1 files changed, 76 insertions, 3 deletions

diff --git a/src/message.cpp b/src/message.cpp
index 05f707f..05fe2c7 100644
--- a/src/message.cpp
+++ b/src/message.cpp
@@ -1,4 +1,4 @@
-/* Copyright 2015 OpenMarket Ltd
+/* Copyright 2015-2016 OpenMarket Ltd
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -14,6 +14,8 @@
  */
 #include "olm/message.hh"
 
+#include "olm/memory.hh"
+
 namespace {
 
 template<typename T>
@@ -131,7 +133,7 @@ static std::uint8_t const * decode(
         std::uint8_t const * len_start = pos;
         pos = varint_skip(pos, end);
         std::size_t len = varint_decode<std::size_t>(len_start, pos);
-        if (len > end - pos) return end;
+        if (len > std::size_t(end - pos)) return end;
         value = pos;
         value_length = len;
         pos += len;
@@ -152,7 +154,7 @@ static std::uint8_t const * skip_unknown(
             std::uint8_t const * len_start = pos;
             pos = varint_skip(pos, end);
             std::size_t len = varint_decode<std::size_t>(len_start, pos);
-            if (len > end - pos) return end;
+            if (len > std::size_t(end - pos)) return end;
             pos += len;
         } else {
             return end;
@@ -323,3 +325,74 @@ void olm::decode_one_time_key_message(
         unknown = pos;
     }
 }
+
+
+
+static const std::uint8_t GROUP_MESSAGE_INDEX_TAG = 010;
+static const std::uint8_t GROUP_CIPHERTEXT_TAG = 022;
+
+size_t _olm_encode_group_message_length(
+    uint32_t message_index,
+    size_t ciphertext_length,
+    size_t mac_length,
+    size_t signature_length
+) {
+    size_t length = VERSION_LENGTH;
+    length += 1 + varint_length(message_index);
+    length += 1 + varstring_length(ciphertext_length);
+    length += mac_length;
+    length += signature_length;
+    return length;
+}
+
+
+size_t _olm_encode_group_message(
+    uint8_t version,
+    uint32_t message_index,
+    size_t ciphertext_length,
+    uint8_t *output,
+    uint8_t **ciphertext_ptr
+) {
+    std::uint8_t * pos = output;
+
+    *(pos++) = version;
+    pos = encode(pos, GROUP_MESSAGE_INDEX_TAG, message_index);
+    pos = encode(pos, GROUP_CIPHERTEXT_TAG, *ciphertext_ptr, ciphertext_length);
+    return pos-output;
+}
+
+void _olm_decode_group_message(
+    const uint8_t *input, size_t input_length,
+    size_t mac_length, size_t signature_length,
+    struct _OlmDecodeGroupMessageResults *results
+) {
+    std::uint8_t const * pos = input;
+    std::size_t trailer_length = mac_length + signature_length;
+    std::uint8_t const * end = input + input_length - trailer_length;
+    std::uint8_t const * unknown = nullptr;
+
+    bool has_message_index = false;
+    results->message_index = 0;
+    results->ciphertext = nullptr;
+    results->ciphertext_length = 0;
+
+    if (input_length < trailer_length) return;
+    results->version = *(pos++);
+
+    while (pos != end) {
+        pos = decode(
+            pos, end, GROUP_MESSAGE_INDEX_TAG,
+            results->message_index, has_message_index
+        );
+        pos = decode(
+            pos, end, GROUP_CIPHERTEXT_TAG,
+            results->ciphertext, results->ciphertext_length
+        );
+        if (unknown == pos) {
+            pos = skip_unknown(pos, end);
+        }
+        unknown = pos;
+    }
+
+    results->has_message_index = (int)has_message_index;
+}