digest: raise DigestError for unsupported algorithm name

We generally raise OpenSSL::OpenSSLError or its subclass for errors
originating from the OpenSSL library, which may include extra details
appended by ossl_raise().

Author: rhenium

ext/openssl/ossl_digest.c

@@ -56,8 +56,9 @@ ossl_evp_get_digestbyname(VALUE obj)
 	    md = EVP_get_digestbyobj(oid);
 	    ASN1_OBJECT_free(oid);
 	}
-	if(!md)
-            ossl_raise(rb_eRuntimeError, "Unsupported digest algorithm (%"PRIsVALUE").", obj);
+        if (!md)
+            ossl_raise(eDigestError, "unsupported digest algorithm: %"PRIsVALUE,
+                       obj);
     } else {
         EVP_MD_CTX *ctx;
 

test/openssl/test_digest.rb

@@ -10,6 +10,12 @@ def setup
     @d2 = OpenSSL::Digest::MD5.new
   end
 
+  def test_initialize
+    assert_raise(OpenSSL::Digest::DigestError) {
+      OpenSSL::Digest.new("no such algorithm")
+    }
+  end
+
   def test_digest
     null_hex = "d41d8cd98f00b204e9800998ecf8427e"
     null_bin = [null_hex].pack("H*")