Fix bugs in lzma_index_read() and lzma_index_cat().

lzma_index_read() didn't skip over Stream Padding
if it was the first record in the Index.

lzma_index_cat() didn't combine small Indexes correctly.

The test suite was updated to check for these bugs.

These bugs didn't affect the xz command line tool or
most users of liblzma in any way.

src/liblzma/common/index.c

@@ -327,16 +327,14 @@ lzma_index_append(lzma_index *i, lzma_allocator *allocator,
 
 
 /// Initialize i->current to point to the first Record.
+/// Return true if there are no Records.
 static bool
 init_current(lzma_index *i)
 {
-	if (i->head == NULL) {
+	if (i->count == 0)
-		assert(i->count == 0);
 		return true;
-	}
-
-	assert(i->count > 0);
 
+	assert(i->head != NULL);
 	i->current.group = i->head;
 	i->current.record = 0;
 	i->current.stream_offset = LZMA_STREAM_HEADER_SIZE;
@@ -432,21 +430,31 @@ set_info(const lzma_index *i, lzma_index_record *info)
 extern LZMA_API(lzma_bool)
 lzma_index_read(lzma_index *i, lzma_index_record *info)
 {
+	bool get_next = true;
+
 	if (i->current.group == NULL) {
 		// We are at the beginning of the Record list. Set up
-		// i->current point at the first Record. Return if there
+		// i->current to point at the first Record. Return if
-		// are no Records.
+		// there are no Records.
 		if (init_current(i))
 			return true;
-	} else do {
+
-		// Try to go the next Record.
+		// This is the first Record. We don't need to look for the
+		// next Record unless this one is Stream Padding.
+		get_next = false;
+	}
+
+	// Find the next Record that isn't Stream Padding.
+	while (get_next || i->current.group->paddings[i->current.record]) {
+		get_next = false;
+
 		if (i->current.record < i->current.group->last)
 			++i->current.record;
 		else if (i->current.group->next == NULL)
 			return true;
 		else
 			next_group(i);
-	} while (i->current.group->paddings[i->current.record]);
+	}
 
 	// We found a new Record. Set the information to *info.
 	set_info(i, info);
@@ -623,7 +631,7 @@ lzma_index_cat(lzma_index *restrict dest, lzma_index *restrict src,
 		++dest->tail->last;
 
 		// Copy the rest.
-		for (size_t i = 1; i < src->head->last; ++i) {
+		for (size_t i = 0; i < src->head->last; ++i) {
 			dest->tail->unpadded_sums[dest->tail->last + 1]
 				= vli_ceil4(dest->tail->unpadded_sums[
 						dest->tail->last])

tests/test_index.c

@@ -14,6 +14,9 @@
 
 #define MEMLIMIT (LZMA_VLI_C(1) << 20)
 
+#define SMALL_COUNT 3
+#define BIG_COUNT 5555
+
 
 static lzma_index *
 create_empty(void)
@@ -46,9 +49,8 @@ create_big(void)
 	lzma_vli uncompressed_size = 0;
 
 	// Add pseudo-random sizes (but always the same size values).
-	const size_t count = 5555;
 	uint32_t n = 11;
-	for (size_t j = 0; j < count; ++j) {
+	for (size_t j = 0; j < BIG_COUNT; ++j) {
 		n = 7019 * n + 7607;
 		const uint32_t t = n * 3011;
 		expect(lzma_index_append(i, NULL, t, n) == LZMA_OK);
@@ -56,7 +58,7 @@ create_big(void)
 		uncompressed_size += n;
 	}
 
-	expect(lzma_index_count(i) == count);
+	expect(lzma_index_count(i) == BIG_COUNT);
 	expect(lzma_index_total_size(i) == total_size);
 	expect(lzma_index_uncompressed_size(i) == uncompressed_size);
 	expect(lzma_index_total_size(i) + lzma_index_size(i)
@@ -166,6 +168,7 @@ test_code(lzma_index *i)
 	// Decode
 	lzma_index *d;
 	expect(lzma_index_decoder(&strm, &d, MEMLIMIT) == LZMA_OK);
+	expect(d == NULL);
 	succeed(decoder_loop(&strm, buf, index_size));
 
 	expect(lzma_index_equal(i, d));
@@ -231,6 +234,7 @@ static void
 test_cat(void)
 {
 	lzma_index *a, *b, *c;
+	lzma_index_record r;
 
 	// Empty Indexes
 	a = create_empty();
@@ -240,6 +244,7 @@ test_cat(void)
 	expect(lzma_index_stream_size(a) == 2 * LZMA_STREAM_HEADER_SIZE + 8);
 	expect(lzma_index_file_size(a)
 			== 2 * (2 * LZMA_STREAM_HEADER_SIZE + 8));
+	expect(lzma_index_read(a, &r));
 
 	b = create_empty();
 	expect(lzma_index_cat(a, b, NULL, 0) == LZMA_OK);
@@ -262,6 +267,9 @@ test_cat(void)
 	expect(lzma_index_file_size(a)
 			== 5 * (2 * LZMA_STREAM_HEADER_SIZE + 8) + 4 + 8);
 
+	expect(lzma_index_read(a, &r));
+	lzma_index_rewind(a);
+	expect(lzma_index_read(a, &r));
 	lzma_index_end(a, NULL);
 
 	// Small Indexes
@@ -279,8 +287,19 @@ test_cat(void)
 	expect(lzma_index_cat(a, b, NULL, 12) == LZMA_OK);
 	expect(lzma_index_file_size(a) == stream_size * 4 + 4 + 8 + 12);
 
+	expect(lzma_index_count(a) == SMALL_COUNT * 4);
+	for (int i = SMALL_COUNT * 4; i >= 0; --i)
+		expect(!lzma_index_read(a, &r) ^ (i == 0));
+
 	lzma_index_end(a, NULL);
 
+	// Mix of empty and small
+	a = create_empty();
+	b = create_small();
+	expect(lzma_index_cat(a, b, NULL, 4) == LZMA_OK);
+	for (int i = SMALL_COUNT; i >= 0; --i)
+		expect(!lzma_index_read(a, &r) ^ (i == 0));
+
 	// Big Indexes
 	a = create_big();
 	stream_size = lzma_index_stream_size(a);
@@ -296,6 +315,9 @@ test_cat(void)
 	expect(lzma_index_cat(a, b, NULL, 12) == LZMA_OK);
 	expect(lzma_index_file_size(a) == stream_size * 4 + 4 + 8 + 12);
 
+	for (int i = BIG_COUNT * 4; i >= 0; --i)
+		expect(!lzma_index_read(a, &r) ^ (i == 0));
+
 	lzma_index_end(a, NULL);
 }