What is the correct Protobuf content type?

JSON has application/json as a standard. For protobuf some people use application/x-protobuf, but I saw something as odd as application/vnd.google.protobuf being proposed. Do we have an RFC or some other standard that I can use as a reference for this?

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There's an expired IETF proposal that suggests application/protobuf. It does not address the question how the receiving side could determine the particular message type. Previous discussions suggested using a parameter to specify package and message, e.g. application/protobuf; proto=org.some.Message

In practice, the types you listed seem to be indeed the ones in use, for example the monitoring system Prometheus uses application/vnd.google.protobuf, and the Charles web debugging proxy recognizes application/x-protobuf; messageType="x.y.Z".

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At the risk of being overly pedantic, the other answers only make sense if we're assuming that "protobuf content type" means the standard wire format for protos.

Content types should map to encoding schemes, and there are multiple encoding schemes for protos. The wire format is the most common and important one, but there's also text format, and potentially others. That being said, I am unable to find any standard content type for proto text format, so I don't know of any other options to add here.

Protos are just a way of describing schema, and are not tightly coupled with any particular way of encoding data in that schema.

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The Content-Type representation header is used to indicate the original media type of the resource (prior to any content encoding applied for sending). Meanwhile, protobuf is serialization/de-serialization schema/library.


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