Shooting from the hip here, but this ("\xb0\x04\x00") could be interpreted as a protobuf with this IDL: message Foo { optional int32 bar = 70; }

Shooting from the hip here, but this ("\xb0\x04\x00") could be interpreted as a protobuf with this IDL: message Foo { optional int32 bar = 70; } that decodes to the following value: bar: 0 (or bar could be bool of value false, or enum at value 0/UNSPECIFIED, or int of any other size) But with such a short message and without other samples it's difficult to prove or disprove that this is indeed a protobuf :). One could try to set &pp=sAQB (bar = true/1), &pp=sAQP (bar = 15), ... and observe what happens.