Query local block number using JSON RPC..

so the healthcheck works for both geth and parity

README.md

@@ -1,6 +1,6 @@
 # geth-healthcheck
 
-Little http node.js server to run along the geth node. Returns **503 Service Unavailable** if the last block number on the local node is off by 4 or more blocks from the last block nubmer from Etherscan. Otherwise returns **200 OK**
+Little http node.js server to run along the ethereum node. Node needs to have JSONRPC enabled. Returns **503 Service Unavailable** if the last block number on the local node is off by 4 or more blocks from the last block nubmer from Etherscan. Otherwise returns **200 OK**
 
 ## Installation
 1. Install node.js if needed:

index.js

@@ -7,11 +7,11 @@ const MAX_BLOCK_DIFFERENCE = 3;
 
 const getLocalBlockNum = () => {
   return new Promise((resolve, reject) => {
-    exec('geth --exec eth.blockNumber attach', (error, stdout, stderr) => {
+    exec('curl --data \'{"method":"eth_blockNumber","params":[],"id":1,"jsonrpc":"2.0"}\' -H "Content-Type: application/json" -X POST localhost:8545', (error, stdout, stderr) => {
       if (error) {
         return reject(`${error}`);
       }
-      resolve(parseInt(stdout.trim()));
+      resolve(parseInt(JSON.parse(stdout.trim()).result));
     });
   });
 };