LibVideo: Parse Matroska from ReadonlyBytes and keep the start position

Keeping the entire Matroska stream available is a prerequisite to being
able to stream from it and seek to cue points.

Userland/Libraries/LibVideo/Containers/Matroska/MatroskaDemuxer.cpp

@@ -15,7 +15,7 @@ DecoderErrorOr<NonnullOwnPtr<MatroskaDemuxer>> MatroskaDemuxer::from_file(String
 
 DecoderErrorOr<NonnullOwnPtr<MatroskaDemuxer>> MatroskaDemuxer::from_data(ReadonlyBytes data)
 {
-    return make<MatroskaDemuxer>(TRY(Reader::parse_matroska_from_data(data.data(), data.size())));
+    return make<MatroskaDemuxer>(TRY(Reader::parse_matroska_from_data(data)));
 }
 
 Vector<Track> MatroskaDemuxer::get_tracks_for_type(TrackType type)

Userland/Libraries/LibVideo/Containers/Matroska/Reader.cpp

@@ -58,12 +58,12 @@ constexpr u32 TIMESTAMP_ID = 0xE7;
 DecoderErrorOr<NonnullOwnPtr<MatroskaDocument>> Reader::parse_matroska_from_file(StringView path)
 {
     auto mapped_file = DECODER_TRY(DecoderErrorCategory::IO, Core::MappedFile::map(path));
-    return parse_matroska_from_data((u8*)mapped_file->data(), mapped_file->size());
+    return parse_matroska_from_data(mapped_file->bytes());
 }
 
-DecoderErrorOr<NonnullOwnPtr<MatroskaDocument>> Reader::parse_matroska_from_data(u8 const* data, size_t size)
+DecoderErrorOr<NonnullOwnPtr<MatroskaDocument>> Reader::parse_matroska_from_data(ReadonlyBytes data)
 {
-    Reader reader(data, size);
+    Reader reader(data);
     return reader.parse();
 }
 
@@ -426,9 +426,10 @@ ErrorOr<u8> Reader::Streamer::read_octet()
         dbgln_if(MATROSKA_TRACE_DEBUG, "Ran out of stream data");
         return Error::from_string_literal("Stream is out of data");
     }
-    m_size_remaining--;
+    u8 byte = *data();
     m_octets_read.last()++;
-    return *(m_data_ptr++);
+    m_position++;
+    return byte;
 }
 
 ErrorOr<i16> Reader::Streamer::read_i16()
@@ -438,7 +439,7 @@ ErrorOr<i16> Reader::Streamer::read_i16()
 
 ErrorOr<u64> Reader::Streamer::read_variable_size_integer(bool mask_length)
 {
-    dbgln_if(MATROSKA_TRACE_DEBUG, "Reading from offset {:p}", m_data_ptr);
+    dbgln_if(MATROSKA_TRACE_DEBUG, "Reading from offset {:p}", data());
     auto length_descriptor = TRY(read_octet());
     dbgln_if(MATROSKA_TRACE_DEBUG, "Reading VINT, first byte is {:#02x}", length_descriptor);
     if (length_descriptor == 0)
@@ -495,9 +496,8 @@ ErrorOr<void> Reader::Streamer::drop_octets(size_t num_octets)
 {
     if (remaining() < num_octets)
         return Error::from_string_literal("Tried to drop octets past the end of the stream");
-    m_size_remaining -= num_octets;
+    m_position += num_octets;
     m_octets_read.last() += num_octets;
-    m_data_ptr += num_octets;
     return {};
 }
 

Userland/Libraries/LibVideo/Containers/Matroska/Reader.h

@@ -20,28 +20,27 @@ namespace Video::Matroska {
 
 class Reader {
 public:
-    Reader(u8 const* data, size_t size)
-        : m_streamer(data, size)
+    Reader(ReadonlyBytes data)
+        : m_streamer(data)
     {
     }
 
     static DecoderErrorOr<NonnullOwnPtr<MatroskaDocument>> parse_matroska_from_file(StringView path);
-    static DecoderErrorOr<NonnullOwnPtr<MatroskaDocument>> parse_matroska_from_data(u8 const*, size_t);
+    static DecoderErrorOr<NonnullOwnPtr<MatroskaDocument>> parse_matroska_from_data(ReadonlyBytes data);
 
     DecoderErrorOr<NonnullOwnPtr<MatroskaDocument>> parse();
 
 private:
     class Streamer {
     public:
-        Streamer(u8 const* data, size_t size)
-            : m_data_ptr(data)
-            , m_size_remaining(size)
+        Streamer(ReadonlyBytes data)
+            : m_data(data)
         {
         }
 
-        u8 const* data() { return m_data_ptr; }
+        u8 const* data() { return m_data.data() + m_position; }
 
-        char const* data_as_chars() { return reinterpret_cast<char const*>(m_data_ptr); }
+        char const* data_as_chars() { return reinterpret_cast<char const*>(data()); }
 
         size_t octets_read() { return m_octets_read.last(); }
 
@@ -70,15 +69,14 @@ private:
 
         ErrorOr<void> drop_octets(size_t num_octets);
 
-        bool at_end() const { return m_size_remaining == 0; }
-        bool has_octet() const { return m_size_remaining >= 1; }
+        bool at_end() const { return remaining() == 0; }
+        bool has_octet() const { return remaining() >= 1; }
 
-        size_t remaining() const { return m_size_remaining; }
-        void set_remaining(size_t remaining) { m_size_remaining = remaining; }
+        size_t remaining() const { return m_data.size() - m_position; }
 
     private:
-        u8 const* m_data_ptr { nullptr };
-        size_t m_size_remaining { 0 };
+        ReadonlyBytes m_data;
+        size_t m_position { 0 };
         Vector<size_t> m_octets_read { 0 };
     };