Fields

• repGetRemote :: forall fs typ. Throws SomeRemoteError => AttemptNr -> RemoteFile fs typ -> Verify (Some (HasFormat fs), down typ)

  Get a file from the server

  Responsibilies of repGetRemote:

  • Download the file from the repository and make it available at a temporary location
  • Use the provided file length to protect against endless data attacks. (Repositories such as local repositories that are not susceptible to endless data attacks can safely ignore this argument.)
  • Move the file from its temporary location to its permanent location if verification succeeds.

  NOTE: Calls to repGetRemote should _always_ be in the scope of repWithMirror.

• repGetCached :: CachedFile -> IO (Maybe (Path Absolute))

  Get a cached file (if available)

• repGetCachedRoot :: IO (Path Absolute)

  Get the cached root

  This is a separate method only because clients must ALWAYS have root information available.

• repClearCache :: IO ()

  Clear all cached data

  In particular, this should remove the snapshot and the timestamp. It would also be okay, but not required, to delete the index.

• repWithIndex :: forall a. (Handle -> IO a) -> IO a

  Open the tarball for reading

  This function has this shape so that:

  • We can read multiple files from the tarball without having to open and close the handle each time
  • We can close the handle immediately when done.
• repGetIndexIdx :: IO TarIndex

  Read the index index

• repLockCache :: IO () -> IO ()

  Lock the cache (during updates)

• repWithMirror :: forall a. Maybe [Mirror] -> IO a -> IO a

  Mirror selection

  The purpose of repWithMirror is to scope mirror selection. The idea is that if we have

  repWithMirror mirrorList $
    someCallback

  then the repository may pick a mirror before calling someCallback, catch exceptions thrown by someCallback, and potentially try the callback again with a different mirror.

  The list of mirrors may be Nothing if we haven't yet downloaded the list of mirrors from the repository, or when our cached list of mirrors is invalid. Of course, if we did download it, then the list of mirrors may still be empty. In this case the repository must fall back to its primary download mechanism.

  Mirrors as currently defined (in terms of a "base URL") are inherently a HTTP (or related) concept, so in repository implementations such as the local-repo repWithMirrors is probably just an identity operation (see ignoreMirrors). Conversely, HTTP implementations of repositories may have other, out-of-band information (for example, coming from a cabal config file) that they may use to influence mirror selection.

• repLog :: LogMessage -> IO ()

  Logging

• repLayout :: RepoLayout

  Layout of this repository

• repIndexLayout :: IndexLayout

  Layout of the index

  Since the repository hosts the index, the layout of the index is not independent of the layout of the repository.

• repDescription :: String

  Description of the repository (used in the show instance)