liblzma: Add new API function lzma_filters_free().

This is small but convenient and should have been added
a long time ago.

src/liblzma/api/lzma/filter.h

@@ -124,6 +124,27 @@ extern LZMA_API(lzma_ret) lzma_filters_copy(
 		lzma_nothrow lzma_attr_warn_unused_result;
 
 
+/**
+ * \brief       Free the options in the array of lzma_filter structures
+ *
+ * This frees the filter chain options. The filters array itself is not freed.
+ *
+ * The filters array must have at most LZMA_FILTERS_MAX + 1 elements
+ * including the terminating element which must have .id = LZMA_VLI_UNKNOWN.
+ * For all elements before the terminating element:
+ *   - options will be freed using the given lzma_allocator or,
+ *     if allocator is NULL, using free().
+ *   - options will be set to NULL.
+ *   - id will be set to LZMA_VLI_UNKNOWN.
+ *
+ * If filters is NULL, this does nothing but remember that this never frees
+ * the filters array itself.
+ */
+extern LZMA_API(void) lzma_filters_free(
+		lzma_filter *filters, const lzma_allocator *allocator)
+		lzma_nothrow;
+
+
 /**
  * \brief       Calculate approximate memory requirements for raw encoder
  *

src/liblzma/common/filter_common.c

@@ -205,6 +205,32 @@ error:
 }
 
 
+extern LZMA_API(void)
+lzma_filters_free(lzma_filter *filters, const lzma_allocator *allocator)
+{
+	if (filters == NULL)
+		return;
+
+	for (size_t i = 0; filters[i].id != LZMA_VLI_UNKNOWN; ++i) {
+		if (i == LZMA_FILTERS_MAX) {
+			// The API says that LZMA_FILTERS_MAX + 1 is the
+			// maximum allowed size including the terminating
+			// element. Thus, we should never get here but in
+			// case there is a bug and we do anyway, don't go
+			// past the (probable) end of the array.
+			assert(0);
+			break;
+		}
+
+		lzma_free(filters[i].options, allocator);
+		filters[i].options = NULL;
+		filters[i].id = LZMA_VLI_UNKNOWN;
+	}
+
+	return;
+}
+
+
 static lzma_ret
 validate_chain(const lzma_filter *filters, size_t *count)
 {

src/liblzma/liblzma_generic.map

@@ -114,4 +114,5 @@ global:
 	lzma_file_info_decoder;
 	lzma_stream_decoder_mt;
 	lzma_lzip_decoder;
+	lzma_filters_free;
 } XZ_5.2;

src/liblzma/liblzma_linux.map

@@ -129,4 +129,5 @@ global:
 	lzma_file_info_decoder;
 	lzma_stream_decoder_mt;
 	lzma_lzip_decoder;
+	lzma_filters_free;
 } XZ_5.2;