[bugfix] Overwrite API client closed errors with `499 - Client Closed Request` (#1857)

* [bugfix] Overwrite client closed errors with 499

* bleep bloop

* review changes

internal/api/util/errorhandling.go

@@ -83,25 +83,44 @@ func genericErrorHandler(c *gin.Context, instanceGet func(ctx context.Context) (
 	}
 }
 
-// ErrorHandler takes the provided gin context and errWithCode and tries to serve
-// a helpful error to the caller. It will do content negotiation to figure out if
-// the caller prefers to see an html page with the error rendered there. If not, or
-// if something goes wrong during the function, it will recover and just try to serve
-// an appropriate application/json content-type error.
+// ErrorHandler takes the provided gin context and errWithCode
+// and tries to serve a helpful error to the caller.
+//
+// It will do content negotiation to figure out if the caller prefers
+// to see an html page with the error rendered there. If not, or if
+// something goes wrong during the function, it will recover and just
+// try to serve an appropriate application/json content-type error.
 // To override the default response type, specify `offers`.
+//
+// If the requester already hung up on the request, ErrorHandler
+// will overwrite the given errWithCode with a 499 error to indicate
+// that the failure wasn't due to something we did, and will avoid
+// trying to write extensive bytes to the caller by just aborting.
+//
+// See: https://en.wikipedia.org/wiki/List_of_HTTP_status_codes#nginx.
 func ErrorHandler(c *gin.Context, errWithCode gtserror.WithCode, instanceGet func(ctx context.Context) (*apimodel.InstanceV1, gtserror.WithCode), offers ...MIME) {
-	// set the error on the gin context so that it can be logged
-	// in the gin logger middleware (internal/router/logger.go)
+	if c.Request.Context().Err() != nil {
+		// Context error means requester probably left already.
+		// Wrap original error with a less alarming one. Then
+		// we can return early, because it doesn't matter what
+		// we send to the client at this point; they're gone.
+		errWithCode = gtserror.NewErrorClientClosedRequest(errWithCode.Unwrap())
+		c.AbortWithStatus(errWithCode.Code())
+		return
+	}
+
+	// Set the error on the gin context so that it can be logged
+	// in the gin logger middleware (internal/middleware/logger.go).
 	c.Error(errWithCode) //nolint:errcheck
 
-	// discover if we're allowed to serve a nice html error page,
+	// Discover if we're allowed to serve a nice html error page,
 	// or if we should just use a json. Normally we would want to
 	// check for a returned error, but if an error occurs here we
 	// can just fall back to default behavior (serve json error).
 	accept, _ := NegotiateAccept(c, JSONOrHTMLAcceptHeaders...)
 
 	if errWithCode.Code() == http.StatusNotFound {
-		// use our special not found handler with useful status text
+		// Use our special not found handler with useful status text.
 		NotFoundHandler(c, instanceGet, accept)
 	} else {
 		genericErrorHandler(c, instanceGet, accept, errWithCode)

internal/gtserror/withcode.go

@@ -23,13 +23,23 @@ import (
 	"strings"
 )
 
+// Custom http response codes + text that
+// aren't included in the net/http package.
+const (
+	StatusClientClosedRequest     = 499
+	StatusTextClientClosedRequest = "Client Closed Request"
+)
+
 // WithCode wraps an internal error with an http code, and a 'safe' version of
 // the error that can be served to clients without revealing internal business logic.
 //
 // A typical use of this error would be to first log the Original error, then return
 // the Safe error and the StatusCode to an API caller.
 type WithCode interface {
-	// Error returns the original internal error for debugging within the GoToSocial logs.
+	// Unwrap returns the original error.
+	// This should *NEVER* be returned to a client as it may contain sensitive information.
+	Unwrap() error
+	// Error serializes the original internal error for debugging within the GoToSocial logs.
 	// This should *NEVER* be returned to a client as it may contain sensitive information.
 	Error() string
 	// Safe returns the API-safe version of the error for serialization towards a client.
@@ -45,6 +55,10 @@ type withCode struct {
 	code     int
 }
 
+func (e withCode) Unwrap() error {
+	return e.original
+}
+
 func (e withCode) Error() string {
 	return e.original.Error()
 }
@@ -173,3 +187,14 @@ func NewErrorGone(original error, helpText ...string) WithCode {
 		code:     http.StatusGone,
 	}
 }
+
+// NewErrorClientClosedRequest returns an ErrorWithCode 499 with the given original error.
+// This error type should only be used when an http caller has already hung up their request.
+// See: https://en.wikipedia.org/wiki/List_of_HTTP_status_codes#nginx
+func NewErrorClientClosedRequest(original error) WithCode {
+	return withCode{
+		original: original,
+		safe:     errors.New(StatusTextClientClosedRequest),
+		code:     StatusClientClosedRequest,
+	}
+}

internal/middleware/logger.go

@@ -27,6 +27,7 @@ import (
 	"codeberg.org/gruf/go-kv"
 	"codeberg.org/gruf/go-logger/v2/level"
 	"github.com/gin-gonic/gin"
+	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
 	"github.com/superseriousbusiness/gotosocial/internal/log"
 )
 
@@ -91,11 +92,23 @@ func Logger(logClientIP bool) gin.HandlerFunc {
 				l = l.WithField("error", c.Errors)
 			}
 
+			// Get appropriate text for this code.
+			statusText := http.StatusText(code)
+			if statusText == "" {
+				// Look for custom codes.
+				switch code {
+				case gtserror.StatusClientClosedRequest:
+					statusText = gtserror.StatusTextClientClosedRequest
+				default:
+					statusText = "Unknown Status"
+				}
+			}
+
 			// Generate a nicer looking bytecount
 			size := bytesize.Size(c.Writer.Size())
 
-			// Finally, write log entry with status text body size
-			l.Logf(lvl, "%s: wrote %s", http.StatusText(code), size)
+			// Finally, write log entry with status text + body size.
+			l.Logf(lvl, "%s: wrote %s", statusText, size)
 		}()
 
 		// Process request