fix(client): validate response content-type

[Vishal-770]

Fixes #2365.

Currently, if the gRPC client receives a response with an incorrect Content-Type (for instance, text/html from a proxy like Envoy returning a 502 Bad Gateway), it ignores the content type and proceeds to attempt decoding the HTML body as if it were a valid gRPC binary stream. This leads to confusing stream parsing errors, such as invalid compression flag: 60 ... while receiving response with status: 502 Bad Gateway.

According to the gRPC specification: "If the Content-Type does not begin with application/grpc, the client SHOULD NOT assume that the body contains gRPC messages, and MUST fail the RPC with a status of UNKNOWN (or the equivalent status code translated from the HTTP status code, if one is present)."

Solution

This PR adds a Content-Type validation step in tonic/src/client/grpc.rs during the initial create_response call.

We now check if the Content-Type header starts with application/grpc (which also properly accommodates application/grpc-web and application/grpc+proto). If it is missing or invalid, we immediately return an error. If there is a recognizable HTTP error code (e.g., 502), we utilize crate::status::infer_grpc_status to convert it to the appropriate gRPC status, but with a clear, custom error message stating that the Content-Type was invalid.

[linux-foundation-easycla]

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