[gRPC-C++] grpc-c++ client seems not to index custom headers to http2 dynamic-table?

[A-SaltedFish]

I want to add a custom header in request with C++ client using “Custom-Metadata”，

and the header-value pair is fixed。

Acrrording to HTTP2， the header should be cached by client and server, and only transfer a  HPACKED header presented by a index-num . but when i check the Tcpdump data,  I found the header was not indexed at all.

the version i used : grpc-v1100. 

I checked the source code, and i found that grpc not support custom-header to be indexed.

I wander why doed grpc  c++ not  impelement this , and any project to add support for indexing custom-header?

[yas...@google.com]

gRPC does support HPACK. By grpc-v1100, do you mean gRPC 1.1? That seems like a really old version? Please use the latest release instead.

[Craig Tiller]

You're right that gRPC C++ doesn't compress arbitrary metadata: we get some performance advantages from being able to predictably compress important protocol metadata, and we've found that compressing arbitrary metadata interferes with this - it's usually not compressible enough, and when it is it's too computationally intensive to do a good job. We've considered ways to improve that, but right now the best paths forward likely need a breaking API change.

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[A-SaltedFish]

Thank you very much for answer . I get it，i think.  And what do you mean by "not compressiable"，is this scenrio you are talking about:  the header value is often changing thus grpc have to compress it in almost every request?