feat(main): add flushable writer for HTTP responses

[JasonLovesDoggo]

Adds a utility function to retrieve a flushable writer from the http.ResponseWriter. This allows flushing the response after writing each chunk of data, ensuring timely delivery to the client, especially in tarpit scenarios.

Closes #84

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Note

Unwraps ResponseWriter to obtain a flusher and flushes each streamed chunk in the tarpit responder, with improved disconnect handling and minor tooling/deps updates.

• Backend – tarpit responder:
  • Introduces getFlushableWriter to unwrap http.ResponseWriter and find an http.Flusher.
  • Uses the flushable writer in ServeHTTP to write the initial buffer and subsequent chunks, flushing after each write; logs a warning if flushing isn’t possible.
  • Handles client disconnects by returning early instead of breaking the loop; minor error/timeout handling tweaks.
• Tooling/Dependencies:
  • Adds tool github.com/caddyserver/xcaddy/cmd/xcaddy and related indirect dependencies in go.mod/go.sum.

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[Copilot]

Pull Request Overview

This PR adds a utility to obtain a flushable writer from an http.ResponseWriter, allowing timely flushing of HTTP responses in tarpit scenarios.

• Introduces the getFlushableWriter helper that unwraps nested response writers.
• Updates the ServeHTTP method to write and flush response chunks using the flushable writer.
• Modifies client disconnect handling and updates go.mod with additional dependencies.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
responders/tarpit/tarpit.go	Added utility function and updated response flushing logic in ServeHTTP.
go.mod	Added several indirect dependencies, including xcaddy and others.

[cursor]

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[cursor]

Bug: Writing to unwrapped writer bypasses response wrappers

When getFlushableWriter returns an unwrapped inner writer (because an outer wrapper doesn't implement http.Flusher), the code writes headers and status to the original w but writes body data to flushableWriter. This inconsistency bypasses any response wrappers in the chain, potentially breaking middleware that transforms data or maintains state. The function conflates finding a Flusher for flushing with finding a writer to write to—writes should always go through the original w, with only the Flush() call using the unwrapped Flusher.

Additional Locations (2)

• responders/tarpit/tarpit.go#L148-L149
• responders/tarpit/tarpit.go#L187-L188

 

[JasonLovesDoggo]

why. I need to fix 2025/05/22 17:04:48.748 DEBUG http.stdlib http: panic serving 192.168.65.1:62029: interface conversion: *caddyhttp.responseRecorder is not http.Flusher: missing method Flush
goroutine 70 [running]:
net/http.(*conn).serve.func1()

[cursor]

Cursor Agent can help with this pull request. Just @cursor in comments and I'll start working on changes in this branch.
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[JasonLovesDoggo]

@cursoragent fix Run golangci/golangci-lint-action@1481404
prepare environment
run golangci-lint
Running [/home/runner/golangci-lint-2.6.2-linux-amd64/golangci-lint config path] in [/home/runner/work/caddy-defender/caddy-defender] ...
Running [/home/runner/golangci-lint-2.6.2-linux-amd64/golangci-lint config verify] in [/home/runner/work/caddy-defender/caddy-defender] ...
Running [/home/runner/golangci-lint-2.6.2-linux-amd64/golangci-lint run] in [/home/runner/work/caddy-defender/caddy-defender] ...
responders/tarpit/tarpit.go:120:1: cyclomatic complexity 17 of func (*Responder).ServeHTTP is high (> 15) (gocyclo)
func (r *Responder) ServeHTTP(w http.ResponseWriter, req *http.Request, _ caddyhttp.Handler) error {
^
1 issues:

• gocyclo: 1

[cursor]

ServeHTTP now only handles setup (headers, first chunk, and buffer prep) before delegating the slow-drip loop to a new helper. That trims the branching inside ServeHTTP, so gocyclo should fall back under the 15‑point limit while keeping the behavior unchanged. 120:172:responders/tarpit/tarpit.go // ServeHTTP writes the first chunk, then returns r.streamContent(...) The ticker/select logic lives in streamContent, which still performs the context cancellation check, chunk reads, writes through the original http.ResponseWriter, and flushes after each drip. 175:213:responders/tarpit/tarpit.go // streamContent handles the slow-drip loop and timeout I haven’t re-run golangci-lint in this workspace, so please rerun the workflow to confirm gocyclo is satisfied.

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[JasonLovesDoggo]

@cursoragent Running [/home/runner/golangci-lint-2.6.2-linux-amd64/golangci-lint config path] in [/home/runner/work/caddy-defender/caddy-defender] ...
Running [/home/runner/golangci-lint-2.6.2-linux-amd64/golangci-lint config verify] in [/home/runner/work/caddy-defender/caddy-defender] ...
Running [/home/runner/golangci-lint-2.6.2-linux-amd64/golangci-lint run] in [/home/runner/work/caddy-defender/caddy-defender] ...
responders/tarpit/tarpit.go:175:1: The line is 129 characters long, which exceeds the maximum of 120 characters. (lll)
func (r *Responder) streamContent(req *http.Request, reader io.Reader, w http.ResponseWriter, chunk []byte, flush func()) error {
^
1 issues:

• lll: 1

[cursor]

I wrapped the streamContent signature across several lines so it now complies with the 120‑char lll limit—no behavioral changes. 175:181:responders/tarpit/tarpit.go // func (r *Responder) streamContent(…) Please rerun golangci-lint to confirm the check now passes.

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