4 files changed, 39 insertions, 5 deletions

diff --git a/src/0x.js.ts b/src/0x.js.ts
index f3da005f8..4c67027fc 100644
--- a/src/0x.js.ts
+++ b/src/0x.js.ts
@@ -137,6 +137,15 @@ export class ZeroEx {
         this.tokenRegistry = new TokenRegistryWrapper(this.web3Wrapper);
     }
     /**
+     * Sets a new provider for the web3 instance used by 0x.js internally and invalidates any instantiated
+     * contract instances instantiated with the old provider.
+     */
+    public setProvider(provider: Web3.Provider) {
+        this.web3Wrapper.setProvider(provider);
+        this.exchange.invalidateContractInstance();
+        this.tokenRegistry.invalidateContractInstance();
+    }
+    /**
      * Signs an orderHash and returns it's elliptic curve signature
      * This method currently supports TestRPC, Geth and Parity above and below V1.6.6
      */
diff --git a/src/contract_wrappers/exchange_wrapper.ts b/src/contract_wrappers/exchange_wrapper.ts
index f0f153c2b..3f6eb0dab 100644
--- a/src/contract_wrappers/exchange_wrapper.ts
+++ b/src/contract_wrappers/exchange_wrapper.ts
@@ -7,9 +7,13 @@ import * as ExchangeArtifacts from '../artifacts/Exchange.json';
 import {ecSignatureSchema} from '../schemas/ec_signature_schema';
 
 export class ExchangeWrapper extends ContractWrapper {
+    private exchangeContractIfExists?: ExchangeContract;
     constructor(web3Wrapper: Web3Wrapper) {
         super(web3Wrapper);
     }
+    public invalidateContractInstance(): void {
+        delete this.exchangeContractIfExists;
+    }
     public async isValidSignatureAsync(dataHex: string, ecSignature: ECSignature,
                                        signerAddressHex: string): Promise<boolean> {
         assert.isHexString('dataHex', dataHex);
@@ -19,10 +23,9 @@ export class ExchangeWrapper extends ContractWrapper {
         const senderAddressIfExists = await this.web3Wrapper.getSenderAddressIfExistsAsync();
         assert.assert(!_.isUndefined(senderAddressIfExists), ZeroExError.USER_HAS_NO_ASSOCIATED_ADDRESSES);
 
-        const contractInstance = await this.instantiateContractIfExistsAsync((ExchangeArtifacts as any));
-        const exchangeInstance = contractInstance as ExchangeContract;
+        const exchangeContract = await this.getExchangeContractAsync();
 
-        const isValidSignature = await exchangeInstance.isValidSignature.call(
+        const isValidSignature = await exchangeContract.isValidSignature.call(
             signerAddressHex,
             dataHex,
             ecSignature.v,
@@ -34,4 +37,12 @@ export class ExchangeWrapper extends ContractWrapper {
         );
         return isValidSignature;
     }
+    private async getExchangeContractAsync(): Promise<ExchangeContract> {
+        if (!_.isUndefined(this.exchangeContractIfExists)) {
+            return this.exchangeContractIfExists;
+        }
+        const contractInstance = await this.instantiateContractIfExistsAsync((ExchangeArtifacts as any));
+        this.exchangeContractIfExists = contractInstance as ExchangeContract;
+        return this.exchangeContractIfExists;
+    }
 }
diff --git a/src/contract_wrappers/token_registry_wrapper.ts b/src/contract_wrappers/token_registry_wrapper.ts
index 8dd79171e..86bea1c5d 100644
--- a/src/contract_wrappers/token_registry_wrapper.ts
+++ b/src/contract_wrappers/token_registry_wrapper.ts
@@ -6,12 +6,15 @@ import {ContractWrapper} from './contract_wrapper';
 import * as TokenRegistryArtifacts from '../artifacts/TokenRegistry.json';
 
 export class TokenRegistryWrapper extends ContractWrapper {
+    private tokenRegistryContractIfExists?: TokenRegistryContract;
     constructor(web3Wrapper: Web3Wrapper) {
         super(web3Wrapper);
     }
+    public invalidateContractInstance(): void {
+        delete this.tokenRegistryContractIfExists;
+    }
     public async getTokensAsync(): Promise<Token[]> {
-        const contractInstance = await this.instantiateContractIfExistsAsync((TokenRegistryArtifacts as any));
-        const tokenRegistryContract = contractInstance as TokenRegistryContract;
+        const tokenRegistryContract = await this.getTokenRegistryContractAsync();
 
         const addresses = await tokenRegistryContract.getTokenAddresses.call();
         const tokenMetadataPromises: Array<Promise<TokenMetadata>> = _.map(
@@ -30,4 +33,12 @@ export class TokenRegistryWrapper extends ContractWrapper {
         });
         return tokens;
     }
+    private async getTokenRegistryContractAsync(): Promise<TokenRegistryContract> {
+        if (!_.isUndefined(this.tokenRegistryContractIfExists)) {
+            return this.tokenRegistryContractIfExists;
+        }
+        const contractInstance = await this.instantiateContractIfExistsAsync((TokenRegistryArtifacts as any));
+        this.tokenRegistryContractIfExists = contractInstance as TokenRegistryContract;
+        return this.tokenRegistryContractIfExists;
+    }
 }
diff --git a/src/web3_wrapper.ts b/src/web3_wrapper.ts
index a915a89e8..e65f29b56 100644
--- a/src/web3_wrapper.ts
+++ b/src/web3_wrapper.ts
@@ -9,6 +9,9 @@ export class Web3Wrapper {
         this.web3 = new Web3();
         this.web3.setProvider(web3.currentProvider);
     }
+    public setProvider(provider: Web3.Provider) {
+        this.web3.setProvider(provider);
+    }
     public isAddress(address: string): boolean {
         return this.web3.isAddress(address);
     }