Add a message encoder/decoder

1 files changed, 63 insertions, 0 deletions

diff --git a/include/axolotl/message.hh b/include/axolotl/message.hh
new file mode 100644
index 0000000..85579cf
--- /dev/null
+++ b/include/axolotl/message.hh
@@ -0,0 +1,63 @@
+#include <cstddef>
+#include <cstdint>
+
+
+namespace axolotl {
+
+/**
+ * The length of the buffer needed to hold a message.
+ */
+std::size_t encode_message_length(
+    std::uint32_t counter,
+    std::size_t ratchet_key_length,
+    std::size_t ciphertext_length,
+    std::size_t mac_length
+);
+
+
+struct MessageWriter {
+    std::size_t body_length;
+    std::uint8_t * ratchet_key;
+    std::uint8_t * ciphertext;
+    std::uint8_t * mac;
+};
+
+
+struct MessageReader {
+    std::size_t body_length;
+    std::uint8_t version;
+    std::uint32_t counter;
+    std::size_t ratchet_key_length;
+    std::size_t ciphertext_length;
+    std::size_t mac_length;
+    std::uint8_t const * ratchet_key;
+    std::uint8_t const * ciphertext;
+    std::uint8_t const * mac;
+};
+
+
+/**
+ * Writes the message headers into the output buffer.
+ * Returns a writer struct populated with pointers into the output buffer.
+ */
+MessageWriter encode_message(
+    std::uint8_t version,
+    std::uint32_t counter,
+    std::size_t ratchet_key_length,
+    std::size_t ciphertext_length,
+    std::uint8_t * output
+);
+
+
+/**
+ * Reads the message headers from the input buffer.
+ * Returns a reader struct populated with pointers into the input buffer.
+ * On failure the returned body_length will be 0.
+ */
+MessageReader decode_message(
+    std::uint8_t const * input, std::size_t input_length,
+    std::size_t mac_length
+);
+
+
+} // namespace axolotl