Add destructors to all the types that need destructing

hash.rs

@@ -25,6 +25,7 @@ mod libcrypto {
     #[link_args = "-lcrypto"]
     extern {
         fn EVP_MD_CTX_create() -> EVP_MD_CTX;
+        fn EVP_MD_CTX_destroy(ctx: EVP_MD_CTX);
 
         fn EVP_md5() -> EVP_MD;
         fn EVP_sha1() -> EVP_MD;
@@ -96,6 +97,14 @@ impl Hasher {
     }
 }
 
+impl Drop for Hasher {
+    fn drop(&self) {
+        unsafe {
+            libcrypto::EVP_MD_CTX_destroy(self.ctx);
+        }
+    }
+}
+
 /**
  * Hashes the supplied input data using hash t, returning the resulting hash
  * value

pkey.rs

@@ -336,6 +336,14 @@ impl PKey {
     }
 }
 
+impl Drop for PKey {
+    fn drop(&self) {
+        unsafe {
+            libcrypto::EVP_PKEY_free(self.evp);
+        }
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

symm.rs

@@ -16,6 +16,7 @@ pub mod libcrypto {
     #[link_args = "-lcrypto"]
         fn EVP_CIPHER_CTX_new() -> EVP_CIPHER_CTX;
         fn EVP_CIPHER_CTX_set_padding(ctx: EVP_CIPHER_CTX, padding: c_int);
+        fn EVP_CIPHER_CTX_free(ctx: EVP_CIPHER_CTX);
 
         fn EVP_aes_128_ecb() -> EVP_CIPHER;
         fn EVP_aes_128_cbc() -> EVP_CIPHER;
@@ -149,6 +150,14 @@ impl Crypter {
     }
 }
 
+impl Drop for Crypter {
+    fn drop(&self) {
+        unsafe {
+            libcrypto::EVP_CIPHER_CTX_free(self.ctx);
+        }
+    }
+}
+
 /**
  * Encrypts data, using the specified crypter type in encrypt mode with the
  * specified key and iv; returns the resulting (encrypted) data.