Merge pull request #7097 from paritytech/panic-payload-with-msg

WASM parse payload from panics

ethcore/wasm/src/runtime.rs

@@ -21,6 +21,7 @@ use std::sync::Arc;
 use byteorder::{LittleEndian, ByteOrder};
 
 use vm;
+use panic_payload;
 use parity_wasm::interpreter;
 use wasm_utils::rules;
 use bigint::prelude::U256;
@@ -626,12 +627,26 @@ impl<'a, 'b> Runtime<'a, 'b> {
 	fn user_panic(&mut self, context: InterpreterCallerContext)
 		-> Result<Option<interpreter::RuntimeValue>, InterpreterError>
 	{
-		let msg_len = context.value_stack.pop_as::<i32>()? as u32;
-		let msg_ptr = context.value_stack.pop_as::<i32>()? as u32;
-
-		let msg = String::from_utf8(self.memory.get(msg_ptr, msg_len as usize)?)
-			.map_err(|_| UserTrap::BadUtf8)?;
+		let payload_len = context.value_stack.pop_as::<i32>()? as u32;
+		let payload_ptr = context.value_stack.pop_as::<i32>()? as u32;
 
+		let raw_payload = self.memory.get(payload_ptr, payload_len as usize)?;
+		let payload = panic_payload::decode(&raw_payload);
+		let msg = format!(
+			"{msg}, {file}:{line}:{col}",
+			msg = payload
+				.msg
+				.as_ref()
+				.map(String::as_ref)
+				.unwrap_or("<msg was stripped>"),
+			file = payload
+				.file
+				.as_ref()
+				.map(String::as_ref)
+				.unwrap_or("<unknown>"),
+			line = payload.line.unwrap_or(0),
+			col = payload.col.unwrap_or(0)
+		);
 		trace!(target: "wasm", "Contract custom panic message: {}", msg);
 
 		Err(UserTrap::Panic(msg).into())