Fix historical event subscriptions when made as first provider request

packages/web3-core-subscriptions/src/subscription.js

@@ -232,9 +232,13 @@ Subscription.prototype.subscribe = function() {
     // get past logs, if fromBlock is available
     if(payload.params[0] === 'logs' && _.isObject(payload.params[1]) && payload.params[1].hasOwnProperty('fromBlock') && isFinite(payload.params[1].fromBlock)) {
         // send the subscription request
+
+        // copy the params to avoid race-condition with deletion below this block
+        var blockParams = Object.assign({}, payload.params[1]);
+
         this.options.requestManager.send({
             method: 'eth_getLogs',
-            params: [payload.params[1]]
+            params: [blockParams]
         }, function (err, logs) {
             if(!err) {
                 logs.forEach(function(log){

test/e2e.contract.events.js

@@ -13,6 +13,7 @@ describe('contract.events [ @E2E ]', function() {
     var accounts;
     var basic;
     var instance;
+    var port;
 
     var basicOptions = {
         data: Basic.bytecode,
@@ -21,7 +22,7 @@ describe('contract.events [ @E2E ]', function() {
     };
 
     beforeEach(async function(){
-        var port = utils.getWebsocketPort();
+        port = utils.getWebsocketPort();
 
         web3 = new Web3('ws://localhost:' + port);
         accounts = await web3.eth.getAccounts();
@@ -73,6 +74,53 @@ describe('contract.events [ @E2E ]', function() {
         });
     });
 
+    // Regression test for a race-condition where a fresh web3 instance
+    // subscribing to past events would have its call parameters deleted while it
+    // made initial Websocket handshake and return an incorrect response.
+    it('can immediately listen for events in the past', async function(){
+        this.timeout(15000);
+
+        const first = await instance
+            .methods
+            .firesEvent(accounts[0], 1)
+            .send({from: accounts[0]});
+
+        const second = await instance
+            .methods
+            .firesEvent(accounts[0], 1)
+            .send({from: accounts[0]});
+
+        // Go forward one block...
+        await utils.mine(web3, accounts[0]);
+        const latestBlock = await web3.eth.getBlockNumber();
+
+        assert(first.blockNumber < latestBlock);
+        assert(second.blockNumber < latestBlock);
+
+        // Re-instantiate web3 & instance to simulate
+        // subscribing to past events as first request
+        web3 = new Web3('ws://localhost:' + port);
+        const newInstance = new web3.eth.Contract(Basic.abi, instance.options.address);
+
+        let counter = 0;
+        await new Promise(async resolve => {
+            newInstance
+                .events
+                .BasicEvent({
+                    fromBlock: 0
+                })
+                .on('data', function(event) {
+                    counter++;
+                    assert(event.blockNumber < latestBlock);
+
+                    if (counter === 2){
+                        this.removeAllListeners();
+                        resolve();
+                    }
+                });
+        });
+    });
+
     it('should not hear the error handler when connection.closed() called', function(){
         this.timeout(15000);