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Decode stream bodies once instead of per chunk #10877

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Decode stream bodies once instead of per chunk #10877

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1 change: 1 addition & 0 deletions CHANGELOG.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
- Fixed `streamToString` corrupting multi-byte UTF-8 characters that span a stream chunk boundary.
9 changes: 6 additions & 3 deletions src/streamUtils.ts
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Expand Up @@ -25,11 +25,14 @@ export function streamToString(s?: NodeJS.ReadableStream | null): Promise<string
return Promise.resolve("");
}
return new Promise((resolve, reject) => {
let b = "";
const chunks: Buffer[] = [];
s.on("error", reject);
s.on("data", (d: Buffer | string) => {
b += d.toString();
// Buffer the raw chunks and decode once at the end. Decoding each chunk
// on its own corrupts any multi-byte character that straddles a chunk
// boundary, turning it into replacement characters.
chunks.push(Buffer.isBuffer(d) ? d : Buffer.from(String(d), "utf8"));
});
Comment on lines +28 to 35

@gemini-code-assist gemini-code-assist Bot Jul 31, 2026

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high

If the stream emits Uint8Array chunks (which is common in modern Node.js and web-compatible streams), Buffer.isBuffer(d) will return false. This falls back to Buffer.from(String(d), "utf8"). Calling String() on a Uint8Array converts it to a comma-separated string of numbers (e.g., "104,101,108,108,111"), which will corrupt the decoded string.

Since Buffer.concat natively accepts both Buffer and Uint8Array instances, we can safely push them directly. We should explicitly check for Uint8Array (which also covers Buffer since Buffer inherits from Uint8Array in Node.js) and string to handle all cases correctly.

    const chunks: Uint8Array[] = [];
    s.on("error", reject);
    s.on("data", (d: Buffer | string | Uint8Array) => {
      // Buffer the raw chunks and decode once at the end. Decoding each chunk
      // on its own corrupts any multi-byte character that straddles a chunk
      // boundary, turning it into replacement characters.
      if (d instanceof Uint8Array) {
        chunks.push(d);
      } else if (typeof d === "string") {
        chunks.push(Buffer.from(d, "utf8"));
      } else {
        chunks.push(Buffer.from(String(d), "utf8"));
      }
    });

s.once("end", () => resolve(b));
s.once("end", () => resolve(Buffer.concat(chunks).toString("utf8")));
});
}
14 changes: 14 additions & 0 deletions src/utils.spec.ts
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Expand Up @@ -4,6 +4,7 @@ import * as sinon from "sinon";
import * as fs from "fs";
import * as os from "os";
import * as path from "path";
import { Readable } from "stream";

import * as utils from "./utils";
import { FirebaseError } from "./error";
Expand Down Expand Up @@ -294,6 +295,19 @@ describe("utils", () => {
await expect(utils.streamToString(undefined)).to.eventually.equal("");
await expect(utils.streamToString(null)).to.eventually.equal("");
});

it("should decode a multi-byte character split across chunks", async () => {
// "café 中文 😀" holds 2-, 3- and 4-byte UTF-8 characters.
const text = "caf\u00e9 \u4e2d\u6587 \u{1F600}";
const buf = Buffer.from(text, "utf8");
const cut = buf.indexOf(Buffer.from("\u00e9", "utf8")) + 1;
const stream = new Readable();
stream.push(buf.subarray(0, cut));
stream.push(buf.subarray(cut));
stream.push(null);

await expect(utils.streamToString(stream)).to.eventually.equal(text);
});
});

describe("allSettled", () => {
Expand Down