From 20aaab47f9dab40b37b85a1044ac43909ab50443 Mon Sep 17 00:00:00 2001
From: Timothy Flynn <trflynn89@pm.me>
Date: Tue, 28 Mar 2023 11:28:04 -0400
Subject: [PATCH] LibCompress: Use a bit stream for the entire GZIP
 decompression process

We currently mix normal and bit streams during GZIP decompression, where
the latter is a wrapper around the former. This isn't causing issues now
as the underlying bit stream buffer is a byte, so the normal stream can
pick up where the bit stream left off.

In order to increase the size of that buffer though, the normal stream
will not be able to assume it can resume reading after the bit stream.
The buffer can easily contain more bits than it was meant to read, so
when the normal stream resumes, there may be N bits leftover in the bit
stream that the normal stream was meant to read.

To avoid weird behavior when mixing streams, this changes the GZIP
decompressor to always read from a bit stream.
---
 Userland/Libraries/LibCompress/Deflate.cpp | 8 ++++----
 Userland/Libraries/LibCompress/Deflate.h   | 4 ++--
 Userland/Libraries/LibCompress/Gzip.cpp    | 7 ++++---
 Userland/Libraries/LibCompress/Gzip.h      | 4 ++--
 4 files changed, 12 insertions(+), 11 deletions(-)

diff --git a/Userland/Libraries/LibCompress/Deflate.cpp b/Userland/Libraries/LibCompress/Deflate.cpp
index a5ac0d1c1d..817b36e1be 100644
--- a/Userland/Libraries/LibCompress/Deflate.cpp
+++ b/Userland/Libraries/LibCompress/Deflate.cpp
@@ -189,14 +189,14 @@ ErrorOr<bool> DeflateDecompressor::UncompressedBlock::try_read_more()
     return true;
 }
 
-ErrorOr<NonnullOwnPtr<DeflateDecompressor>> DeflateDecompressor::construct(MaybeOwned<Stream> stream)
+ErrorOr<NonnullOwnPtr<DeflateDecompressor>> DeflateDecompressor::construct(MaybeOwned<LittleEndianInputBitStream> stream)
 {
     auto output_buffer = TRY(CircularBuffer::create_empty(32 * KiB));
     return TRY(adopt_nonnull_own_or_enomem(new (nothrow) DeflateDecompressor(move(stream), move(output_buffer))));
 }
 
-DeflateDecompressor::DeflateDecompressor(MaybeOwned<Stream> stream, CircularBuffer output_buffer)
-    : m_input_stream(make<LittleEndianInputBitStream>(move(stream)))
+DeflateDecompressor::DeflateDecompressor(MaybeOwned<LittleEndianInputBitStream> stream, CircularBuffer output_buffer)
+    : m_input_stream(move(stream))
     , m_output_buffer(move(output_buffer))
 {
 }
@@ -317,7 +317,7 @@ void DeflateDecompressor::close()
 ErrorOr<ByteBuffer> DeflateDecompressor::decompress_all(ReadonlyBytes bytes)
 {
     auto memory_stream = TRY(try_make<FixedMemoryStream>(bytes));
-    auto deflate_stream = TRY(DeflateDecompressor::construct(move(memory_stream)));
+    auto deflate_stream = TRY(DeflateDecompressor::construct(make<LittleEndianInputBitStream>(move(memory_stream))));
     AllocatingMemoryStream output_stream;
 
     auto buffer = TRY(ByteBuffer::create_uninitialized(4096));
diff --git a/Userland/Libraries/LibCompress/Deflate.h b/Userland/Libraries/LibCompress/Deflate.h
index c62f1bd34e..feb6e088ec 100644
--- a/Userland/Libraries/LibCompress/Deflate.h
+++ b/Userland/Libraries/LibCompress/Deflate.h
@@ -76,7 +76,7 @@ public:
     friend CompressedBlock;
     friend UncompressedBlock;
 
-    static ErrorOr<NonnullOwnPtr<DeflateDecompressor>> construct(MaybeOwned<Stream> stream);
+    static ErrorOr<NonnullOwnPtr<DeflateDecompressor>> construct(MaybeOwned<LittleEndianInputBitStream> stream);
     ~DeflateDecompressor();
 
     virtual ErrorOr<Bytes> read_some(Bytes) override;
@@ -88,7 +88,7 @@ public:
     static ErrorOr<ByteBuffer> decompress_all(ReadonlyBytes);
 
 private:
-    DeflateDecompressor(MaybeOwned<Stream> stream, CircularBuffer buffer);
+    DeflateDecompressor(MaybeOwned<LittleEndianInputBitStream> stream, CircularBuffer buffer);
 
     ErrorOr<u32> decode_length(u32);
     ErrorOr<u32> decode_distance(u32);
diff --git a/Userland/Libraries/LibCompress/Gzip.cpp b/Userland/Libraries/LibCompress/Gzip.cpp
index fce7a5fc09..10b6788b6b 100644
--- a/Userland/Libraries/LibCompress/Gzip.cpp
+++ b/Userland/Libraries/LibCompress/Gzip.cpp
@@ -7,6 +7,7 @@
 
 #include <LibCompress/Gzip.h>
 
+#include <AK/BitStream.h>
 #include <AK/DeprecatedString.h>
 #include <AK/MemoryStream.h>
 #include <LibCore/DateTime.h>
@@ -38,9 +39,9 @@ bool BlockHeader::supported_by_implementation() const
     return true;
 }
 
-ErrorOr<NonnullOwnPtr<GzipDecompressor::Member>> GzipDecompressor::Member::construct(BlockHeader header, Stream& stream)
+ErrorOr<NonnullOwnPtr<GzipDecompressor::Member>> GzipDecompressor::Member::construct(BlockHeader header, LittleEndianInputBitStream& stream)
 {
-    auto deflate_stream = TRY(DeflateDecompressor::construct(MaybeOwned<Stream>(stream)));
+    auto deflate_stream = TRY(DeflateDecompressor::construct(MaybeOwned<LittleEndianInputBitStream>(stream)));
     return TRY(adopt_nonnull_own_or_enomem(new (nothrow) Member(header, move(deflate_stream))));
 }
 
@@ -51,7 +52,7 @@ GzipDecompressor::Member::Member(BlockHeader header, NonnullOwnPtr<DeflateDecomp
 }
 
 GzipDecompressor::GzipDecompressor(NonnullOwnPtr<Stream> stream)
-    : m_input_stream(move(stream))
+    : m_input_stream(make<LittleEndianInputBitStream>(move(stream)))
 {
 }
 
diff --git a/Userland/Libraries/LibCompress/Gzip.h b/Userland/Libraries/LibCompress/Gzip.h
index 85a33eae90..de5d103a9c 100644
--- a/Userland/Libraries/LibCompress/Gzip.h
+++ b/Userland/Libraries/LibCompress/Gzip.h
@@ -58,7 +58,7 @@ public:
 private:
     class Member {
     public:
-        static ErrorOr<NonnullOwnPtr<Member>> construct(BlockHeader header, Stream&);
+        static ErrorOr<NonnullOwnPtr<Member>> construct(BlockHeader header, LittleEndianInputBitStream&);
 
         BlockHeader m_header;
         NonnullOwnPtr<DeflateDecompressor> m_stream;
@@ -72,7 +72,7 @@ private:
     Member const& current_member() const { return *m_current_member; }
     Member& current_member() { return *m_current_member; }
 
-    NonnullOwnPtr<Stream> m_input_stream;
+    NonnullOwnPtr<LittleEndianInputBitStream> m_input_stream;
     u8 m_partial_header[sizeof(BlockHeader)];
     size_t m_partial_header_offset { 0 };
     OwnPtr<Member> m_current_member {};