liblzma: Add .lz (lzip) decompression support (format versions 0 and 1).

Support for format version 0 was removed from lzip 1.18 for some
reason. .lz format version 0 files are rare (and old) but some
source packages were released in this format, and some people might
have personal files in this format too. It's very little extra code
to support it along side format version 1 so this commits adds
support for both.

The Sync Flush marker extentension to the original .lz format
version 1 isn't supported. It would require changes to the
LZMA decoder itself. Such files are very rare anyway.

See the API doc for lzma_lzip_decoder() for more details about
the .lz format support.

Thanks to Michał Górny for the original patch.

1 files changed, 60 insertions, 2 deletions

diff --git a/src/liblzma/api/lzma/container.h b/src/liblzma/api/lzma/container.h
index 0fbe9778..6a2f4d78 100644
--- a/src/liblzma/api/lzma/container.h
+++ b/src/liblzma/api/lzma/container.h
@@ -602,8 +602,8 @@ extern LZMA_API(lzma_ret) lzma_microlzma_encoder(
 /**
  * This flag enables decoding of concatenated files with file formats that
  * allow concatenating compressed files as is. From the formats currently
- * supported by liblzma, only the .xz format allows concatenated files.
- * Concatenated files are not allowed with the legacy .lzma format.
+ * supported by liblzma, only the .xz and .lz formats allow concatenated
+ * files. Concatenated files are not allowed with the legacy .lzma format.
  *
  * This flag also affects the usage of the `action' argument for lzma_code().
  * When LZMA_CONCATENATED is used, lzma_code() won't return LZMA_STREAM_END
@@ -758,6 +758,64 @@ extern LZMA_API(lzma_ret) lzma_alone_decoder(
 
 
 /**
+ * \brief       Initialize .lz (lzip) decoder (a foreign file format)
+ *
+ * \param       strm        Pointer to properly prepared lzma_stream
+ * \param       memlimit    Memory usage limit as bytes. Use UINT64_MAX
+ *                          to effectively disable the limiter.
+ * \param       flags       Bitwise-or of flags, or zero for no flags.
+ *                          All decoder flags listed above are supported
+ *                          although only LZMA_CONCATENATED and (in very rare
+ *                          cases) LZMA_IGNORE_CHECK are actually useful.
+ *                          LZMA_TELL_NO_CHECK, LZMA_TELL_UNSUPPORTED_CHECK,
+ *                          and LZMA_FAIL_FAST do nothing. LZMA_TELL_ANY_CHECK
+ *                          is supported for consistency only as CRC32 is
+ *                          always used in the .lz format.
+ *
+ * This decoder supports the .lz format version 0 and the unextended .lz
+ * format version 1:
+ *
+ *   - Files in the format version 0 were produced by lzip 1.3 and older.
+ *     Such files aren't common but may be found from file archives
+ *     as a few source packages were released in this format. People
+ *     might have old personal files in this format too. Decompression
+ *     support for the format version 0 was removed in lzip 1.18.
+ *
+ *   - lzip 1.3 added decompression support for .lz format version 1 files.
+ *     Compression support was added in lzip 1.4. In lzip 1.6 the .lz format
+ *     version 1 was extended to support the Sync Flush marker. This extension
+ *     is not supported by liblzma. lzma_code() will return LZMA_DATA_ERROR
+ *     at the location of the Sync Flush marker. In practice files with
+ *     the Sync Flush marker are very rare and thus liblzma can decompress
+ *     almost all .lz files.
+ *
+ * Just like with lzma_stream_decoder() for .xz files, LZMA_CONCATENATED
+ * should be used when decompressing normal standalone .lz files.
+ *
+ * The .lz format allows putting non-.lz data at the end of a file after at
+ * least one valid .lz member. That is, one can append custom data at the end
+ * of a .lz file and the decoder is required to ignore it. In liblzma this
+ * is relevant only when LZMA_CONCATENATED is used. In that case lzma_code()
+ * will return LZMA_STREAM_END and leave lzma_stream.next_in pointing to
+ * the first byte of the non-.lz data. An exception to this is if the first
+ * 1-3 bytes of the non-.lz data are identical to the .lz magic bytes
+ * (0x4C, 0x5A, 0x49, 0x50; "LZIP" in US-ASCII). In such a case the 1-3 bytes
+ * will have been ignored by lzma_code(). If one wishes to locate the non-.lz
+ * data reliably, one must ensure that the first byte isn't 0x4C. Actually
+ * one should ensure that none of the first four bytes of trailing data are
+ * equal to the magic bytes because lzip >= 1.20 requires it by default.
+ *
+ * \return      - LZMA_OK: Initialization was successful.
+ *              - LZMA_MEM_ERROR: Cannot allocate memory.
+ *              - LZMA_OPTIONS_ERROR: Unsupported flags
+ *              - LZMA_PROG_ERROR
+ */
+extern LZMA_API(lzma_ret) lzma_lzip_decoder(
+		lzma_stream *strm, uint64_t memlimit, uint32_t flags)
+		lzma_nothrow lzma_attr_warn_unused_result;
+
+
+/**
  * \brief       Single-call .xz Stream decoder
  *
  * \param       memlimit    Pointer to how much memory the decoder is allowed