1. docker
  2. Commit 405a787917f8d1e4daa60deef8336ecc600661ab
Browse code

daemon/server: don't log context cancelation as error

The [httpstatus.FromError] utility currently maps context cancellation and
deadline errors to a 500 ("internal server error"). As a result, a client
disconnecting would produce an error log:

ERRO[2026-03-11T11:54:39.872784425Z] Handler for POST /v1.54/images/create returned error: failed to resolve reference "docker.io/library/alpine:latest": failed to do request: Head "https://registry-1.docker.io/v2/library/alpine/manifests/latest": context canceled

This patch:

- Checks for context-cancelation on the context, and instead logs an "INFO"
message. For tracing/OTEL, it produces a "499" status code, which is non-
standard, but commonly accepted (and used by NGINX, CloudFront). Given that
no client should be listening anymore, it omits an actual response.
- Adds more structured logs, to align with the logs we produce in our Debug
middleware.

With this patch:

INFO[2026-03-11T16:43:55.567731845Z] API listen on /var/run/docker.sock
INFO[2026-03-11T16:43:58.152254638Z] fetch failed error="failed to do request: Head \"https://registry-1.docker.io/v2/library/alpine/manifests/latest\": context canceled" host=registry-1.docker.io
INFO[2026-03-11T16:43:58.152608805Z] Cancel with lease, leased resources will remain until expiration expires_at="2026-03-12 00:43:57.965872638 +0000 UTC m=+28803.424778128" lease=965878679-Q_SJ
INFO[2026-03-11T16:43:58.152917138Z] request cancelled by client error="failed to resolve reference \"docker.io/library/alpine:latest\": failed to do request: Head \"https://registry-1.docker.io/v2/library/alpine/manifests/latest\": context canceled" method=POST module=api request-url="/v1.54/images/create?fromImage=docker.io%2Flibrary%2Falpine&tag=latest" status=499 vars="map[version:1.54]"

Note some duplication in logs, as some logs are produced by containerd code.

[httpstatus.FromError]: https://github.com/moby/moby/blob/v2.0.0-beta.7/daemon/server/httpstatus/status.go#L44-L45

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

Sebastiaan van Stijn authored on 2026/03/12 01:37:09
Showing 1 changed files
daemon/server/server.go
History View file @ 405a787
... ... 
@@ -22,6 +22,19 @@ import (
22 22 
 // when a request is about to be served.
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 const versionMatcher = "/v{version:[0-9.]+}"
24 24
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+// statusClientClosedRequest (HTTP 499 Client Closed Request) is a non-standard
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+// HTTP status code used by NGINX to indicate that the client closed the connection
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+// before the server was able to send a response.
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+//
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+// It is not part of the IANA HTTP status code registry and is primarily used
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+// for logging and telemetry. The client will typically not observe this status,
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+// as the connection is already closed.
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+//
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+// See:
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+//   - https://developers.cloudflare.com/support/troubleshooting/http-status-codes/4xx-client-error/error-499/
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+//   - https://nginx.org/en/docs/http/ngx_http_log_module.html
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+const statusClientClosedRequest = 499
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+
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 // Server contains instance details for the server
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 type Server struct {
27 40 
 	middlewares []middleware.Middleware
... ... 
@@ -33,9 +46,9 @@ func (s *Server) UseMiddleware(m middleware.Middleware) {
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 	s.middlewares = append(s.middlewares, m)
34 34 
 }
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-func (s *Server) makeHTTPHandler(r router.Route) http.HandlerFunc {
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-	handler := r.Handler()
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-	operation := r.Method() + " " + r.Path()
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+func (s *Server) makeHTTPHandler(route router.Route) http.HandlerFunc {
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+	handler := route.Handler()
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+	operation := route.Method() + " " + route.Path()
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 	return otelhttp.NewHandler(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
40 40 
 		// Define the context that we'll pass around to share info
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 		// like the docker-request-id.
... ... 
@@ -61,10 +74,24 @@ func (s *Server) makeHTTPHandler(r router.Route) http.HandlerFunc {
61 61 
 		}
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 		if err := handlerFunc(ctx, w, r, vars); err != nil {
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-			statusCode := httpstatus.FromError(err)
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-			if statusCode >= http.StatusInternalServerError {
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-				log.G(ctx).Errorf("Handler for %s %s returned error: %v", r.Method, r.URL.Path, err)
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+			if r.Context().Err() != nil {
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+				// Request is canceled, and client likely went away. Don't attempt
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+				// to write JSON body, but log for debugging. Log the status as
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+				// "499 Client Closed Request", which is non-standard, but aligns
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+				// with NGINX and CloudFlare.
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+				w.WriteHeader(statusClientClosedRequest) // for OTEL/metrics
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+				log.G(ctx).WithFields(log.Fields{
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+					"module":      "api",
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+					"method":      route.Method(),
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+					"request-url": r.RequestURI,
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+					"vars":        vars,
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+					"error":       err,
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+					"status":      statusClientClosedRequest,
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+				}).Info("request cancelled by client")
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+				return
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 			}
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+
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+			statusCode := httpstatus.FromError(err)
68 82 
 			// While we no longer support API versions older than 1.24 [config.DefaultMinAPIVersion],
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 			// a client may try to connect using an older version and expect a plain-text error
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 			// instead of a JSON error. This would result in an "API version too old" error
... ... 
@@ -79,6 +106,16 @@ func (s *Server) makeHTTPHandler(r router.Route) http.HandlerFunc {
79 79 
 					Message: err.Error(),
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 				})
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 			}
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+			if statusCode >= http.StatusInternalServerError {
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+				log.G(ctx).WithFields(log.Fields{
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+					"module":         "api",
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+					"method":         route.Method(),
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+					"request-url":    r.RequestURI,
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+					"vars":           vars,
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+					"error-response": err,
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+					"status":         statusCode,
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+				}).Errorf("Handler for %s %s returned error", route.Method(), route.Path())
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+			}
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 		}
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 	}), operation).ServeHTTP
84 94 
 }