[BEAM-4359] String encoding for a spanner mutation assumes that string length equals bytes length

• Type: Bug
• Status: Resolved
• Priority: P2
• Resolution: Fixed
• Affects Version/s: 2.4.0
• Fix Version/s: 2.7.0
• Component/s: io-java-gcp
• Assignee: Chamikara Madhusanka Jayalath
• Reporter: Sivanand
• Created: 18/May/18 04:12
• Updated: 16/May/20 14:01
• Resolved: 04/Oct/18 20:45

Description

The bug is here:

https://github.com/apache/beam/blob/3ba96003d31ce98a54c0c51c1c0a9cf7c06e2fa2/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/spanner/MutationGroupEncoder.java#L231-L235

case STRING: {
        String str = value.getString();
        VarInt.encode(str.length(), bos);
        bos.write(str.getBytes(StandardCharsets.UTF_8));
        break;
}

 

The code assumes that the number of bytes used to represent a UTF-8 String equals the string length. This is not true because a UTF-8 character can be encoded using 1 - 4 bytes.

From wikipedia: https://en.wikipedia.org/wiki/UTF-8

UTF-8 is a variable width character encoding capable of encoding all 1,112,064 valid code points in Unicode using one to four 8-bit bytes

Code to recreate the issue:

/*
Schema in spanner
CREATE TABLE test (
  id INT64,
  testString STRING(MAX),
  number INT64,
) PRIMARY KEY (id)
*/

    import com.google.cloud.spanner.Mutation;
    import com.google.common.collect.Lists;
    import org.apache.beam.runners.direct.DirectRunner;
    import org.apache.beam.sdk.io.gcp.spanner.SpannerIO;
    import org.apache.beam.sdk.testing.TestPipeline;
    import org.apache.beam.sdk.transforms.Create;
    import org.apache.beam.sdk.transforms.DoFn;
    import org.apache.beam.sdk.transforms.ParDo;
    import org.junit.Rule;
    import org.junit.Test;
    
    import java.io.Serializable;
    import java.util.List;
    
    public class BeamSpannerTest implements Serializable {
    
        @Rule
        public transient TestPipeline pipeline = TestPipeline.create();
    
        @Test
        public void testSpanner() {
            pipeline.getOptions().setRunner(DirectRunner.class);
    
            List<String> strdata = Lists.newArrayList("၃7");
    
    
            pipeline.apply(
                Create.of(strdata)
            ).apply(ParDo.of(new DoFn<String, Mutation>() {
                @ProcessElement
                public void processElement(ProcessContext c) {
                    String value = c.element();
                    c.output(Mutation.newInsertOrUpdateBuilder("test")
                        .set("id").to(1)
                        .set("testString").to(value)
                        .set("number").to(10)
                        .build());
                }
            })
           ).apply("Write to Spanner", SpannerIO.write()
                    .withProjectId("my-project")
                    .withInstanceId("spanner-instance")
                    .withDatabaseId("test")
            );
    
            pipeline.run();
        }
    }

After running the code, the value in the column number will be 7043 and not 10 because the bytes from the previous column testString have spilled into the number

Issue Links

• links to: GitHub Pull Request #7747