Support constant value messages in DRS template 42

grib/src/main/java/ucar/nc2/grib/grib2/Grib2DataReader.java

@@ -1092,54 +1092,62 @@ private float[] getData42(RandomAccessFile raf, Grib2Drs.Type42 gdrs) throws IOE
     byte[] inputData = new byte[encodedLength];
     raf.readFully(inputData);
 
-    int nbytesPerSample = (gdrs.numberOfBits + 7) / 8;
-
-    try (Memory inputMemory = new Memory(encodedLength);
-        Memory outputMemory = new Memory((long) nbytesPerSample * totalNPoints)) {
+    float[] data;
+    if (encodedLength > 0) {
+      int nbytesPerSample = (gdrs.numberOfBits + 7) / 8;
 
-      // set encoding parameters
-      AecStream aecStreamDecode = AecStream.create(gdrs.numberOfBits, gdrs.blockSize, gdrs.referenceSampleInterval,
-          gdrs.compressionOptionsMask);
+      try (Memory inputMemory = new Memory(encodedLength);
+          Memory outputMemory = new Memory((long) nbytesPerSample * totalNPoints)) {
 
-      // load data from grib message into memory
-      inputMemory.write(0, inputData, 0, inputData.length);
+        // set encoding parameters
+        AecStream aecStreamDecode = AecStream.create(gdrs.numberOfBits, gdrs.blockSize, gdrs.referenceSampleInterval,
+            gdrs.compressionOptionsMask);
 
-      aecStreamDecode.setInputMemory(inputMemory);
-      aecStreamDecode.setOutputMemory(outputMemory);
+        // load data from grib message into memory
+        inputMemory.write(0, inputData, 0, inputData.length);
 
-      // decode
-      int ok = LibAec.aec_buffer_decode(aecStreamDecode);
-      if (ok != AEC_OK) {
-        System.out.printf("AEC Error: %s%n", ok);
-      }
+        aecStreamDecode.setInputMemory(inputMemory);
+        aecStreamDecode.setOutputMemory(outputMemory);
 
-      // read decoded data from native memory
-      decodedData = new byte[nbytesPerSample * totalNPoints];
-      outputMemory.read(0, decodedData, 0, decodedData.length);
-    }
-
-    // will use this to read out a long value using nbytesPerSample bytes
-    // see long getNextLong(ByteBuffer bb, int numberOfBytes)
-    ByteBuffer bb = ByteBuffer.wrap(decodedData);
+        // decode
+        int ok = LibAec.aec_buffer_decode(aecStreamDecode);
+        if (ok != AEC_OK) {
+          System.out.printf("AEC Error: %s%n", ok);
+        }
 
-    // decode following regulation 92.9.4, Note 4
-    int D = gdrs.decimalScaleFactor;
-    float DD = (float) Math.pow((double) 10, (double) D);
-    float R = gdrs.referenceValue;
-    int E = gdrs.binaryScaleFactor;
-    float EE = (float) Math.pow(2.0, (double) E);
-    float[] data = new float[decodedData.length];
-    if (bitmap == null) {
-      for (int i = 0; i < totalNPoints; i++) {
-        data[i] = (R + getNextLong(bb, nbytesPerSample) * EE) / DD;
+        // read decoded data from native memory
+        decodedData = new byte[nbytesPerSample * totalNPoints];
+        outputMemory.read(0, decodedData, 0, decodedData.length);
       }
-    } else {
-      for (int i = 0; i < totalNPoints; i++) {
-        if (GribNumbers.testBitIsSet(bitmap[i / 8], i % 8)) {
+
+      // will use this to read out a long value using nbytesPerSample bytes
+      // see long getNextLong(ByteBuffer bb, int numberOfBytes)
+      ByteBuffer bb = ByteBuffer.wrap(decodedData);
+
+      // decode following regulation 92.9.4, Note 4
+      int D = gdrs.decimalScaleFactor;
+      float DD = (float) Math.pow((double) 10, (double) D);
+      float R = gdrs.referenceValue;
+      int E = gdrs.binaryScaleFactor;
+      float EE = (float) Math.pow(2.0, (double) E);
+      data = new float[decodedData.length];
+      if (bitmap == null) {
+        for (int i = 0; i < totalNPoints; i++) {
           data[i] = (R + getNextLong(bb, nbytesPerSample) * EE) / DD;
-        } else {
-          data[i] = staticMissingValue;
         }
+      } else {
+        for (int i = 0; i < totalNPoints; i++) {
+          if (GribNumbers.testBitIsSet(bitmap[i / 8], i % 8)) {
+            data[i] = (R + getNextLong(bb, nbytesPerSample) * EE) / DD;
+          } else {
+            data[i] = staticMissingValue;
+          }
+        }
+      }
+    } else {
+      data = new float[totalNPoints];
+      if (gdrs.referenceValue != 0) {
+        Arrays.fill(data, gdrs.referenceValue);
       }
     }
     return data;

grib/src/test/java/ucar/nc2/grib/grib2/TestDrs42.java

@@ -8,10 +8,13 @@
 import static com.google.common.truth.Truth.assertThat;
 
 import java.io.IOException;
+import java.util.Arrays;
 import java.util.Formatter;
 import org.junit.Test;
 import org.junit.experimental.categories.Category;
 import ucar.ma2.Array;
+import ucar.ma2.DataType;
+import ucar.ma2.InvalidRangeException;
 import ucar.ma2.MAMath;
 import ucar.ma2.MAMath.MinMax;
 import ucar.nc2.NetcdfFile;
@@ -92,4 +95,53 @@ public void checkVariable2Bytes() throws IOException {
       assertThat(MAMath.sumDouble(data) / data.getSize()).isWithin(tol).of(expectedAverage);
     }
   }
+
+  @Test
+  public void constantValueDrs42() throws IOException, InvalidRangeException {
+    // See https://github.com/Unidata/netcdf-java/issues/1498
+    // GRIB2 CCSDS reader fails to read messages with constant values
+    //
+    // Message 1: constant 0.0
+    // Message 2: constant 5.5
+    // Message 3: 80 in the south, 160 in the north
+    // Message 4: typical precipitation field
+
+    // uncompressed messages
+    String origFile = TestDir.localTestDataDir + "GRIB2_section7_testfile_bavaria.grib2";
+    // compressed messages
+    String drs42File = TestDir.localTestDataDir + "GRIB2_section7_testfile_ccsds_bavaria.grib2";
+    final String variableName = "Total_precipitation_rate_surface_Mixed_intervals_Accumulation";
+
+    final int expectedLength = 28712;
+    final int[] singleMessageShape = new int[] {1, 74, 97};
+    final int singleMessageLength = singleMessageShape[0] * singleMessageShape[1] * singleMessageShape[2];
+
+    float[] expected = new float[singleMessageLength];
+    try (NetcdfFile nc42 = NetcdfFiles.open(drs42File)) {
+      Variable v = nc42.findVariable(variableName);
+      assertThat(v != null).isTrue();
+      Array data = v.read();
+
+      assertThat(data).isNotNull();
+      assertThat(data.getSize()).isEqualTo(expectedLength);
+
+      // test known constant values
+      Arrays.fill(expected, 0);
+      assertThat(data.section(new int[] {0, 0, 0}, singleMessageShape).get1DJavaArray(DataType.FLOAT))
+          .isEqualTo(expected);
+
+      Arrays.fill(expected, 5.5f);
+      assertThat(data.section(new int[] {1, 0, 0}, singleMessageShape).get1DJavaArray(DataType.FLOAT))
+          .isEqualTo(expected);
+
+      // compare compressed and uncompressed messages
+      try (NetcdfFile ncOrig = NetcdfFiles.open(origFile)) {
+        Formatter f = new Formatter();
+        CompareNetcdf2 compare = new CompareNetcdf2(f, false, false, true);
+        boolean ok = compare.compare(ncOrig, nc42, null);
+        System.out.printf("%s %s%n", ok ? "OK" : "NOT OK", f);
+        assertThat(ok).isTrue();
+      }
+    }
+  }
 }

uicdm/build.gradle

@@ -42,6 +42,7 @@ dependencies {
 
   runtimeOnly project(':cdm:cdm-s3')
   runtimeOnly project(':cdm:cdm-zarr')
+  runtimeOnly project(':native-compression:libaec-native')
 
   // constrained by netcdf-java-platform
   runtimeOnly 'ch.qos.logback:logback-classic'