Use a typesize of 1 in Blosc for zero-itemsize buffers

docs/release.md

@@ -19,6 +19,10 @@
 * Allow building against a system Zlib. Note, this is only required if blosc is still
   vendored, and a vendored Zlib is no longer built if blosc is not.
   By {user}`Elliott Sales de Andrade <QuLogic>`, {issue}`860`
+* `Blosc` can now encode an array whose dtype has an itemsize of 0 (e.g. a structured
+  dtype with a zero-length field), which failed with a `RuntimeError` (or crashed with a
+  floating point exception with older bundled c-blosc versions).
+  By {user}`Raashish Aggarwal <raashish1601>`, {issue}`516`
 
 ## 0.17.0
 

src/numcodecs/blosc.pyx

@@ -267,6 +267,11 @@ def compress(source, char* cname, int clevel, int shuffle=SHUFFLE,
         itemsize = typesize
     else:
         itemsize = source_pb.itemsize
+        if itemsize == 0:
+            # blosc does not accept a typesize of 0 (older versions crashed on it),
+            # which zero-size dtypes such as a structured dtype with a zero-length
+            # field give; the buffer is empty in that case, so any typesize works
+            itemsize = 1
 
     # determine shuffle
     if shuffle == AUTOSHUFFLE:

tests/test_blosc.py

@@ -326,6 +326,19 @@ def test_typesize_less_than_1():
         compressor.encode(arr.tobytes())
 
 
+@pytest.mark.parametrize(
+    "shuffle", [Blosc.NOSHUFFLE, Blosc.SHUFFLE, Blosc.BITSHUFFLE, Blosc.AUTOSHUFFLE]
+)
+def test_zero_itemsize(shuffle):
+    # a structured dtype with a zero-length field has itemsize 0, which blosc
+    # rejects as a typesize (and older versions crashed on, #516)
+    arr = np.zeros((5,), dtype=[("foo", int, (0,))])
+    assert arr.dtype.itemsize == 0
+    enc = Blosc(shuffle=shuffle).encode(arr)
+    nbytes, _, _ = blosc._cbuffer_sizes(enc)
+    assert nbytes == 0
+
+
 def test_config_no_typesize():
     codec = Blosc(shuffle=Blosc.SHUFFLE, typesize=5)
     config = codec.get_config()