refactor: define TrustSet transaction model (#1549)

- Defines a TypeScript type for TrustSet
- Provides an optional function to users for verifying a TrustSet instance at runtime: verifyTrustSet()
- Adds tests for verifyTrustSet()

src/models/transactions/index.ts

@@ -7,5 +7,6 @@ export * from './checkCash'
 export * from './checkCancel'
 export * from './accountDelete'
 export * from './signerListSet'
+export * from './trustSet'
 export * from './depositPreauth'
 export * from './paymentTransaction'

src/models/transactions/transaction.ts

@@ -9,6 +9,7 @@ import { OfferCancel } from "./offerCancel"
 import { OfferCreate } from "./offerCreate"
 import { PaymentTransaction } from "./paymentTransaction"
 import { SignerListSet } from "./signerListSet"
+import { TrustSet } from "./trustSet"
 
 export type Transaction =
        AccountDelete
@@ -30,7 +31,7 @@ export type Transaction =
 //   | SetRegularKey
      | SignerListSet
 //   | TicketCreate
-//   | TrustSet
+     | TrustSet
 
 export interface TransactionAndMetadata {
     transaction: Transaction

src/models/transactions/trustSet.ts

@@ -0,0 +1,54 @@
+import { ValidationError } from '../../common/errors'
+import { Amount } from '../common'
+import { BaseTransaction, GlobalFlags, isAmount, verifyBaseTransaction } from './common'
+
+export enum TrustSetFlagsEnum {
+    tfSetfAuth = 0x00010000,
+    tfSetNoRipple = 0x00020000,
+    tfClearNoRipple = 0x00040000,
+    tfSetFreeze = 0x00100000,
+    tfClearFreeze = 0x00200000,
+}
+
+export interface TrustSetFlags extends GlobalFlags {
+    tfSetfAuth?: boolean
+    tfSetNoRipple?: boolean
+    tfClearNoRipple?: boolean
+    tfSetFreeze?: boolean
+    tfClearFreeze?: boolean
+}
+
+export interface TrustSet extends BaseTransaction {
+    TransactionType: 'TrustSet'
+    LimitAmount: Amount
+    QualityIn?: number
+    QualityOut?: number
+    Flags?: number | TrustSetFlags
+}
+
+/**
+ * 
+ * @param tx A TrustSet Transaction.
+ * @returns {void}
+ * @throws {ValidationError} When the TrustSet is malformed.
+ */
+export function verifyTrustSet(tx: TrustSet): void {
+    verifyBaseTransaction(tx)
+    const { LimitAmount, QualityIn, QualityOut } = tx
+
+    if (LimitAmount === undefined) {
+        throw new ValidationError('TrustSet: missing field LimitAmount')
+    }
+
+    if (!isAmount(LimitAmount)) {
+        throw new ValidationError('TrustSet: invalid LimitAmount')
+    }
+
+    if (QualityIn !== undefined && typeof QualityIn !== 'number') {
+        throw new ValidationError('TrustSet: QualityIn must be a number')
+    }
+
+    if (QualityOut !== undefined && typeof QualityOut !== 'number') {
+        throw new ValidationError('TrustSet: QualityOut must be a number')
+    }
+}