Fix encoding of array in signTypedData_v4

Currently the behavior of signTypedData_v4 is not according to
https://eips.ethereum.org/EIPS/eip-712 when it comes to encoding arrays.

The eip states: "The array values are encoded as the keccak256 hash of the
concatenated encodeData of their contents".

The behavior instead was to encode array values as the keccak256 of the
concatenated keccak256 of the values.

This worked well for primary types, but not for struct, as encodeData
per spec is: "The encoding of a struct instance is
enc(value₁) ‖ enc(value₂) ‖ … ‖ enc(valueₙ) , i.e. the concatenation of the
encoded member values in the order that they appear in the type.
Each encoded member value is exactly 32-byte long.".

Instead, we were using basically `hashStruct` instead of `encodeData`

index.ts

@@ -117,6 +117,15 @@ const TypedDataUtils = {
 
         if (type.lastIndexOf(']') === type.length - 1) {
           const parsedType = type.slice(0, type.lastIndexOf('['));
+
+          // If it's a struct, we concatenate their encodedData and then take the keccak256
+          // as per "The array values are encoded as the keccak256 hash of the concatenated encodeData of their contents"
+          if (types[parsedType] !== undefined) {
+             const typeValuePairs = value.map((item) => this.encodeData(parsedType, item, types));
+             return ['bytes32', ethUtil.sha3(Buffer.concat(typeValuePairs))]
+          }
+
+          // Otherwise we use encodeField as it's not a struct
           const typeValuePairs = value.map((item) => encodeField(name, parsedType, item));
           return ['bytes32', ethUtil.sha3(ethAbi.rawEncode(
             typeValuePairs.map(([t]) => t),

test/index.ts

@@ -657,15 +657,15 @@ test('signedTypeData_v4', (t) => {
     `0x${[
       '4bd8a9a2b93427bb184aca81e24beb30ffa3c747e2a33d4225ec08bf12e2e753',
       '9b4846dd48b866f0ac54d61b9b21a9e746f921cefa4ee94c4c0a1c49c774f67f',
-      'ca322beec85be24e374d18d582a6f2997f75c54e7993ab5bc07404ce176ca7cd',
+      'efa62530c7ae3a290f8a13a5fc20450bdb3a6af19d9d9d2542b5a94e631a9168',
       'b5aadf3154a261abdd9086fc627b61efca26ae5702701d05cd2305f7c52a2fc8',
     ].join('')}`);
   t.equal(ethUtil.bufferToHex(utils.hashStruct(typedData.primaryType, typedData.message, typedData.types)),
-    '0xeb4221181ff3f1a83ea7313993ca9218496e424604ba9492bb4052c03d5c3df8');
+    '0x99b97a26b830a26d5ca27ced87ba4d73c6276a2b8315656882a771d6f98b01f3');
   t.equal(ethUtil.bufferToHex(utils.hashStruct('EIP712Domain', typedData.domain, typedData.types)),
     '0xf2cee375fa42b42143804025fc449deafd50cc031ca257e0b194a650a912090f');
   t.equal(ethUtil.bufferToHex(utils.sign(typedData)),
-    '0xa85c2e2b118698e88db68a8105b794a8cc7cec074e89ef991cb4f5f533819cc2');
+    '0x66c6a7d830704b2b1c4a4245129d468a84449b50a6237f6fad4a38a0ace770a1');
 
   const privateKey = ethUtil.sha3('cow');
 
@@ -674,7 +674,7 @@ test('signedTypeData_v4', (t) => {
 
   const sig = sigUtil.signTypedData_v4(privateKey, { data: typedData });
 
-  t.equal(sig, '0x65cbd956f2fae28a601bebc9b906cea0191744bd4c4247bcd27cd08f8eb6b71c78efdf7a31dc9abee78f492292721f362d296cf86b4538e07b51303b67f749061b');
+  t.equal(sig, '0xf632e305033e23de75545fcdd0a481d83d9d41954e12c07004327cddf4e3c762757652b04d11dd022e0018e6160723f322d0b4bd9b41c87db93755405f5548391b')
 });
 
 
@@ -766,15 +766,15 @@ test('signedTypeData_v4', (t) => {
     `0x${[
       '4bd8a9a2b93427bb184aca81e24beb30ffa3c747e2a33d4225ec08bf12e2e753',
       '9b4846dd48b866f0ac54d61b9b21a9e746f921cefa4ee94c4c0a1c49c774f67f',
-      'ca322beec85be24e374d18d582a6f2997f75c54e7993ab5bc07404ce176ca7cd',
+      'efa62530c7ae3a290f8a13a5fc20450bdb3a6af19d9d9d2542b5a94e631a9168',
       'b5aadf3154a261abdd9086fc627b61efca26ae5702701d05cd2305f7c52a2fc8',
     ].join('')}`);
   t.equal(ethUtil.bufferToHex(utils.hashStruct(typedData.primaryType, typedData.message, typedData.types)),
-    '0xeb4221181ff3f1a83ea7313993ca9218496e424604ba9492bb4052c03d5c3df8');
+    '0x99b97a26b830a26d5ca27ced87ba4d73c6276a2b8315656882a771d6f98b01f3');
   t.equal(ethUtil.bufferToHex(utils.hashStruct('EIP712Domain', typedData.domain, typedData.types)),
     '0xf2cee375fa42b42143804025fc449deafd50cc031ca257e0b194a650a912090f');
   t.equal(ethUtil.bufferToHex(utils.sign(typedData)),
-    '0xa85c2e2b118698e88db68a8105b794a8cc7cec074e89ef991cb4f5f533819cc2');
+    '0x66c6a7d830704b2b1c4a4245129d468a84449b50a6237f6fad4a38a0ace770a1');
 
   const privateKey = ethUtil.sha3('cow');
 
@@ -783,7 +783,7 @@ test('signedTypeData_v4', (t) => {
 
   const sig = sigUtil.signTypedData_v4(privateKey, { data: typedData });
 
-  t.equal(sig, '0x65cbd956f2fae28a601bebc9b906cea0191744bd4c4247bcd27cd08f8eb6b71c78efdf7a31dc9abee78f492292721f362d296cf86b4538e07b51303b67f749061b');
+  t.equal(sig, '0xf632e305033e23de75545fcdd0a481d83d9d41954e12c07004327cddf4e3c762757652b04d11dd022e0018e6160723f322d0b4bd9b41c87db93755405f5548391b')
 });
 
 test('signedTypeData_v4 with recursive types', (t) => {