Answer 504, not 408, when a request outlasts its time limit (closes #70)
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A request past the server's 30-second limit answered 408, which tells the client it was too slow sending its request, and /api/v1/stats answered 500 when its 4-second read ran out. The limit is now chi's middleware.Timeout, which answers 504 and never writes from a second goroutine while the handler is writing. Right after each database read or host name lookup, whatever came back, a handler asks deadlinePassed whether its time limit has passed and, if so, answers 504, with the JSON error body on JSON routes: a cut-off read can return part of its rows without an error. The health check is unchanged. Model: opus-5-5
This commit was merged in pull request #80.
This commit is contained in:
+20
-130
@@ -4,6 +4,7 @@ import (
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"bytes"
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"context"
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"encoding/json"
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"errors"
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"fmt"
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"log/slog"
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"net/http"
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@@ -109,142 +110,28 @@ func JSONResponseMiddleware(next http.Handler) http.Handler {
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})
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}
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// timeoutWriter wraps ResponseWriter to prevent concurrent writes after timeout
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type timeoutWriter struct {
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http.ResponseWriter
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mu sync.Mutex
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written bool
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header http.Header // cached header to prevent concurrent access
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}
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// requestTimeoutMessage is the error message sent with 504 Gateway Timeout.
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const requestTimeoutMessage = "Request timeout"
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func (tw *timeoutWriter) Write(b []byte) (int, error) {
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tw.mu.Lock()
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defer tw.mu.Unlock()
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if tw.written {
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return 0, nil // Discard writes after timeout
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}
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return tw.ResponseWriter.Write(b)
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}
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func (tw *timeoutWriter) WriteHeader(statusCode int) {
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tw.mu.Lock()
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defer tw.mu.Unlock()
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if tw.written {
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return // Discard writes after timeout
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}
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tw.ResponseWriter.WriteHeader(statusCode)
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}
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func (tw *timeoutWriter) Header() http.Header {
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tw.mu.Lock()
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defer tw.mu.Unlock()
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if tw.written {
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// Return a copy to prevent modifications after timeout
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if tw.header == nil {
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tw.header = make(http.Header)
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}
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return tw.header
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}
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return tw.ResponseWriter.Header()
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}
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func (tw *timeoutWriter) markWritten() {
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tw.mu.Lock()
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defer tw.mu.Unlock()
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tw.written = true
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}
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// TimeoutMiddleware creates an HTTP middleware that enforces a request timeout.
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// If the handler does not complete within the specified duration, the middleware
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// returns a JSON error response with HTTP status 408 (Request Timeout).
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// deadlinePassed reports whether ctx ended because its deadline passed.
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//
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// The timeout parameter specifies the maximum duration allowed for request processing.
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// The returned middleware handles panics from the wrapped handler by re-panicking
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// after cleanup, and prevents concurrent writes to the response after timeout occurs.
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func TimeoutMiddleware(timeout time.Duration, logger *slog.Logger) func(http.Handler) http.Handler {
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return func(next http.Handler) http.Handler {
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return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
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startTime := time.Now()
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ctx, cancel := context.WithTimeout(r.Context(), timeout)
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defer cancel()
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tw := &timeoutWriter{
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ResponseWriter: w,
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header: make(http.Header),
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}
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done := make(chan struct{})
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panicChan := make(chan interface{}, 1)
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go func() {
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defer func() {
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if p := recover(); p != nil {
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panicChan <- p
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}
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}()
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next.ServeHTTP(tw, r.WithContext(ctx))
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close(done)
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}()
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select {
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case p := <-panicChan:
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panic(p)
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case <-done:
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return
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case <-ctx.Done():
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tw.markWritten() // Prevent the handler from writing after timeout
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execTime := time.Since(startTime)
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// Log the timeout as a warning
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logger.Warn("Request timeout",
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"method", r.Method,
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"path", r.URL.Path,
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"duration_ms", execTime.Milliseconds(),
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"remote_addr", r.RemoteAddr,
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)
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// Write directly to the underlying writer since we've marked tw as written
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// This is safe because markWritten() prevents the handler from writing
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tw.mu.Lock()
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w.Header().Set("Content-Type", "application/json")
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w.WriteHeader(http.StatusRequestTimeout)
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tw.mu.Unlock()
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response := map[string]interface{}{
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"status": "error",
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"error": map[string]interface{}{
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"msg": "Request timeout",
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"code": http.StatusRequestTimeout,
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},
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"@meta": map[string]interface{}{
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"time_zone": "UTC",
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"api_version": 1,
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"execution_time": fmt.Sprintf("%d ms", execTime.Milliseconds()),
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},
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}
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_ = json.NewEncoder(w).Encode(response)
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}
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})
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}
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// A handler calls it right after each database read or host name lookup,
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// before it looks at what came back, error or not, and answers 504 if it
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// reports true. A read cut off by the time limit can return an error, or part
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// of its rows or none of them without one, so only this check tells a cut-off
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// read from a complete one.
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func deadlinePassed(ctx context.Context) bool {
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return errors.Is(ctx.Err(), context.DeadlineExceeded)
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}
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// JSONValidationMiddleware is an HTTP middleware that validates JSON API responses.
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// It ensures that responses with Content-Type "application/json" contain valid JSON.
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//
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// If a response is not valid JSON or is empty when JSON is expected, the middleware
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// returns a properly formatted JSON error response. For timeout errors (status 408),
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// the error message will be "Request timeout". For other errors, it returns
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// "Internal server error" with status 500 if the original status was 200.
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// returns a properly formatted JSON error response. If the request's time limit
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// has passed, it answers 504 with the error message "Request timeout". For other
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// errors, it returns "Internal server error" with status 500 if the original
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// status was 200.
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//
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// Non-JSON responses are passed through unchanged.
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func JSONValidationMiddleware(next http.Handler) http.Handler {
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@@ -293,11 +180,14 @@ func JSONValidationMiddleware(next http.Handler) http.Handler {
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if statusCode == http.StatusOK {
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statusCode = http.StatusInternalServerError
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}
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if deadlinePassed(r.Context()) {
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statusCode = http.StatusGatewayTimeout
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}
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w.WriteHeader(statusCode)
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errorMsg := "Internal server error"
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if statusCode == http.StatusRequestTimeout {
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errorMsg = "Request timeout"
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if statusCode == http.StatusGatewayTimeout {
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errorMsg = requestTimeoutMessage
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}
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response := map[string]interface{}{
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