Zarr V2 creation: fix bug when creating dataset with partial blocks a…

…nd need to re-read them in the writing process when compression is involved

Embarassingly, we were trying to decompress chunks with the ...
compressor ... instead of the decompressor.

Fixes OSGeo#11016

autotest/gdrivers/zarr_driver.py

@@ -5523,3 +5523,25 @@ def test_zarr_read_cf1_zarrv3():
         ds.GetSpatialRef().ExportToProj4()
         == "+proj=utm +zone=11 +ellps=clrk66 +units=m +no_defs"
     )
+
+
+###############################################################################
+# Test bug fix for https://github.com/OSGeo/gdal/issues/11016
+
+
+@gdaltest.enable_exceptions()
+@pytest.mark.require_driver("PNG")
+def test_zarr_write_partial_blocks_compressed(tmp_vsimem):
+
+    if "lz4" not in gdal.GetDriverByName("Zarr").GetMetadataItem("BLOSC_COMPRESSORS"):
+        pytest.skip("LZ4 compression missing")
+
+    out_filename = "/vsimem/test.zarr"
+    src_ds = gdal.Open("data/png/rgba16.png")
+    gdal.Translate(
+        out_filename,
+        src_ds,
+        options="-of ZARR -co FORMAT=ZARR_V2 -co BLOCKSIZE=4,5,6 -co COMPRESS=LZ4 -co INTERLEAVE=BAND",
+    )
+    out_ds = gdal.Open(out_filename)
+    assert out_ds.ReadRaster() == src_ds.ReadRaster()

frmts/zarr/zarr_v2_group.cpp

@@ -871,7 +871,7 @@ std::shared_ptr<GDALMDArray> ZarrV2Group::CreateMDArray(
     if (!EQUAL(pszCompressor, "NONE"))
     {
         psCompressor = CPLGetCompressor(pszCompressor);
-        psDecompressor = CPLGetCompressor(pszCompressor);
+        psDecompressor = CPLGetDecompressor(pszCompressor);
         if (psCompressor == nullptr || psDecompressor == nullptr)
         {
             CPLError(CE_Failure, CPLE_NotSupported,