[Haskell-cafe] ANN (2 Libs) -- hvac 0.1b, a lightweight web framework and HStringTemplate 0.3

[Sterling Clover]

Probably best not to keep this discussion in -cafe after this, as  
this is more of a debugging-type issue, but in my experience, I bet  
the lighttpd server is trying to serve the hvac-board fcgi file  
directly as a binary, rather than launching it as a fastcgi instance  
at all.  The configurations files I've built have worked fine for me,  
but your milage may vary -- getting fastcgi up and running can be a  
bit of a bear at times. At a minimum, you should make sure that the  
lh.conf file points correctly to your binary in the fastcgi.server  
variable, and that you have all the proper fastcgi libraries  
installed on your system.

Regards,
Sterl

On Jun 3, 2008, at 1:08 PM, Thomas Hartman wrote:

> I just tried out hvac. I was trying to run the hvac examples
> after following the readme in the samples directory.
>
> sudo lighttpd -D -f lh.conf
> [sudo] password for thartman:
> 2008-06-03 09:30:02: (log.c.75) server started
>
> so that's okay, but
>
> http://localhost:3000/hvac-board/board/1
>
> in firefox attempted to open a binary file "1".
>
> Same result for http://localhost:3000/hvac-board
>
> I don't know if this is an hvac issue or a fastcgi issue (seems more
> likely) but any
> advice?
>
> Thomas.
>
> 2008/3/22 Sterling Clover <s.clover at gmail.com>:
>> 1) hvac 0.1b: transactional, declarative framework for lightweight  
>> web
>> applications.
>> 2) HStringTemplate 0.3
>>
>> 1) hvac 0.1b
>>
>> hvac (short for http view and controller) has been my project for  
>> the last
>> little while, and is finally in a fairly usable state, so I'm  
>> opening up the
>> repo (darcs get http://community.haskell.org/~sclv/hvac/) for  
>> folks to play
>> with and to get some feedback. While not quite yet ready for  
>> hackage, the
>> package as provided should be fully cabal installable.  
>> Documentation is
>> available at http://community.haskell.org/~sclv/hvac/html_docs/hvac/
>>
>> The aim of hvac is to provide an environment that makes the  
>> creation of
>> lightweight fastcgi based web applications as simple as possible,  
>> with an
>> emphasis on concise, declarative style code, correct concurrent
>> transactional logic, and transparency in adding caching combinators.
>>
>> There are two included example programs, naturally neither of  
>> which is
>> feature complete. They share a common login module of about 50  
>> lines of
>> code, excluding imports, templates, and database schema.
>>
>> The first program is a classic, greenspun-style message board with  
>> basic
>> login functionality. It totals roughly 40 lines and tends to use  
>> just under
>> 4mb of resident memory on my system.
>>
>> The second is a wiki based on Pandoc and the PandocWiki code. The  
>> code
>> totals roughly 30 lines (rendering borrowed from PandocWiki aside)  
>> and uses
>> about 5mb of memory.
>>
>> hvac processes all requests in the STM monad, with some bells  
>> attached to
>> properly interleave STM with session, database and filesystem  
>> operations
>> such that they all conceptually occur together in a single  
>> transaction per
>> request. Currently it is only fully tested with sqlite, but it should
>> operate, modulo a few tweaks, with any database accessible via HDBC.
>>
>> hvac is particularly designed to use the HStringTemplate library  
>> as an
>> output layer, in a simple declarative fashion. As the  
>> StringTemplate grammar
>> is explicitly sub-turing, this ensures a clean separation of  
>> program logic
>> from presentation, while providing a nonetheless fairly powerful  
>> language to
>> express typical display tasks.
>>
>> The included cache combinators, still experimental, should allow a  
>> simple
>> and fine-grained control over the level of caching of various disk- 
>> bound
>> operations. Phantom types are used to ensure that no functions  
>> that modify
>> state may be cached.
>>
>> To give a flavor of hvac code, the following is the complete  
>> (twenty lines!)
>> source of the wiki controller (due to sql statements, some lines  
>> are rather
>> long):
>>
>> wikiController tmpl =
>>  h |/ "login" *> login_plug tmpl
>>  <|>
>>  (h |/ "wiki" |\\ \pageName ->    h |// "POST" *>
>>          withValidation [ ("contents", return) ]
>>          (\ [contents] -> do
>>             pageId <- selectVal "id from pages where name=?" [toSql
>> pageName]
>>             maybe (addErrors [("Login","must be logged in.")] >>  
>> continue)
>>                (\user -> case fromSql pageId of
>>                            Just (_::Int) ->
>>                              execStat "insert into
>> page_hist(pageId,contents,author) values(?,?,?)" [pageId, toSql  
>> contents,
>> toSql . userName $ user]
>>                            Nothing -> do
>>                              execStat "insert into pages(name,locked)
>> values(?,?)" [toSql pageName, toSql (0::Int)]
>>                              pid <- selectVal "max(id) from pages" []
>>                              execStat "insert into
>> page_hist(pageId,contents,author) values(?,?,?)" [pid, toSql  
>> contents, toSql
>> . userName $ user]) =<< getSes
>>             continue)
>>       <|> do
>>         pageId <- selectVal "id from pages where name=?" [toSql  
>> pageName]
>>         (join $ renderf (tmpl "showPage") ("pageName", pageName)
>>              <$> "pageContents" |= selectRow "* from page_hist where
>> pageId=? order by time desc limit 1" [pageId] ))
>>  <|> (redirect . ( ++ "/wiki/Index") =<< scriptName)
>>
>> Future directions for work on hvac include: Stress testing for  
>> correctness
>> of transactional logic and benchmarks. Exploration of various  
>> efficiency
>> tweaks. Unit tests. Further development of the cache combinator API.
>> Improvement of the example apps and addition of a few others (a  
>> blog maybe).
>> Expansion of the library of validator functions. Exploration of  
>> transferring
>> hvac to the standard FastCGI bindings (currently it uses a custom  
>> modified
>> version to work properly with STM). Improvement of the database  
>> layer,
>> particularly with regards to common paging functions. Creation of  
>> a set of
>> simple combinators for generating CRUD (create read update delete)  
>> pages.
>> Creation of a minimal set of standard templates (maybe).
>>
>> 2) HStringTemplate 0.3.1
>>
>> This release of HStringTemplate (up now at Hackage) fixes a number  
>> of bugs
>> pointed out to me by its small but growing user base (thanks, cinema,
>> elliottt!) ranging from the minor (a particular two-level  
>> iteration pattern
>> wasn't working properly) to the truly irritating (poor handling of  
>> file
>> groups). It's still unfortunately skimpy on the docs, outside of the
>> haddocks and the main StringTemplate grammar documentation at
>> http://www.stringtemplate.org (although the examples from hvac  
>> should also
>> prove helpful). However, it does have a set of very nice and handy  
>> new
>> features for development.
>>
>> * renderf, a function similar in spirit to printf, that takes an  
>> arbitrary
>> number of heterogeneous (String, value) tuples as arguments. This  
>> should cut
>> down considerably on long setAttribute chains. Additionally, with  
>> custom
>> instances (not, I'll grant, trivial to write) it can be used to
>> declaratively chain together strings of attribute retrieval  
>> functions in
>> arbitrary monads, as in the above code example from hvac.
>>
>> * dumpAttribs, a function/template that prints out the tree of the  
>> entire
>> attribute environment a template is operating in -- extremely  
>> handy for
>> development.
>>
>> * nullGroup, also for use in development, a simple way to display  
>> more
>> information about templates that can't be found. Error messages in
>> usafeVolatileDirectoryGroup have also been significantly improved.
>>
>> * getStringTemplate', a version of getStringTemplate guaranteed  
>> not to be
>> inlined. While the optimizer will still sometimes rearrange code  
>> such that a
>> volatile group is not updated properly, this at least helps remedy  
>> the
>> situation (I think).
>>
>> * Some minor changes: For grammar reasons, dots have been removed  
>> from
>> template names -- however, underscores and slashes are now available.
>> Additionally, there's a much improved logic for which aspects of a  
>> local
>> environment are overridden and preserved when a template is called  
>> from
>> another.
>>
>> For both of these libraries, patches, comments, bug reports,  
>> requests, and
>> of course contributions more than welcome!
>>
>> Regards,
>> Sterl._______________________________________________
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