buffer: make Blob's slice method more spec-compliant

PR-URL: #37361
Backport-PR-URL: #39704
Fixes: #37335
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/internal/blob.js

@@ -2,6 +2,8 @@
 
 const {
   ArrayFrom,
+  MathMax,
+  MathMin,
   ObjectDefineProperty,
   ObjectSetPrototypeOf,
   PromiseResolve,
@@ -43,21 +45,21 @@ const {
   codes: {
     ERR_INVALID_ARG_TYPE,
     ERR_BUFFER_TOO_LARGE,
-    ERR_OUT_OF_RANGE,
   }
 } = require('internal/errors');
 
 const {
   validateObject,
   validateString,
-  validateUint32,
   isUint32,
 } = require('internal/validators');
 
 const kHandle = Symbol('kHandle');
 const kType = Symbol('kType');
 const kLength = Symbol('kLength');
 
+const disallowedTypeCharacters = /[^\u{0020}-\u{007E}]/u;
+
 let Buffer;
 
 function lazyBuffer() {
@@ -141,7 +143,7 @@ class Blob extends JSTransferable {
     super();
     this[kHandle] = createBlob(sources_, length);
     this[kLength] = length;
-    this[kType] = RegExpPrototypeTest(/[^\u{0020}-\u{007E}]/u, type) ?
+    this[kType] = RegExpPrototypeTest(disallowedTypeCharacters, type) ?
       '' : StringPrototypeToLowerCase(type);
   }
 
@@ -180,18 +182,32 @@ class Blob extends JSTransferable {
 
   get size() { return this[kLength]; }
 
-  slice(start = 0, end = (this[kLength]), type = this[kType]) {
-    validateUint32(start, 'start');
-    if (end < 0) end = this[kLength] + end;
-    validateUint32(end, 'end');
-    validateString(type, 'type');
-    if (end < start)
-      throw new ERR_OUT_OF_RANGE('end', 'greater than start', end);
-    if (end > this[kLength])
-      throw new ERR_OUT_OF_RANGE('end', 'less than or equal to length', end);
+  slice(start = 0, end = this[kLength], contentType = '') {
+    if (start < 0) {
+      start = MathMax(this[kLength] + start, 0);
+    } else {
+      start = MathMin(start, this[kLength]);
+    }
+    start |= 0;
+
+    if (end < 0) {
+      end = MathMax(this[kLength] + end, 0);
+    } else {
+      end = MathMin(end, this[kLength]);
+    }
+    end |= 0;
+
+    contentType = `${contentType}`;
+    if (RegExpPrototypeTest(disallowedTypeCharacters, contentType)) {
+      contentType = '';
+    } else {
+      contentType = StringPrototypeToLowerCase(contentType);
+    }
+
+    const span = MathMax(end - start, 0);
+
     return new InternalBlob(
-      this[kHandle].slice(start, end),
-      end - start, type);
+      this[kHandle].slice(start, start + span), span, contentType);
   }
 
   async arrayBuffer() {

test/fixtures/wpt/FileAPI/blob/Blob-constructor-dom.window.js

@@ -0,0 +1,53 @@
+// META: title=Blob constructor
+// META: script=../support/Blob.js
+'use strict';
+
+var test_error = {
+  name: "test",
+  message: "test error",
+};
+
+test(function() {
+  var args = [
+    document.createElement("div"),
+    window,
+  ];
+  args.forEach(function(arg) {
+    assert_throws_js(TypeError, function() {
+      new Blob(arg);
+    }, "Should throw for argument " + format_value(arg) + ".");
+  });
+}, "Passing platform objects for blobParts should throw a TypeError.");
+
+test(function() {
+  var element = document.createElement("div");
+  element.appendChild(document.createElement("div"));
+  element.appendChild(document.createElement("p"));
+  var list = element.children;
+  Object.defineProperty(list, "length", {
+    get: function() { throw test_error; }
+  });
+  assert_throws_exactly(test_error, function() {
+    new Blob(list);
+  });
+}, "A platform object that supports indexed properties should be treated as a sequence for the blobParts argument (overwritten 'length'.)");
+
+test_blob(function() {
+  var select = document.createElement("select");
+  select.appendChild(document.createElement("option"));
+  return new Blob(select);
+}, {
+  expected: "[object HTMLOptionElement]",
+  type: "",
+  desc: "Passing an platform object that supports indexed properties as the blobParts array should work (select)."
+});
+
+test_blob(function() {
+  var elm = document.createElement("div");
+  elm.setAttribute("foo", "bar");
+  return new Blob(elm.attributes);
+}, {
+  expected: "[object Attr]",
+  type: "",
+  desc: "Passing an platform object that supports indexed properties as the blobParts array should work (attributes)."
+});