gateway: add WithContextHint to handler and implement it on BlocksBackend

gateway/blocks_backend.go

@@ -684,6 +684,12 @@
 	return has
 }
 
+var _ WithContextHint = (*BlocksBackend)(nil)
+
+func (bb *BlocksBackend) WrapContextForRequest(ctx context.Context) context.Context {
+	return blockservice.ContextWithSession(ctx, bb.blockService)
+}
+
 func (bb *BlocksBackend) ResolvePath(ctx context.Context, path path.ImmutablePath) (ContentPathMetadata, error) {
 	roots, lastSeg, remainder, err := bb.getPathRoots(ctx, path)
 	if err != nil {

gateway/gateway.go

@@ -386,6 +386,14 @@ type IPFSBackend interface {
 	GetDNSLinkRecord(context.Context, string) (path.Path, error)
 }
 
+// WithContextHint allows an [IPFSBackend] to inject custom [context.Context] configurations.
+// This should be considered optional, consumers might only make a best effort attempt at calling WrapContextForRequest on requests.
+type WithContextHint interface {
+	// WrapContextForRequest allows the backend to add request scopped modifications to the context, like debug values or value caches.
+	// There are no promises on actual usage in consumers.
+	WrapContextForRequest(context.Context) context.Context
+}
+
 // cleanHeaderSet is an helper function that cleans a set of headers by
 // (1) canonicalizing, (2) de-duplicating and (3) sorting.
 func cleanHeaderSet(headers []string) []string {

gateway/handler.go

@@ -152,6 +152,11 @@
 	// the hour is a hard fallback, we don't expect it to happen, but just in case
 	ctx, cancel := context.WithTimeout(r.Context(), time.Hour)
 	defer cancel()
+
+	if withCtxWrap, ok := i.backend.(WithContextHint); ok {
+		ctx = withCtxWrap.WrapContextForRequest(ctx)
+	}
+
 	r = r.WithContext(ctx)
 
 	switch r.Method {