Protocol message end-group tag did not match expec

Question

I keep getting the following stack trace and am not sure what it means.

Caused by: com.google.protobuf.InvalidProtocolBufferException: Protocol message end-group tag did not match expected tag.
    at com.google.protobuf.InvalidProtocolBufferException.invalidEndTag(InvalidProtocolBufferException.java:73)
    at com.google.protobuf.CodedInputStream.checkLastTagWas(CodedInputStream.java:124)
    at com.google.protobuf.AbstractMessageLite$Builder.mergeFrom(AbstractMessageLite.java:189)
    at com.google.protobuf.AbstractMessage$Builder.mergeFrom(AbstractMessage.java:732)
    at com.google.protobuf.AbstractMessage$Builder.mergeFrom(AbstractMessage.java:238)
    at com.google.protobuf.AbstractMessageLite$Builder.mergeFrom(AbstractMessageLite.java:178)
    at com.google.protobuf.AbstractMessage$Builder.mergeFrom(AbstractMessage.java:724)

• What does "Protocol message end-group tag did not match expected tag." mean?
• What is a "message end-group tag"?
• Is this documented somewhere?

Answer 1

Groups in protobuf are written as a start/end numeric pair - kinda like how <foo> needs a </foo>, but in a different format. Essentially it is complaining that it found a </bar> instead (just: the xml is only a metaphor). The details are in the encoding specification, but the long and short is that one of:

• the data is inherently corrupt (either by damage of by a faulty encoder), or
• the data is becoming corrupt while reading, or
• the data is fine and you gave a faulty decoder

If I had to guess, the data has been damaged in transit - because that is so frighteningly common