buffer: add from(ArrayBufferView) support

doc/api/buffer.md

@@ -1207,10 +1207,14 @@ console.log(buf);
 
 <!-- YAML
 added: v5.10.0
+changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/43863
+    description: The `buffer` parameter can now be an any `ArrayBufferView`.
 -->
 
-* `buffer` {Buffer|Uint8Array} An existing `Buffer` or [`Uint8Array`][] from
-  which to copy data.
+* `buffer` {Buffer|ArrayBufferView} An existing `Buffer`, [`TypedArray`][],
+  or [`DataView`][] from which to copy data.
 
 Copies the passed `buffer` data onto a new `Buffer` instance.
 
@@ -1242,8 +1246,8 @@ console.log(buf2.toString());
 // Prints: buffer
 ```
 
-A `TypeError` will be thrown if `buffer` is not a `Buffer` or another type
-appropriate for `Buffer.from()` variants.
+A `TypeError` will be thrown if `buffer` is not an `ArrayBufferView`
+or another type appropriate for `Buffer.from()` variants.
 
 ### Static method: `Buffer.from(object[, offsetOrEncoding[, length]])`
 

lib/buffer.js

@@ -83,7 +83,8 @@ const {
 const {
   isAnyArrayBuffer,
   isArrayBufferView,
-  isUint8Array
+  isTypedArray,
+  isUint8Array,
 } = require('internal/util/types');
 const {
   inspect: utilInspect
@@ -306,6 +307,15 @@ Buffer.from = function from(value, encodingOrOffset, length) {
     if (isAnyArrayBuffer(value))
       return fromArrayBuffer(value, encodingOrOffset, length);
 
+    if (isArrayBufferView(value) && !isUint8Array(value)) {
+      if (!isTypedArray(value)) {
+        // DataView is not a TypedArray
+        return fromArrayBuffer(value.buffer.slice(value.byteOffset,
+                                                  value.byteOffset + value.byteLength));
+      }
+      return fromArrayBuffer(value.slice().buffer);
+    }
+
     const valueOf = value.valueOf && value.valueOf();
     if (valueOf != null &&
         valueOf !== value &&

test/parallel/test-buffer-alloc.js

@@ -3,9 +3,12 @@ const common = require('../common');
 
 const assert = require('assert');
 const vm = require('vm');
+const os = require('os');
 
 const SlowBuffer = require('buffer').SlowBuffer;
 
+const isBigEnd = os.endianness() === 'BE';
+
 // Verify the maximum Uint8Array size. There is no concrete limit by spec. The
 // internal limits should be updated if this fails.
 assert.throws(
@@ -59,22 +62,102 @@ assert.strictEqual(d.length, 0);
 }
 
 // Test creating a Buffer from a Uint32Array
-// Note: it is implicitly interpreted as Array of integers modulo 256
 {
   const ui32 = new Uint32Array(4).fill(42);
   const e = Buffer.from(ui32);
-  for (const [index, value] of e.entries()) {
-    assert.strictEqual(value, ui32[index]);
-  }
+  assert.deepStrictEqual(e, Buffer.from(isBigEnd ? [
+    0, 0, 0, 42,
+    0, 0, 0, 42,
+    0, 0, 0, 42,
+    0, 0, 0, 42,
+  ] : [
+    42, 0, 0, 0,
+    42, 0, 0, 0,
+    42, 0, 0, 0,
+    42, 0, 0, 0,
+  ]));
 }
 // Test creating a Buffer from a Uint32Array (old constructor)
-// Note: it is implicitly interpreted as Array of integers modulo 256
 {
   const ui32 = new Uint32Array(4).fill(42);
   const e = Buffer(ui32);
-  for (const [key, value] of e.entries()) {
-    assert.strictEqual(value, ui32[key]);
-  }
+  assert.deepStrictEqual(e, Buffer.from(isBigEnd ? [
+    0, 0, 0, 42,
+    0, 0, 0, 42,
+    0, 0, 0, 42,
+    0, 0, 0, 42,
+  ] : [
+    42, 0, 0, 0,
+    42, 0, 0, 0,
+    42, 0, 0, 0,
+    42, 0, 0, 0,
+  ]));
+}
+
+// Test creating a Buffer from a BigUint64Array
+{
+  const bui64 = new BigUint64Array(4).fill(42n);
+  const e = Buffer.from(bui64);
+  assert.deepStrictEqual(e, Buffer.from(isBigEnd ? [
+    0, 0, 0, 0, 0, 0, 0, 42,
+    0, 0, 0, 0, 0, 0, 0, 42,
+    0, 0, 0, 0, 0, 0, 0, 42,
+    0, 0, 0, 0, 0, 0, 0, 42,
+  ] : [
+    42, 0, 0, 0, 0, 0, 0, 0,
+    42, 0, 0, 0, 0, 0, 0, 0,
+    42, 0, 0, 0, 0, 0, 0, 0,
+    42, 0, 0, 0, 0, 0, 0, 0,
+  ]));
+}
+// Test creating a Buffer from a BigUint64Array (old constructor)
+{
+  const bui64 = new BigUint64Array(4).fill(42n);
+  const e = Buffer(bui64);
+  assert.deepStrictEqual(e, Buffer.from(isBigEnd ? [
+    0, 0, 0, 0, 0, 0, 0, 42,
+    0, 0, 0, 0, 0, 0, 0, 42,
+    0, 0, 0, 0, 0, 0, 0, 42,
+    0, 0, 0, 0, 0, 0, 0, 42,
+  ] : [
+    42, 0, 0, 0, 0, 0, 0, 0,
+    42, 0, 0, 0, 0, 0, 0, 0,
+    42, 0, 0, 0, 0, 0, 0, 0,
+    42, 0, 0, 0, 0, 0, 0, 0,
+  ]));
+}
+
+// Test creating a Buffer from a Float64Array
+{
+  const f64 = new Float64Array(4).fill(42);
+  const e = Buffer.from(f64);
+  assert.deepStrictEqual(e, Buffer.from(isBigEnd ? [
+    64, 69, 0, 0, 0, 0, 0, 0,
+    64, 69, 0, 0, 0, 0, 0, 0,
+    64, 69, 0, 0, 0, 0, 0, 0,
+    64, 69, 0, 0, 0, 0, 0, 0,
+  ] : [
+    0, 0, 0, 0, 0, 0, 69, 64,
+    0, 0, 0, 0, 0, 0, 69, 64,
+    0, 0, 0, 0, 0, 0, 69, 64,
+    0, 0, 0, 0, 0, 0, 69, 64,
+  ]));
+}
+// Test creating a Buffer from a Float64Array (old constructor)
+{
+  const f64 = new Float64Array(4).fill(42);
+  const e = Buffer(f64);
+  assert.deepStrictEqual(e, Buffer.from(isBigEnd ? [
+    64, 69, 0, 0, 0, 0, 0, 0,
+    64, 69, 0, 0, 0, 0, 0, 0,
+    64, 69, 0, 0, 0, 0, 0, 0,
+    64, 69, 0, 0, 0, 0, 0, 0,
+  ] : [
+    0, 0, 0, 0, 0, 0, 69, 64,
+    0, 0, 0, 0, 0, 0, 69, 64,
+    0, 0, 0, 0, 0, 0, 69, 64,
+    0, 0, 0, 0, 0, 0, 69, 64,
+  ]));
 }
 
 // Test invalid encoding for Buffer.toString