[Hackage] #448: cabal-install needs new http download component

[Hackage]

#448: cabal-install needs new http download component
----------------------------+-----------------------------------------------
  Reporter:  duncan         |        Owner:         
      Type:  enhancement    |       Status:  new    
  Priority:  normal         |    Milestone:         
 Component:  Cabal library  |      Version:  1.2.3.0
  Severity:  normal         |     Keywords:         
Difficulty:  normal         |   Ghcversion:  6.8.3  
  Platform:                 |  
----------------------------+-----------------------------------------------
 The way in which cabal-install currently uses the HTTP library API is
 quite sub-optimal. It starts a new `Broswer` session for each connection.
 This means that it cannot take advantage of HTTP pipelining, connection
 pooling and other goodies.

 One design would involve making some HTTP download object and making
 requests through that. The download object would start a thread to make
 the actual requests. Requests would be serialised, eg using a `Chan`. It
 probably wants to work by directing URLS be downloaded to local files. On
 top of this we should build some caching mechanism so that we can check
 for example if our package index is up to date before downloading the
 whole thing. It would also be nice to check the length and md5 header to
 catch short or corrupted downloads.

 Something like:

 {{{
 downloader :: Settings -> IO Downloader

 download :: Downloader -> URL -> FilePath -> IO ()
 }}}

 The `download` function is given the URL and the local file path. If the
 local file exists it is taken to be the cached file. It should download
 the URL to a temp file in the target directory and if all successful it
 should atomically rename it over the target file.

 Perhaps error handling needs to be more explicit than just using
 `IOError`s.

-- 
Ticket URL: <http://hackage.haskell.org/trac/hackage/ticket/448>
Hackage <http://haskell.org/cabal/>
Hackage: Cabal and related projects