| Safe Haskell | None |
|---|---|
| Language | Haskell2010 |
Data.ProtoLens.JSONPB
Contents
Synopsis
- class FromJSONPB a where
- parseJSONPB :: Value -> Parser a
- class ToJSONPB a where
- (.:) :: (FromJSONPB a, FieldDefault a) => Object -> Text -> Parser a
- (.=) :: (ToJSONPB v, KeyValuePB kvp, FieldDefault v, Eq v) => Text -> v -> Options -> kvp
- data Options = Options {}
- defaultOptions :: Options
- eitherDecode :: FromJSONPB a => ByteString -> Either String a
- encode :: ToJSONPB a => Options -> a -> ByteString
- object :: [Options -> [Pair]] -> Options -> Value
- pair :: (KeyValuePB m, ToJSONPB v) => Text -> v -> Options -> m
- pairs :: [Options -> Series] -> Options -> Encoding
- parseField :: FromJSONPB a => Object -> Text -> Parser a
- toAesonEncoding :: ToJSONPB a => a -> Encoding
- toAesonValue :: ToJSONPB a => a -> Value
- data Value
- class ToJSON a where
- toJSON :: a -> Value
- toEncoding :: a -> Encoding
- toJSONList :: [a] -> Value
- toEncodingList :: [a] -> Encoding
- class FromJSON a where
- typeMismatch :: String -> Value -> Parser a
- withObject :: String -> (Object -> Parser a) -> Value -> Parser a
Typeclasses
class FromJSONPB a where Source #
Instances
class ToJSONPB a where Source #
Minimal complete definition
Methods
toJSONPB :: a -> Options -> Value Source #
toJSON variant for JSONPB encoders.
toEncodingPB :: a -> Options -> Encoding Source #
toEncoding variant for JSONPB encoders. If an implementation is not
provided, uses toJSONPB (which is less efficient since it indirects
through the Value IR).
Instances
| ToJSONPB Bool Source # | |
| ToJSONPB Double Source # | |
| ToJSONPB Float Source # | |
| ToJSONPB Int32 Source # | |
| ToJSONPB Int64 Source # | |
| ToJSONPB Word32 Source # | |
| ToJSONPB Word64 Source # | |
| ToJSONPB ByteString Source # | |
Defined in Data.ProtoLens.JSONPB.Class Methods toJSONPB :: ByteString -> Options -> Value Source # toEncodingPB :: ByteString -> Options -> Encoding Source # | |
| ToJSONPB Text Source # | |
| ToJSONPB Text Source # | |
| ToJSONPB a => ToJSONPB [a] Source # | |
| ToJSONPB a => ToJSONPB (Maybe a) Source # | |
| ToJSONPB a => ToJSONPB (Vector a) Source # | |
Operators
(.:) :: (FromJSONPB a, FieldDefault a) => Object -> Text -> Parser a Source #
.: variant for JSONPB; if the given key is missing from the
object, or if it is present but its value is null, we produce the default
protobuf value for the field type
(.=) :: (ToJSONPB v, KeyValuePB kvp, FieldDefault v, Eq v) => Text -> v -> Options -> kvp Source #
Options for controlling codec behavior (e.g., emitting default-valued
Constructors
| Options | |
Fields | |
defaultOptions :: Options Source #
Default options for JSONPB encoding. By default, all options are False.
JSONPB codec entry points
eitherDecode :: FromJSONPB a => ByteString -> Either String a Source #
eitherDecode variant for deserializing a JSONPB value from a
lazy ByteString.
encode :: ToJSONPB a => Options -> a -> ByteString Source #
encode variant for serializing a JSONPB value as a lazy
ByteString.
Helper functions
parseField :: FromJSONPB a => Object -> Text -> Parser a Source #
toAesonEncoding :: ToJSONPB a => a -> Encoding Source #
A direct Encoding for values which can be JSONPB-encoded
toAesonValue :: ToJSONPB a => a -> Value Source #
Aeson re-exports
A JSON value represented as a Haskell value.
Instances
| Eq Value | |
| Data Value | |
Defined in Data.Aeson.Types.Internal Methods gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> Value -> c Value # gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c Value # dataTypeOf :: Value -> DataType # dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c Value) # dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c Value) # gmapT :: (forall b. Data b => b -> b) -> Value -> Value # gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> Value -> r # gmapQr :: (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> Value -> r # gmapQ :: (forall d. Data d => d -> u) -> Value -> [u] # gmapQi :: Int -> (forall d. Data d => d -> u) -> Value -> u # gmapM :: Monad m => (forall d. Data d => d -> m d) -> Value -> m Value # gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> Value -> m Value # gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> Value -> m Value # | |
| Read Value | |
| Show Value | |
| IsString Value | |
Defined in Data.Aeson.Types.Internal Methods fromString :: String -> Value # | |
| Generic Value | |
| Lift Value | |
| Hashable Value | |
Defined in Data.Aeson.Types.Internal | |
| ToJSON Value | |
Defined in Data.Aeson.Types.ToJSON | |
| KeyValue Object | Constructs a singleton |
| KeyValue Pair | |
| FromJSON Value | |
| NFData Value | |
Defined in Data.Aeson.Types.Internal | |
| FromString Encoding | |
Defined in Data.Aeson.Types.ToJSON Methods fromString :: String -> Encoding | |
| FromString Value | |
Defined in Data.Aeson.Types.ToJSON Methods fromString :: String -> Value | |
| GToJSON Encoding arity (U1 :: Type -> Type) | |
| GToJSON Value arity (V1 :: Type -> Type) | |
| GToJSON Value arity (U1 :: Type -> Type) | |
| ToJSON1 f => GToJSON Encoding One (Rec1 f) | |
| ToJSON1 f => GToJSON Value One (Rec1 f) | |
| ToJSON a => GToJSON Encoding arity (K1 i a :: Type -> Type) | |
| (EncodeProduct arity a, EncodeProduct arity b) => GToJSON Encoding arity (a :*: b) | |
| ToJSON a => GToJSON Value arity (K1 i a :: Type -> Type) | |
| (WriteProduct arity a, WriteProduct arity b, ProductSize a, ProductSize b) => GToJSON Value arity (a :*: b) | |
| (ToJSON1 f, GToJSON Encoding One g) => GToJSON Encoding One (f :.: g) | |
| (ToJSON1 f, GToJSON Value One g) => GToJSON Value One (f :.: g) | |
| FromPairs Value (DList Pair) | |
Defined in Data.Aeson.Types.ToJSON | |
| v ~ Value => KeyValuePair v (DList Pair) | |
Defined in Data.Aeson.Types.ToJSON | |
| KeyValuePB [Pair] Source # | |
| (GToJSON Encoding arity a, ConsToJSON Encoding arity a, Constructor c) => SumToJSON' TwoElemArray Encoding arity (C1 c a) | |
Defined in Data.Aeson.Types.ToJSON | |
| (GToJSON Value arity a, ConsToJSON Value arity a, Constructor c) => SumToJSON' TwoElemArray Value arity (C1 c a) | |
Defined in Data.Aeson.Types.ToJSON | |
| type Rep Value | |
Defined in Data.Aeson.Types.Internal type Rep Value = D1 (MetaData "Value" "Data.Aeson.Types.Internal" "aeson-1.4.5.0-9XSSP6ZPFFF88DbQdSrF7g" False) ((C1 (MetaCons "Object" PrefixI False) (S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness SourceStrict DecidedStrict) (Rec0 Object)) :+: (C1 (MetaCons "Array" PrefixI False) (S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness SourceStrict DecidedStrict) (Rec0 Array)) :+: C1 (MetaCons "String" PrefixI False) (S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness SourceStrict DecidedStrict) (Rec0 Text)))) :+: (C1 (MetaCons "Number" PrefixI False) (S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness SourceStrict DecidedStrict) (Rec0 Scientific)) :+: (C1 (MetaCons "Bool" PrefixI False) (S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness SourceStrict DecidedStrict) (Rec0 Bool)) :+: C1 (MetaCons "Null" PrefixI False) (U1 :: Type -> Type)))) | |
A type that can be converted to JSON.
Instances in general must specify toJSON and should (but don't need
to) specify toEncoding.
An example type and instance:
-- Allow ourselves to writeTextliterals. {-# LANGUAGE OverloadedStrings #-} data Coord = Coord { x :: Double, y :: Double } instanceToJSONCoord wheretoJSON(Coord x y) =object["x".=x, "y".=y]toEncoding(Coord x y) =pairs("x".=x<>"y".=y)
Instead of manually writing your ToJSON instance, there are two options
to do it automatically:
- Data.Aeson.TH provides Template Haskell functions which will derive an instance at compile time. The generated instance is optimized for your type so it will probably be more efficient than the following option.
- The compiler can provide a default generic implementation for
toJSON.
To use the second, simply add a deriving clause to your
datatype and declare a GenericToJSON instance. If you require nothing other than
defaultOptions, it is sufficient to write (and this is the only
alternative where the default toJSON implementation is sufficient):
{-# LANGUAGE DeriveGeneric #-}
import GHC.Generics
data Coord = Coord { x :: Double, y :: Double } deriving Generic
instance ToJSON Coord where
toEncoding = genericToEncoding defaultOptions
If on the other hand you wish to customize the generic decoding, you have to implement both methods:
customOptions =defaultOptions{fieldLabelModifier=maptoUpper} instanceToJSONCoord wheretoJSON=genericToJSONcustomOptionstoEncoding=genericToEncodingcustomOptions
Previous versions of this library only had the toJSON method. Adding
toEncoding had two reasons:
- toEncoding is more efficient for the common case that the output of
toJSONis directly serialized to aByteString. Further, expressing either method in terms of the other would be non-optimal. - The choice of defaults allows a smooth transition for existing users:
Existing instances that do not define
toEncodingstill compile and have the correct semantics. This is ensured by making the default implementation oftoEncodingusetoJSON. This produces correct results, but since it performs an intermediate conversion to aValue, it will be less efficient than directly emitting anEncoding. (this also means that specifying nothing more thaninstance ToJSON Coordwould be sufficient as a generically decoding instance, but there probably exists no good reason to not specifytoEncodingin new instances.)
Minimal complete definition
Nothing
Methods
Convert a Haskell value to a JSON-friendly intermediate type.
toEncoding :: a -> Encoding #
Encode a Haskell value as JSON.
The default implementation of this method creates an
intermediate Value using toJSON. This provides
source-level compatibility for people upgrading from older
versions of this library, but obviously offers no performance
advantage.
To benefit from direct encoding, you must provide an
implementation for this method. The easiest way to do so is by
having your types implement Generic using the DeriveGeneric
extension, and then have GHC generate a method body as follows.
instanceToJSONCoord wheretoEncoding=genericToEncodingdefaultOptions
toJSONList :: [a] -> Value #
toEncodingList :: [a] -> Encoding #
Instances
A type that can be converted from JSON, with the possibility of failure.
In many cases, you can get the compiler to generate parsing code for you (see below). To begin, let's cover writing an instance by hand.
There are various reasons a conversion could fail. For example, an
Object could be missing a required key, an Array could be of
the wrong size, or a value could be of an incompatible type.
The basic ways to signal a failed conversion are as follows:
failyields a custom error message: it is the recommended way of reporting a failure;empty(ormzero) is uninformative: use it when the error is meant to be caught by some(;<|>)typeMismatchcan be used to report a failure when the encountered value is not of the expected JSON type;unexpectedis an appropriate alternative when more than one type may be expected, or to keep the expected type implicit.
prependFailure (or modifyFailure) add more information to a parser's
error messages.
An example type and instance using typeMismatch and prependFailure:
-- Allow ourselves to writeTextliterals. {-# LANGUAGE OverloadedStrings #-} data Coord = Coord { x :: Double, y :: Double } instanceFromJSONCoord whereparseJSON(Objectv) = Coord<$>v.:"x"<*>v.:"y" -- We do not expect a non-Objectvalue here. -- We could useemptyto fail, buttypeMismatch-- gives a much more informative error message.parseJSONinvalid =prependFailure"parsing Coord failed, " (typeMismatch"Object" invalid)
For this common case of only being concerned with a single
type of JSON value, the functions withObject, withScientific, etc.
are provided. Their use is to be preferred when possible, since
they are more terse. Using withObject, we can rewrite the above instance
(assuming the same language extension and data type) as:
instanceFromJSONCoord whereparseJSON=withObject"Coord" $ \v -> Coord<$>v.:"x"<*>v.:"y"
Instead of manually writing your FromJSON instance, there are two options
to do it automatically:
- Data.Aeson.TH provides Template Haskell functions which will derive an instance at compile time. The generated instance is optimized for your type so it will probably be more efficient than the following option.
- The compiler can provide a default generic implementation for
parseJSON.
To use the second, simply add a deriving clause to your
datatype and declare a GenericFromJSON instance for your datatype without giving
a definition for parseJSON.
For example, the previous example can be simplified to just:
{-# LANGUAGE DeriveGeneric #-}
import GHC.Generics
data Coord = Coord { x :: Double, y :: Double } deriving Generic
instance FromJSON Coord
The default implementation will be equivalent to
parseJSON = ; if you need different
options, you can customize the generic decoding by defining:genericParseJSON defaultOptions
customOptions =defaultOptions{fieldLabelModifier=maptoUpper} instanceFromJSONCoord whereparseJSON=genericParseJSONcustomOptions
Minimal complete definition
Nothing
Instances
Arguments
| :: String | The name of the JSON type being parsed
( |
| -> Value | The actual value encountered. |
| -> Parser a |
Fail parsing due to a type mismatch, with a descriptive message.
The following wrappers should generally be prefered:
withObject, withArray, withText, withBool.
Error message example
typeMismatch "Object" (String "oops") -- Error: "expected Object, but encountered String"
withObject :: String -> (Object -> Parser a) -> Value -> Parser a #
withObject name f valuef to the Object when value
is an Object and fails otherwise.
Error message example
withObject "MyType" f (String "oops") -- Error: "parsing MyType failed, expected Object, but encountered String"