Add protections on frame/chunk versions and forward compatibility improvements

Author: FrancescAlted

RELEASING.rst

@@ -57,6 +57,32 @@ Then, test the file created with the new version with::
 Repeat this for every codec shipped with Blosc (blosclz, lz4, lz4hc, zlib and
 zstd).
 
+For VL-block cframe compatibility checks, use ``compat/filegen-vl``.
+This utility can generate two kinds of persistent cframes:
+
+* a cframe with VL-block chunks and fixed chunk sizes
+* a cframe with VL-block chunks and variable chunk sizes
+
+Generate them with the current version::
+
+  $ cd ../compat
+  $ export LD_LIBRARY_PATH=../build/blosc
+  $ gcc -o filegen-vl filegen-vl.c -L$LD_LIBRARY_PATH -lblosc2 -I../include
+  $ ./filegen-vl compress lz4 vlblocks-lz4-fixed-2.y.z.b2frame
+  $ ./filegen-vl compress lz4 vlblocks-lz4-variable-2.y.z.b2frame --variable-chunks
+
+Then, build ``compat/filegen-vl`` against the target Blosc library and check
+the fixtures with::
+
+  $ ./filegen-vl decompress vlblocks-lz4-fixed-2.y.z.b2frame
+  $ ./filegen-vl decompress vlblocks-lz4-variable-2.y.z.b2frame
+
+Expected results:
+
+* These VL-block fixtures are only expected to work with releases that support
+  the VL-block cframe format.
+* Pre-vlblocks releases are expected to reject them.
+
 Tagging
 -------
 

blosc/frame.c

@@ -113,7 +113,7 @@ void *new_header_frame(blosc2_schunk *schunk, blosc2_frame_s *frame) {
     return NULL;
   }
   // General flags
-  if (schunk->flags2 & BLOSC2_VL_BLOCKS) {
+  if (schunk->chunksize == 0 || (schunk->flags2 & BLOSC2_VL_BLOCKS)) {
     *h2p = BLOSC2_VERSION_FRAME_FORMAT_VL_BLOCKS;  // version
   }
   else {
@@ -418,6 +418,11 @@ int get_header_info(blosc2_frame_s *frame, int32_t *header_len, int64_t *frame_l
 
   // Consistency check for frame type
   uint8_t frame_type = framep[FRAME_TYPE];
+  uint8_t frame_version = framep[FRAME_FLAGS] & 0x0fu;
+  if (frame_version > BLOSC2_VERSION_FRAME_FORMAT) {
+    BLOSC_TRACE_ERROR("Unsupported cframe version: %u", frame_version);
+    return BLOSC2_ERROR_VERSION_SUPPORT;
+  }
   if (frame->sframe) {
     if (frame_type != FRAME_DIRECTORY_TYPE) {
       return BLOSC2_ERROR_FRAME_TYPE;
@@ -1115,7 +1120,7 @@ int64_t frame_from_schunk(blosc2_schunk *schunk, blosc2_frame_s *frame) {
   else {
     h2[FRAME_FLAGS] &= (uint8_t)~FRAME_VARIABLE_CHUNKS;
   }
-  if (schunk->flags2 & BLOSC2_VL_BLOCKS) {
+  if (schunk->chunksize == 0 || (schunk->flags2 & BLOSC2_VL_BLOCKS)) {
     h2[FRAME_FLAGS] = (uint8_t)((h2[FRAME_FLAGS] & (uint8_t)~0x0fu) | BLOSC2_VERSION_FRAME_FORMAT_VL_BLOCKS);
     h2[FRAME_FLAGS] |= FRAME_VL_BLOCKS;
   }

compat/CMakeLists.txt

@@ -4,6 +4,10 @@ add_executable(filegen filegen.c)
 target_link_libraries(filegen blosc_testing)
 add_dependencies(filegen blosc_testing)
 
+add_executable(filegen-vl filegen-vl.c)
+target_link_libraries(filegen-vl blosc_testing)
+add_dependencies(filegen-vl blosc_testing)
+
 # tests
 if(BUILD_TESTS)
     option(TEST_INCLUDE_COMPAT "Include compat checks in the tests" ON)