refactor: add update method to digest engines for consistent write interface

src/digest_engine/none.rs

@@ -19,4 +19,6 @@ impl DigestEngine for DigestEngineNone {
     fn finalize(&mut self) -> io::Result<String> {
         Ok("none".to_string())
     }
+    
+    fn update(&mut self, _data: &[u8]) {}
 }

src/digest_engine/program.rs

@@ -16,6 +16,7 @@ pub struct DigestEngineProgram {
     pub program: String,
     pub args: Vec<String>,
     pub supported: bool,
+    pub stdin: Option<tokio::io::BufWriter<std::process::ChildStdin>>,
 }
 
 impl DigestEngineProgram {
@@ -26,6 +27,7 @@ impl DigestEngineProgram {
             program: program_path.unwrap_or(program.to_string()),
             args: args.iter().map(|s| s.to_string()).collect(),
             supported,
+            stdin: None,
         }
     }
 }
@@ -34,6 +36,7 @@ impl DigestEngine for DigestEngineProgram {
     fn is_supported(&self) -> bool {
         self.supported
     }
+    
     fn create(&self) -> Result<Box<dyn Write>> {
         debug!("DIGEST: Writting using {:?}", *self);
 
@@ -45,7 +48,7 @@ impl DigestEngine for DigestEngineProgram {
             program, args
         );
 
-        let process = Command::new(program.clone())
+        let mut process = Command::new(program.clone())
             .args(args.clone())
             .stdin(Stdio::piped())
             .stdout(Stdio::piped())
@@ -56,12 +59,26 @@ impl DigestEngine for DigestEngineProgram {
                 args
             ))?;
 
-        Ok(Box::new(process.stdin.unwrap()))
+        let stdin = process.stdin.unwrap();
+        let stdin = tokio::io::BufWriter::new(stdin);
+        
+        Ok(Box::new(Self {
+            program: program.clone(),
+            args: args.clone(),
+            stdin: Some(stdin),
+            supported: self.supported,
+        }))
     }
 
     fn finalize(&mut self) -> io::Result<String> {
         Ok("program".to_string())
     }
+    
+    fn update(&mut self, data: &[u8]) {
+        if let Some(stdin) = &mut self.stdin {
+            let _ = stdin.write(data);
+        }
+    }
 }
 
 fn get_program_path(program: &str) -> Result<String> {

src/digest_engine/sha2.rs

@@ -31,4 +31,8 @@ impl DigestEngine for DigestEngineSha256 {
         let result = self.hasher.clone().finalize();
         Ok(format!("{:x}", result))
     }
+    
+    fn update(&mut self, data: &[u8]) {
+        self.hasher.update(data);
+    }
 }