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serialization | ||
tests | ||
.travis.yml | ||
README.md | ||
serialization.nim | ||
serialization.nimble |
README.md
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.
Reader = JsonReader, # The associated Reader type.
Writer = JsonWriter, # The associated Writer type.
PreferedOutput = string, # APIs such as `Json.encode` will return this type.
# The type must support the following operations:
# proc initWithCapacity(_: type T, n: int)
# proc add(v: var T, bytes: openarray[byte])
# By default, the PreferedOutput is `seq[byte]`.
mimeType = "application/json", # Mime type associated with the format (Optional).
fileExt = "json" # File extension associated with the format (Optional).
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.PreferedOutput
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, params: varargs)
Similar to encode
, but saves the result in a file.
Format.loadFile
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 paticular 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(varargs[Format])
pragma
to black-list fields or the serialize(varargs[Format])
to white-list fields.
If no formats are listed in the pragmas above, they will affect all formats.
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 serializedFields
macro to achive the same in less
instrusive way.
The following two definitions can be consired equivalent:
type
Foo = object
a: string
b {.dontSerialize.}: int
c {.dontSerialize(JSON).}: float
d {.serializedFieldName("z").}: int
serializedFields Foo:
a
c [-JSON]
# The `d` field is renamed to `z`:
d -> z
As you can see, serializedFields
accepts a block where each serialzied
field is listed on a separate line. The ->
operator is used to indicate
field renames, while the optional []
modifiers can be used to while-list
or black-list specific formats where the field should appear (using +
and -
respectively).
customSerialization(RecordType: type, spec)
Format.customSerialization(RecordType, spec)
customSerialization(RecordType.field, spec)
Format.customSerialization(Record.field, spec)
Record.totalSerializedFields(Format)
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.