Uri cannot preserve percent-encoded path segments, breaking AWS SigV4 in aws-spi-pekko-http

[pjfanning]

Problem

Uri cannot round-trip a percent-encoded path. Parsing decodes %XX triplets in path segments (UriParser), and UriRendering.renderPath re-encodes segments with the pchar-base keep-set ("pchar without percent"). Two consequences:

• A percent-encoded pchar character can never be rendered back in encoded form: %2B becomes +, %3D becomes =, etc. (sub-delims, : and @ are kept raw by the renderer).
• A literal % in a Path segment is always re-encoded to %25, so constructing Uri.Path from the still-encoded string does not work either.

Uri("https://b.s3.amazonaws.com/a%2Bb%20c%3Dx/d?x=%2B7&y=a+b").toString
// https://b.s3.amazonaws.com/a+b%20c=x/d?x=%2B7&y=a+b

The query is preserved verbatim via rawQueryString; the path is not. There is no raw-path escape hatch in the Uri model or the client request renderer, so no downstream construction can produce a byte-identical request target.

Why it matters

pekko-connectors aws-spi-pekko-http implements the AWS SDK async HTTP client SPI with Http().singleRequest. The SDK signs the request (SigV4) with the URI-encoded path it built, e.g. /a%2Bb for S3 object key a+b; the transport must send that path byte-identically. After the Uri round trip the wire path is /a+b, and S3 — which verifies the signature against the path as received, without normalization — rejects the request with SignatureDoesNotMatch. Any S3 object key containing sub-delims characters (+ = ! ( ) , ; ' & $ @ : *) is affected. The same applies to any proxy/pass-through use case that must not alter the request target.

Proposal

Add a way to send a request whose path renders exactly as provided. Options, roughly in order of preference:

1. A raw Uri.Path representation (e.g. a segment/path variant flagged as already-encoded) that renderPath emits verbatim.
2. An HttpRequest attribute carrying a pre-rendered request target that the client renderer honors (analogous in spirit to the server-side raw-request-uri-header).

With either, aws-spi-pekko-http can pass SdkHttpRequest.encodedPath() through untouched.

References

• UriParser percent-decodes matched strings when a % was seen.
• Uri.scala renderPath/encode: keep-set is pchar-base (excludes %), so encoded pchars are irrecoverable and literal % double-encodes.