From 28b4110593de37e337068079c9ba074a921266a8 Mon Sep 17 00:00:00 2001
From: Tom Deseyn <tom.deseyn@gmail.com>
Date: Sat, 13 Aug 2022 16:02:44 +0200
Subject: [PATCH] Emit channel_write_wontblock when remote window becomes
 non-zero.

Signed-off-by: Tom Deseyn <tom.deseyn@gmail.com>
---
 src/channels.c | 18 +++++++++++++++++-
 src/packet.c   | 25 -------------------------
 2 files changed, 17 insertions(+), 26 deletions(-)

diff --git a/src/channels.c b/src/channels.c
index 7405ea6e4..83b89c96e 100644
--- a/src/channels.c
+++ b/src/channels.c
@@ -512,6 +512,8 @@ SSH_PACKET_CALLBACK(channel_rcv_change_window) {
   ssh_channel channel;
   uint32_t bytes;
   int rc;
+  bool was_empty;
+
   (void)user;
   (void)type;
 
@@ -535,8 +537,21 @@ SSH_PACKET_CALLBACK(channel_rcv_change_window) {
       channel->remote_channel,
       channel->remote_window);
 
+  was_empty = channel->remote_window == 0;
+
   channel->remote_window += bytes;
 
+  /* Writing to the channel is non-blocking until the receive window is empty.
+     When the receive window becomes non-zero again, call channel_write_wontblock_function. */
+  if (was_empty && bytes > 0) {
+    ssh_callbacks_execute_list(channel->callbacks,
+                               ssh_channel_callbacks,
+                               channel_write_wontblock_function,
+                               session,
+                               channel,
+                               channel->remote_window);
+  }
+
   return SSH_PACKET_USED;
 }
 
@@ -1510,7 +1525,7 @@ static int channel_write_common(ssh_channel channel,
           "Remote window is %" PRIu32 " bytes. going to write %" PRIu32 " bytes",
           channel->remote_window,
           len);
-      /* What happens when the channel window is zero? */
+      /* When the window is zero, wait for it to grow */
       if(channel->remote_window == 0) {
           /* nothing can be written */
           SSH_LOG(SSH_LOG_DEBUG,
@@ -1524,6 +1539,7 @@ static int channel_write_common(ssh_channel channel,
             goto out;
           continue;
       }
+      /* When the window is non-zero, accept data up to the window size */
       effectivelen = MIN(len, channel->remote_window);
     } else {
       effectivelen = len;
diff --git a/src/packet.c b/src/packet.c
index 8233d1b7a..eae8563d7 100644
--- a/src/packet.c
+++ b/src/packet.c
@@ -1394,34 +1394,9 @@ error:
     return processed;
 }
 
-static void ssh_packet_socket_controlflow_callback(int code, void *userdata)
-{
-    ssh_session session = userdata;
-    struct ssh_iterator *it;
-    ssh_channel channel;
-
-    if (code == SSH_SOCKET_FLOW_WRITEWONTBLOCK) {
-        SSH_LOG(SSH_LOG_TRACE, "sending channel_write_wontblock callback");
-
-        /* the out pipe is empty so we can forward this to channels */
-        it = ssh_list_get_iterator(session->channels);
-        while (it != NULL) {
-            channel = ssh_iterator_value(ssh_channel, it);
-            ssh_callbacks_execute_list(channel->callbacks,
-                                       ssh_channel_callbacks,
-                                       channel_write_wontblock_function,
-                                       session,
-                                       channel,
-                                       channel->remote_window);
-            it = it->next;
-        }
-    }
-}
-
 void ssh_packet_register_socket_callback(ssh_session session, ssh_socket s){
 	session->socket_callbacks.data=ssh_packet_socket_callback;
 	session->socket_callbacks.connected=NULL;
-    session->socket_callbacks.controlflow = ssh_packet_socket_controlflow_callback;
 	session->socket_callbacks.userdata=session;
 	ssh_socket_set_callbacks(s,&session->socket_callbacks);
 }
-- 
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