AK: Remove history from DuplexMemoryStream.

That feature was really only useful for Compress::DeflateDecompressor
but that is now using CircularDuplexBuffer instead.

Author: asynts

AK/Stream.h

@@ -326,13 +326,9 @@ class InputMemoryStream final : public InputStream {
 // All data written to this stream can be read from it. Reading and writing is done
 // using different offsets, meaning that it is not necessary to seek to the start
 // before reading; this behaviour differs from BufferStream.
-//
-// The stream keeps a history of 64KiB which means that seeking backwards is well
-// defined. Data past that point will be discarded.
 class DuplexMemoryStream final : public DuplexStream {
 public:
     static constexpr size_t chunk_size = 4 * 1024;
-    static constexpr size_t history_size = 64 * 1024;
 
     bool eof() const override { return m_write_offset == m_read_offset; }
 
@@ -411,22 +407,6 @@ class DuplexMemoryStream final : public DuplexStream {
         return nread;
     }
 
-    size_t read(Bytes bytes, size_t offset)
-    {
-        const auto backup = this->roffset();
-
-        bool do_discard_chunks = false;
-        exchange(m_do_discard_chunks, do_discard_chunks);
-
-        rseek(offset);
-        const auto count = read(bytes);
-        rseek(backup);
-
-        exchange(m_do_discard_chunks, do_discard_chunks);
-
-        return count;
-    }
-
     bool read_or_error(Bytes bytes) override
     {
         if (m_write_offset - m_read_offset < bytes.size()) {
@@ -461,22 +441,12 @@ class DuplexMemoryStream final : public DuplexStream {
     size_t roffset() const { return m_read_offset; }
     size_t woffset() const { return m_write_offset; }
 
-    void rseek(size_t offset)
-    {
-        ASSERT(offset >= m_base_offset);
-        ASSERT(offset <= m_write_offset);
-        m_read_offset = offset;
-    }
-
     size_t remaining() const { return m_write_offset - m_read_offset; }
 
 private:
     void try_discard_chunks()
     {
-        if (!m_do_discard_chunks)
-            return;
-
-        while (m_read_offset - m_base_offset >= history_size + chunk_size) {
+        while (m_read_offset - m_base_offset >= chunk_size) {
             m_chunks.take_first();
             m_base_offset += chunk_size;
         }
@@ -486,7 +456,6 @@ class DuplexMemoryStream final : public DuplexStream {
     size_t m_write_offset { 0 };
     size_t m_read_offset { 0 };
     size_t m_base_offset { 0 };
-    bool m_do_discard_chunks { false };
 };
 
 }

AK/Tests/TestStream.cpp

@@ -123,61 +123,27 @@ TEST_CASE(duplex_simple)
     EXPECT(stream.eof());
 }
 
-TEST_CASE(duplex_seek_into_history)
+TEST_CASE(duplex_large_buffer)
 {
     DuplexMemoryStream stream;
 
     FixedArray<u8> one_kibibyte { 1024 };
 
     EXPECT_EQ(stream.remaining(), 0ul);
 
-    for (size_t idx = 0; idx < 256; ++idx) {
+    for (size_t idx = 0; idx < 256; ++idx)
         stream << one_kibibyte;
-    }
 
     EXPECT_EQ(stream.remaining(), 256 * 1024ul);
 
-    for (size_t idx = 0; idx < 128; ++idx) {
+    for (size_t idx = 0; idx < 128; ++idx)
         stream >> one_kibibyte;
-    }
 
     EXPECT_EQ(stream.remaining(), 128 * 1024ul);
 
-    // We now have 128KiB on the stream. Because the stream has a
-    // history size of 64KiB, we should be able to seek to 64KiB.
-    static_assert(DuplexMemoryStream::history_size == 64 * 1024);
-    stream.rseek(64 * 1024);
-
-    EXPECT_EQ(stream.remaining(), 192 * 1024ul);
-
-    for (size_t idx = 0; idx < 192; ++idx) {
+    for (size_t idx = 0; idx < 128; ++idx)
         stream >> one_kibibyte;
-    }
-
-    EXPECT(stream.eof());
-}
-
-TEST_CASE(duplex_wild_seeking)
-{
-    DuplexMemoryStream stream;
-
-    int input0 = 42, input1 = 13, input2 = -12;
-    int output0, output1, output2;
-
-    stream << input2;
-    stream << input0 << input1;
-    stream.rseek(0);
-    stream << input2 << input0;
-
-    stream.rseek(4);
-    stream >> output0 >> output1 >> output2;
-
-    EXPECT(!stream.eof());
-    EXPECT_EQ(input0, output0);
-    EXPECT_EQ(input1, output1);
-    EXPECT_EQ(input2, output2);
 
-    stream.discard_or_error(4);
     EXPECT(stream.eof());
 }