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Add Data.ProtoLens.Any for storing arbitrary Messages.
Fixes google#22. Provides simple `pack` and `unpack` functions. Since the `unpack` operation is partial (and has multiple types of "failure"), I wasn't sure how to fit it into a `Lens`; so I left that alone for the time being. I turned this into a minor version bump. It does add a new field to `MessageDescriptor` which usually requires a major bump; but since that field is internal to codegen, it shouldn't break any individual users.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,68 @@ | ||
| {-# LANGUAGE OverloadedStrings #-} | ||
| {-# LANGUAGE ScopedTypeVariables #-} | ||
| module Data.ProtoLens.Any | ||
| ( Any | ||
| , pack | ||
| , packWithPrefix | ||
| , unpack | ||
| , UnpackError(..) | ||
| ) where | ||
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| import Control.Exception (Exception(..)) | ||
| import Data.Monoid ((<>)) | ||
| import Data.Text (Text, breakOnEnd) | ||
| import Data.Typeable (Typeable) | ||
| import Data.ProtoLens | ||
| ( decodeMessage | ||
| , def | ||
| , encodeMessage | ||
| , Message(..) | ||
| , MessageDescriptor(..) | ||
| ) | ||
| import Lens.Family2 ((&), (.~), (^.)) | ||
| import Proto.Google.Protobuf.Any | ||
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| -- | Packs the given message into an 'Any' using the default type URL prefix | ||
| -- "type.googleapis.com". | ||
| pack :: forall a . Message a => a -> Any | ||
| pack = packWithPrefix googleApisPrefix | ||
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| googleApisPrefix :: Text | ||
| googleApisPrefix = "type.googleapis.com" | ||
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| -- | Packs the given message into an 'Any' using the given type URL prefix. | ||
| packWithPrefix :: forall a . Message a => Text -> a -> Any | ||
| packWithPrefix prefix x = | ||
| def & typeUrl .~ (prefix <> "/" <> name) | ||
| & value .~ encodeMessage x | ||
| where | ||
| name = messageName (descriptor :: MessageDescriptor a) | ||
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| data UnpackError | ||
| = DifferentType | ||
| { expectedMessageType :: Text -- ^ The expected @packagename.messagename@ | ||
| , actualUrl :: Text -- ^ The typeUrl in the 'Any' being unpacked | ||
| } | ||
| | DecodingError String -- ^ The error from decodeMessage | ||
| deriving (Show, Eq, Typeable) | ||
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| instance Exception UnpackError | ||
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| -- | Unpacks the given 'Any' into the given message type. Returns 'Nothing' | ||
| -- if the type doesn't match or parsing the payload has failed. | ||
| -- | ||
| -- Ignores the type URL prefix. | ||
| unpack :: forall a . Message a => Any -> Either UnpackError a | ||
| unpack a | ||
| | expectedName /= snd (breakOnEnd "/" $ a ^. typeUrl) | ||
| = Left DifferentType | ||
| { expectedMessageType = expectedName | ||
| , actualUrl = a ^. typeUrl | ||
| } | ||
| | otherwise = case decodeMessage (a ^. value) of | ||
| Left e -> Left $ DecodingError e | ||
| Right x -> Right x | ||
| where | ||
| expectedName = messageName (descriptor :: MessageDescriptor a) |
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