Disable OpenSSL engines when building for Android.

Apparently the Android developers dumped OpenSSL's support for hardware
acceleration in order to save some memory, so you can't build programs using
engines on Android.

[Patch revised by nickm]

src/common/crypto.c

@@ -62,6 +62,11 @@
 
 #include <openssl/engine.h>
 
+#ifdef ANDROID
+/* Android's OpenSSL seems to have removed all of its Engine support. */
+#define DISABLE_ENGINES
+#endif
+
 #if OPENSSL_VERSION_NUMBER < 0x00908000l
 /* On OpenSSL versions before 0.9.8, there is no working SHA256
  * implementation, so we use Tom St Denis's nice speedy one, slightly adapted
@@ -174,6 +179,7 @@ crypto_log_errors(int severity, const char *doing)
   }
 }
 
+#ifndef DISABLE_ENGINES
 /** Log any OpenSSL engines we're using at NOTICE. */
 static void
 log_engine(const char *fn, ENGINE *e)
@@ -188,7 +194,9 @@ log_engine(const char *fn, ENGINE *e)
     log(LOG_INFO, LD_CRYPTO, "Using default implementation for %s", fn);
   }
 }
+#endif
 
+#ifndef DISABLE_ENGINES
 /** Try to load an engine in a shared library via fully qualified path.
  */
 static ENGINE *
@@ -206,6 +214,7 @@ try_load_engine(const char *path, const char *engine)
   }
   return e;
 }
+#endif
 
 /** Initialize the crypto library.  Return 0 on success, -1 on failure.
  */
@@ -218,10 +227,17 @@ crypto_global_init(int useAccel, const char *accelName, const char *accelDir)
     _crypto_global_initialized = 1;
     setup_openssl_threading();
     if (useAccel > 0) {
+#ifdef DISABLE_ENGINES
+      (void)accelName;
+      (void)accelDir;
+      log_warn(LD_CRYPTO, "No OpenSSL hardware acceleration support enabled.");
+#else
       ENGINE *e = NULL;
+
       log_info(LD_CRYPTO, "Initializing OpenSSL engine support.");
       ENGINE_load_builtin_engines();
       ENGINE_register_all_complete();
+
       if (accelName) {
         if (accelDir) {
           log_info(LD_CRYPTO, "Trying to load dynamic OpenSSL engine \"%s\""
@@ -251,6 +267,7 @@ crypto_global_init(int useAccel, const char *accelName, const char *accelDir)
       log_engine("SHA1", ENGINE_get_digest_engine(NID_sha1));
       log_engine("3DES", ENGINE_get_cipher_engine(NID_des_ede3_ecb));
       log_engine("AES", ENGINE_get_cipher_engine(NID_aes_128_ecb));
+#endif
     } else {
       log_info(LD_CRYPTO, "NOT using OpenSSL engine support.");
     }
@@ -274,7 +291,11 @@ crypto_global_cleanup(void)
   EVP_cleanup();
   ERR_remove_state(0);
   ERR_free_strings();
+
+#ifndef DISABLE_ENGINES
   ENGINE_cleanup();
+#endif
+
   CONF_modules_unload(1);
   CRYPTO_cleanup_all_ex_data();
 #ifdef TOR_IS_MULTITHREADED