make git-remote-daemon ssh transport robust

* Remote system might be available, and connection get lost. Should
  reconnect, but needs to avoid bad behavior (ie, constant reconnect
  attempts.) Use exponential backoff.

* Detect if old system had a too old git-annex-shell, and show the user
  a nice message in the webapp. Required parsing error messages, so perhaps
  this code shoudl be removed once enough time has passed..

* Switch the protocol to using remote URI's, rather than remote names.
  Names change. Also avoids issues with serialization of names containing
  whitespace.

This is nearly ready for merge into master now. I'd still like to make the ssh
transport smarter about reusing ssh connection caching during git pull.

This commit was sponsored by Jim Paris.
This commit is contained in:
Joey Hess 2014-04-09 14:10:29 -04:00
parent f67d5abc41
commit fb73792f72
6 changed files with 179 additions and 78 deletions

View file

@ -13,60 +13,103 @@ import RemoteDaemon.Common
import Remote.Helper.Ssh
import qualified RemoteDaemon.Transport.Ssh.Types as SshRemote
import Utility.SimpleProtocol
import qualified Git
import Git.Command
import Utility.ThreadScheduler
import Control.Concurrent.Chan
import Control.Concurrent.Async
import System.Process (std_in, std_out)
import System.Process (std_in, std_out, std_err)
transport :: Transport
transport r remotename transporthandle ichan ochan = do
transport r url transporthandle ichan ochan = do
v <- liftAnnex transporthandle $ git_annex_shell r "notifychanges" [] []
case v of
Nothing -> noop
Just (cmd, params) -> go cmd (toCommand params)
Just (cmd, params) -> robustly 1 $
connect cmd (toCommand params)
where
go cmd params = do
(Just toh, Just fromh, _, pid) <- createProcess (proc cmd params)
connect cmd params = do
(Just toh, Just fromh, Just errh, pid) <-
createProcess (proc cmd params)
{ std_in = CreatePipe
, std_out = CreatePipe
, std_err = CreatePipe
}
let shutdown = do
hClose toh
hClose fromh
void $ waitForProcess pid
send DISCONNECTED
-- Run all threads until one finishes and get the status
-- of the first to finish. Cancel the rest.
status <- catchDefaultIO (Right ConnectionClosed) $
handlestderr errh
`race` handlestdout fromh
`race` handlecontrol
let fromshell = forever $ do
l <- hGetLine fromh
case parseMessage l of
Just SshRemote.READY -> send CONNECTED
Just (SshRemote.CHANGED shas) ->
whenM (checkNewShas transporthandle shas) $
fetch
Nothing -> shutdown
send (DISCONNECTED url)
hClose toh
hClose fromh
void $ waitForProcess pid
-- The only control message that matters is STOP.
--
-- Note that a CHANGED control message is not handled;
-- we don't push to the ssh remote. The assistant
-- and git-annex sync both handle pushes, so there's no
-- need to do it here.
let handlecontrol = forever $ do
msg <- readChan ichan
case msg of
STOP -> ioError (userError "done")
_ -> noop
return $ either (either id id) id status
-- Run both threads until one finishes.
void $ tryIO $ concurrently fromshell handlecontrol
shutdown
send msg = writeChan ochan (msg remotename)
send msg = writeChan ochan msg
fetch = do
send SYNCING
send (SYNCING url)
ok <- inLocalRepo transporthandle $
runBool [Param "fetch", Param remotename]
send (DONESYNCING ok)
runBool [Param "fetch", Param $ Git.repoDescribe r]
send (DONESYNCING url ok)
handlestdout fromh = do
l <- hGetLine fromh
case parseMessage l of
Just SshRemote.READY -> do
send (CONNECTED url)
handlestdout fromh
Just (SshRemote.CHANGED shas) -> do
whenM (checkNewShas transporthandle shas) $
fetch
handlestdout fromh
-- avoid reconnect on protocol error
Nothing -> return Stopping
handlecontrol = do
msg <- readChan ichan
case msg of
STOP -> return Stopping
_ -> handlecontrol
-- Old versions of git-annex-shell that do not support
-- the notifychanges command will exit with a not very useful
-- error message. Detect that error, and avoid reconnecting.
-- Propigate all stderr.
handlestderr errh = do
s <- hGetSomeString errh 1024
hPutStr stderr s
hFlush stderr
if "git-annex-shell: git-shell failed" `isInfixOf` s
then do
send $ WARNING url $ unwords
[ "Remote", Git.repoDescribe r
, "needs its git-annex upgraded"
, "to 5.20140405 or newer"
]
return Stopping
else handlestderr errh
data Status = Stopping | ConnectionClosed
{- Make connection robustly, with exponentioal backoff on failure. -}
robustly :: Int -> IO Status -> IO ()
robustly backoff a = handle =<< catchDefaultIO ConnectionClosed a
where
handle Stopping = return ()
handle ConnectionClosed = do
threadDelaySeconds (Seconds backoff)
robustly increasedbackoff a
increasedbackoff
| b2 > maxbackoff = maxbackoff
| otherwise = b2
where
b2 = backoff * 2
maxbackoff = 3600 -- one hour