spans[chunk_count - 1].trim(m_write_offset % CHUNK_SIZE);
     search_spans[0] = search_spans[0].slice(m_read_offset);
 
     return AK::memmem(search_spans.begin(), search_spans.end(), needle);
@@ -220,9 +220,9 @@ ErrorOr<ReadonlyBytes> AllocatingMemoryStream::next_read_range()
 {
     VERIFY(m_write_offset >= m_read_offset);
 
-    size_t const chunk_index = m_read_offset / chunk_size;
+    size_t const chunk_index = m_read_offset / CHUNK_SIZE;
-    size_t const chunk_offset = m_read_offset % chunk_size;
+    size_t const chunk_offset = m_read_offset % CHUNK_SIZE;
-    size_t const read_size = min(chunk_size - m_read_offset % chunk_size, m_write_offset - m_read_offset);
+    size_t const read_size = min(CHUNK_SIZE - m_read_offset % CHUNK_SIZE, m_write_offset - m_read_offset);
 
     if (read_size == 0)
         return ReadonlyBytes { static_cast<u8*>(nullptr), 0 };
@@ -236,12 +236,12 @@ ErrorOr<Bytes> AllocatingMemoryStream::next_write_range()
 {
     VERIFY(m_write_offset >= m_read_offset);
 
-    size_t const chunk_index = m_write_offset / chunk_size;
+    size_t const chunk_index = m_write_offset / CHUNK_SIZE;
-    size_t const chunk_offset = m_write_offset % chunk_size;
+    size_t const chunk_offset = m_write_offset % CHUNK_SIZE;
-    size_t const write_size = chunk_size - m_write_offset % chunk_size;
+    size_t const write_size = CHUNK_SIZE - m_write_offset % CHUNK_SIZE;
 
     if (chunk_index >= m_chunks.size())
-        TRY(m_chunks.try_append(TRY(Chunk::create_uninitialized(chunk_size))));
+        TRY(m_chunks.try_append(TRY(Chunk::create_uninitialized(CHUNK_SIZE))));
 
     VERIFY(chunk_index < m_chunks.size());
 
@@ -251,12 +251,12 @@ ErrorOr<Bytes> AllocatingMemoryStream::next_write_range()
 void AllocatingMemoryStream::cleanup_unused_chunks()
 {
     // FIXME: Move these all at once.
-    while (m_read_offset >= chunk_size) {
+    while (m_read_offset >= CHUNK_SIZE) {
         VERIFY(m_write_offset >= m_read_offset);
 
         auto buffer = m_chunks.take_first();
-        m_read_offset -= chunk_size;
+        m_read_offset -= CHUNK_SIZE;
-        m_write_offset -= chunk_size;
+        m_write_offset -= CHUNK_SIZE;
 
         m_chunks.append(move(buffer));
     }

AK/MemoryStream.h

@@ -45,6 +45,8 @@ private:
 /// and reading back the written data afterwards.
 class AllocatingMemoryStream final : public Stream {
 public:
+    static constexpr size_t CHUNK_SIZE = 4096;
+
     virtual ErrorOr<Bytes> read_some(Bytes) override;
     virtual ErrorOr<size_t> write_some(ReadonlyBytes) override;
     virtual ErrorOr<void> discard(size_t) override;
@@ -59,7 +61,6 @@ public:
 private:
     // Note: We set the inline buffer capacity to zero to make moving chunks as efficient as possible.
     using Chunk = AK::Detail::ByteBuffer<0>;
-    static constexpr size_t chunk_size = 4096;
 
     ErrorOr<ReadonlyBytes> next_read_range();
     ErrorOr<Bytes> next_write_range();

Tests/AK/TestMemoryStream.cpp

@@ -73,16 +73,15 @@ TEST_CASE(allocating_memory_stream_offset_of_oob)
     AllocatingMemoryStream stream;
     // NOTE: This test is to make sure that offset_of() doesn't read past the end of the "initialized" data.
     //       So we have to assume some things about the behavior of this class:
-    //       - The chunk size is 4096 bytes.
     //       - A chunk is moved to the end when it's fully read from
     //       - A free chunk is used as-is, no new ones are allocated if one exists.
 
-    // First, fill exactly one chunk.
+    // First, fill exactly one chunk (in groups of 16 bytes).
-    for (size_t i = 0; i < 256; ++i)
+    for (size_t i = 0; i < AllocatingMemoryStream::CHUNK_SIZE / 16; ++i)
         MUST(stream.write_until_depleted("AAAAAAAAAAAAAAAA"sv.bytes()));
 
     // Then discard it all.
-    MUST(stream.discard(4096));
+    MUST(stream.discard(AllocatingMemoryStream::CHUNK_SIZE));
     // Now we can write into this chunk again, knowing that it's initialized to all 'A's.
     MUST(stream.write_until_depleted("Well Hello Friends! :^)"sv.bytes()));