rebalance: adds a check for no incoming liquidity

rebalance/rebalance.py

@@ -490,12 +490,23 @@ def rebalanceall(plugin: Plugin, min_amount: Millisatoshi = Millisatoshi("50000s
     To be economical, it tries to fix the liquidity cheaper than it can be ruined by transaction forwards.
     It may run for a long time (hours) in the background, but can be stopped with the rebalancestop method.
     """
+    # some early checks before we start the async thread
     if plugin.mutex.locked():
         return {"message": "Rebalance is already running, this may take a while. To stop it use the cli method 'rebalancestop'."}
-    if len(get_open_channels(plugin)) <= 1:
-        return {"message": "Error: Not enough open channels to balance anything"}
+    channels = get_open_channels(plugin)
+    if len(channels) <= 1:
+        return {"message": "Error: Not enough open channels to rebalance anything"}
+    our = sum(ch["to_us_msat"] for ch in channels)
+    total = sum(ch["total_msat"] for ch in channels)
+    min_amount = Millisatoshi(min_amount)
+    if total - our < min_amount or our < min_amount:
+        return {"message": "Error: Not enough liquidity to rebalance anything"}
+
+    # param parsing ensure correct type
     plugin.feeratio = float(feeratio)
-    plugin.min_amount = Millisatoshi(min_amount)
+    plugin.min_amount = min_amount
+
+    # run the job
     t = Thread(target=rebalanceall_thread, args=(plugin, ))
     t.start()
     return {"message": f"Rebalance started with min rebalancable amount: {plugin.min_amount}, feeratio: {plugin.feeratio}"}

rebalance/test_rebalance.py

@@ -85,9 +85,21 @@ def test_rebalance_all(node_factory, bitcoind):
 
     # check we get an error if theres just one channel
     result = l1.rpc.rebalanceall()
-    assert result['message'] == 'Error: Not enough open channels to balance anything'
+    assert result['message'] == 'Error: Not enough open channels to rebalance anything'
 
-    # now we form a circle so we can do rebalanceall
+    # now we add another 100% outgoing liquidity to l1 which does not help
+    l4 = node_factory.get_node()
+    l1.connect(l4)
+    l1.fundchannel(l4)
+
+    # test this is still not possible
+    result = l1.rpc.rebalanceall()
+    assert result['message'] == 'Error: Not enough liquidity to rebalance anything'
+
+    # remove l4 it does not distort further testing
+    l1.rpc.close(l1.get_channel_scid(l4))
+
+    # now we form a circle so we can do actually rebalanceall
     l3.connect(l1)
     l3.fundchannel(l1)