Add NBytesHasher custom hasher

libimagref/src/hashers/mod.rs

@@ -0,0 +1 @@
+pub mod nbytes;

libimagref/src/hashers/nbytes.rs

@@ -0,0 +1,52 @@
+use std::io::Read;
+use std::path::PathBuf;
+use std::result::Result as RResult;
+
+use crypto::sha1::Sha1;
+use crypto::digest::Digest;
+
+use libimagerror::into::IntoError;
+
+use hasher::Hasher;
+use result::Result;
+use error::RefErrorKind as REK;
+use error::MapErrInto;
+
+pub struct NBytesHasher {
+    hasher: Sha1,
+    n: usize,
+}
+
+impl NBytesHasher {
+
+    pub fn new(n: usize) -> NBytesHasher {
+        NBytesHasher {
+            hasher: Sha1::new(),
+            n: n,
+        }
+    }
+
+}
+
+impl Hasher for NBytesHasher {
+
+    fn hash_name(&self) -> &'static str {
+        "n-bytes-hasher"
+    }
+
+    fn create_hash<R: Read>(&mut self, _: &PathBuf, contents: &mut R) -> Result<String> {
+        let s = contents
+            .bytes()
+            .take(self.n)
+            .collect::<RResult<Vec<u8>, _>>()
+            .map_err_into(REK::IOError)
+            .and_then(|v| String::from_utf8(v).map_err_into(REK::IOError))
+            .map_err(Box::new)
+            .map_err(|e| REK::UTF8Error.into_error_with_cause(e))
+            .map_err_into(REK::IOError);
+        self.hasher.input_str(&try!(s)[..]);
+        Ok(self.hasher.result_str())
+    }
+
+}
+

libimagref/src/lib.rs

@@ -30,6 +30,7 @@ module_entry_path_mod!("ref", "0.2.0");
 pub mod error;
 pub mod flags;
 pub mod hasher;
+pub mod hashers;
 pub mod lister;
 pub mod reference;
 pub mod result;