fix(gw): send 200 for empty files

Fixes ipfs#9238

core/corehttp/gateway_handler_unixfs_file.go

@@ -37,6 +37,13 @@ func (i *gatewayHandler) serveFile(ctx context.Context, w http.ResponseWriter, r
 		return
 	}
 
+	if size == 0 {
+		// We override null files to 200 to avoid issues with fragment caching reverse proxies.
+		// Also whatever you are asking for, it's cheaper to just give you the complete file (nothing).
+		w.WriteHeader(http.StatusOK)
+		return
+	}
+
 	// Lazy seeker enables efficient range-requests and HTTP HEAD responses
 	content := &lazySeeker{
 		size:   size,

test/sharness/t0110-gateway.sh

@@ -103,6 +103,13 @@ test_expect_success "GET IPFS inlined zero-length data object returns ok code (2
   test_should_contain "Content-Length: 0" empty_ok_response
 '
 
+# https://github.com/ipfs/kubo/issues/9238
+test_expect_success "GET IPFS inlined zero-length data object with byte range starting at 0 returns ok code (200)" '
+  curl -sD - "http://127.0.0.1:$port/ipfs/bafkqaaa" -H "Range: bytes=0-1048575" > empty_ok_response &&
+  test_should_contain "HTTP/1.1 200 OK" empty_ok_response &&
+  test_should_contain "Content-Length: 0" empty_ok_response
+'
+
 test_expect_success "GET /ipfs/ipfs/{cid} returns redirect to the valid path" '
   curl -sD - "http://127.0.0.1:$port/ipfs/ipfs/bafkqaaa?query=to-remember" > response_with_double_ipfs_ns &&
   test_should_contain "<meta http-equiv=\"refresh\" content=\"10;url=/ipfs/bafkqaaa?query=to-remember\" />" response_with_double_ipfs_ns &&