encoder: add payload position capability

Allows to read the current payload offset from the dedicated payload
input stream. This is required to get the current offset for calculation
of forced boundaries in the proxmox-backup-client, when injecting reused
payload chunks into the payload stream.

Signed-off-by: Christian Ebner <c.ebner@proxmox.com>

src/encoder/aio.rs

@@ -75,6 +75,11 @@ impl<'a, T: SeqWrite + 'a> Encoder<'a, T> {
         })
     }
 
+    /// Get current position for payload stream
+    pub fn payload_position(&self) -> io::Result<PayloadOffset> {
+        self.inner.payload_position()
+    }
+
     // /// Convenience shortcut to add a *regular* file by path including its contents to the archive.
     // pub async fn add_file<P, F>(
     //     &mut self,

src/encoder/mod.rs

@@ -524,6 +524,10 @@ impl<'a, T: SeqWrite + 'a> EncoderImpl<'a, T> {
         Ok(offset)
     }
 
+    pub fn payload_position(&self) -> io::Result<PayloadOffset> {
+        Ok(PayloadOffset(self.state()?.payload_position()))
+    }
+
     /// Encode a payload reference pointing to given offset in the separate payload output
     ///
     /// Returns a file offset usable with `add_hardlink` or with error if the encoder instance has

src/encoder/sync.rs

@@ -97,6 +97,11 @@ impl<'a, T: SeqWrite + 'a> Encoder<'a, T> {
         ))
     }
 
+    /// Get current payload position for payload stream
+    pub fn payload_position(&self) -> io::Result<PayloadOffset> {
+        self.inner.payload_position()
+    }
+
     /// Encode a payload reference pointing to given offset in the separate payload output
     ///
     /// Returns with error if the encoder instance has no separate payload output or encoding