Rewrite _olm_cipher_aes_sha_256 initialisation

Replace the init-static-var dance with some preprocessor macros

include/olm/cipher.h

@@ -102,28 +102,33 @@ struct _olm_cipher {
 struct _olm_cipher_aes_sha_256 {
     struct _olm_cipher base_cipher;
 
+    /** context string for the HKDF used for deriving the AES256 key, HMAC key,
+     * and AES IV, from the key material passed to encrypt/decrypt.
+     */
     uint8_t const * kdf_info;
+
+    /** length of context string kdf_info */
     size_t kdf_info_length;
 };
 
+extern const struct _olm_cipher_ops _olm_cipher_aes_sha_256_ops;
 
 /**
- * initialises a cipher type which uses AES256 for encryption and SHA256 for
- * authentication.
+ * get an initializer for an instance of struct _olm_cipher_aes_sha_256.
  *
- * cipher: structure to be initialised
+ * To use it, declare:
  *
- * kdf_info: context string for the HKDF used for deriving the AES256 key, HMAC
- * key, and AES IV, from the key material passed to encrypt/decrypt. Note that
- * this is NOT copied so must have a lifetime at least as long as the cipher
- * instance.
- *
- * kdf_info_length: length of context string kdf_info
+ *   struct _olm_cipher_aes_sha_256 MY_CIPHER =
+ *        OLM_CIPHER_INIT_AES_SHA_256("MY_KDF");
+ *   struct _olm_cipher *cipher = OLM_CIPHER_BASE(&MY_CIPHER);
  */
-struct _olm_cipher *_olm_cipher_aes_sha_256_init(
-    struct _olm_cipher_aes_sha_256 *cipher,
-    uint8_t const * kdf_info,
-    size_t kdf_info_length);
+#define OLM_CIPHER_INIT_AES_SHA_256(KDF_INFO) {     \
+    .base_cipher = { &_olm_cipher_aes_sha_256_ops },\
+    .kdf_info = (uint8_t *)(KDF_INFO),              \
+    .kdf_info_length = sizeof(KDF_INFO) - 1         \
+}
+#define OLM_CIPHER_BASE(CIPHER) \
+    (&((CIPHER)->base_cipher))
 
 
 #ifdef __cplusplus

src/cipher.cpp

@@ -130,25 +130,12 @@ size_t aes_sha_256_cipher_decrypt(
     return plaintext_length;
 }
 
+} // namespace
 
-const _olm_cipher_ops aes_sha_256_cipher_ops = {
+const struct _olm_cipher_ops _olm_cipher_aes_sha_256_ops = {
   aes_sha_256_cipher_mac_length,
   aes_sha_256_cipher_encrypt_ciphertext_length,
   aes_sha_256_cipher_encrypt,
   aes_sha_256_cipher_decrypt_max_plaintext_length,
   aes_sha_256_cipher_decrypt,
 };
-
-} // namespace
-
-
-_olm_cipher *_olm_cipher_aes_sha_256_init(
-    struct _olm_cipher_aes_sha_256 *cipher,
-    uint8_t const * kdf_info,
-    size_t kdf_info_length
-) {
-    cipher->base_cipher.ops = &aes_sha_256_cipher_ops;
-    cipher->kdf_info = kdf_info;
-    cipher->kdf_info_length = kdf_info_length;
-    return &(cipher->base_cipher);
-}

src/olm.cpp

@@ -57,24 +57,13 @@ static std::uint8_t const * from_c(void const * bytes) {
     return reinterpret_cast<std::uint8_t const *>(bytes);
 }
 
-static const std::uint8_t CIPHER_KDF_INFO[] = "Pickle";
-
-const _olm_cipher *get_pickle_cipher() {
-    static _olm_cipher *cipher = NULL;
-    static _olm_cipher_aes_sha_256 PICKLE_CIPHER;
-    if (!cipher) {
-        cipher = _olm_cipher_aes_sha_256_init(
-            &PICKLE_CIPHER,
-            CIPHER_KDF_INFO, sizeof(CIPHER_KDF_INFO) - 1
-        );
-    }
-    return cipher;
-}
+static const struct _olm_cipher_aes_sha_256 PICKLE_CIPHER =
+    OLM_CIPHER_INIT_AES_SHA_256("Pickle");
 
 std::size_t enc_output_length(
     size_t raw_length
 ) {
-    auto *cipher = get_pickle_cipher();
+    auto *cipher = OLM_CIPHER_BASE(&PICKLE_CIPHER);
     std::size_t length = cipher->ops->encrypt_ciphertext_length(cipher, raw_length);
     length += cipher->ops->mac_length(cipher);
     return olm::encode_base64_length(length);
@@ -85,7 +74,7 @@ std::uint8_t * enc_output_pos(
     std::uint8_t * output,
     size_t raw_length
 ) {
-    auto *cipher = get_pickle_cipher();
+    auto *cipher = OLM_CIPHER_BASE(&PICKLE_CIPHER);
     std::size_t length = cipher->ops->encrypt_ciphertext_length(cipher, raw_length);
     length += cipher->ops->mac_length(cipher);
     return output + olm::encode_base64_length(length) - length;
@@ -95,7 +84,7 @@ std::size_t enc_output(
     std::uint8_t const * key, std::size_t key_length,
     std::uint8_t * output, size_t raw_length
 ) {
-    auto *cipher = get_pickle_cipher();
+    auto *cipher = OLM_CIPHER_BASE(&PICKLE_CIPHER);
     std::size_t ciphertext_length = cipher->ops->encrypt_ciphertext_length(
         cipher, raw_length
     );
@@ -124,7 +113,7 @@ std::size_t enc_input(
         return std::size_t(-1);
     }
     olm::decode_base64(input, b64_length, input);
-    auto *cipher = get_pickle_cipher();
+    auto *cipher = OLM_CIPHER_BASE(&PICKLE_CIPHER);
     std::size_t raw_length = enc_length - cipher->ops->mac_length(cipher);
     std::size_t result = cipher->ops->decrypt(
         cipher,

src/session.cpp

@@ -35,22 +35,13 @@ static const olm::KdfInfo OLM_KDF_INFO = {
     RATCHET_KDF_INFO, sizeof(RATCHET_KDF_INFO) - 1
 };
 
-const _olm_cipher *get_cipher() {
-    static _olm_cipher *cipher;
-    static _olm_cipher_aes_sha_256 OLM_CIPHER;
-    if (!cipher) {
-        cipher = _olm_cipher_aes_sha_256_init(
-            &OLM_CIPHER,
-            CIPHER_KDF_INFO, sizeof(CIPHER_KDF_INFO) - 1
-        );
-    }
-    return cipher;
-}
+static const struct _olm_cipher_aes_sha_256 OLM_CIPHER =
+    OLM_CIPHER_INIT_AES_SHA_256(CIPHER_KDF_INFO);
 
 } // namespace
 
 olm::Session::Session(
-) : ratchet(OLM_KDF_INFO, get_cipher()),
+) : ratchet(OLM_KDF_INFO, OLM_CIPHER_BASE(&OLM_CIPHER)),
     last_error(OlmErrorCode::OLM_SUCCESS),
     received_message(false) {
 

tests/test_ratchet.cpp

@@ -28,10 +28,8 @@ olm::KdfInfo kdf_info = {
     ratchet_info, sizeof(ratchet_info) - 1
 };
 
-_olm_cipher_aes_sha_256 cipher0;
-_olm_cipher *cipher = _olm_cipher_aes_sha_256_init(
-    &cipher0, message_info, sizeof(message_info) - 1
-);
+_olm_cipher_aes_sha_256 cipher0 = OLM_CIPHER_INIT_AES_SHA_256(message_info);
+_olm_cipher *cipher = OLM_CIPHER_BASE(&cipher0);
 
 std::uint8_t random_bytes[] = "0123456789ABDEF0123456789ABCDEF";
 olm::Curve25519KeyPair alice_key;