grpc-ecosystem/grpc-gateway

Support query param unmarshalling to a map with a slice value-type

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#1108 opened on Jan 9, 2020

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enhancementhelp wanted

Description

grpc-gateway has an odd restriction on query parameters with map types. Specifically, it refuses to unmarshal a map type whether the value type is a string slice, such as map[string][]string.

grpc-gateway makes the assumption that the underlying Go type is authoritative for it's representation in query parameters.

I would expect ?q[foobar]=hello&q[foobar]=world to successfully unmarshal to both a map[string][]string if using GoGo protobuf's custom type mappings as well as the following type raw protobuf type:

message MapStringSlice {
  string key = 1;
  string value = 2;
}

message RPC {
   repeated MapStringSlice q = 1;
}

The wire representation of this type is identical to proto's map<string, string> and is recommended for backwards compatibility by the documentation for implementations that may not support map:

I'm happy to write a patch for this functionality if it's welcomed by the maintainers.

Contributor guide

Tech stack
gogrpcrest api
Domain
backendapi
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Go programmingProtocol BuffersgRPCHTTP query parameters
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
45
Research direction
The issue requests support for unmarshalling query parameters like ?q[foobar]=hello&q[foobar]=world into map types with slice values, e.g., map[string][]string. The relevant code is in runtime/query.go at line 142, which currently rejects such types. The fix would involve modifying the unmarshalling logic to handle repeated query keys for map entries. Review the existing unit tests in runtime/query test.go to understand the expected behavior. No linked PRs or assignees, so the issue is open for contribution.