1 files changed, 108 insertions, 0 deletions
diff --git a/eth/tracers/internal/tracers/prestate_tracer.js b/eth/tracers/internal/tracers/prestate_tracer.js
new file mode 100644
index 0000000..e0a22bf
--- /dev/null
+++ b/eth/tracers/internal/tracers/prestate_tracer.js
@@ -0,0 +1,108 @@
+// Copyright 2017 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+// prestateTracer outputs sufficient information to create a local execution of
+// the transaction from a custom assembled genesis block.
+{
+	// prestate is the genesis that we're building.
+	prestate: null,
+
+	// lookupAccount injects the specified account into the prestate object.
+	lookupAccount: function(addr, db){
+		var acc = toHex(addr);
+		if (this.prestate[acc] === undefined) {
+			this.prestate[acc] = {
+				balance: '0x' + db.getBalance(addr).toString(16),
+				nonce:   db.getNonce(addr),
+				code:    toHex(db.getCode(addr)),
+				storage: {}
+			};
+		}
+	},
+
+	// lookupStorage injects the specified storage entry of the given account into
+	// the prestate object.
+	lookupStorage: function(addr, key, db){
+		var acc = toHex(addr);
+		var idx = toHex(key);
+
+		if (this.prestate[acc].storage[idx] === undefined) {
+			this.prestate[acc].storage[idx] = toHex(db.getState(addr, key));
+		}
+	},
+
+	// result is invoked when all the opcodes have been iterated over and returns
+	// the final result of the tracing.
+	result: function(ctx, db) {
+		// At this point, we need to deduct the 'value' from the
+		// outer transaction, and move it back to the origin
+		this.lookupAccount(ctx.from, db);
+
+		var fromBal = bigInt(this.prestate[toHex(ctx.from)].balance.slice(2), 16);
+		var toBal   = bigInt(this.prestate[toHex(ctx.to)].balance.slice(2), 16);
+
+		this.prestate[toHex(ctx.to)].balance   = '0x'+toBal.subtract(ctx.value).toString(16);
+		this.prestate[toHex(ctx.from)].balance = '0x'+fromBal.add(ctx.value).toString(16);
+
+		// Decrement the caller's nonce, and remove empty create targets
+		this.prestate[toHex(ctx.from)].nonce--;
+		if (ctx.type == 'CREATE') {
+			// We can blibdly delete the contract prestate, as any existing state would
+			// have caused the transaction to be rejected as invalid in the first place.
+			delete this.prestate[toHex(ctx.to)];
+		}
+		// Return the assembled allocations (prestate)
+		return this.prestate;
+	},
+
+	// step is invoked for every opcode that the VM executes.
+	step: function(log, db) {
+		// Add the current account if we just started tracing
+		if (this.prestate === null){
+			this.prestate = {};
+			// Balance will potentially be wrong here, since this will include the value
+			// sent along with the message. We fix that in 'result()'.
+			this.lookupAccount(log.contract.getAddress(), db);
+		}
+		// Whenever new state is accessed, add it to the prestate
+		switch (log.op.toString()) {
+			case "EXTCODECOPY": case "EXTCODESIZE": case "BALANCE":
+				this.lookupAccount(toAddress(log.stack.peek(0).toString(16)), db);
+				break;
+			case "CREATE":
+				var from = log.contract.getAddress();
+				this.lookupAccount(toContract(from, db.getNonce(from)), db);
+				break;
+			case "CREATE2":
+				var from = log.contract.getAddress();
+				// stack: salt, size, offset, endowment
+				var offset = log.stack.peek(1).valueOf()
+				var size = log.stack.peek(2).valueOf()
+				var end = offset + size
+				this.lookupAccount(toContract2(from, log.stack.peek(3).toString(16), log.memory.slice(offset, end)), db);
+				break;
+			case "CALL": case "CALLCODE": case "DELEGATECALL": case "STATICCALL":
+				this.lookupAccount(toAddress(log.stack.peek(1).toString(16)), db);
+				break;
+			case 'SSTORE':case 'SLOAD':
+				this.lookupStorage(log.contract.getAddress(), toWord(log.stack.peek(0).toString(16)), db);
+				break;
+		}
+	},
+
+	// fault is invoked when the actual execution of an opcode fails.
+	fault: function(log, db) {}
+}