From 1ffb19e65c0852e58a485689675158c1f1ebfdb1 Mon Sep 17 00:00:00 2001
From: Sebastian Markbage <sema@fb.com>
Date: Thu, 5 Nov 2020 19:45:21 -0500
Subject: [PATCH] Reuse symbol ids that have already been written earlier in
 the stream

---
 packages/react-server/src/ReactFlightServer.js | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/packages/react-server/src/ReactFlightServer.js b/packages/react-server/src/ReactFlightServer.js
index ae90ef7e24cf9..b6afb5f2e824c 100644
--- a/packages/react-server/src/ReactFlightServer.js
+++ b/packages/react-server/src/ReactFlightServer.js
@@ -79,6 +79,7 @@ export type Request = {
   completedModuleChunks: Array<Chunk>,
   completedJSONChunks: Array<Chunk>,
   completedErrorChunks: Array<Chunk>,
+  writtenSymbols: Map<Symbol, number>,
   flowing: boolean,
   toJSON: (key: string, value: ReactModel) => ReactJSONValue,
 };
@@ -100,6 +101,7 @@ export function createRequest(
     completedModuleChunks: [],
     completedJSONChunks: [],
     completedErrorChunks: [],
+    writtenSymbols: new Map(),
     flowing: false,
     toJSON: function(key: string, value: ReactModel): ReactJSONValue {
       return resolveModelToJSON(request, this, key, value);
@@ -528,9 +530,15 @@ export function resolveModelToJSON(
       describeKeyForErrorMessage(key),
       describeObjectForErrorMessage(parent),
     );
+    const writtenSymbols = request.writtenSymbols;
+    const existingId = writtenSymbols.get(value);
+    if (existingId !== undefined) {
+      return serializeByValueID(existingId);
+    }
     request.pendingChunks++;
     const symbolId = request.nextChunkId++;
     emitSymbolChunk(request, symbolId, name);
+    writtenSymbols.set(value, symbolId);
     return serializeByValueID(symbolId);
   }