[PATCH] Add request_denied and unimplemented_packet callbacks on server side

[Nicolas Viennot <nicolas@xxxxxxxxxxx>]

When dealing with keepalive packets sent from the server, the clients
reply. Having a callback on that reply allows measuring client latency.
However, clients behave differently:
* libssh sends an unimplemented packet reply to keepalive requests.
* other clients like openssh sends a request denied packet to keepalive
requests.
These callbacks allow the server to measure the latency to the clients when
sending keepalive requests.
---
 include/libssh/callbacks.h | 25 +++++++++++++++++++++++++
 src/channels.c             |  5 +++++
 src/packet.c               |  8 ++++++--
 3 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/include/libssh/callbacks.h b/include/libssh/callbacks.h
index 20c540e..22f8b08 100644
--- a/include/libssh/callbacks.h
+++ b/include/libssh/callbacks.h
@@ -296,6 +296,21 @@ typedef int (*ssh_gssapi_accept_sec_ctx_callback)
(ssh_session session,
 typedef int (*ssh_gssapi_verify_mic_callback) (ssh_session session,
  ssh_string mic, void *mic_buffer, size_t mic_buffer_size, void *userdata);

+/**
+ * @brief Handle a notification from the client that it received an
unimplemented packet.
+ * @param session current session handler
+ * @param seq packet sequence number
+ * @param userdata Userdata to be passed to the callback function.
+ */
+typedef void (*ssh_client_unimplemented_packet_callback) (ssh_session
session, uint32_t seq, void *userdata);
+
+/**
+ * @brief Handle an unhandled client request denied callback.
+ * @param session current session handler
+ * @param userdata Userdata to be passed to the callback function.
+ */
+typedef void (*ssh_client_request_denied_callback) (ssh_session
session, void *userdata);
+

 /**
  * This structure can be used to implement a libssh server, with
appropriate callbacks.
@@ -345,6 +360,16 @@ struct ssh_server_callbacks_struct {
   /* This function will be called when a MIC needs to be verified.
    */
   ssh_gssapi_verify_mic_callback gssapi_verify_mic_function;
+
+  /** This function will be called when the client notifies the server of an
+   * unimplemented packet.
+   */
+  ssh_client_unimplemented_packet_callback
client_unimplemented_packet_function;
+
+  /** This function will be called when the client notifies the server of an
+   * non handled deny of request.
+   */
+  ssh_client_request_denied_callback client_request_denied_function;
 };
 typedef struct ssh_server_callbacks_struct *ssh_server_callbacks;

diff --git a/src/channels.c b/src/channels.c
index ffcb1d5..6a179f9 100644
--- a/src/channels.c
+++ b/src/channels.c
@@ -2039,6 +2039,11 @@ SSH_PACKET_CALLBACK(ssh_request_denied){
   if(session->global_req_state != SSH_CHANNEL_REQ_STATE_PENDING){
     SSH_LOG(SSH_LOG_RARE, "SSH_REQUEST_DENIED received in incorrect state %d",
         session->global_req_state);
+
+    if (ssh_callbacks_exists(session->server_callbacks,
client_request_denied_function)){
+      session->server_callbacks->client_request_denied_function(
+        session, session->server_callbacks->userdata);
+    }
   } else {
     session->global_req_state=SSH_CHANNEL_REQ_STATE_DENIED;
   }
diff --git a/src/packet.c b/src/packet.c
index 7d6957c..7b98811 100644
--- a/src/packet.c
+++ b/src/packet.c
@@ -464,8 +464,7 @@ SSH_PACKET_CALLBACK(ssh_packet_unimplemented){
     uint32_t seq;
     int rc;

-    (void)session; /* unused */
-    (void)type;
+    (void)type; /* unused */
     (void)user;

     rc = ssh_buffer_unpack(packet, "d", &seq);
@@ -477,6 +476,11 @@ SSH_PACKET_CALLBACK(ssh_packet_unimplemented){
     SSH_LOG(SSH_LOG_RARE,
             "Received SSH_MSG_UNIMPLEMENTED (sequence number %d)",seq);

+    if (ssh_callbacks_exists(session->server_callbacks,
client_unimplemented_packet_function)){
+      session->server_callbacks->client_unimplemented_packet_function(
+        session, seq, session->server_callbacks->userdata);
+    }
+
     return SSH_PACKET_USED;
 }

-- 
2.7.1