Configurable query parameters parser

[wp0pw]

Implementing changes for #1128
Added new mux Option to configure query parameter parser to use with instance of mux.

[johanbrandhorst]

This is very nearly there, but I think we have to make one major change; instead of changing the generated code (which will inevitably break our users), lets change the PopulateQueryParameters function to call runtime.customQueryParameterParser if it is non-nil, and have a new runtime.WithQueryParameterParser set this unexported field. It would mean the parser can only be set globally, not per-servemux. Is that still okay for you?

[wp0pw]

Global parser is fine I think, if we don't want to change the generated code there is not much else we can do here - I'll try to make changes some time this week, thanks for quick feedback.

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@18b7146). Click here to learn what that means.
The diff coverage is 75.86%.

@@            Coverage Diff            @@
##             master    #1138   +/-   ##
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  Coverage          ?   53.79%           
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  Files             ?       42           
  Lines             ?     4207           
  Branches          ?        0           
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  Hits              ?     2263           
  Misses            ?     1696           
  Partials          ?      248

Impacted Files	Coverage Δ
protoc-gen-grpc-gateway/gengateway/template.go	80.58% <ø> (ø)
protoc-gen-swagger/genswagger/types.go	0% <ø> (ø)
runtime/mux.go	54.13% <0%> (ø)
examples/server/a_bit_of_everything.go	0% <0%> (ø)
runtime/query.go	72.22% <100%> (ø)
runtime/errors.go	49.31% <100%> (ø)
protoc-gen-swagger/genswagger/template.go	56.72% <86.36%> (ø)

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[wp0pw]

Changed to use global parser. Added interface for parser implementations.
No changes to generated code.

[johanbrandhorst]

LGTM, thanks for the contribution!

[wp0pw]

Pleasure!

[anilcse]

Is there any example implementation for this? I was looking at the docs, didn't find any info

[johanbrandhorst]

The default implementation in both master and v2 implements the interface. You'll just have to design your own with the same signature. See https://github.com/grpc-ecosystem/grpc-gateway/blob/master/runtime/query.go#L37

[anilcse]

Looks like there's some issue with gogoproto support.

 cannot use &customQueryParser literal (type *customQueryParser) as type runtime.QueryParameterParser in assignment:
        *customQueryParser does not implement runtime.QueryParameterParser (wrong type for Parse method)
                have Parse("github.com/gogo/protobuf/proto".Message, url.Values, *utilities.DoubleArray) error
                want Parse(protoiface.MessageV1, url.Values, *utilities.DoubleArray) error

Any known workarounds for this?

[johanbrandhorst]

No, you can't use it with Gogo protobuf.

[anilcse]

Oh okay, thank you for the info @johanbrandhorst . We are trying to convert query parameters to grpc server specific types in grpc-gateway. Is there an easy way to achieve this? For the sake of UX, we want to keep human-readable parameters for clients and convert them to bytes in grpc-gateway's middleware/interceptor (?).

[johanbrandhorst]

Any parameters not captured in the body or the path automatically become query parameters, are you sure you need to do anything?

[anilcse]

No issues in reading query parameters. But I need to typecast the query parameters before forwarding them to grpc server. We have some prefix encoded strings for clients as that gives better UX. our gRPC server uses bytes (proto definitions are bytes). We want to support strings from client and typecast them to bytes in grpc gateway middleware

[achew22]

@anilcse you should be able to write anything you want in some kind of Go middleware. grpc-gateway doesn't have any provisions for doing this directly so you will have to write something custom up.