keyfork-frame: bugfix, add try_encode_to, try_encode_from

keyfork-frame/src/asyncext.rs

@@ -15,7 +15,8 @@ pub async fn try_decode_from(
 ) -> Result<Vec<u8>, DecodeError> {
     let len = readable.read_u32().await?;
 
-    let mut data = Vec::with_capacity(len as usize);
+    // Note: Pre-filling the vec is *required* as read_exact uses len, not capacity.
+    let mut data = vec![0u8; len as usize];
     readable.read_exact(&mut data[..]).await?;
 
     let content = verify_checksum(&data[..])?;

keyfork-frame/src/lib.rs

@@ -12,6 +12,8 @@
 //! | checksum: [u8; 32] sha256 hash of `raw_data` | raw_data: &[u8] |
 //! ```
 
+use std::io::{Read, Write};
+
 #[cfg(feature = "async")]
 pub mod asyncext;
 
@@ -51,8 +53,6 @@ pub enum EncodeError {
     Io(#[from] std::io::Error),
 }
 
-const LEN_SIZE: usize = std::mem::size_of::<u32>();
-
 pub(crate) fn hash(data: &[u8]) -> Vec<u8> {
     let mut hashobj = Sha256::new();
     hashobj.update(data);
@@ -65,14 +65,19 @@ pub(crate) fn hash(data: &[u8]) -> Vec<u8> {
 /// An error may be returned if the given `data` is more than [`u32::MAX`] bytes. This is a
 /// constraint on a protocol level.
 pub fn try_encode(data: &[u8]) -> Result<Vec<u8>, EncodeError> {
+    let mut output = vec![];
+    try_encode_to(data, &mut output)?;
+    Ok(output)
+}
+
+pub fn try_encode_to(data: &[u8], writable: &mut impl Write) -> Result<(), EncodeError> {
     let hash = hash(data);
-    let content = hash.iter().chain(data.iter()).copied().collect::<Vec<_>>();
-    let mut result = (u32::try_from(content.len())
-        .map_err(|_| EncodeError::InputTooLarge(content.len()))?)
-    .to_be_bytes()
-    .to_vec();
-    result.extend(content);
-    Ok(result)
+    let len = hash.len() + data.len();
+    let len = u32::try_from(len).map_err(|_| EncodeError::InputTooLarge(len))?;
+    writable.write_all(&len.to_be_bytes())?;
+    writable.write_all(&hash)?;
+    writable.write_all(data)?;
+    Ok(())
 }
 
 pub(crate) fn verify_checksum(data: &[u8]) -> Result<&[u8], DecodeError> {
@@ -99,18 +104,16 @@ pub(crate) fn verify_checksum(data: &[u8]) -> Result<&[u8], DecodeError> {
 /// * The given `data` does not contain the given length's worth of data,
 /// * The given `data` has a checksum that does not match what we build locally.
 pub fn try_decode(data: &[u8]) -> Result<Vec<u8>, DecodeError> {
-    // check length and advance data pointer beyond length check
-    let len_bytes: [u8; LEN_SIZE] = data[..LEN_SIZE]
-        .try_into()
-        .map_err(DecodeError::InvalidLength)?;
-    let len = u32::from_be_bytes(len_bytes);
-    if len as usize + LEN_SIZE > data.len() {
-        return Err(DecodeError::IncorrectLength(data.len() - LEN_SIZE, len));
+    try_decode_from(&mut &data[..])
 }
-    let data = &data[LEN_SIZE..];
-
-    let content = verify_checksum(data)?;
 
+pub fn try_decode_from(readable: &mut impl Read) -> Result<Vec<u8>, DecodeError> {
+    let mut bytes = 0u32.to_be_bytes();
+    readable.read_exact(&mut bytes)?;
+    let len = u32::from_be_bytes(bytes);
+    let mut data = vec![0u8; len as usize];
+    readable.read_exact(&mut data)?;
+    let content = verify_checksum(&data)?;
     Ok(content.to_vec())
 }