zlib: report premature ends earlier

Report end-of-stream when decompressing when we detect it,
and do not wait until the writable side of a zlib stream
is closed as well.

Refs: https://github.com/nodejs/node/issues/26332

PR-URL: https://github.com/nodejs/node/pull/26363
Refs: https://github.com/nodejs/node/issues/26332
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/zlib.js

@@ -546,6 +546,16 @@ function processCallback() {
     return;
   }
 
+  if (availInAfter > 0) {
+    // If we have more input that should be written, but we also have output
+    // space available, that means that the compression library was not
+    // interested in receiving more data, and in particular that the input
+    // stream has ended early.
+    // This applies to streams where we don't check data past the end of
+    // what was consumed; that is, everything except Gunzip/Unzip.
+    self.push(null);
+  }
+
   // finished with the chunk.
   this.buffer = null;
   this.cb();

test/parallel/test-zlib-premature-end.js

@@ -0,0 +1,33 @@
+'use strict';
+const common = require('../common');
+const zlib = require('zlib');
+const assert = require('assert');
+
+const input = '0123456789'.repeat(4);
+
+for (const [ compress, decompressor ] of [
+  [ zlib.deflateRawSync, zlib.createInflateRaw ],
+  [ zlib.deflateSync, zlib.createInflate ],
+  [ zlib.brotliCompressSync, zlib.createBrotliDecompress ]
+]) {
+  const compressed = compress(input);
+  const trailingData = Buffer.from('not valid compressed data');
+
+  for (const variant of [
+    (stream) => { stream.end(compressed); },
+    (stream) => { stream.write(compressed); stream.write(trailingData); },
+    (stream) => { stream.write(compressed); stream.end(trailingData); },
+    (stream) => { stream.write(Buffer.concat([compressed, trailingData])); },
+    (stream) => { stream.end(Buffer.concat([compressed, trailingData])); }
+  ]) {
+    let output = '';
+    const stream = decompressor();
+    stream.setEncoding('utf8');
+    stream.on('data', (chunk) => output += chunk);
+    stream.on('end', common.mustCall(() => {
+      assert.strictEqual(output, input);
+      assert.strictEqual(stream.bytesWritten, compressed.length);
+    }));
+    variant(stream);
+  }
+}