Fixed out-of-safe-range hexlify values to throw an exception (#420).

src.ts/utils/bytes.ts

@@ -168,6 +168,15 @@ export function hexlify(value: Arrayish | Hexable | number): string {
             errors.throwError('cannot hexlify negative value', errors.INVALID_ARGUMENT, { arg: 'value', value: value });
         }
 
+        // @TODO: Roll this into the above error as a numeric fault (overflow); next version, not backward compatible
+        // We can about (value == MAX_INT) to as well, since that may indicate we underflowed already
+        if (value >= 9007199254740991) {
+            errors.throwError("out-of-range", errors.NUMERIC_FAULT, {
+                operartion: "hexlify",
+                fault: "out-of-safe-range"
+            });
+        }
+
         var hex = '';
         while (value) {
             hex = HexCharacters[value & 0x0f] + hex;

tests/test-utils.js

@@ -348,3 +348,20 @@ describe('Test BigNumber', function() {
         ].forEach(testAbs);
     });
 });
+
+describe("Hexlify", function() {
+    it("hexlify on string of unsafe number", function() {
+        assert(ethers.utils.hexlify(ethers.utils.bigNumberify("9985956830000000000")), "0x8a953ed43a892c00", "hexlify on large BigNumber");
+    });
+
+    [9007199254740991, 9985956830000000000].forEach((value) => {
+        it('hexlify fails on unsafe number - ' + value, function() {
+            assert.throws(function() {
+                var result = ethers.utils.hexlify(value);
+                console.log('Result', result);
+            }, function(error) {
+                return (error.code === "NUMERIC_FAULT" && error.fault === "out-of-safe-range");
+            }, "hexlify throws on out-of-range value - " + value);
+        });
+    });
+});