Return encoded length from WriteExt::emit_slice

We would like to add a `emit_varint` function, however doing so requires
that we can get access to the length of a slice when we are encoding it
so we can use `emit_slice` to implement `emit_varint`. It would be
easier to do so if `emit_slice` returned the length of the slice.

In preparation for adding `emit_varint` (and removing the `VarInt` type)
return the encoded length of a slice from `WriteExt::emit_slice`.

(Patch originally written by Steven, cherry-pick and patch description
written by Tobin.)

Co-developed-by: Tobin C. Harding <me@tobin.cc>

bitcoin/src/blockdata/witness.rs

@@ -239,8 +239,7 @@ impl Encodable for Witness {
         let content_with_indices_len = self.content.len();
         let indices_size = self.witness_elements * 4;
         let content_len = content_with_indices_len - indices_size;
-        w.emit_slice(&self.content[..content_len])?;
+        Ok(w.emit_slice(&self.content[..content_len])? + len.size())
-        Ok(content_len + len.size())
     }
 }
 

bitcoin/src/consensus/encode.rs

@@ -209,7 +209,7 @@ pub trait WriteExt: Write {
     fn emit_bool(&mut self, v: bool) -> Result<(), io::Error>;
 
     /// Outputs a byte slice.
-    fn emit_slice(&mut self, v: &[u8]) -> Result<(), io::Error>;
+    fn emit_slice(&mut self, v: &[u8]) -> Result<usize, io::Error>;
 }
 
 /// Extensions of `Read` to decode data as per Bitcoin consensus.
@@ -274,7 +274,10 @@ impl<W: Write + ?Sized> WriteExt for W {
     #[inline]
     fn emit_bool(&mut self, v: bool) -> Result<(), io::Error> { self.write_all(&[v as u8]) }
     #[inline]
-    fn emit_slice(&mut self, v: &[u8]) -> Result<(), io::Error> { self.write_all(v) }
+    fn emit_slice(&mut self, v: &[u8]) -> Result<usize, io::Error> {
+        self.write_all(v)?;
+        Ok(v.len())
+    }
 }
 
 impl<R: Read + ?Sized> ReadExt for R {
@@ -546,8 +549,7 @@ impl Encodable for String {
     fn consensus_encode<W: Write + ?Sized>(&self, w: &mut W) -> Result<usize, io::Error> {
         let b = self.as_bytes();
         let vi_len = VarInt(b.len().to_u64()).consensus_encode(w)?;
-        w.emit_slice(b)?;
+        Ok(vi_len + w.emit_slice(b)?)
-        Ok(vi_len + b.len())
     }
 }
 
@@ -564,8 +566,7 @@ impl Encodable for Cow<'static, str> {
     fn consensus_encode<W: Write + ?Sized>(&self, w: &mut W) -> Result<usize, io::Error> {
         let b = self.as_bytes();
         let vi_len = VarInt(b.len().to_u64()).consensus_encode(w)?;
-        w.emit_slice(b)?;
+        Ok(vi_len + w.emit_slice(b)?)
-        Ok(vi_len + b.len())
     }
 }
 
@@ -586,8 +587,7 @@ macro_rules! impl_array {
                 &self,
                 w: &mut W,
             ) -> core::result::Result<usize, io::Error> {
-                w.emit_slice(&self[..])?;
+                Ok(w.emit_slice(&self[..])?)
-                Ok(self.len())
             }
         }
 
@@ -701,8 +701,7 @@ pub(crate) fn consensus_encode_with_size<W: Write + ?Sized>(
     w: &mut W,
 ) -> Result<usize, io::Error> {
     let vi_len = VarInt(data.len().to_u64()).consensus_encode(w)?;
-    w.emit_slice(data)?;
+    Ok(vi_len + w.emit_slice(data)?)
-    Ok(vi_len + data.len())
 }
 
 struct ReadBytesFromFiniteReaderOpts {
@@ -779,8 +778,7 @@ impl Encodable for CheckedData {
             .expect("network message use u32 as length")
             .consensus_encode(w)?;
         self.checksum().consensus_encode(w)?;
-        w.emit_slice(&self.data)?;
+        Ok(8 + w.emit_slice(&self.data)?)
-        Ok(8 + self.data.len())
     }
 }
 

bitcoin/src/p2p/address.rs

@@ -148,8 +148,7 @@ impl Encodable for AddrV2 {
         ) -> Result<usize, io::Error> {
             let len = network.consensus_encode(w)?
                 + VarInt::from(bytes.len()).consensus_encode(w)?
-                + bytes.len();
+                + w.emit_slice(bytes)?;
-            w.emit_slice(bytes)?;
             Ok(len)
         }
         Ok(match *self {