Add docstrings for the Session methods

include/olm/session.hh

@@ -39,8 +39,13 @@ struct Session {
     Curve25519PublicKey alice_base_key;
     Curve25519PublicKey bob_one_time_key;
 
+    /** The number of random bytes that are needed to create a new outbound
+     * session. This will be 64 bytes since two ephemeral keys are needed. */
     std::size_t new_outbound_session_random_length();
 
+    /** Start a new outbound session. Returns std::size_t(-1) on failure. On
+     * failure last_error will be set with an error code. The last_error will be
+     * NOT_ENOUGH_RANDOM if the number of random bytes was too small. */
     std::size_t new_outbound_session(
         Account const & local_account,
         Curve25519PublicKey const & identity_key,
@@ -48,42 +53,79 @@ struct Session {
         std::uint8_t const * random, std::size_t random_length
     );
 
+    /** Start a new inbound session from a pre-key message.
+     * Returns std::size_t(-1) on failure. On failure last_error will be set
+     * with an error code. The last_error will be BAD_MESSAGE_FORMAT if
+     * the message headers could not be decoded. */
     std::size_t new_inbound_session(
         Account & local_account,
         Curve25519PublicKey const * their_identity_key,
-        std::uint8_t const * one_time_key_message, std::size_t message_length
+        std::uint8_t const * pre_key_message, std::size_t message_length
     );
 
+    /** The number of bytes written by session_id() */
     std::size_t session_id_length();
 
+    /** An identifier for this session. Generated by hashing the public keys
+     * used to create the session. Returns the length of the session id on
+     * success or std::size_t(-1) on failure. On failure last_error will be set
+     * with an error code. The last_error will be OUTPUT_BUFFER_TOO_SMALL if
+     * the id buffer was too small. */
     std::size_t session_id(
         std::uint8_t * id, std::size_t id_length
     );
 
+    /** True if this session can be used to decode an inbound pre-key message.
+     * This can be used to test whether a pre-key message should be decoded
+     * with an existing session or if a new session will need to be created.
+     * Returns true if the session is the same. Returns false if either the
+     * session does not match or the pre-key message could not be decoded.
+     */
     bool matches_inbound_session(
         Curve25519PublicKey const * their_identity_key,
-        std::uint8_t const * one_time_key_message, std::size_t message_length
+        std::uint8_t const * pre_key_message, std::size_t message_length
     );
 
+    /** Whether the next message will be a pre-key message or a normal message.
+     * An outbound session will send pre-key messages until it receives a
+     * message with a ratchet key. */
     MessageType encrypt_message_type();
 
     std::size_t encrypt_message_length(
         std::size_t plaintext_length
     );
 
+    /** The number of bytes of random data the encrypt method will need to
+     * encrypt a message. This will be 32 bytes if the session needs to
+     * generate a new ephemeral key, or will be 0 bytes otherwise. */
     std::size_t encrypt_random_length();
 
+    /** Encrypt some plain-text. Returns the length of the encrypted message
+      * or std::size_t(-1) on failure. On failure last_error will be set with
+      * an error code. The last_error will be NOT_ENOUGH_RANDOM if the number
+      * of random bytes is too small. The last_error will be
+      * OUTPUT_BUFFER_TOO_SMALL if the output buffer is too small. */
     std::size_t encrypt(
         std::uint8_t const * plaintext, std::size_t plaintext_length,
         std::uint8_t const * random, std::size_t random_length,
         std::uint8_t * message, std::size_t message_length
     );
 
+    /** An upper bound on the number of bytes of plain-text the decrypt method
+     * will write for a given input message length. */
     std::size_t decrypt_max_plaintext_length(
         MessageType message_type,
         std::uint8_t const * message, std::size_t message_length
     );
 
+    /** Decrypt a message. Returns the length of the decrypted plain-text or
+     * std::size_t(-1) on failure. On failure last_error will be set with an
+     * error code. The last_error will be OUTPUT_BUFFER_TOO_SMALL if the
+     * plain-text buffer is too small. The last_error will be
+     * BAD_MESSAGE_VERSION if the message was encrypted with an unsupported
+     * version of the protocol. The last_error will be BAD_MESSAGE_FORMAT if
+     * the message headers could not be decoded. The last_error will be
+     * BAD_MESSAGE_MAC if the message could not be verified */
     std::size_t decrypt(
         MessageType message_type,
         std::uint8_t const * message, std::size_t message_length,