Zarr: report COMPRESSOR and FILTERS in structural metadata

rouault · Mar 6, 2025 · e782e03 · e782e03
1 parent fe5ec96
commit e782e03
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Showing 8 changed files with 128 additions and 8 deletions.
diff --git a/autotest/gdrivers/data/zarr/v3/gzip.zarr/gzip/c/0/0 b/autotest/gdrivers/data/zarr/v3/gzip.zarr/gzip/c/0/0
diff --git a/autotest/gdrivers/data/zarr/v3/gzip.zarr/gzip/zarr.json b/autotest/gdrivers/data/zarr/v3/gzip.zarr/gzip/zarr.json
@@ -0,0 +1,44 @@
+{
+  "zarr_format":3,
+  "node_type":"array",
+  "shape":[
+    1,
+    2
+  ],
+  "data_type":"uint8",
+  "chunk_grid":{
+    "name":"regular",
+    "configuration":{
+      "chunk_shape":[
+        1,
+        2
+      ]
+    }
+  },
+  "chunk_key_encoding":{
+    "name":"default",
+    "configuration":{
+      "separator":"\/"
+    }
+  },
+  "fill_value":0,
+  "codecs":[
+    {
+      "name":"bytes",
+      "configuration":{
+        "endian":"little"
+      }
+    },
+    {
+      "name":"gzip",
+      "configuration":{
+        "level":6
+      }
+    }
+  ],
+  "attributes":{},
+  "dimension_names":[
+    "Y",
+    "X"
+  ]
+}
diff --git a/autotest/gdrivers/data/zarr/v3/gzip.zarr/zarr.json b/autotest/gdrivers/data/zarr/v3/gzip.zarr/zarr.json
@@ -0,0 +1,5 @@
+{
+    "zarr_format": 3,
+    "node_type": "group",
+    "attributes": {}
+}
diff --git a/autotest/gdrivers/zarr_driver.py b/autotest/gdrivers/zarr_driver.py
@@ -534,6 +534,33 @@ def test_zarr_read_compression_methods(datasetname, compressor):
         ar = rg.OpenMDArray(rg.GetMDArrayNames()[0])
         assert ar
         assert ar.Read() == array.array("b", [1, 2])
+        assert json.loads(ar.GetStructuralInfo()["COMPRESSOR"])["id"] == compressor
+
+
+# Check reading different compression methods
+@pytest.mark.parametrize(
+    "datasetname,compressor",
+    [
+        ("gzip.zarr", "gzip"),
+    ],
+)
+def test_zarr_v3_read_compression_methods(datasetname, compressor):
+
+    compressors = gdal.GetDriverByName("Zarr").GetMetadataItem("COMPRESSORS")
+    filename = "data/zarr/v3/" + datasetname
+
+    if compressor not in compressors:
+        with gdal.quiet_errors():
+            ds = gdal.OpenEx(filename, gdal.OF_MULTIDIM_RASTER)
+        assert ds is None
+    else:
+        ds = gdal.OpenEx(filename, gdal.OF_MULTIDIM_RASTER)
+        rg = ds.GetRootGroup()
+        assert rg
+        ar = rg.OpenMDArray(rg.GetMDArrayNames()[0])
+        assert ar
+        assert ar.Read() == array.array("b", [1, 2])
+        assert json.loads(ar.GetStructuralInfo()["COMPRESSOR"])["name"] == compressor
 
 
 def test_zarr_read_shuffle_filter():
@@ -545,6 +572,9 @@ def test_zarr_read_shuffle_filter():
     ar = rg.OpenMDArray(rg.GetMDArrayNames()[0])
     assert ar
     assert ar.Read() == array.array("h", [1, 2])
+    assert json.loads(ar.GetStructuralInfo()["FILTERS"]) == [
+        {"elementsize": 2, "id": "shuffle"}
+    ]
 
 
 def test_zarr_read_shuffle_filter_update(tmp_path):

diff --git a/frmts/zarr/zarr.h b/frmts/zarr/zarr.h
@@ -752,6 +752,7 @@ class ZarrArray CPL_NON_FINAL : public GDALPamMDArray
     const GDALExtendedDataType m_oType;
     const std::vector<DtypeElt> m_aoDtypeElts;
     const std::vector<GUInt64> m_anBlockSize;
+    CPLStringList m_aosStructuralInfo{};
     CPLJSONObject m_dtype{};
     GByte *m_pabyNoData = nullptr;
     std::string m_osDimSeparator{"."};
@@ -903,6 +904,11 @@ class ZarrArray CPL_NON_FINAL : public GDALPamMDArray
         return m_anBlockSize;
     }
 
+    CSLConstList GetStructuralInfo() const override
+    {
+        return m_aosStructuralInfo.List();
+    }
+
     const void *GetRawNoDataValue() const override
     {
         return m_pabyNoData;
@@ -1038,6 +1044,11 @@ class ZarrArray CPL_NON_FINAL : public GDALPamMDArray
 
     bool CacheTilePresence();
 
+    void SetStructuralInfo(const char *pszKey, const char *pszValue)
+    {
+        m_aosStructuralInfo.SetNameValue(pszKey, pszValue);
+    }
+
     static void DecodeSourceElt(const std::vector<DtypeElt> &elts,
                                 const GByte *pSrc, GByte *pDst);
 
@@ -1099,10 +1110,7 @@ class ZarrV2Array final : public ZarrArray
            const std::vector<DtypeElt> &aoDtypeElts,
            const std::vector<GUInt64> &anBlockSize, bool bFortranOrder);
 
-    void SetCompressorJson(const CPLJSONObject &oCompressor)
-    {
-        m_oCompressorJSon = oCompressor;
-    }
+    void SetCompressorJson(const CPLJSONObject &oCompressor);
 
     void SetCompressorDecompressor(const std::string &osDecompressorId,
                                    const CPLCompressor *psComp,
@@ -1113,10 +1121,7 @@ class ZarrV2Array final : public ZarrArray
         m_psDecompressor = psDecomp;
     }
 
-    void SetFilters(const CPLJSONArray &oFiltersArray)
-    {
-        m_oFiltersArray = oFiltersArray;
-    }
+    void SetFilters(const CPLJSONArray &oFiltersArray);
 
     void Flush() override;
 

diff --git a/frmts/zarr/zarr_v2_array.cpp b/frmts/zarr/zarr_v2_array.cpp
@@ -1964,3 +1964,27 @@ ZarrV2Group::LoadArray(const std::string &osArrayName,
 
     return poArray;
 }
+
+/************************************************************************/
+/*                    ZarrV2Group::SetCompressorJson()                  */
+/************************************************************************/
+
+void ZarrV2Array::SetCompressorJson(const CPLJSONObject &oCompressor)
+{
+    m_oCompressorJSon = oCompressor;
+    if (oCompressor.GetType() != CPLJSONObject::Type::Null)
+        m_aosStructuralInfo.SetNameValue("COMPRESSOR",
+                                         oCompressor.ToString().c_str());
+}
+
+/************************************************************************/
+/*                     ZarrV2Group::SetFilters()                        */
+/************************************************************************/
+
+void ZarrV2Array::SetFilters(const CPLJSONArray &oFiltersArray)
+{
+    m_oFiltersArray = oFiltersArray;
+    if (oFiltersArray.Size() > 0)
+        m_aosStructuralInfo.SetNameValue("FILTERS",
+                                         oFiltersArray.ToString().c_str());
+}
diff --git a/frmts/zarr/zarr_v3_array.cpp b/frmts/zarr/zarr_v3_array.cpp
@@ -1585,6 +1585,12 @@ ZarrV3Group::LoadArray(const std::string &osArrayName,
     poArray->ParseSpecialAttributes(m_pSelf.lock(), oAttributes);
     poArray->SetAttributes(oAttributes);
     poArray->SetDtype(oDtype);
+    if (oCodecs.Size() > 0 &&
+        oCodecs[oCodecs.Size() - 1].GetString("name") != "bytes")
+    {
+        poArray->SetStructuralInfo(
+            "COMPRESSOR", oCodecs[oCodecs.Size() - 1].ToString().c_str());
+    }
     if (poCodecs)
         poArray->SetCodecs(std::move(poCodecs));
     RegisterArray(poArray);

diff --git a/frmts/zarr/zarr_v3_group.cpp b/frmts/zarr/zarr_v3_group.cpp
@@ -706,6 +706,12 @@ std::shared_ptr<GDALMDArray> ZarrV3Group::CreateMDArray(
     poArray->SetFilename(osFilename);
     poArray->SetDimSeparator(pszDimSeparator);
     poArray->SetDtype(dtype);
+    if (oCodecs.Size() > 0 &&
+        oCodecs[oCodecs.Size() - 1].GetString("name") != "bytes")
+    {
+        poArray->SetStructuralInfo(
+            "COMPRESSOR", oCodecs[oCodecs.Size() - 1].ToString().c_str());
+    }
     if (poCodecs)
         poArray->SetCodecs(std::move(poCodecs));
     poArray->SetUpdatable(true);