Custom error class for minimum amount error (#321)

* custom error class for minimum amount error

this should be used to communicate that validate()
or quote() have failed, but only because the user's
transfer amount was too small. UI should use this to
show a helpful error so the user can increase their
transfer size.

* new special error type: UnavailableError

connect/src/routes/tokenBridge/automatic.ts

@@ -14,6 +14,9 @@ import { TransferState } from "../../types.js";
 import { Wormhole } from "../../wormhole.js";
 import type { StaticRouteMethods } from "../route.js";
 import { AutomaticRoute } from "../route.js";
+import {
+  MinAmountError,
+} from '../types.js';
 import type {
   Quote,
   QuoteResult,
@@ -167,12 +170,7 @@ export class AutomaticTokenBridgeRoute<N extends Network>
     // Min amount is fee + 5%
     const minAmount = (fee * 105n) / 100n;
     if (amount.units(amt) < minAmount) {
-      throw new Error(
-        `Minimum amount is ${amount.display({
-          amount: minAmount.toString(),
-          decimals: amt.decimals,
-        })}`,
-      );
+      throw new MinAmountError(amount.fromBaseUnits(minAmount, amt.decimals));
     }
 
     const redeemableAmount = amount.units(amt) - fee;

connect/src/routes/types.ts

@@ -1,6 +1,6 @@
 import type { TokenId } from "@wormhole-foundation/sdk-definitions";
 import type { AttestationReceipt, TransferReceipt } from "../types.js";
-import type { amount } from "@wormhole-foundation/sdk-base";
+import { amount } from "@wormhole-foundation/sdk-base";
 import type { QuoteWarning } from "../warnings.js";
 
 // Extend Options to provide custom options
@@ -84,3 +84,30 @@ export type QuoteError = {
   success: false;
   error: Error;
 };
+
+// Special error to return from quote() or validate() when the
+// given transfer amount is too small. Used to helpfully
+// show a minimum amount in the interface.
+export class MinAmountError extends Error {
+  min: amount.Amount;
+
+  constructor(min: amount.Amount) {
+    super(`Minimum transfer amount is ${amount.display(min)}`);
+    this.min = min;
+  }
+
+  minAmount(): amount.Amount {
+    return this.min;
+  }
+}
+
+// Special error to return from quote() or validate() when the
+// protocol can't provide a quote.
+export class UnavailableError extends Error {
+  internalError: Error;
+
+  constructor(internalErr: Error) {
+    super(`Unable to fetch a quote`);
+    this.internalError = internalErr;
+  }
+}