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…onse Deno.serve exposes `info.completed`, which settles when the response has been sent or could not be sent. The span now ends on it, so it stays open for streamed responses of every content type, and the SDK returns the handler's response unchanged. Before, the SDK replaced responses it classified as streaming, which moved string bodies off Deno's static fast path and replaced Content-Length with chunked encoding. `completed` is read before the handler runs, because Deno creates it on first access and settles it on the next close of the request, which a WebSocket upgrade does inside the handler. Runtimes without `completed` keep the stream wrapper. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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added this pull request to stack #24934
October 1, 2026 11:32
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Streamed responses on Deno had the same problem as #22876.
Deno.servepassesinfo.completedto the handler, a promise that settles when the response has been sent or could not be sent. Ending thehttp.serverspan on it keeps the span open for streamed responses of every content type, without a content-type classifier, and the SDK can return the handler's response unchanged.Before, the SDK replaced every response that it classified as streaming with a new
Responsearound a JS stream. For a string body, this skips Deno's static fast path and sends the body chunked instead of with aContent-Length. In a local benchmark with a 20 KB HTML string, the replaced response handled about 23% to 32% fewer requests per second. Readingcompletedhad no measurable cost.Details that are not obvious from the diff:
completedis read before the user handler runs. Deno creates the promise on first access and settles it on the next close of the request, and a WebSocket upgrade closes the request inside the handler.completedrejects withInterruptedwhen the response could not be sent (docs: document that ServeHandlerInfo.completed can reject denoland/deno#35747), so the SDK handles the rejection and still ends the span. Deno 2.9.0 resolved it on a client disconnect in my tests.completedwhen it takes the body, not when the client has received it, so these spans end at the same time as before.completedkeep the old stream wrapper. It is in the Deno runtime since 1.46 or earlier, and in the types since 2.0.--unstable-no-legacy-abort, readingcompletedmakes Deno also abortrequest.signalwhen a response fails.🤖 Generated with Claude Code