ociregistry/ociserver: pass request into WriteError

This gives the `WriteError` function the capability to
inspect the request in order to form the error (for example
to extract the context or log some request parameters).
We also change its signature so it's clear that the
error is discarded - in general this is the strategy taken
by most HTTP servers anyway as clients tend to
disappear without warning, so logging errors in this case is just noise.
We leave the signature of `ociregistry.WriteError` the same
so it's possible for a caller to use that error if they want,
and also to make it clear that it does not use the `http.Request`
to inform the result.

Signed-off-by: Roger Peppe <rogpeppe@gmail.com>
Change-Id: Ifdbc2ea509385b28479a064f4c2b13686cba5f7f
Dispatch-Trailer: {"type":"trybot","CL":1193024,"patchset":1,"ref":"refs/changes/24/1193024/1","targetBranch":"main"}

ociregistry/ociserver/error_test.go

@@ -31,9 +31,9 @@ func TestCustomErrorWriter(t *testing.T) {
 	// HTTP status code is derived from the OCI error code in preference
 	// to the HTTPError status code.
 	r := New(&ociregistry.Funcs{}, &Options{
-		WriteError: func(w http.ResponseWriter, err error) error {
+		WriteError: func(w http.ResponseWriter, _ *http.Request, err error) {
 			w.Header().Set("Some-Header", "a value")
-			return ociregistry.WriteError(w, err)
+			ociregistry.WriteError(w, err)
 		},
 	})
 	s := httptest.NewServer(r)

ociregistry/ociserver/registry.go

@@ -42,10 +42,12 @@ var v2 = ocispecroot.Versioned{
 // Options holds options for the server.
 type Options struct {
 	// WriteError is used to write error responses. It is passed the
-	// error an API call has returned and is responsible for writing
-	// it to w. If WriteError is nil, [ociregistry.WriteError] will
-	// be used.
-	WriteError func(w http.ResponseWriter, err error) error
+	// writer to write the error response to, the request that
+	// the error is in response to, and the error itself.
+	//
+	// If WriteError is nil, [ociregistry.WriteError] will
+	// be used and any error discarded.
+	WriteError func(w http.ResponseWriter, req *http.Request, err error)
 
 	// DisableReferrersAPI, when true, causes the registry to behave as if
 	// it does not understand the referrers API.
@@ -140,7 +142,9 @@ func New(backend ociregistry.Interface, opts *Options) http.Handler {
 		r.opts.DebugID = fmt.Sprintf("ociserver%d", atomic.AddInt32(&debugID, 1))
 	}
 	if r.opts.WriteError == nil {
-		r.opts.WriteError = ociregistry.WriteError
+		r.opts.WriteError = func(w http.ResponseWriter, _ *http.Request, err error) {
+			ociregistry.WriteError(w, err)
+		}
 	}
 	return r
 }
@@ -176,7 +180,7 @@ var handlers = []func(r *registry, ctx context.Context, w http.ResponseWriter, r
 
 func (r *registry) ServeHTTP(resp http.ResponseWriter, req *http.Request) {
 	if rerr := r.v2(resp, req); rerr != nil {
-		r.opts.WriteError(resp, rerr)
+		r.opts.WriteError(resp, req, rerr)
 		return
 	}
 }