November 2011 - web-devel

"Wiki" section of the Yesod doc site
by Michael Snoyman 13 May '12

13 May '12

Hi everyone, I've added a new section to the Yesod doc site: the wiki[1]. This section is intended to be user-writable, so if you have any content you'd like to submit, please go ahead. In particular, this section contains the "Powered by Yesod" page: please add your sites. Unfortunately, the list from the old wiki was lost when my previous VPS died. (All my databases were backed up, I just forgot to backup the Wiki content as well...) Michael [1] http://www.yesodweb.com/page/wiki

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Advice on implementing a web proxy
by Erik de Castro Lopo 08 Dec '11

08 Dec '11

Hi all, I'm working on a simple web proxy. I have the proxying of HTTP working correctly (as least as far as I have tested it) and would like to work on proxying HTTPS. The way HTTPS proxying works is as follows: a) Client sends "CONNECT host:port HTTP/1.1" to the proxy in clear text. b) Proxy makes a connection to host:port and if successful sends "HTTP/1.0 200 Connection established" to the client. c) The proxy then blindly transfers bytes from the client to the server and bytes from server to the client. d) The client does TLS negotiation over the bi-directional pipe established and maintained by the proxy. The git repo containing the code for my proxy is here: https://github.com/erikd/simple-web-proxy and the core of the actual proxy is here: https://github.com/erikd/simple-web-proxy/blob/master/src/simple-web-proxy.… The proxying function should have a type signature of: sslConnectRequest :: ByteString -> Int -> Wai.Request -> Proxy Wai.Response where the ByteString contains the host name and the Int the port number. My plans for the sslConnectRequest function is for it to open a socket connection to the server and then wrap that socket inside and enumerator. Is that a reasonable plan? Is there a better way? Any existing code that does something similar for me to hack? Clues? Cheers, Erik -- ---------------------------------------------------------------------- Erik de Castro Lopo http://www.mega-nerd.com/

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blaze-textual-native and aeson-native are being deprecated
by Michael Snoyman 28 Nov '11

28 Nov '11

Hi all, In the last Yesod release, we created two new packages: blaze-textual-native and aeson-native. These were direct forks of their source packages, with just two changes: blaze-textual-native did not include a double-conversion dependency, and aeson-native depended on blaze-textual-native instead of blaze-textual. The reason for all this is that there is a GHC bug which prevents C++ code from working correctly with GHCi and Template Haskell[1]. Bryan recently released a new version of blaze-textual which no longer uses double-conversion by default (it's still available with compile-time flags if you want the extra speed and don't need TH/GHCi), and as a result, we are very happy to be deprecating the native siblings. Fortunately, there are not that many packages on Hackage using these libraries; in fact, the only packages for which I'm not a maintainer are dingo-core, dingo-widgets and hledger-web. However, since these are Yesod dependencies, I'm guessing many Yesod users reference aeson-native in their site cabal files. Technically speaking, switching from aeson-native to aeson in a library should constitute a major version bump. However, in this case, I think we want these deprecated packages to die as quickly as possible. So my plan is to switch all of my packages from using aeson-native to aeson some time next week. The result will likely be broken builds for some people; all you'll need to do is edit your cabal file and replace aeson-native with aeson (likewise for blaze-textual). Are there any objections to this course of action, or better ideas on how to handle the situation? Michael [1] Please don't ask me for details, I don't know them. And for all I know, the bug has already be fixed in newer GHCs.

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ANNOUNCE: clientsession-0.7.3.4 (performance enhancement)
by Michael Snoyman 26 Nov '11

26 Nov '11

Hi all, tl;dr: randomIV is now much faster, API is the same, upgrade ASAP to avoid painful slowdowns. Version 0.7 of clientsession brought with it a much enhanced encryption and hashing algorithm, courtesy of Felipe Lessa. Beginning with this version, you now need to provide an Initialization Vector (IV) for encrypting cookies, and these IVs need to be randomly generated. To start off with, we simply used the getIVIO[1] function to generate these values. Recently, some Yesod users reported that version 0.9 of Yesod no longer lived up to previous benchmarks. After some research, I determined that the slowdown came from the call to randomIV in clientsession. The initial fix was simply to disable this call when it wasn't used, but it was still a significant slowdown for most users of Yesod. Over the past few days, Felipe and I put together a significantly more efficient version of randomIV. getIVIO simply opens up /dev/urandom on each request, which involves I/O. As a result, the average run time of the function in our testing was 1.686ms. Instead, our new code initializes with a call to /dev/urandom for the base randomness. It then uses AES encryption to work as a cryptographic random number generator for generating successive IVs. Additionally, every 1000 calls (we'll probably change that number over time), it spawns a new thread to reseed the generator from /dev/urandom again. The result is a function that takes 7.144764 us, aka 236 times faster. Thanks for the initial reporters who commented on the slowdown in Yesod. If you install the newest clientsession and rerun the benchmarks, you should see *significantly* better results. Michael [1] http://hackage.haskell.org/packages/archive/crypto-api/0.8/doc/html/Crypto-…

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reverse proxy
by Kazu Yamamoto 15 Nov '11

15 Nov '11

Hello, I'm implementing a reverse proxy with http-enumerator on Warp. My reverse proxy can rely HTTP headers but I have no idea on how to relay HTTP bodies. I want to know how to specify Network.HTTP.Enumerator.Request.requestBody on WAI. My current code is available from: https://github.com/kazu-yamamoto/wai-app-file-cgi/blob/master/Network/Wai/A… Thanks in advance. --Kazu

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ANN: websockets 0.4.0.0
by Jasper Van der Jeugt 04 Nov '11

04 Nov '11

Hello all, I'm pleased to announce the release of websockets [1] 0.4.0.0 today. You can grab it on Hackage [2]. This update brings an (almost completely rewritten) library which has support for multiple versions of the protocol, meaning you can choose to write backwards-compatible applications, or use the latest and greatest, all using a common API. All feedback is obviously welcome, I'd be glad to hear what you guys think. For the next version, client-side support is planned, so the library user can write clients in addition to servers. If there's any other feature you would like to see, feel free to let me know. [1]: http://jaspervdj.be/websockets/ [2]: http://hackage.haskell.org/package/websockets Cheers, Jasper

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[persistent] [postgres] PoolExhaustedException in Persistent
by Max Cantor 04 Nov '11

04 Nov '11

Hi, I'm getting PoolExhaustedException's on persistent-postgres. I'm on persistent 6 and yesod 9. any ideas where to start looking for a source? my runDB is straight out of the foundation: runDB f = liftIOHandler $ fmap connPool getYesod >>= Settings.runConnectionPool f thanks, max

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[Yesod] Need help resolving this compiler error.
by Michael Litchard 03 Nov '11

03 Nov '11

I'm doing a database action, inside a Form action. I had wanted to do it inside a Handler, as I had figured out how to make it work. But I could not figure out how to pass the data the Form needs from the Handler. Here's the error, followed by the code I am trying to use. >Handler/Manager.hs:68:16: No instance for (PersistBackend (YesodPersistBackend master0) (GGHandler sub0 master0 IO) ) arising from a use of `isFree' Possible fix: add an instance declaration for (PersistBackend (YesodPersistBackend master0) (GGHandler sub0 master0 IO)) In a stmt of a 'do' expression: testFree <- isFree testDay In the expression: do { pInfo <- liftIO getUIdata; let products = V.toList $ V.map productACC $ fst pInfo versions = V.toList $ V.map versionsACC $ snd pInfo ....; testFree <- isFree testDay; (productRes, productView) <- mreq (radioField products) "Placeholder" No thing; .... } In an equation for `productForm': productForm extra = do { pInfo <- liftIO getUIdata; let products = ... ....; testFree <- isFree testDay; .... } >Handler/Manager.hs:68:16: Couldn't match expected type `Control.Monad.Trans.RWS.Lazy.RWST (Maybe (Env, FileEnv), Scheduler, [Yesod.For m.Types.Lang]) Enctype Ints (GGHandler Scheduler Scheduler IO) t0' with actual type `GGHandler sub0 master0 monad0 Bool' In the return type of a call of `isFree' In a stmt of a 'do' expression: testFree <- isFree testDay In the expression: do { pInfo <- liftIO getUIdata; let products = V.toList $ V.map productACC $ fst pInfo versions = V.toList $ V.map versionsACC $ snd pInfo ....; testFree <- isFree testDay; (productRes, productView) <- mreq (radioField products) "Placeholder" Nothing; >postManagerR :: Handler RepHtml postManagerR = do ((res, widget), enctype) <- runFormPost productForm dataInsert <- case (addEntry res) of Left blank -> blank Right result -> result -- let testDay = C.fromGregorian 2011 12 27 -- I would prefer to have the code in the Handler if I could figure out how to get it to the Form? State Monad? -- testFree <- isFree testDay defaultLayout [whamlet| <p>Result:#{show dataInsert} <form enctype=#{enctype}> ^{widget} |] >productForm :: Html -> Form Scheduler Scheduler (FormResult SelectedProduct, Widget) productForm extra = do pInfo <- liftIO getUIdata let products = V.toList $ V.map productACC $ fst pInfo versions = V.toList $ V.map versionsACC $ snd pInfo testDay = C.fromGregorian 2011 12 27 testFree <- isFree testDay (productRes, productView) <- mreq (radioField products) "Placeholder" Nothing versionInfo <- mapM generateVersionSelectFields versions -- (dateRes, dateView) <- mreq requestedDayField "Schedule" Nothing (dateRes, dateView) <- mreq (jqueryDayField def { jdsChangeYear = True , jdsYearRange = "2011:2012" }) "Schedule" Nothing let versionRes = map fst versionInfo versionViews = map snd versionInfo widget = do toWidget [whamlet| #{extra} <p> ^{fvInput productView} $forall versionView <- versionViews ^{fvInput versionView} ^{fvInput dateView} <input type=submit value="Request Test"> |] return (makeSelected productRes versionRes dateRes, widget) >isFree day = do match <- runDB $ selectList [TestStartDate ==. day, TestStatus !=. Passed, TestStatus !=. Failed] [] if (L.null match) then liftIOHandler (return True) else liftIOHandler (return False) I don't think the lack of an instance declaration is the real problem but an indication I am just doing it wrong. What 'it' is, is a mystery to me. ghci tells me this >isFree :: (YesodPersist master, PersistBackend (YesodPersistBackend master) (GGHandler sub master IO), Control.Monad.IO.Class.MonadIO monad) => Day -> GGHandler sub master monad Bool I believe I am using liftIOHandler correctly, I'm not sure what I am doing wrong. What I am sure of is it probably has to do with not understanding Yesod monads well enough. Feedback welcome.

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Persistent and caching
by Konstantin Litvinenko 03 Nov '11

03 Nov '11

Hi All I want to know how to archive db object memory caching like it done in Java Hibernate. Using persistent I can more-less easily CRUD object. My application working with lots of individual objects (most of the time I need to read objects) and I want to have some transparent cache system to lower database pressure. Is there some plans to implement such functionality?

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