refactor: update digest engine to use Result and Write, add is_supported method

src/digest_engine.rs

@@ -1,15 +1,22 @@
+use anyhow::{anyhow, Context, Result};
 use std::io;
+use std::io::{Read, Write};
 
+use log::*;
+
+use lazy_static::lazy_static;
+
+extern crate enum_map;
+use enum_map::enum_map;
+use enum_map::{Enum, EnumMap};
 
 pub mod none;
-pub mod sha2_digest;
 pub mod program;
+pub mod sha2;
 
 use crate::digest_engine::none::DigestEngineNone;
-use crate::digest_engine::sha2_digest::DigestEngineSha256;
 use crate::digest_engine::program::DigestEngineProgram;
-
-use enum_map::Enum;
+use crate::digest_engine::sha2::DigestEngineSha256;
 
 #[derive(Debug, Eq, PartialEq, Clone, strum::EnumIter, strum::Display, strum::EnumString, Enum)]
 #[strum(ascii_case_insensitive)]
@@ -20,17 +27,29 @@ pub enum DigestType {
 }
 
 pub trait DigestEngine {
-    fn create(&self) -> Box<dyn DigestEngine>;
-    
-    fn update(&mut self, data: &[u8]) -> io::Result<()>;
-    
+    fn is_supported(&self) -> bool {
+        true
+    }
+    fn create(&self) -> Result<Box<dyn Write>>;
     fn finalize(&mut self) -> io::Result<String>;
 }
 
+lazy_static! {
+    pub static ref DIGEST_PROGRAMS: EnumMap<DigestType, Option<DigestEngineProgram>> = enum_map! {
+        DigestType::Sha256 => None,
+        DigestType::Md5 => {
+            let program = DigestEngineProgram::new("bzip2", vec![]);
+            if program.supported { Some(program) } else { None }
+        }
+        DigestType::None => None
+    };
+}
+
+
 pub fn get_engine(digest_type: DigestType) -> Box<dyn DigestEngine> {
     match digest_type {
         DigestType::Sha256 => Box::new(DigestEngineSha256::new()),
-        DigestType::Md5 => Box::new(DigestEngineProgram::new("md5sum")),
+        DigestType::Md5 => Box::new(DigestEngineProgram::new("md5sum", vec![])),
         DigestType::None => Box::new(DigestEngineNone::new()),
     }
 }