Add test to measure size overhead (#8)

* Don't use parity-wasm directly

* Add test that output size over head of metering

tests/diff.rs

@@ -1,10 +1,9 @@
-use parity_wasm::elements;
 use std::{
 	fs,
 	io::{self, Read, Write},
 	path::{Path, PathBuf},
 };
-use wasm_instrument as instrument;
+use wasm_instrument::{self as instrument, parity_wasm::elements};
 use wasmparser::validate;
 
 fn slurp<P: AsRef<Path>>(path: P) -> io::Result<Vec<u8>> {

tests/overhead.rs

@@ -0,0 +1,73 @@
+use std::{
+	fs::{read, read_dir},
+	path::PathBuf,
+};
+use wasm_instrument::{
+	gas_metering, inject_stack_limiter,
+	parity_wasm::{deserialize_buffer, elements::Module, serialize},
+};
+
+fn fixture_dir() -> PathBuf {
+	let mut path = PathBuf::from(env!("CARGO_MANIFEST_DIR"));
+	path.push("benches");
+	path.push("fixtures");
+	path
+}
+
+/// Print the overhead of applying gas metering, stack height limiting or both.
+///
+/// Use `cargo test print_overhead -- --nocapture`.
+#[test]
+fn print_size_overhead() {
+	let mut results: Vec<_> = read_dir(fixture_dir())
+		.unwrap()
+		.map(|entry| {
+			let entry = entry.unwrap();
+			let (orig_len, orig_module) = {
+				let bytes = read(&entry.path()).unwrap();
+				let len = bytes.len();
+				let module: Module = deserialize_buffer(&bytes).unwrap();
+				(len, module)
+			};
+			let (gas_metering_len, gas_module) = {
+				let module = gas_metering::inject(
+					orig_module.clone(),
+					&gas_metering::ConstantCostRules::default(),
+					"env",
+				)
+				.unwrap();
+				let bytes = serialize(module.clone()).unwrap();
+				let len = bytes.len();
+				(len, module)
+			};
+			let stack_height_len = {
+				let module = inject_stack_limiter(orig_module, 128).unwrap();
+				let bytes = serialize(module).unwrap();
+				bytes.len()
+			};
+			let both_len = {
+				let module = inject_stack_limiter(gas_module, 128).unwrap();
+				let bytes = serialize(module).unwrap();
+				bytes.len()
+			};
+
+			let overhead = both_len * 100 / orig_len;
+
+			(
+				overhead,
+				format!(
+					"{:30}: orig = {:4} kb, gas_metering = {} %, stack_limiter = {} %, both = {} %",
+					entry.file_name().to_str().unwrap(),
+					orig_len / 1024,
+					gas_metering_len * 100 / orig_len,
+					stack_height_len * 100 / orig_len,
+					overhead,
+				),
+			)
+		})
+		.collect();
+	results.sort_unstable_by(|a, b| b.0.cmp(&a.0));
+	for entry in results {
+		println!("{}", entry.1);
+	}
+}