From 9b64d4f859f83809471f58ab298b31fb8c16695c Mon Sep 17 00:00:00 2001
From: Igor Stadnyk <fallenmi@users.noreply.github.com>
Date: Sun, 16 Aug 2026 05:22:35 +0100
Subject: [PATCH] Fix empty Blosc buffer round-trips

---
 docs/release.md           |  6 ++++++
 src/numcodecs/blosc.pyx   | 14 +++++++++++---
 src/numcodecs/meson.build |  6 +++++-
 tests/test_blosc.py       |  8 ++++++++
 4 files changed, 30 insertions(+), 4 deletions(-)

diff --git a/docs/release.md b/docs/release.md
index 78e8901c..2996de5a 100644
--- a/docs/release.md
+++ b/docs/release.md
@@ -14,6 +14,12 @@
 
 ## Unreleased
 
+### Fixes
+
+* Validate Blosc frames before decompression, allowing valid zero-length frames to round-trip
+  while rejecting truncated or size-mismatched frames. System Blosc builds now require version
+  1.16.0 or newer. By {user}`Igor Stadnyk <fallenmi>`, {issue}`831`.
+
 ### Maintenance
 
 * **Migrate build system from setuptools/setup.py to meson-python.** This replaces the
diff --git a/src/numcodecs/blosc.pyx b/src/numcodecs/blosc.pyx
index d61f7358..75b15be4 100644
--- a/src/numcodecs/blosc.pyx
+++ b/src/numcodecs/blosc.pyx
@@ -49,6 +49,7 @@ cdef extern from "blosc.h":
                            int numinternalthreads) nogil
     int blosc_decompress_ctx(const void* src, void* dest, size_t destsize,
                              int numinternalthreads) nogil
+    int blosc_cbuffer_validate(const void* cbuffer, size_t cbytes, size_t* nbytes)
     void blosc_cbuffer_sizes(const void* cbuffer, size_t* nbytes, size_t* cbytes,
                              size_t* blocksize)
     char* blosc_cbuffer_complib(const void* cbuffer)
@@ -350,7 +351,7 @@ def decompress(source, dest=None):
         memoryview dest_mv
         Py_buffer* dest_pb
         char* dest_ptr
-        size_t nbytes, cbytes, blocksize
+        size_t nbytes
 
     # obtain source memoryview
     source_mv = ensure_contiguous_memoryview(source)
@@ -359,8 +360,10 @@ def decompress(source, dest=None):
     # get source pointer
     source_ptr = <const char*>source_pb.buf
 
-    # determine buffer size
-    blosc_cbuffer_sizes(source_ptr, &nbytes, &cbytes, &blocksize)
+    # validate source and determine decompressed buffer size
+    ret = blosc_cbuffer_validate(source_ptr, <size_t>source_pb.len, &nbytes)
+    if ret != 0:
+        raise RuntimeError('error during blosc decompression: %d' % ret)
 
     # setup destination buffer
     if dest is None:
@@ -382,6 +385,11 @@ def decompress(source, dest=None):
             raise ValueError('destination buffer too small; expected at least %s, '
                              'got %s' % (nbytes, dest_nbytes))
 
+        # Blosc reports the number of decompressed bytes, so zero is successful
+        # for a validated empty frame rather than an error.
+        if nbytes == 0:
+            return dest
+
         # perform decompression
         if _get_use_threads():
             # allow blosc to use threads internally
diff --git a/src/numcodecs/meson.build b/src/numcodecs/meson.build
index eca2b2c6..117b67b6 100644
--- a/src/numcodecs/meson.build
+++ b/src/numcodecs/meson.build
@@ -153,7 +153,11 @@ zlib_dep = declare_dependency(
 )
 
 # --- Vendored blosc ---
-blosc_dep = dependency('blosc', required: get_option('system_blosc'))
+blosc_dep = dependency(
+  'blosc',
+  version: '>=1.16.0',
+  required: get_option('system_blosc'),
+)
 
 if not blosc_dep.found()
   blosc_sources = files(
diff --git a/tests/test_blosc.py b/tests/test_blosc.py
index 537dc350..dc032119 100644
--- a/tests/test_blosc.py
+++ b/tests/test_blosc.py
@@ -75,6 +75,14 @@ def test_encode_decode(array, codec):
     check_encode_decode(array, codec)
 
 
+def test_empty_encode_decode(use_threads):
+    blosc.use_threads = use_threads
+    try:
+        check_encode_decode(np.empty(0, dtype='u1'), Blosc())
+    finally:
+        blosc.use_threads = None
+
+
 def test_config():
     codec = Blosc(cname='zstd', clevel=3, shuffle=1)
     check_config(codec)