Give SSHDecode a remaining() instead of pos()

There's only one instance of it currently, and that changed to have the
equivalent of remaining() in 06992a3

src/sshwire.rs

@@ -33,7 +33,7 @@ pub trait SSHSink {
 /// A generic source for a packet, used similarly to `serde::Deserializer`
 pub trait SSHSource<'de> {
     fn take(&mut self, len: usize) -> WireResult<&'de [u8]>;
-    fn pos(&self) -> usize;
+    fn remaining(&self) -> usize;
     fn ctx(&mut self) -> &mut ParseContext;
 }
 
@@ -184,7 +184,6 @@ struct EncodeBytes<'a> {
 }
 
 impl<'a> SSHSink for EncodeBytes<'a> {
-    #[inline]
     fn push(&mut self, v: &[u8]) -> WireResult<()> {
         if v.len() > self.target.len() {
             return Err(WireError::NoRoom);
@@ -235,8 +234,8 @@ impl<'de> SSHSource<'de> for DecodeBytes<'de> {
         Ok(t)
     }
 
-    fn pos(&self) -> usize {
-        usize::MAX - self.input.len()
+    fn remaining(&self) -> usize {
+        self.input.len()
     }
 
     fn ctx(&mut self) -> &mut ParseContext {
@@ -414,23 +413,22 @@ impl<'de, B: SSHDecode<'de>> SSHDecode<'de> for Blob<B> {
     fn dec<S>(s: &mut S) -> WireResult<Self>
     where S: sshwire::SSHSource<'de> {
         let len = u32::dec(s)? as usize;
-        let pos1 = s.pos();
+        let rem1 = s.remaining();
         let inner = SSHDecode::dec(s)?;
-        let pos2 = s.pos();
+        let rem2 = s.remaining();
 
         // Sanity check the length matched
-        let used_len = pos2 - pos1;
+        let used_len = rem1 - rem2;
         if used_len != len {
-            let extra = len.checked_sub(used_len).ok_or(WireError::SSHProto)?;
-
             if s.ctx().seen_unknown {
                 // Skip over unconsumed bytes in the blob.
                 // This can occur with Unknown variants
+                let extra = len.checked_sub(used_len).ok_or(WireError::SSHProto)?;
                 s.take(extra)?;
             } else {
                 trace!("SSH blob length differs. \
-                    Expected {} bytes, got {} bytes {}..{}",
-                    len, used_len, pos1, pos2);
+                    Expected {} bytes, got {} remaining {}, {}",
+                    len, used_len, rem1, rem2);
                 return Err(WireError::SSHProto)
             }
         }