Fix Proxy to correctly forward Transfer-Encoding: chunked responses

[Copilot]

Suave.Proxy forwarded the origin's Transfer-Encoding: chunked header verbatim while streaming the body from HttpWebResponse.GetResponseStream(), which transparently de-chunks. Clients received a chunked response whose payload was not actually chunked, e.g. curl: (56) Illegal or missing hexadecimal sequence in chunked-encoding.

Changes in src/Suave/Proxy.fs

• Detect chunked upstream by matching chunked as a comma-separated token (case-insensitive) in Transfer-Encoding, not a substring — avoids false positives from values like gzip, chunked being treated correctly and rules out spurious matches.
• Filter hop-by-hop headers when re-framing: on the chunked path, strip Transfer-Encoding and the mutually-exclusive Content-Length from the forwarded header set before re-adding Transfer-Encoding: chunked.
• Re-chunk on egress using the existing transferStreamChunked helper (same one used by okStreamChunked), instead of writing the de-chunked bytes raw.
• Non-chunked responses continue through the original Content-Length / close-delimited path unchanged.

let isChunked =
  match allHeaders ? ("Transfer-Encoding") with
  | Some v ->
    v.Split(',')
    |> Array.exists (fun t -> String.Equals(t.Trim(), "chunked", StringComparison.OrdinalIgnoreCase))
  | None -> false

// ...
if isChunked then do! transferStreamChunked conn stream
else                do! transferStream conn stream

Verification

Smoke-tested against a hand-rolled upstream that emits Transfer-Encoding: chunked with a multi-chunk body: the proxy output now contains a single Transfer-Encoding: chunked, no Content-Length, and correctly framed chunks terminated by 0\r\n\r\n.

Known limitation (out of scope)

Exotic stacks like Transfer-Encoding: gzip, chunked (gzip applied as a transfer coding rather than Content-Encoding) will lose the gzip layer since the entire header is dropped. This encoding form is essentially unused in practice; happy to extend if reviewers want it preserved.

[ademar]

@copilot Since you Smoke-tested it; can you make that into a unit test.

[Copilot]

@copilot Since you Smoke-tested it; can you make that into a unit test.

Done in ce0dc25 — added src/Suave.Tests/Proxy.fs with an Expecto test Proxy.forwards a chunked upstream response as a valid chunked response. It spins up a hand-rolled TCP upstream that emits Transfer-Encoding: chunked with a multi-chunk body, points Suave.Proxy at it, and asserts on the raw wire response — exactly one Transfer-Encoding: chunked, no Content-Length, correct hex length prefix, and the 0\r\n\r\n terminator. Verified locally: Proxy.forwards a chunked upstream response as a valid chunked response passed in 00:00:00.1500000.