Merge pull request #1872 from near/legacy-keystore

feat: add legacy keystore signer

Author: denbite

.changeset/moody-knives-win.md

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+---
+"near-api-js": minor
+---
+
+Added a signer that knows how to use the legacy keystore

src/signers/legacy_keystore.ts

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+import fs from 'fs';
+import os from 'os';
+import path from 'path';
+import { KeyPair, type KeyPairString } from '../crypto/index.js';
+import { KeyPairSigner } from './key_pair_signer.js';
+
+/**
+ * Signs using local credentials stored in the .near-credentials directory.
+ *
+ * @param accountId - The NEAR account ID for which to load credentials.
+ * @param networkId - The NEAR network ID (e.g., "mainnet", "testnet"). Defaults to "testnet".
+ * @returns A KeyPairSigner instance initialized with the loaded credentials.
+ * @throws Will throw an error if the credentials path or file does not exist, or if the file format is invalid.
+ *
+ * @example
+ * const signer = new LegacyKeyStore("my-account.testnet");
+ * const publicKey = await signer.getPublicKey();
+ * console.log(publicKey.toString());
+ */
+export class LegacyKeyStoreSigner extends KeyPairSigner {
+    constructor(accountId: string, networkId: 'testnet' | 'mainnet' = 'testnet') {
+        const localCredentialsPath = path.join(os.homedir(), '.near-credentials', networkId);
+        if (!fs.existsSync(localCredentialsPath)) {
+            throw new Error(`Credential path does not exist: ${localCredentialsPath}`);
+        }
+
+        const credentialFile = path.join(localCredentialsPath, `${accountId}.json`);
+        if (!fs.existsSync(credentialFile)) {
+            throw new Error(`Credentials not found for ${accountId} at path: ${credentialFile}`);
+        }
+
+        const credentialData = JSON.parse(fs.readFileSync(credentialFile, 'utf-8'));
+        if (!credentialData || !credentialData.private_key) {
+            throw new Error(`Invalid credential file format at: ${credentialFile}`);
+        }
+
+        const keyPair = KeyPair.fromString(credentialData.private_key as KeyPairString);
+        super(keyPair);
+    }
+}