What is the server behavior for routing based on query strings when multiple values appear for the same query key parameter?

[david-perez]

The docs don't specify a behavior. Relevant section in the docs: https://awslabs.github.io/smithy/1.0/spec/core/http-traits.html#query-string-literals

There are also no protocol tests.

An example. Consider two routes with URI request patterns:

1. /path?fooKey=bar
2. /path?fooKey=baz

And we receive an HTTP request with URI http://yourhost/path?fooKey=bar&fooKey=baz. Where should we route it to?

Note that currently this scenario is accepted by Smithy i.e. this minimal model builds fine:

$version: "1.0"

namespace com.amazonaws.simple

use aws.protocols#restJson1

@restJson1
@title("SimpleService")
service SimpleService {
    version: "2022-01-01",
    operations: [
        Healthcheck1,
        Healthcheck2,
    ],
}

@http(uri: "/healthcheck?fooKey=bar", method: "GET")
operation Healthcheck1 {
    input: HealthcheckInputRequest,
    output: HealthcheckOutputResponse
}

@http(uri: "/healthcheck?fooKey=baz", method: "GET")
operation Healthcheck2 {
    input: HealthcheckInputRequest,
    output: HealthcheckOutputResponse
}

structure HealthcheckInputRequest {
}

structure HealthcheckOutputResponse {
}

[JordonPhillips]

If the operation can't be determined, you throw a serialization exception. It's pretty clear that this would be indeterminable, though I suppose your question could also be phrased as "How should duplicate query keys be treated?". The answer to that can be found here:

List and set members are serialized by adding multiple query string parameters to the query string using the same name. For example, given a member bound to foo that targets a list of strings with a value of ["a", "b"], the value is serialized in the query string as foo=a&foo=b.

So since we treat duplicate entries as lists, the query params in your example could be represented in JSON as:

{
    "fooKey": ["bar", "baz"]
}

But you're expecting fooKey to have a value of bar or baz. Since it has neither of those values, the intended request cannot be determined and you must then return an error.