Add top-level address module error handling (#356)

Summary:
This commit implements all the code needed for the top-level
`makeAddressModule` function, without implementing any of the address
functions. This mostly comprises handling of errors in the module
options.

Test Plan:
Unit tests added. Run `yarn travis`.

wchargin-branch: address-error-handling

src/v3/core/address.js

@@ -1,5 +1,7 @@
 // @flow
 
+import stringify from "json-stable-stringify";
+
 export interface AddressModule<Address> {
   /**
    * Assert at runtime that the provided address is actually a valid
@@ -89,7 +91,31 @@ export type Options = {|
 
 export function makeAddressModule(options: Options): AddressModule<string> {
   type Address = string; // for readability and interface consistency
-  const _ = options;
+  const {name, nonce} = options;
+  const otherNonces = new Map(options.otherNonces || new Map());
+
+  const separator = "\0";
+  if (nonce.indexOf(separator) !== -1) {
+    throw new Error(`invalid nonce (contains NUL): ${stringify(nonce)}`);
+  }
+
+  const nonceWithSeparator = nonce + separator;
+  const otherNoncesWithSeparators = new Map();
+  for (const [otherNonce, otherName] of otherNonces.entries()) {
+    if (otherNonce === nonce) {
+      throw new Error(
+        `primary nonce listed as otherNonce: ${stringify(nonce)}`
+      );
+    }
+    if (otherNonce.indexOf(separator) !== -1) {
+      throw new Error(
+        `invalid otherNonce (contains NUL): ${stringify(otherNonce)}`
+      );
+    }
+    otherNoncesWithSeparators.set(otherNonce + separator, otherName);
+  }
+
+  const _ = {name, nonceWithSeparator};
 
   function assertValid(address: Address, what?: string): void {
     const _ = {address, what};

src/v3/core/address.test.js

@@ -28,6 +28,29 @@ describe("core/address", () => {
     it("makes address modules using all the options", () => {
       makeModules();
     });
+    it("rejects a module whose nonce contains NUL", () => {
+      expect(() => {
+        makeAddressModule({name: "BadAddress", nonce: "n\0o"});
+      }).toThrow("invalid nonce (contains NUL):");
+    });
+    it("rejects a module with `otherNonces` containing NUL", () => {
+      expect(() => {
+        makeAddressModule({
+          name: "GoodAddress",
+          nonce: "G",
+          otherNonces: new Map().set("n\0o", "BadAddress"),
+        });
+      }).toThrow("invalid otherNonce (contains NUL):");
+    });
+    it("rejects a module with `nonce` in `otherNonces`", () => {
+      expect(() => {
+        makeAddressModule({
+          name: "GoodAddress",
+          nonce: "G",
+          otherNonces: new Map().set("G", "WatAddress"),
+        });
+      }).toThrow("primary nonce listed as otherNonce");
+    });
     it("returns an object with read-only properties", () => {
       const {FooAddress} = makeModules();
       expect(() => {