Support EVP_get_digestbyname binding

openssl/src/hash.rs

@@ -1,4 +1,5 @@
 use ffi;
+use std::ffi::CString;
 use std::fmt;
 use std::io;
 use std::io::prelude::*;
@@ -46,6 +47,25 @@ impl MessageDigest {
         }
     }
 
+    /// Returns the `MessageDigest` corresponding to an algorithm name.
+    ///
+    /// This corresponds to [`EVP_get_digestbyname`].
+    ///
+    /// [`EVP_get_digestbyname`]: https://www.openssl.org/docs/man1.1.0/crypto/EVP_DigestInit.html
+    pub fn from_name(name: &str) -> Option<MessageDigest> {
+        #[cfg(not(ossl110))]
+        ffi::init();
+        let name = CString::new(name).ok()?;
+        unsafe {
+            let ptr = ffi::EVP_get_digestbyname(name.as_ptr());
+            if ptr.is_null() {
+                None
+            } else {
+                Some(MessageDigest(ptr))
+            }
+        }
+    }
+
     pub fn null() -> MessageDigest {
         unsafe { MessageDigest(ffi::EVP_md_null()) }
     }
@@ -614,4 +634,12 @@ mod tests {
             MessageDigest::sha256().as_ptr()
         );
     }
+
+    #[test]
+    fn from_name() {
+        assert_eq!(
+            MessageDigest::from_name("SHA256").unwrap().as_ptr(),
+            MessageDigest::sha256().as_ptr()
+        )
+    }
 }