Introduce CountedInput. a wrapper which counts the number of bytes …

…successfully read (#630)

* impl

* use u32

* Revert "use u32"

This reverts commit 72bd97c.

* easy impl

* fix tests

* fmt

src/counted_input.rs

@@ -0,0 +1,149 @@
+// Copyright 2017-2024 Parity Technologies
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+/// A wrapper for `Input` which tracks the number fo bytes that are successfully read.
+///
+/// If inner `Input` fails to read, the counter is not incremented.
+///
+/// It can count until `u64::MAX - 1` accurately then saturate.
+pub struct CountedInput<'a, I: crate::Input> {
+	input: &'a mut I,
+	counter: u64,
+}
+
+impl<'a, I: crate::Input> CountedInput<'a, I> {
+	/// Create a new `CountedInput` with the given input.
+	pub fn new(input: &'a mut I) -> Self {
+		Self { input, counter: 0 }
+	}
+
+	/// Get the number of bytes successfully read.
+	pub fn count(&self) -> u64 {
+		self.counter
+	}
+}
+
+impl<I: crate::Input> crate::Input for CountedInput<'_, I> {
+	fn remaining_len(&mut self) -> Result<Option<usize>, crate::Error> {
+		self.input.remaining_len()
+	}
+
+	fn read(&mut self, into: &mut [u8]) -> Result<(), crate::Error> {
+		self.input.read(into).map(|r| {
+			self.counter = self.counter.saturating_add(into.len().try_into().unwrap_or(u64::MAX));
+			r
+		})
+	}
+
+	fn read_byte(&mut self) -> Result<u8, crate::Error> {
+		self.input.read_byte().map(|r| {
+			self.counter = self.counter.saturating_add(1);
+			r
+		})
+	}
+
+	fn ascend_ref(&mut self) {
+		self.input.ascend_ref()
+	}
+
+	fn descend_ref(&mut self) -> Result<(), crate::Error> {
+		self.input.descend_ref()
+	}
+}
+
+#[cfg(test)]
+mod test {
+	use super::*;
+	use crate::Input;
+
+	#[test]
+	fn test_counted_input_input_impl() {
+		let mut input = &[1u8, 2, 3, 4, 5][..];
+		let mut counted_input = CountedInput::new(&mut input);
+
+		assert_eq!(counted_input.remaining_len().unwrap(), Some(5));
+		assert_eq!(counted_input.count(), 0);
+
+		counted_input.read_byte().unwrap();
+
+		assert_eq!(counted_input.remaining_len().unwrap(), Some(4));
+		assert_eq!(counted_input.count(), 1);
+
+		counted_input.read(&mut [0u8; 2][..]).unwrap();
+
+		assert_eq!(counted_input.remaining_len().unwrap(), Some(2));
+		assert_eq!(counted_input.count(), 3);
+
+		counted_input.ascend_ref();
+		counted_input.descend_ref().unwrap();
+
+		counted_input.read(&mut [0u8; 2][..]).unwrap();
+
+		assert_eq!(counted_input.remaining_len().unwrap(), Some(0));
+		assert_eq!(counted_input.count(), 5);
+
+		assert_eq!(counted_input.read_byte(), Err("Not enough data to fill buffer".into()));
+
+		assert_eq!(counted_input.remaining_len().unwrap(), Some(0));
+		assert_eq!(counted_input.count(), 5);
+
+		assert_eq!(
+			counted_input.read(&mut [0u8; 2][..]),
+			Err("Not enough data to fill buffer".into())
+		);
+
+		assert_eq!(counted_input.remaining_len().unwrap(), Some(0));
+		assert_eq!(counted_input.count(), 5);
+	}
+
+	#[test]
+	fn test_counted_input_max_count_read_byte() {
+		let max_exact_count = u64::MAX - 1;
+
+		let mut input = &[0u8; 1000][..];
+		let mut counted_input = CountedInput::new(&mut input);
+
+		counted_input.counter = max_exact_count;
+
+		assert_eq!(counted_input.count(), max_exact_count);
+
+		counted_input.read_byte().unwrap();
+
+		assert_eq!(counted_input.count(), u64::MAX);
+
+		counted_input.read_byte().unwrap();
+
+		assert_eq!(counted_input.count(), u64::MAX);
+	}
+
+	#[test]
+	fn test_counted_input_max_count_read() {
+		let max_exact_count = u64::MAX - 1;
+
+		let mut input = &[0u8; 1000][..];
+		let mut counted_input = CountedInput::new(&mut input);
+
+		counted_input.counter = max_exact_count;
+
+		assert_eq!(counted_input.count(), max_exact_count);
+
+		counted_input.read(&mut [0u8; 2][..]).unwrap();
+
+		assert_eq!(counted_input.count(), u64::MAX);
+
+		counted_input.read(&mut [0u8; 2][..]).unwrap();
+
+		assert_eq!(counted_input.count(), u64::MAX);
+	}
+}

src/lib.rs

@@ -45,6 +45,7 @@ mod codec;
 mod compact;
 #[cfg(feature = "max-encoded-len")]
 mod const_encoded_len;
+mod counted_input;
 mod decode_all;
 mod decode_finished;
 mod depth_limit;
@@ -66,6 +67,7 @@ pub use self::{
 		FullEncode, Input, OptionBool, Output, WrapperTypeDecode, WrapperTypeEncode,
 	},
 	compact::{Compact, CompactAs, CompactLen, CompactRef, HasCompact},
+	counted_input::CountedInput,
 	decode_all::DecodeAll,
 	decode_finished::DecodeFinished,
 	depth_limit::DecodeLimit,