Tentative fix for the HTTP client connection state assertion failures (#272)

* Tentative fix for the HTTP client connection state assertion failures

I've traced the problem to a HTTP connection being closed while there
are outstanding requests that still go through the motions (the crash
occurs when a requests reaches its `finish` processing step, but it
was already put in a Closed state by the connection that owns it).

* Use distinct error exception instead of cancellation error.

Co-authored-by: cheatfate <eugene.kabanov@status.im>

chronos/apps/http/httpclient.nim

@@ -1073,6 +1073,11 @@ proc finish*(request: HttpClientRequestRef): Future[HttpClientResponseRef] {.
   ## Finish sending request and receive response.
   doAssert(not(isNil(request.connection)),
            "Request missing connection instance")
+  if request.connection.state in {HttpClientConnectionState.Closing,
+                                  HttpClientConnectionState.Closed}:
+    let e = newHttpUseClosedError()
+    request.setError(e)
+    raise e
   doAssert(request.state == HttpReqRespState.Open,
            "Request's state is " & $request.state)
   doAssert(request.connection.state ==

chronos/apps/http/httpcommon.nim

@@ -53,6 +53,7 @@ type
   HttpProtocolError* = object of HttpError
   HttpRedirectError* = object of HttpError
   HttpAddressError* = object of HttpError
+  HttpUseClosedError* = object of HttpError
 
   KeyValueTuple* = tuple
     key: string
@@ -111,6 +112,9 @@ template newHttpReadError*(message: string): ref HttpReadError =
 template newHttpWriteError*(message: string): ref HttpWriteError =
   newException(HttpWriteError, message)
 
+template newHttpUseClosedError*(): ref HttpUseClosedError =
+  newException(HttpUseClosedError, "Connection was already closed")
+
 iterator queryParams*(query: string,
                       flags: set[QueryParamsFlag] = {}): KeyValueTuple {.
          raises: [Defect].} =