Add option to not accept maps with duplicate keys

packages/cbor/lib/decoder.js

@@ -79,6 +79,8 @@ class UnexpectedDataError extends Error {
  * @property {boolean} [extendedResults=false] If true, emit extended
  *   results, which will be an object with shape {@link ExtendedResults}.
  *   The value will already have been null-checked.
+ * @property {boolean} [preventDuplicateKeys=false] If true, error is
+ *   thrown if a map has duplicate keys.
  */
 /**
  * @callback decodeCallback
@@ -129,6 +131,7 @@ class Decoder extends BinaryParseStream {
       required = false,
       encoding = 'hex',
       extendedResults = false,
+      preventDuplicateKeys = false,
       ...superOpts
     } = options
 
@@ -140,6 +143,7 @@ class Decoder extends BinaryParseStream {
     this.preferWeb = preferWeb
     this.extendedResults = extendedResults
     this.required = required
+    this.preventDuplicateKeys = preventDuplicateKeys
 
     if (extendedResults) {
       this.bs.on('read', this._onRead.bind(this))
@@ -594,11 +598,18 @@ class Decoder extends BinaryParseStream {
               if (allstrings) {
                 val = {}
                 for (let i = 0, len = parent.length; i < len; i += 2) {
+                  if (this.preventDuplicateKeys &&
+                    Object.prototype.hasOwnProperty.call(val, parent[i])) {
+                    throw new Error('Duplicate keys in a map')
+                  }
                   val[parent[i]] = parent[i + 1]
                 }
               } else {
                 val = new Map()
                 for (let i = 0, len = parent.length; i < len; i += 2) {
+                  if (this.preventDuplicateKeys && val.has(parent[i])) {
+                    throw new Error('Duplicate keys in a map')
+                  }
                   val.set(parent[i], parent[i + 1])
                 }
               }

packages/cbor/package.json

@@ -41,7 +41,8 @@
     "Artyom Yagilev <github@scorpi.org> (http://scorpi.org/)",
     "Denis Lapaev <den@lapaev.me> (http://lapaev.me/)",
     "Ruben Bridgewater <ruben@bridgewater.de>",
-    "Burt Harris <Burt_Harris_cbor@azxs.33mail.com>"
+    "Burt Harris <Burt_Harris_cbor@azxs.33mail.com>",
+    "Jakub Arbet <hi@jakubarbet.me> (https://jakubarbet.me/)"
   ],
   "types": "./types/lib/cbor.d.ts",
   "dependencies": {

packages/cbor/test/decoder.ava.js

@@ -308,3 +308,33 @@ test('Buffers', t => {
     ],
   })
 })
+
+test('duplicate map keys', t => {
+  // Default behaviour is unchanged and allows parsing maps with duplicate keys
+  t.deepEqual(
+    cbor.decode(Buffer.from('a200010002', 'hex')),
+    new Map([[0, 2]])
+  )
+  // When the new decoder option is set the decode will throw
+  t.throws(() => cbor.decode(Buffer.from('a200010002', 'hex'), {preventDuplicateKeys: true}))
+
+  // Default behaviour for maps with only string keys is also unchanged
+  t.deepEqual(
+    cbor.decode(Buffer.from('a268746f537472696e670068746f537472696e6701', 'hex')),
+    {
+      toString: 1,
+    }
+  )
+
+  // When parsing a map with only strings as keys the result is an object and
+  // we ignore keys from the object's prototype when checking for duplicates
+  t.deepEqual(
+    cbor.decode(Buffer.from('a268746f537472696e670063666f6f01', 'hex'), {preventDuplicateKeys: true}),
+    {
+      toString: 0,
+      foo: 1,
+    }
+  )
+
+  t.throws(() => cbor.decode(Buffer.from('a268746f537472696e670068746f537472696e6701', 'hex'), {preventDuplicateKeys: true}))
+})

packages/cbor/types/lib/decoder.d.ts

@@ -104,6 +104,7 @@ declare class Decoder extends BinaryParseStream {
     preferWeb: boolean;
     extendedResults: boolean;
     required: boolean;
+    preventDuplicateKeys: boolean;
     valueBytes: NoFilter;
     /**
      * Stop processing.
@@ -163,6 +164,11 @@ type DecoderOptions = {
      * The value will already have been null-checked.
      */
     extendedResults?: boolean;
+    /**
+     * If true, error is
+     * thrown if a map has duplicate keys.
+     */
+    preventDuplicateKeys?: boolean;
 };
 type ExtendedResults = {
     /**