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Extend the CORS errors with information about the problematic URLs #2691

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Extend the CORS errors with information about the problematic URLs #2691

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868d0af
Extend the error report with more details
nikita-volkov Feb 2, 2026
033dc25
Use prettyprinter for rendering URLs in CORS error messages
nikita-volkov Feb 2, 2026
7447f48
Reimplement using Prettyprinter
nikita-volkov Feb 2, 2026
1d8694e
Reorg
nikita-volkov Feb 3, 2026
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102 changes: 72 additions & 30 deletions dhall/ghc-src/Dhall/Import/HTTP.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -46,6 +46,8 @@ import qualified Data.Text.Encoding
import qualified Dhall.Util
import qualified Network.HTTP.Client as HTTP
import qualified Network.HTTP.Types
import qualified Prettyprinter
import qualified Prettyprinter.Render.String

mkPrettyHttpException :: String -> HttpException -> PrettyHttpException
mkPrettyHttpException url ex =
Expand Down Expand Up @@ -178,43 +180,83 @@ newManager = do
data NotCORSCompliant = NotCORSCompliant
{ expectedOrigins :: [ByteString]
, actualOrigin :: ByteString
, childURL :: URL
, parentURL :: URL
}

instance Exception NotCORSCompliant

instance Show NotCORSCompliant where
show (NotCORSCompliant {..}) =
Dhall.Util._ERROR <> ": Not CORS compliant\n"
<> "\n"
<> "Dhall supports transitive imports, meaning that an imported expression can\n"
<> "import other expressions. However, a remote import (the \"parent\" import)\n"
<> "cannot import another remote import (the \"child\" import) unless the child\n"
<> "import grants permission to do using CORS. The child import must respond with\n"
<> "an `Access-Control-Allow-Origin` response header that matches the parent\n"
<> "import, otherwise Dhall rejects the import.\n"
<> "\n" <> prologue
render doc
where
prologue =
case expectedOrigins of
[ expectedOrigin ] ->
"The following parent import:\n"
<> "\n"
<> "↳ " <> show actualOrigin <> "\n"
<> "\n"
<> "... did not match the expected origin:\n"
<> "\n"
<> "↳ " <> show expectedOrigin <> "\n"
<> "\n"
<> "... so import resolution failed.\n"
[] ->
"The child response did not include any `Access-Control-Allow-Origin` header,\n"
<> "so import resolution failed.\n"
_:_:_ ->
"The child response included more than one `Access-Control-Allow-Origin` header,\n"
<> "when only one such header should have been present, so import resolution\n"
<> "failed.\n"
<> "\n"
<> "This may indicate that the server for the child import is misconfigured.\n"
render =
Prettyprinter.Render.String.renderString
. Prettyprinter.layoutPretty Prettyprinter.defaultLayoutOptions

doc =
Prettyprinter.vcat
[ Dhall.Util._ERROR <> ": " <> "Not CORS compliant"
, ""
, Prettyprinter.fillSep
[ "Dhall supports transitive imports, meaning that an imported expression can"
, "import other expressions. However, a remote import (the \"parent\" import)"
, "cannot import another remote import (the \"child\" import) unless the child"
, "import grants permission to do using CORS. The child import must respond with"
, "an `Access-Control-Allow-Origin` response header that matches the parent"
, "import, otherwise Dhall rejects the import."
]
, ""
, case expectedOrigins of
[ expectedOrigin ] ->
Prettyprinter.vcat
[ "The following parent import:"
, ""
, "↳ " <> Prettyprinter.pretty parentURL
, ""
, "... did not match the expected origin:"
, ""
, "↳ " <> Prettyprinter.viaShow expectedOrigin
, ""
, "... so import resolution of the following child import failed:"
, ""
, "↳ " <> Prettyprinter.pretty childURL
]
[] ->
Prettyprinter.vcat
[ Prettyprinter.fillSep
[ "The child response did not include any `Access-Control-Allow-Origin` header,"
, "so resolution of the following import failed:"
]
, ""
, "↳ " <> Prettyprinter.pretty parentURL
, ""
, "Child import:"
, ""
, "↳ " <> Prettyprinter.pretty childURL
]
_:_:_ ->
Prettyprinter.vcat
[ Prettyprinter.fillSep
[ "The child response included more than one `Access-Control-Allow-Origin` header,"
, "when only one such header should have been present, so import resolution"
, "failed."
]
, ""
, "This may indicate that the server for the child import is misconfigured."
, ""
, "Parent import:"
, ""
, "↳ " <> Prettyprinter.pretty parentURL
, ""
, "Child import:"
, ""
, "↳ " <> Prettyprinter.pretty childURL
, ""
, "Expected origins:"
, Prettyprinter.vcat (map (\o -> "\n↳ " <> Prettyprinter.viaShow o) expectedOrigins)
]
]

corsCompliant
:: MonadIO io
Expand Down