diff --git a/lib/buffer.js b/lib/buffer.js index a4d14305f7..94cfc2c8af 100644 --- a/lib/buffer.js +++ b/lib/buffer.js @@ -311,6 +311,14 @@ Buffer.concat = function(list, length) { pos += buf.length; } + // Note: `length` is always equal to `buffer.length` at this point + if (pos < length) { + // Zero-fill the remaining bytes if the specified `length` was more than + // the actual total length, i.e. if we have some remaining allocated bytes + // there were not initialized. + buffer.fill(0, pos, length); + } + return buffer; }; diff --git a/test/parallel/test-buffer-concat.js b/test/parallel/test-buffer-concat.js index 3946b22141..800f1055aa 100644 --- a/test/parallel/test-buffer-concat.js +++ b/test/parallel/test-buffer-concat.js @@ -1,5 +1,5 @@ 'use strict'; -require('../common'); +const common = require('../common'); const assert = require('assert'); const zero = []; @@ -38,3 +38,25 @@ function assertWrongList(value) { err.message === '"list" argument must be an Array of Buffers'; }); } + +const random10 = common.hasCrypto + ? require('crypto').randomBytes(10) + : Buffer.alloc(10, 1); +const empty = Buffer.alloc(0); + +assert.notDeepStrictEqual(random10, empty); +assert.notDeepStrictEqual(random10, Buffer.alloc(10)); + +assert.deepStrictEqual(Buffer.concat([], 100), empty); +assert.deepStrictEqual(Buffer.concat([random10], 0), empty); +assert.deepStrictEqual(Buffer.concat([random10], 10), random10); +assert.deepStrictEqual(Buffer.concat([random10, random10], 10), random10); +assert.deepStrictEqual(Buffer.concat([empty, random10]), random10); +assert.deepStrictEqual(Buffer.concat([random10, empty, empty]), random10); + +// The tail should be zero-filled +assert.deepStrictEqual(Buffer.concat([empty], 100), Buffer.alloc(100)); +assert.deepStrictEqual(Buffer.concat([empty], 4096), Buffer.alloc(4096)); +assert.deepStrictEqual( + Buffer.concat([random10], 40), + Buffer.concat([random10, Buffer.alloc(30)]));