archive/iso9660: fix unaligned reads

NEWS

@@ -5,6 +5,7 @@ ver 0.21.26 (not yet released)
 * archive
   - bzip2: fix crash on corrupt bzip2 file
   - bzip2: flush output at end of input file
+  - iso9660: fix unaligned reads
   - zzip: fix crash on corrupt ZIP file
 * decoder
   - sndfile: fix lost samples at end of file

src/archive/plugins/Iso9660ArchivePlugin.cxx

@@ -29,9 +29,12 @@
 #include "fs/Path.hxx"
 #include "util/RuntimeError.hxx"
 #include "util/StringCompare.hxx"
+#include "util/WritableBuffer.hxx"
 
 #include <cdio/iso9660.h>
 
+#include <array>
+
 #include <stdlib.h>
 #include <string.h>
 
@@ -144,6 +147,47 @@ class Iso9660InputStream final : public InputStream {
 
 	const lsn_t lsn;
 
+	/**
+	 * libiso9660 can only read whole sectors at a time, and this
+	 * buffer is used to store one whole sector and allow Read()
+	 * to handle partial sector reads.
+	 */
+	class BlockBuffer {
+		size_t position = 0, fill = 0;
+
+		std::array<uint8_t, ISO_BLOCKSIZE> data;
+
+	public:
+		ConstBuffer<uint8_t> Read() const noexcept {
+			assert(fill <= data.size());
+			assert(position <= fill);
+
+			return {&data[position], &data[fill]};
+		}
+
+		void Consume(size_t nbytes) noexcept {
+			assert(nbytes <= Read().size);
+
+			position += nbytes;
+		}
+
+		WritableBuffer<uint8_t> Write() noexcept {
+			assert(Read().empty());
+
+			return {data.data(), data.size()};
+		}
+
+		void Append(size_t nbytes) noexcept {
+			assert(Read().empty());
+			assert(nbytes <= data.size());
+
+			fill = nbytes;
+			position = 0;
+		}
+	};
+
+	BlockBuffer buffer;
+
 public:
 	Iso9660InputStream(const std::shared_ptr<Iso9660> &_iso,
 			   const char *_uri,
@@ -182,35 +226,56 @@ Iso9660ArchiveFile::OpenStream(const char *pathname,
 size_t
 Iso9660InputStream::Read(void *ptr, size_t read_size)
 {
-	const ScopeUnlock unlock(mutex);
+	const offset_type remaining = size - offset;
+	if (remaining == 0)
+		return 0;
 
-	int readed = 0;
-	int no_blocks, cur_block;
-	size_t left_bytes = size - offset;
+	if (offset_type(read_size) > remaining)
+		read_size = remaining;
 
-	if (left_bytes < read_size) {
-		no_blocks = CEILING(left_bytes, ISO_BLOCKSIZE);
-	} else {
-		no_blocks = read_size / ISO_BLOCKSIZE;
-	}
+	auto r = buffer.Read();
 
-	if (no_blocks == 0)
-		return 0;
+	if (r.empty()) {
+		/* the buffer is empty - read more data from the ISO file */
+
+		assert(offset % ISO_BLOCKSIZE == 0);
 
-	cur_block = offset / ISO_BLOCKSIZE;
+		const ScopeUnlock unlock(mutex);
 
-	readed = iso->SeekRead(ptr, lsn + cur_block, no_blocks);
+		const lsn_t read_lsn = lsn + offset / ISO_BLOCKSIZE;
 
-	if (readed != no_blocks * ISO_BLOCKSIZE)
-		throw FormatRuntimeError("error reading ISO file at lsn %lu",
-					 (unsigned long)cur_block);
+		if (read_size >= ISO_BLOCKSIZE) {
+			/* big read - read right into the caller's buffer */
 
-	if (left_bytes < read_size) {
-		readed = left_bytes;
+			auto nbytes = iso->SeekRead(ptr, read_lsn,
+						    read_size / ISO_BLOCKSIZE);
+			if (nbytes <= 0)
+				throw std::runtime_error("Failed to read ISO9660 file");
+
+			offset += nbytes;
+			return nbytes;
+		}
+
+		/* fill the buffer */
+
+		auto w = buffer.Write();
+		auto nbytes = iso->SeekRead(w.data, read_lsn,
+					    w.size / ISO_BLOCKSIZE);
+		if (nbytes <= 0)
+			throw std::runtime_error("Failed to read ISO9660 file");
+
+		buffer.Append(nbytes);
+
+		r = buffer.Read();
 	}
 
-	offset += readed;
-	return readed;
+	assert(!r.empty());
+
+	size_t nbytes = std::min(read_size, r.size);
+	memcpy(ptr, r.data, nbytes);
+	buffer.Consume(nbytes);
+	offset += nbytes;
+	return nbytes;
 }
 
 bool