Add olm_session_describe

As a way to dump the state of an olm session, ie. the chain indicies,
so we can debug why olm sessions break and get out of sync.

2 files changed, 35 insertions, 0 deletions

diff --git a/src/olm.cpp b/src/olm.cpp
index d626c84..65e506d 100644
--- a/src/olm.cpp
+++ b/src/olm.cpp
@@ -535,6 +535,12 @@ int olm_session_has_received_message(
     return from_c(session)->received_message;
 }
 
+const char * olm_session_describe(
+    OlmSession * session
+) {
+    return from_c(session)->describe();
+}
+
 size_t olm_matches_inbound_session(
     OlmSession * session,
     void * one_time_key_message, size_t message_length
diff --git a/src/session.cpp b/src/session.cpp
index f1bc5a7..bad19de 100644
--- a/src/session.cpp
+++ b/src/session.cpp
@@ -21,6 +21,7 @@
 #include "olm/pickle.hh"
 
 #include <cstring>
+#include <stdio.h>
 
 namespace {
 
@@ -397,6 +398,34 @@ std::size_t olm::Session::decrypt(
     return result;
 }
 
+const char * olm::Session::describe() {
+    describe_buffer[0] = '\0';
+    char *buf_pos = describe_buffer;
+
+    buf_pos += snprintf(
+        buf_pos, DESCRIBE_BUFFER_LEN - (buf_pos - describe_buffer),
+        "sender chain index: %d ", ratchet.sender_chain[0].chain_key.index
+    );
+
+    buf_pos += snprintf(buf_pos, DESCRIBE_BUFFER_LEN - (buf_pos - describe_buffer), "receiver chain indcies:");
+    for (size_t i = 0; i < ratchet.receiver_chains.size(); ++i) {
+        buf_pos += snprintf(
+            buf_pos, DESCRIBE_BUFFER_LEN - (buf_pos - describe_buffer),
+            " %d", ratchet.receiver_chains[i].chain_key.index
+        );
+    }
+
+    buf_pos += snprintf(buf_pos, DESCRIBE_BUFFER_LEN - (buf_pos - describe_buffer), " skipped message keys:");
+    for (size_t i = 0; i < ratchet.skipped_message_keys.size(); ++i) {
+        buf_pos += snprintf(
+            buf_pos, DESCRIBE_BUFFER_LEN - (buf_pos - describe_buffer),
+            " %d", ratchet.skipped_message_keys[i].message_key.index
+        );
+    }
+
+    return describe_buffer;
+}
+
 namespace {
 // the master branch writes pickle version 1; the logging_enabled branch writes
 // 0x80000001.