offchain-gas-oracle: add config check

offchain-gas-oracle/src/config.ts

@@ -16,5 +16,23 @@ export interface Config {
 }
 
 export function readConfig(configPath: string): Config {
-  return JSON.parse(fs.readFileSync(configPath, "utf8"));
+  const config: Config = JSON.parse(fs.readFileSync(configPath, "utf8"));
+  // check that there are no duplicate chainIds or rpcs
+  const chainIds = new Set<number>();
+  const rpcs = new Set<string>();
+  for (const oracleConfig of config.oracles) {
+    // chainId
+    const chainId = oracleConfig.chainId;
+    if (chainIds.has(chainId)) {
+      throw new Error("duplicate chainId found");
+    }
+    chainIds.add(chainId);
+    // rpc
+    const rpc = oracleConfig.rpc;
+    if (rpcs.has(rpc)) {
+      throw new Error("duplicate rpc found");
+    }
+    rpcs.add(rpc);
+  }
+  return config;
 }