Implement functions to get the state of outbound session

We need to be able to inspect an outbound session so that we can tell our peer
how to set up an inbound session.

include/olm/outbound_group_session.h

@@ -90,7 +90,7 @@ size_t olm_init_outbound_group_session_random_length(
 );
 
 /**
- * Start a new outbound group session. Returns std::size_t(-1) on failure. On
+ * Start a new outbound group session. Returns olm_error() 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.
  */
@@ -109,7 +109,7 @@ size_t olm_group_encrypt_message_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
+ * olm_error() on failure. On failure last_error will be set with an
  * error code. The last_error will be OUTPUT_BUFFER_TOO_SMALL if the output
  * buffer is too small.
  */
@@ -119,6 +119,61 @@ size_t olm_group_encrypt(
     uint8_t * message, size_t message_length
 );
 
+
+/**
+ * Get the number of bytes returned by olm_outbound_group_session_id()
+ */
+size_t olm_outbound_group_session_id_length(
+    const OlmOutboundGroupSession *session
+);
+
+/**
+ * Get a base64-encoded identifier for this session.
+ *
+ * Returns the length of the session id on success or olm_error() 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.
+ */
+size_t olm_outbound_group_session_id(
+    OlmOutboundGroupSession *session,
+    uint8_t * id, size_t id_length
+);
+
+/**
+ * Get the current message index for this session.
+ *
+ * Each message is sent with an increasing index; this returns the index for
+ * the next message.
+ */
+uint32_t olm_outbound_group_session_message_index(
+    OlmOutboundGroupSession *session
+);
+
+/**
+ * Get the number of bytes returned by olm_outbound_group_session_key()
+ */
+size_t olm_outbound_group_session_key_length(
+    const OlmOutboundGroupSession *session
+);
+
+/**
+ * Get the base64-encoded current ratchet key for this session.
+ *
+ * Each message is sent with a diffent ratchet key. This function returns the
+ * ratchet key that will be used for the next message.
+ *
+ * Returns the length of the ratchet key on success or olm_error() on
+ * failure. On failure last_error will be set with an error code. The
+ * last_error will be OUTPUT_BUFFER_TOO_SMALL if the buffer was too small.
+ */
+size_t olm_outbound_group_session_key(
+    OlmOutboundGroupSession *session,
+    uint8_t * key, size_t key_length
+);
+
+
+
 #ifdef __cplusplus
 } // extern "C"
 #endif

python/olm/outbound_group_session.py

@@ -34,12 +34,21 @@ outbound_group_session_function(
 
 outbound_group_session_function(lib.olm_init_outbound_group_session_random_length)
 outbound_group_session_function(lib.olm_init_outbound_group_session, c_void_p, c_size_t)
+
+lib.olm_outbound_group_session_message_index.argtypes = [c_void_p]
+lib.olm_outbound_group_session_message_index.restype = c_uint32
+
 outbound_group_session_function(lib.olm_group_encrypt_message_length, c_size_t)
 outbound_group_session_function(lib.olm_group_encrypt,
     c_void_p, c_size_t,  # Plaintext
     c_void_p, c_size_t,  # Message
 )
 
+outbound_group_session_function(lib.olm_outbound_group_session_id_length)
+outbound_group_session_function(lib.olm_outbound_group_session_id, c_void_p, c_size_t)
+outbound_group_session_function(lib.olm_outbound_group_session_key_length)
+outbound_group_session_function(lib.olm_outbound_group_session_key, c_void_p, c_size_t)
+
 
 class OutboundGroupSession(object):
     def __init__(self):
@@ -81,3 +90,18 @@ class OutboundGroupSession(object):
             message_buffer, message_length,
         )
         return message_buffer.raw
+
+    def session_id(self):
+        id_length = lib.olm_outbound_group_session_id_length(self.ptr)
+        id_buffer = create_string_buffer(id_length)
+        lib.olm_outbound_group_session_id(self.ptr, id_buffer, id_length);
+        return id_buffer.raw
+
+    def message_index(self):
+        return lib.olm_outbound_group_session_message_index(self.ptr)
+
+    def session_key(self):
+        key_length = lib.olm_outbound_group_session_key_length(self.ptr)
+        key_buffer = create_string_buffer(key_length)
+        lib.olm_outbound_group_session_key(self.ptr, key_buffer, key_length);
+        return key_buffer.raw

src/outbound_group_session.c

@@ -254,7 +254,52 @@ size_t olm_group_encrypt(
     megolm_advance(&(session->ratchet));
 
     return _olm_encode_base64(
-        message_pos, rawmsglen,
-        message
+        message_pos, rawmsglen, message
+    );
+}
+
+
+size_t olm_outbound_group_session_id_length(
+    const OlmOutboundGroupSession *session
+) {
+    return _olm_encode_base64_length(GROUP_SESSION_ID_LENGTH);
+}
+
+size_t olm_outbound_group_session_id(
+    OlmOutboundGroupSession *session,
+    uint8_t * id, size_t id_length
+) {
+    if (id_length < olm_outbound_group_session_id_length(session)) {
+        session->last_error = OLM_OUTPUT_BUFFER_TOO_SMALL;
+        return (size_t)-1;
+    }
+
+    return _olm_encode_base64(session->session_id, GROUP_SESSION_ID_LENGTH, id);
+}
+
+uint32_t olm_outbound_group_session_message_index(
+    OlmOutboundGroupSession *session
+) {
+    return session->ratchet.counter;
+}
+
+size_t olm_outbound_group_session_key_length(
+    const OlmOutboundGroupSession *session
+) {
+    return _olm_encode_base64_length(MEGOLM_RATCHET_LENGTH);
+}
+
+size_t olm_outbound_group_session_key(
+    OlmOutboundGroupSession *session,
+    uint8_t * key, size_t key_length
+) {
+    if (key_length < olm_outbound_group_session_key_length(session)) {
+        session->last_error = OLM_OUTPUT_BUFFER_TOO_SMALL;
+        return (size_t)-1;
+    }
+
+    return _olm_encode_base64(
+        megolm_get_data(&session->ratchet),
+        MEGOLM_RATCHET_LENGTH, key
     );
 }