I can get a simple http-conduit program to crash or hang fairly often when the connection has occasional data corruption. I've also observed the hang when only simulating packet loss. Here's a repo with my test case. The program is tiny:
module Main where
import Network.HTTP.Conduit
import qualified Data.ByteString.Lazy.Char8 as LC8
main :: IO ()
main = do
man <- newManager tlsManagerSettings
req <- parseUrl "https://s3.amazonaws.com/hackage.fpcomplete.com/package/lens-4.12.3.tar.gz"
response <- httpLbs req man
LC8.putStrLn $ responseBody responseUsing Clumsy in tamper mode set to 20%, it'll crash or hang maybe half the time.
When I instrument API calls with API Monitor I can see that the crashes happen immediately after a call to recv() fails. recv() returns SOCKET_ERROR which is a constant equal to -1. (When it's successful, recv() returns the number of bytes received.) Then memcpy() is called with the length set to -1. This causes the Windows equivalent of a segfault. Somewhere, the return value of recv() isn't getting checked.
The same thing with a cleartext HTTP connection is no problem. I also set up a simple cleartext HTTP server on a Linux machine and injected RSTs with tcpkill. This doesn't make it crash either.
I found this in the course of debugging commercialhaskell/stack#1689 (in the course of getting Idris building on AppVeyor). Stack hasn't ever crashed on me, but it seems likely the hangs and crashes in the simple http-conduit program are related to the hangs in Stack.
To reproduce:
- Clone the testcase repo
stack build- Download Clumsy
- Set Clumsy parameters to something like this and hit start.
stack exec bad-memcpy-crash
You may have to run it several times. When it crashes you should see the Windows crash dialog and if you have Visual Studio installed, an offer to open a debugger.
Let me know if there's more I can do to figure this out.
I can get a simple http-conduit program to crash or hang fairly often when the connection has occasional data corruption. I've also observed the hang when only simulating packet loss. Here's a repo with my test case. The program is tiny:
Using Clumsy in tamper mode set to 20%, it'll crash or hang maybe half the time.
When I instrument API calls with API Monitor I can see that the crashes happen immediately after a call to
recv()fails.recv()returnsSOCKET_ERRORwhich is a constant equal to -1. (When it's successful,recv()returns the number of bytes received.) Thenmemcpy()is called with the length set to -1. This causes the Windows equivalent of a segfault. Somewhere, the return value ofrecv()isn't getting checked.The same thing with a cleartext HTTP connection is no problem. I also set up a simple cleartext HTTP server on a Linux machine and injected RSTs with
tcpkill. This doesn't make it crash either.I found this in the course of debugging commercialhaskell/stack#1689 (in the course of getting Idris building on AppVeyor). Stack hasn't ever crashed on me, but it seems likely the hangs and crashes in the simple http-conduit program are related to the hangs in Stack.
To reproduce:
stack buildstack exec bad-memcpy-crashYou may have to run it several times. When it crashes you should see the Windows crash dialog and if you have Visual Studio installed, an offer to open a debugger.
Let me know if there's more I can do to figure this out.