Merge pull request ethereumjs#378 from Agusx1211/master

Add emitFreeLogs option - Used for debugging/coverage

Author: holgerd77

docs/index.md

@@ -54,6 +54,7 @@ VM Class, `new VM(opts)` creates a new VM object
     -   `opts.hardfork` **[String][32]** hardfork rules to be used [default: 'byzantium', supported: 'byzantium' (will throw on unsupported)]
     -   `opts.activatePrecompiles` **[Boolean][34]** create entries in the state tree for the precompiled contracts
     -   `opts.allowUnlimitedContractSize` **[Boolean][34]** allows unlimited contract sizes while debugging. By setting this to `true`, the check for contract size limit of 24KB (see [EIP-170][35]) is bypassed. (default: `false`; ONLY set to `true` during debugging)
+    -   `opts.emitFreeLogs` **[Boolean][34]** Changes the behavior of the LOG opcode, the gas cost of the opcode becomes zero and calling it using STATICCALL won't throw. (default: `false`; ONLY set to `true` during debugging)
 
 ## vm.runBlock
 

lib/index.js

@@ -38,6 +38,7 @@ VM.deps = {
  * @param {String} opts.hardfork hardfork rules to be used [default: 'byzantium', supported: 'byzantium' (will throw on unsupported)]
  * @param {Boolean} opts.activatePrecompiles create entries in the state tree for the precompiled contracts
  * @param {Boolean} opts.allowUnlimitedContractSize allows unlimited contract sizes while debugging. By setting this to `true`, the check for contract size limit of 24KB (see [EIP-170](https://git.io/vxZkK)) is bypassed. (default: `false`; ONLY set to `true` during debugging)
+ * @param {Boolean} opts.emitFreeLogs Changes the behavior of the LOG opcode, the gas cost of the opcode becomes zero and calling it using STATICCALL won't throw. (default: `false`; ONLY set to `true` during debugging)
  */
 function VM (opts = {}) {
   this.opts = opts
@@ -63,6 +64,7 @@ function VM (opts = {}) {
   this.blockchain = opts.blockchain || fakeBlockchain
 
   this.allowUnlimitedContractSize = opts.allowUnlimitedContractSize === undefined ? false : opts.allowUnlimitedContractSize
+  this.emitFreeLogs = opts.emitFreeLogs === undefined ? false : opts.emitFreeLogs
 
   // precompiled contracts
   this._precompiled = {}

lib/opcodes.js

@@ -160,7 +160,7 @@ const codes = {
   0xff: ['SELFDESTRUCT', 5000, 1, 0, false, true]
 }
 
-module.exports = function (op, full) {
+module.exports = function (op, full, freeLogs) {
   var code = codes[op] ? codes[op] : ['INVALID', 0, 0, 0, false, false]
   var opcode = code[0]
 
@@ -182,5 +182,11 @@ module.exports = function (op, full) {
     }
   }
 
+  if (freeLogs) {
+    if (opcode === 'LOG') {
+      code[1] = 0
+    }
+  }
+
   return {name: opcode, opcode: op, fee: code[1], in: code[2], out: code[3], dynamic: code[4], async: code[5]}
 }

lib/runCode.js

@@ -127,7 +127,7 @@ module.exports = function (opts, cb) {
 
   function iterateVm (done) {
     var opCode = runState.code[runState.programCounter]
-    var opInfo = lookupOpInfo(opCode)
+    var opInfo = lookupOpInfo(opCode, false, self.emitFreeLogs)
     var opName = opInfo.name
     var opFn = opFns[opName]
 
@@ -145,7 +145,7 @@ module.exports = function (opts, cb) {
       var eventObj = {
         pc: runState.programCounter,
         gasLeft: runState.gasLeft,
-        opcode: lookupOpInfo(opCode, true),
+        opcode: lookupOpInfo(opCode, true, self.emitFreeLogs),
         stack: runState.stack,
         depth: runState.depth,
         address: runState.address,
@@ -230,6 +230,12 @@ module.exports = function (opts, cb) {
         })
       }
 
+      // if opcode is log and emitFreeLogs is enabled, remove static context
+      let prevStatic = runState.static
+      if (self.emitFreeLogs && opName === 'LOG') {
+        runState.static = false
+      }
+
       try {
         // run the opcode
         var result = opFn.apply(null, args)
@@ -242,6 +248,9 @@ module.exports = function (opts, cb) {
         }
       }
 
+      // restore previous static context
+      runState.static = prevStatic
+
       // save result to the stack
       if (result !== undefined) {
         if (retNum !== 1) {

tests/api/freeLogs.js

@@ -0,0 +1,52 @@
+const tape = require('tape')
+const VM = require('../../lib/index')
+
+/*
+contract Contract1 {
+    event Event();
+    function() external {
+        emit Event();
+    }
+}
+*/
+
+const code = Buffer.from('6080604052348015600f57600080fd5b506040517f57050ab73f6b9ebdd9f76b8d4997793f48cf956e965ee070551b9ca0bb71584e90600090a10000a165627a7a72305820f80265dc41ca5376abe548a02070b68b91119b77dc54c76563b9c19a758cf26f0029', 'hex')
+
+tape('VM with free logs', async (t) => {
+  t.test('should run code without charging for log opcode', async (st) => {
+    const vm = new VM({ emitFreeLogs: true })
+    vm.runCode({
+      code: code,
+      gasLimit: 810
+    }, function (err, val) {
+      st.notOk(err)
+      st.ok(val.runState.gasLeft >= 0x177, 'should expend less gas')
+      st.ok(val.logs.length === 1, 'should emit event')
+      st.end()
+    })
+  })
+  t.test('should emit event on static context', async (st) => {
+    const vm = new VM({ emitFreeLogs: true })
+    vm.runCode({
+      code: code,
+      gasLimit: 24000,
+      static: true
+    }, function (err, val) {
+      st.notOk(err)
+      st.ok(val.logs.length === 1, 'should emit event')
+      st.end()
+    })
+  })
+  t.test('should not emit event on static context if flag is not set', async (st) => {
+    const vm = new VM()
+    vm.runCode({
+      code: code,
+      gasLimit: 24000,
+      static: true
+    }, function (err, val) {
+      st.ok(err)
+      st.ok(val.logs.length === 0, 'should emit zero events')
+      st.end()
+    })
+  })
+})