test: Test for concurrent channel open/close

This reproduces the problem reported in github #321

asyncssh is used to drive the connection for this test.

.github/workflows/build.yml

@@ -250,6 +250,8 @@ jobs:
           # remove old files so we can rerun in-place with "act -r" during test development
           rm -vf ~/.ssh/id_dropbear*
           ~/inst/bin/dropbearkey -t ecdsa -f ~/.ssh/id_dropbear | grep ^ecdsa > ~/.ssh/authorized_keys
+          # Convert to openssh format so that asyncssh can find it in tests
+          ~/inst/bin/dropbearconvert dropbear openssh ~/.ssh/id_dropbear ~/.ssh/id_ecdsa
 
           # to test setting SSH_PUBKEYINFO, replace the trailing comment
           ~/inst/bin/dropbearkey -t ecdsa -f ~/.ssh/id_dropbear_key2 | grep ^ecdsa | sed 's/[^ ]*$/key2 extra/' >> ~/.ssh/authorized_keys

test/requirements.txt

@@ -6,3 +6,4 @@ psutil==6.0.0
 pyparsing==2.4.7
 pytest==8.3.2
 toml==0.10.2
+asyncssh==2.17.0

test/test_concurrent.py

@@ -0,0 +1,34 @@
+"""
+Tests opening and closing several (up to 4) channels concurrently.
+"""
+from test_dropbear import *
+
+import asyncssh
+import asyncio
+import random
+
+async def run(addr, port):
+    async with asyncssh.connect(addr, port = port) as conn:
+
+        chans = []
+        MAX=4
+
+        for x in range(10000):
+            if len(chans) < MAX:
+                pipes = await conn.open_session(command = "df")
+                chans.append(pipes)
+                l = len(chans)
+                print(f" add, len {l}")
+
+            if random.random() < 0.2:
+                i = random.randrange(0, len(chans))
+                l = len(chans)
+                print(f" del {i}/{l}")
+                del chans[i]
+
+def test_concurrent(request, dropbear):
+    opt = request.config.option
+    host = opt.remote or LOCALADDR
+    port = int(opt.port)
+
+    asyncio.run(run(host, port))