4.8 KiB
nim-serialization
Introduction
The serialization package aims to provide a common generic and efficient
interface for marshaling Nim values to and from various serialized formats.
Individual formats are implemented in separated packages such as
json_serialization
while this package provides the common interfaces shared between all of them
and the means to customize your Nim types for the purposes of serialization.
The internal mechanisms of the library allow for implementing the required marshaling logic in highly efficient way that goes from bytes to Nim values and vice versa without allocating any intermediate structures.
Defining serialization formats
A serialization format is implemented through defining a Reader and Writer
type for the format and then by providing the following type declaration:
serializationFormat Json, # This is the name of the format.
# Most APIs provided by the library will accept
# this identifier as a required parameter.
mimeType = "application/json" # Mime type associated with the format (Optional).
Json.setReader JsonReader # The associated Reader type.
Json.setWriter JsonWriter, # The associated Writer type.
PreferredOutput = string # APIs such as `Json.encode` will return this type.
Common API
Most of the time, you'll be using the following high-level APIs when encoding and decoding values:
Format.encode(value: auto, params: varargs): Format.PreferredOutput
Encodes a value in the specified format returning the preferred output type
for the format (usually string or seq[byte]). All extra params will be
forwarded without modification to the constructor of the used Writer type.
Example:
assert Json.encode(@[1, 2, 3], pretty = false) == "[1, 2, 3]"
Format.decode(input: openArray[byte]|string, RecordType: type, params: varargs): RecordType
Decodes and returns a value of the specified RecordType. All params will
be forwarded without modification to the used Reader type. A Format-specific
descendant of SerializationError may be thrown in case of error.
Format.saveFile(filename: string, value: auto, params: varargs)
Similar to encode, but saves the result in a file.
Format.loadFile(filename: string, RecordType: type, params: varargs): RecordType
Similar to decode, but treats the contents of a file as an input.
reader.readValue(RecordType: type): RecordType
Reads a single value of the designated type from the stream associated with a particular reader.
writer.writeValue(value: auto)
Encodes a single value and writes it to the output stream of a particular writer.
Custom serialization of user-defined types
By default, record types will have all of their fields serialized. You can
alter this behavior by attaching the dontSerialize pragma to exclude fields.
The pragma serializedFieldName(name: string) can be used to modify the name
of the field in formats such as Json and XML.
Alternatively, if you are not able to modify the definition of a particular
Nim type, you can use the setSerializedFields macro to achieve the same
in a less intrusive way.
The following two definitions can be considered equivalent:
type
Foo = object
a: string
b {.dontSerialize.}: int
setSerializedFields Foo:
a
As you can see, setSerializedFields accepts a block where each serialized
field is listed on a separate line.
customSerialization(RecordType: type, spec)
totalSerializedFields(RecordType: type)
Returns the number of serialized fields in the specified format.
Implementing Readers
Implementing Writers
Contributing
When submitting pull requests, please add test cases for any new features
or fixes and make sure nimble test is still able to execute the entire
test suite successfully.
License
Licensed and distributed under either of
- MIT license: LICENSE-MIT or http://opensource.org/licenses/MIT
or
- Apache License, Version 2.0, (LICENSE-APACHEv2 or http://www.apache.org/licenses/LICENSE-2.0)
at your option. These files may not be copied, modified, or distributed except according to those terms.