问题
I am trying to dynamically parse a given .proto file in Java to decode a Protobuf-encoded binary.
I have the following parsing method, in which the "proto" string contains the content of the .proto file:
public static Descriptors.FileDescriptor parseProto (String proto) throws InvalidProtocolBufferException, Descriptors.DescriptorValidationException {
DescriptorProtos.FileDescriptorProto descriptorProto = DescriptorProtos.FileDescriptorProto.parseFrom(proto.getBytes());
return Descriptors.FileDescriptor.buildFrom(descriptorProto, null);
}
Though, on execution the previous method throws an exception with the message "Protocol message tag had invalid wire type.". I use the example .proto file from Google so I guess it is valid: https://github.com/google/protobuf/blob/master/examples/addressbook.proto
Here is the stack trace:
15:43:24.707 [pool-1-thread-1] ERROR com.github.whiver.nifi.processor.ProtobufDecoderProcessor - ProtobufDecoderProcessor[id=42c8ab94-2d8a-491b-bd99-b4451d127ae0] Protocol message tag had invalid wire type.
com.google.protobuf.InvalidProtocolBufferException$InvalidWireTypeException: Protocol message tag had invalid wire type.
at com.google.protobuf.InvalidProtocolBufferException.invalidWireType(InvalidProtocolBufferException.java:115)
at com.google.protobuf.UnknownFieldSet$Builder.mergeFieldFrom(UnknownFieldSet.java:551)
at com.google.protobuf.GeneratedMessageV3.parseUnknownField(GeneratedMessageV3.java:293)
at com.google.protobuf.DescriptorProtos$FileDescriptorSet.<init>(DescriptorProtos.java:88)
at com.google.protobuf.DescriptorProtos$FileDescriptorSet.<init>(DescriptorProtos.java:53)
at com.google.protobuf.DescriptorProtos$FileDescriptorSet$1.parsePartialFrom(DescriptorProtos.java:773)
at com.google.protobuf.DescriptorProtos$FileDescriptorSet$1.parsePartialFrom(DescriptorProtos.java:768)
at com.google.protobuf.AbstractParser.parsePartialFrom(AbstractParser.java:163)
at com.google.protobuf.AbstractParser.parseFrom(AbstractParser.java:197)
at com.google.protobuf.AbstractParser.parseFrom(AbstractParser.java:209)
at com.google.protobuf.AbstractParser.parseFrom(AbstractParser.java:214)
at com.google.protobuf.AbstractParser.parseFrom(AbstractParser.java:49)
at com.google.protobuf.DescriptorProtos$FileDescriptorSet.parseFrom(DescriptorProtos.java:260)
at com.github.whiver.nifi.parser.SchemaParser.parseProto(SchemaParser.java:9)
at com.github.whiver.nifi.processor.ProtobufDecoderProcessor.lambda$onTrigger$0(ProtobufDecoderProcessor.java:103)
at org.apache.nifi.util.MockProcessSession.write(MockProcessSession.java:895)
at org.apache.nifi.util.MockProcessSession.write(MockProcessSession.java:62)
at com.github.whiver.nifi.processor.ProtobufDecoderProcessor.onTrigger(ProtobufDecoderProcessor.java:100)
at org.apache.nifi.processor.AbstractProcessor.onTrigger(AbstractProcessor.java:27)
at org.apache.nifi.util.StandardProcessorTestRunner$RunProcessor.call(StandardProcessorTestRunner.java:251)
at org.apache.nifi.util.StandardProcessorTestRunner$RunProcessor.call(StandardProcessorTestRunner.java:245)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:180)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
Any idea? Thank you!
回答1:
It looks like you're trying to use FileDescriptorProto.parseFrom
to populate a FileDescriptorProto
. This will only work if the bytes you're providing are the binary protobuf contents - which is to say: a compiled schema. You can get a compiled schema by using the protoc
command-line-tool with the --descriptor_set_out
option. What you're actually passing it right now is the text bytes that make up the text schema, which is not what parseFrom
expects.
Without a compiled schema, you would need a runtime .proto parser. I'm not aware of one for Java; protobuf-net includes one (protobuf-net.Reflection), but that is C#/.NET. Without an available runtime .proto parser, you'd need to shell-execute protoc
instead.
回答2:
Don't use java String
to hold the protobuf payload. The issue is that String
does translations behind the scenes, and makes assumptions about character sets.
Protobuf works on byte arrays, and the exact representation in the array has to be unchanged. Going to and from String
does not work.
来源:https://stackoverflow.com/questions/47635038/protocol-buffers-how-to-parse-a-proto-file-in-java