Prevent possible race condition when reading metadata #3451

docs/changelog.md

@@ -4,6 +4,11 @@
 
 Requires libvips v8.13.3
 
+### v0.31.3 - TBD
+
+* Prevent possible race condition awaiting metadata of Stream-based input.
+  [#3451](https://github.com/lovell/sharp/issues/3451)
+
 ### v0.31.2 - 4th November 2022
 
 * Upgrade to libvips v8.13.3 for upstream bug fixes.

lib/input.js

@@ -469,7 +469,7 @@ function metadata (callback) {
   } else {
     if (this._isStreamInput()) {
       return new Promise((resolve, reject) => {
-        this.on('finish', () => {
+        const finished = () => {
           this._flattenBufferIn();
           sharp.metadata(this.options, (err, metadata) => {
             if (err) {
@@ -478,7 +478,12 @@ function metadata (callback) {
               resolve(metadata);
             }
           });
-        });
+        };
+        if (this.writableFinished) {
+          finished();
+        } else {
+          this.once('finish', finished);
+        }
       });
     } else {
       return new Promise((resolve, reject) => {

test/unit/metadata.js

@@ -439,6 +439,19 @@ describe('Image metadata', function () {
       );
   });
 
+  it('Stream in, finish event fires before metadata is requested', (done) => {
+    const create = { width: 1, height: 1, channels: 3, background: 'red' };
+    const image1 = sharp({ create }).png().pipe(sharp());
+    const image2 = sharp({ create }).png().pipe(sharp());
+    process.nextTick(async () => {
+      const data1 = await image1.metadata();
+      assert.strictEqual('png', data1.format);
+      const data2 = await image2.metadata();
+      assert.strictEqual('png', data2.format);
+      done();
+    });
+  });
+
   it('Stream', function (done) {
     const readable = fs.createReadStream(fixtures.inputJpg);
     const pipeline = sharp().metadata(function (err, metadata) {