feat(jellyfish-api-core): add signMessage RPC (#1934)

**What this PR does / why we need it:** 
/kind feature

**Which issue(s) does this PR fixes?:** 
Adding `signMessage()` from
[Issue#48](#48)

This features allow users to sign an arbitrary message using the private
key of an address.
It requires wallet passphrase to be set with `walletpassphrase` call if
the wallet is encrypted.

**Additional comments?:**
The primary purpose of `signMessage()` is to present a signature to
showcase that the funds are in the control of the private key holder.
The holder may also generate a signature with custom prefixes to
showcase proof of authorisation.

Usage Example: [Here](https://bitcoin.stackexchange.com/a/3339/160)

docs/node/CATEGORIES/05-wallet.md

@@ -397,3 +397,13 @@ interface wallet {
   listWallets (): Promise<string[]>
 }
 ```
+
+## signMessage
+
+Sign a message with the private key of an address. Requires wallet to be unlocked for usage. Use `walletpassphrase` to unlock wallet.
+
+```ts title="client.wallet.signMessage()"
+interface wallet {
+  signMessage (address: string, message: string): Promise<string>
+}
+```

packages/jellyfish-api-core/__tests__/category/wallet/signMessage.test.ts

@@ -0,0 +1,124 @@
+import { MasterNodeRegTestContainer } from '@defichain/testcontainers'
+import { ContainerAdapterClient } from '../../container_adapter_client'
+import { RpcApiError } from '@defichain/jellyfish-api-core'
+import { wallet } from '../../../src'
+
+describe('Sign Message on masternode by unlocking encrpyted wallet', () => {
+  const container = new MasterNodeRegTestContainer()
+  const client = new ContainerAdapterClient(container)
+
+  beforeAll(async () => {
+    await container.start()
+    await client.call('encryptwallet', ['password'], 'number')
+    await client.call('walletpassphrase', ['password', 10000], 'number')
+  })
+
+  afterAll(async () => {
+    await container.stop()
+  })
+
+  it('should throw error if BECH32 address is provided', async () => {
+    // getNewAddress() generates a BECH32 address by default
+    // signMessage() is not compatible with BECH32 address
+    const address = await client.wallet.getNewAddress()
+    const message = 'This is a test message'
+
+    const promise = client.wallet.signMessage(address, message)
+
+    await expect(promise).rejects.toThrow(RpcApiError)
+    await expect(promise).rejects.toMatchObject({
+      payload: {
+        code: -3,
+        message: 'Address does not refer to key',
+        method: 'signmessage'
+      }
+    })
+  })
+
+  it('should throw error if P2SH address is provided', async () => {
+    // signMessage() is not compatible with P2SH address
+    const address = await client.wallet.getNewAddress('', wallet.AddressType.P2SH_SEGWIT)
+    const message = 'This is a test message'
+
+    const promise = client.wallet.signMessage(address, message)
+
+    await expect(promise).rejects.toThrow(RpcApiError)
+    await expect(promise).rejects.toMatchObject({
+      payload: {
+        code: -3,
+        message: 'Address does not refer to key',
+        method: 'signmessage'
+      }
+    })
+  })
+
+  it('should throw error if invalid/no address is provided', async () => {
+    const message = 'This is a test message'
+    const promise = client.wallet.signMessage('', message)
+
+    await expect(promise).rejects.toThrow(RpcApiError)
+    await expect(promise).rejects.toMatchObject({
+      payload: {
+        code: -3,
+        message: 'Invalid address',
+        method: 'signmessage'
+      }
+    })
+  })
+
+  it('should throw error if address provided does not contain private key', async () => {
+    const message = 'This is a test message'
+    const address = 'mpLQjfK79b7CCV4VMJWEWAj5Mpx8Up5zxB'
+    const promise = client.wallet.signMessage(address, message)
+
+    await expect(promise).rejects.toThrow(RpcApiError)
+    await expect(promise).rejects.toMatchObject({
+      payload: {
+        code: -4,
+        message: 'Private key not available',
+        method: 'signmessage'
+      }
+    })
+  })
+
+  it('should be verifiable using verifyMessage()', async () => {
+    // signMessage() is compatible with LEGACY address
+    const address = await client.wallet.getNewAddress('', wallet.AddressType.LEGACY)
+    const message = 'This is a test message'
+
+    const signature = await client.wallet.signMessage(address, message)
+
+    const verify = await client.call('verifymessage', [address, signature, message], 'number')
+    expect(verify).toStrictEqual(true)
+  })
+})
+
+describe('Sign Message on masternode without unlocking encrypted wallet', () => {
+  const container = new MasterNodeRegTestContainer()
+  const client = new ContainerAdapterClient(container)
+
+  beforeAll(async () => {
+    await container.start()
+    await client.call('encryptwallet', ['password'], 'number')
+  })
+
+  afterAll(async () => {
+    await container.stop()
+  })
+
+  it('should throw error even with compatible address', async () => {
+    // signMessage() is compatible with LEGACY address
+    const address = await client.wallet.getNewAddress('LEGACY example', wallet.AddressType.LEGACY)
+    const message = 'This is a test message'
+
+    const promise = client.wallet.signMessage(address, message)
+
+    await expect(promise).rejects.toThrow(RpcApiError)
+    await expect(promise).rejects.toMatchObject({
+      payload: {
+        code: -13,
+        message: 'Error: Please enter the wallet passphrase with walletpassphrase first.'
+      }
+    })
+  })
+})

packages/jellyfish-api-core/src/category/wallet.ts

@@ -324,6 +324,18 @@ export class Wallet {
   async listWallets (): Promise<string[]> {
     return await this.client.call('listwallets', [], 'number')
   }
+
+  /**
+   * Sign a message with the private key of an address
+   * Requires wallet to be unlocked for usage. Use `walletpassphrase` to unlock wallet.
+   *
+   * @param {string} address The DeFi address to use for the private key.
+   * @param {string} message The message to create a signature of.
+   * @return {Promise<string>}
+   */
+  async signMessage (address: string, message: string): Promise<string> {
+    return await this.client.call('signmessage', [address, message], 'number')
+  }
 }
 
 export interface UTXO {