tests if key exists in subscriptionMapping when unsubscribing

Author: marcinczenko

ethers/providers/jsonrpc/subscriptions.nim

@@ -252,15 +252,16 @@ method unsubscribe*(subscriptions: PollingSubscriptions,
                   {.async.} =
   subscriptions.logFilters.del(id)
   subscriptions.callbacks.del(id)
-  let sub = subscriptions.subscriptionMapping[id]
-  subscriptions.subscriptionMapping.del(id)
-  try:
-    discard await subscriptions.client.eth_uninstallFilter(sub)
-  except CancelledError as e:
-    raise e
-  except CatchableError:
-    # Ignore if uninstallation of the filter fails. If it's the last step in our
-    # cleanup, then filter changes for this filter will no longer be polled so
-    # if the filter continues to live on in geth for whatever reason then it
-    # doesn't matter.
-    discard
+  if subscriptions.subscriptionMapping.hasKey(id):
+    let sub = subscriptions.subscriptionMapping[id]
+    subscriptions.subscriptionMapping.del(id)
+    try:
+      discard await subscriptions.client.eth_uninstallFilter(sub)
+    except CancelledError as e:
+      raise e
+    except CatchableError:
+      # Ignore if uninstallation of the filter fails. If it's the last step in our
+      # cleanup, then filter changes for this filter will no longer be polled so
+      # if the filter continues to live on in geth for whatever reason then it
+      # doesn't matter.
+      discard

testmodule/providers/jsonrpc/testJsonRpcSubscriptions.nim

@@ -48,6 +48,15 @@ template subscriptionTests(subscriptions, client) =
     discard await client.call("evm_mine", newJArray())
     await sleepAsync(100.millis)
     check count == 0
+  
+  test "unsubscribing from a non-existent subscription does not do any harm":
+    await subscriptions.unsubscribe(newJInt(0))
+  
+  test "duplicate unsubscribe is harmless":
+    proc callback(blck: Block) = discard
+    let subscription = await subscriptions.subscribeBlocks(callback)
+    await subscriptions.unsubscribe(subscription)
+    await subscriptions.unsubscribe(subscription)
 
   test "stops listening to new blocks when provider is closed":
     var count = 0