The separator in case of headers with list values

[trivikr]

RestJsonInputAndOutputWithStringHeaders

The protocol test RestJsonInputAndOutputWithStringHeaders was using space as a separator for headers with list values.
https://github.com/awslabs/smithy/blob/78a3ac958ea442695cf66ad0f5808768e1f553bf/smithy-aws-protocol-tests/model/restJson1/http-headers.smithy#L31-L48

• input: headerStringList: ["a", "b", "c"],
• output: "X-StringList": "a, b, c",

RestJsonInputAndOutputWithQuotedStringHeaders

The new protocol test for quoted strings RestJsonInputAndOutputWithQuotedStringHeaders removes this separator
https://github.com/awslabs/smithy/blob/78a3ac958ea442695cf66ad0f5808768e1f553bf/smithy-aws-protocol-tests/model/restJson1/http-headers.smithy#L49-L63

• input: headerStringList: ["b,c", "\"def\"", "a"]
• output:

"X-StringList": """
            "b,c","\"def\"",a"""

If the whitespace separator needs to be used, the output should be:

"X-StringList": """
            "b,c", "\"def\"", a"""

Question

What separator should be used in case of headers with list values?

Additional Context

• This issue was noticed while bumping AWS SDK for JavaScript (v3) to smithy 1.15.x chore(codegen): bump smithy to 1.15.x aws/aws-sdk-js-v3#3091 (comment)
• The protocol tests for quotes string were added in Add tests for quoted strings in headers #986

[kstich]

This was fixed in #1049