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Make hackageIndexLayout faster #343

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b94131c
hackageIndexLayout: speed up computation of PackageIdentifier
Bodigrim Jul 10, 2026
2570117
hackageIndexLayout: speed up splitting path into components
Bodigrim Jul 10, 2026
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44 changes: 34 additions & 10 deletions hackage-security/src/Hackage/Security/TUF/Layout/Index.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -10,9 +10,12 @@ module Hackage.Security.TUF.Layout.Index (
) where

import Prelude
import Data.Char (ord)
import Data.Kind (Type)
import Distribution.Package
import Distribution.Text
import Distribution.Types.Version (mkVersion)
import System.FilePath.Posix (isPathSeparator)

import Hackage.Security.TUF.Paths
import Hackage.Security.TUF.Signed
Expand Down Expand Up @@ -91,17 +94,38 @@ hackageIndexLayout = IndexLayout {
fromFragments :: [String] -> IndexPath
fromFragments = rootPath . joinFragments

-- This function is called in a hot loop, take care when modifying it.
-- Especially avoid 'splitFragments' / 'splitDirectories' and other high-level helpers,
-- they are very slow.
fromPath :: IndexPath -> Maybe (Some IndexFile)
fromPath fp = case splitFragments (unrootPath fp) of
[pkg, version, _file] -> do
pkgId <- simpleParse (pkg ++ "-" ++ version)
case takeExtension fp of
".cabal" -> return $ Some $ IndexPkgCabal pkgId
".json" -> return $ Some $ IndexPkgMetadata pkgId
_otherwise -> Nothing
[pkg, "preferred-versions"] ->
Some . IndexPkgPrefs <$> simpleParse pkg
_otherwise -> Nothing
fromPath fp = case break isPathSeparator (toUnrootedFilePath (unrootPath fp)) of
(pkg, "/preferred-versions") ->
return $ Some $ IndexPkgPrefs $ mkPackageName pkg
(pkg, rest) -> case break isPathSeparator (drop 1 rest) of
(_, []) -> Nothing
(version, basename) -> do
let pkgName = mkPackageName pkg
pkgVersion = mkVersion $ readVersion version
pkgId = PackageIdentifier { pkgName, pkgVersion }
case reverse basename of
-- ".cabal" reversed
'l' : 'a' : 'b' : 'a' : 'c' : '.' : _ ->
return $ Some $ IndexPkgCabal pkgId
-- ".json" reversed
'n' : 'o' : 's' : 'j' : '.' : _ ->
return $ Some $ IndexPkgMetadata pkgId
_ -> Nothing
Comment on lines +110 to +117

@fgaz fgaz Jul 11, 2026

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Is this faster than isSuffixOf?

@Bodigrim Bodigrim Jul 11, 2026

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Yes, at least twice faster because you need to check for two extensions. Here is a benchmark:

#!/usr/bin/env cabal
{- cabal:
build-depends: base, deepseq, tasty-bench
default-language: GHC2021
-}

import Control.DeepSeq
import Data.List
import GHC.Generics
import Test.Tasty.Bench

data Extension = Cabal | Json | Other
  deriving (Eq, Show, Generic)

instance NFData Extension

classifyExtensionUsingIsSuffix :: FilePath -> Extension
classifyExtensionUsingIsSuffix xs
  | ".cabal" `isSuffixOf` xs = Cabal
  | ".json" `isSuffixOf` xs = Json
  | otherwise = Other

classifyExtensionUsingReverse :: FilePath -> Extension
classifyExtensionUsingReverse xs = case reverse xs of
  'l' : 'a' : 'b' : 'a' : 'c' : '.' : _ -> Cabal
  'n' : 'o' : 's' : 'j' : '.' : _ -> Json
  _ -> Other

filepaths :: [FilePath]
filepaths = ["cabal-install.cabal", "cabal-install.json"]

main :: IO ()
main = do
  print $ map classifyExtensionUsingIsSuffix filepaths == map classifyExtensionUsingReverse filepaths
  defaultMain
    [ bench "isSuffix-based" $ nf (map classifyExtensionUsingIsSuffix) filepaths
    , bench "reverse-based" $ nf (map classifyExtensionUsingReverse) filepaths
    ]

Results:

True
All
  isSuffix-based: OK
    294  ns ±  26 ns
  reverse-based:  OK
    135  ns ±  13 ns


-- Convert "3.12.1.0" to [3,12,1,0].
-- Copied from hackage-revdeps package.
readVersion :: String -> [Int]
readVersion = (\(acc, _mult, rest) -> acc : rest) . foldr go (0, 1, [])
where
go c (acc, mult, rest)
| fromIntegral d < (10 :: Word) = (acc + d * mult, mult * 10, rest)
| otherwise = (0, 1, acc : rest)
where
d = ord c - ord '0'

{-------------------------------------------------------------------------------
Utility
Expand Down
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