HTTP User-Agent string-building no longer supports comments

[gdavison]

Describe the bug

In the HTTP spec, User-Agent strings support a combination of products and comments. A comment is text contained within parentheses.

Prior to aws-sdk-go-v2 v1.19.0, comments could be added using

middleware.AddSDKAgentKey("(" + comment + ")")

Expected Behavior

I expected

middleware.AddSDKAgentKey("(" + comment + ")")

to continue working.

For example, a comment with the text this is a comment should be included in the User-Agent string as

(this is a comment)

Current Behavior

Several characters in the comment are replaced by -. For example, a comment with the text this is a comment is included in the User-Agent string as

-this-is-a-comment-

instead of

(this is a comment)

Reproduction Steps

Generate an HTTP User-Agent string after setting

comment := "this is a comment"
middleware.AddSDKAgentKey("(" + comment + ")")

Possible Solution

One of two solutions:

1. Directly support HTTP User-Agent comment with a function like middleware.AddUserAgentComment()

2. Update the escaping rules to not escape keys that match the comment pattern defined in the HTTP spec

Additional Information/Context

No response

AWS Go SDK V2 Module Versions Used

aws-sdk-go-v2 v1.19.0

Compiler and Version used

go version go1.20.3 darwin/arm64

Operating System and version

macOS 12.6.7

[lucix-aws]

This is definitely a side effect of a recent User-Agent change.

Note that for the time being you can reclaim this behavior through a build-phase middleware:

import (
	"context"
	"fmt"

	"github.com/aws/smithy-go/middleware"
	smithyhttp "github.com/aws/smithy-go/transport/http"
)

type userAgentAppender struct {
	v string
}

func (*userAgentAppender) ID() string {
	return "userAgentAppender"
}

func (m *userAgentAppender) HandleBuild(ctx context.Context, in middleware.BuildInput, next middleware.BuildHandler) (
	out middleware.BuildOutput, metadata middleware.Metadata, err error,
) {
	r, ok := in.Request.(*smithyhttp.Request)
	if !ok {
		return out, metadata, fmt.Errorf("unknown transport type %T", in.Request)
	}

	if ua := r.Header.Get("user-agent"); ua != "" {
		r.Header.Set("user-agent", fmt.Sprintf("%s %s", ua, m.v))
	}

	return next.HandleBuild(ctx, in)
}

func withUserAgentAppender(v string) func(*middleware.Stack) error {
	return func(stack *middleware.Stack) error {
		return stack.Build.Add(&userAgentAppender{v: v}, middleware.After)
	}
}

EDIT: added missing imports

[gdavison]

Thanks, the workaround works

[lucix-aws]

Ive created #2202 to re-add this through the new middleware.WithHeaderComment.

The AddUserAgentKey (and friends) APIs were created with the express purpose of allowing a user to add metadata to the User-Agent header in a manner befitting how it's handled throughout AWS (including encoding specifications, which as you can see have since tightened). The ability to inject comments through the AddUserAgentKey was an unintended side-effect of its existence.

For that reason I believe a new, separate API (which can also apply to any header generically) was the most sensible way forward here.

[lucix-aws]

Hi @gdavison -- apologies for dropping the ball on this. I've just now re-spawned the PR in smithy-go, we decided to expose it there instead back in July and it never happened.

[lucix-aws]

Fixed by aws/smithy-go#461. This will be available in the next release.

[github-actions]

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