liblzma: Add .lz support to lzma_auto_decoder().

Thanks to Michał Górny for the original patch.

src/liblzma/api/lzma/container.h

@@ -700,11 +700,13 @@ extern LZMA_API(lzma_ret) lzma_stream_decoder_mt(
 
 
 /**
- * \brief       Decode .xz Streams and .lzma files with autodetection
+ * \brief       Decode .xz, .lzma, and .lz (lzip) files with autodetection
  *
- * This decoder autodetects between the .xz and .lzma file formats, and
- * calls lzma_stream_decoder() or lzma_alone_decoder() once the type
- * of the input file has been detected.
+ * This decoder autodetects between the .xz, .lzma, and .lz file formats,
+ * and calls lzma_stream_decoder(), lzma_alone_decoder(), or
+ * lzma_lzip_decoder() once the type of the input file has been detected.
+ *
+ * Support for .lz was added in 5.4.0.
  *
  * If the flag LZMA_CONCATENATED is used and the input is a .lzma file:
  * For historical reasons concatenated .lzma files aren't supported.

src/liblzma/common/Makefile.inc

@@ -97,6 +97,7 @@ endif
 
 if COND_LZIP_DECODER
 liblzma_la_SOURCES += \
-	common/lzip_decoder.c
+	common/lzip_decoder.c \
+	common/lzip_decoder.h
 endif
 endif

src/liblzma/common/auto_decoder.c

@@ -1,7 +1,7 @@
 ///////////////////////////////////////////////////////////////////////////////
 //
 /// \file       auto_decoder.c
-/// \brief      Autodetect between .xz Stream and .lzma (LZMA_Alone) formats
+/// \brief      Autodetect between .xz, .lzma (LZMA_Alone), and .lz (lzip)
 //
 //  Author:     Lasse Collin
 //
@@ -12,10 +12,13 @@
 
 #include "stream_decoder.h"
 #include "alone_decoder.h"
+#ifdef HAVE_LZIP_DECODER
+#	include "lzip_decoder.h"
+#endif
 
 
 typedef struct {
-	/// Stream decoder or LZMA_Alone decoder
+	/// .xz Stream decoder, LZMA_Alone decoder, or lzip decoder
 	lzma_next_coder next;
 
 	uint64_t memlimit;
@@ -46,14 +49,22 @@ auto_decode(void *coder_ptr, const lzma_allocator *allocator,
 		// SEQ_CODE even if we return some LZMA_*_CHECK.
 		coder->sequence = SEQ_CODE;
 
-		// Detect the file format. For now this is simple, since if
-		// it doesn't start with 0xFD (the first magic byte of the
-		// new format), it has to be LZMA_Alone, or something that
-		// we don't support at all.
+		// Detect the file format. .xz files start with 0xFD which
+		// cannot be the first byte of .lzma (LZMA_Alone) format.
+		// The .lz format starts with 0x4C which could be the
+		// first byte of a .lzma file but luckily it would mean
+		// lc/lp/pb being 4/3/1 which liblzma doesn't support because
+		// lc + lp > 4. So using just 0x4C to detect .lz is OK here.
 		if (in[*in_pos] == 0xFD) {
 			return_if_error(lzma_stream_decoder_init(
 					&coder->next, allocator,
 					coder->memlimit, coder->flags));
+#ifdef HAVE_LZIP_DECODER
+		} else if (in[*in_pos] == 0x4C) {
+			return_if_error(lzma_lzip_decoder_init(
+					&coder->next, allocator,
+					coder->memlimit, coder->flags));
+#endif
 		} else {
 			return_if_error(lzma_alone_decoder_init(&coder->next,
 					allocator, coder->memlimit, true));

src/liblzma/common/lzip_decoder.h

@@ -0,0 +1,22 @@
+///////////////////////////////////////////////////////////////////////////////
+//
+/// \file       lzip_decoder.h
+/// \brief      Decodes .lz (lzip) files
+//
+//  Author:     Michał Górny
+//
+//  This file has been put into the public domain.
+//  You can do whatever you want with this file.
+//
+///////////////////////////////////////////////////////////////////////////////
+
+#ifndef LZMA_LZIP_DECODER_H
+#define LZMA_LZIP_DECODER_H
+
+#include "common.h"
+
+extern lzma_ret lzma_lzip_decoder_init(
+		lzma_next_coder *next, const lzma_allocator *allocator,
+		uint64_t memlimit, uint32_t flags);
+
+#endif