PMJSON provides a pure-Swift strongly-typed JSON encoder/decoder as well as a set of convenience methods for converting to/from Foundation objects and for decoding JSON structures.
The entire JSON encoder/decoder can be used without Foundation, by removing the files ObjectiveC.swift
and DecimalNumber.swift
from the project. The only dependency the rest of the project has is on Darwin
, for strtod()
and strtoll()
. The file ObjectiveC.swift
adds convenience methods for translating between JSON
values and Foundation objects as well as decoding from a Data
, and DecimalNumber.swift
adds convenience accessors for converting values into NSDecimalNumber
.
Before diving into the details, here's a simple example of writing a decoder for a struct. There are a few different options for how to deal with malformed data (e.g. whether to ignore values of wrong types, and whether to try and coerce non-string values to strings or vice versa), but the following example will be fairly strict and throw an error for incorrectly-typed values:
struct Address {
var streetLine1: String
var streetLine2: String?
var city: String
var state: String?
var postalCode: String
var country: String?
init(json: JSON) throws {
streetLine1 = try json.getString("street_line1")
streetLine2 = try json.getStringOrNil("street_line2")
city = try json.getString("city")
state = try json.getStringOrNil("state")
postalCode = try json.toString("postal_code") // coerce numbers to strings
country = try json.getStringOrNil("country")
}
}
And here's an example of decoding a nested array of values:
struct Person {
var firstName: String
var lastName: String? // some people don't have last names
var age: Int
var addresses: [Address]
init(json: JSON) throws {
firstName = try json.getString("firstName")
lastName = try json.getStringOrNil("lastName")
age = try json.getInt("age")
addresses = try json.mapArray("addresses", Address.init(json:))
}
}
If you don't want to deal with errors and just want to handle optionals, you can do that too:
struct Config {
var name: String?
var doThatThing: Bool
var maxRetries: Int
init(json: JSON) {
name = json["name"]?.string
doThatThing = json["doThatThing"]?.bool ?? false
maxRetries = json["maxRetries"]?.int ?? 10
}
}
The JSON decoder is split into separate parser and decoder stages. The parser consums any sequence of unicode scalars, and produces a sequence of JSON "events" (similar to a SAX XML parser). The decoder accepts a sequence of JSON events and produces a JSON
value. This architecture is designed such that you can use just the parser alone in order to decode directly to your own data structures and bypass the JSON
representation entirely if desired. However, most clients are expected to use both components, and this is exposed via a simple method JSON.decode(_:options:)
.
Parsing a JSON string into a JSON
value is as simple as:
let json = try JSON.decode(jsonString)
Any errors in the JSON parser are represented as JSONParserError
values and are thrown from the decode()
method. The error contains the precise line and column of the error, and a code that describes the problem.
A convenience method is also provided for decoding from a Data
containing data encoded as UTF-8, UTF-16, or UTF-32:
let json = try JSON.decode(data)
Encoding a JSON
value is also simple:
let jsonString = JSON.encodeAsString(json)
You can also encode directly to any TextOutputStream
:
JSON.encode(json, toStream: &output)
And, again, a convenience method is provided for working with Data
:
let data = JSON.encodeAsData(json)
PMJSON supports parsing JSON streams, which are multiple top-level JSON values with optional whitespace delimiters (such as {"a": 1}{"a": 2}
). The easiest way to use this is with JSON.decodeStream(_:)
which returns a lazy sequence of JSONStreamValue
s, which contain either a JSON
value or a JSONParserError
error. You can also use JSONParser
s and JSONDecoder
s directly for more fine-grained control over streaming.
As mentioned above, the JSON decoder is split into separate parser and decoder stages. JSONParser
is the parser stage, and it wraps any sequence of UnicodeScalar
s, and itself is a sequence of JSONEvent
s. A JSONEvent
is a single step of JSON parsing, such as .objectStart
when a {
is encountered, or .stringValue(_)
when a "string"
is encountered. You can use JSONParser
directly to emit a stream of events if you want to do any kind of lazy processing of JSON (such as if you're dealing with a single massive JSON blob and don't want to decode the whole thing into memory at once).
Similarly, JSONDecoder
is the decoder stage. It wraps a sequence of JSONEvent
s, and decodes that sequence into a proper JSON
value. The wrapped sequence must also conform to a separate protocol JSONEventIterator
that provides line/column information, which are used when emitting errors. You can use JSONDecoder
directly if you want to wrap a sequence of events other than JSONParser
, or if you want a different interface to JSON stream decoding than JSONStreamDecoder
provides.
Because of this split nature, you can easily provide your own event stream, or your own decoding stage. Or you can do things like wrap JSONParser
in an adaptor that modfiies the events before passing them to the decoder (which may be more efficient than converting the resulting JSON
value).
Besides encoding/decoding, this library also provides a comprehensive suite of accessors for getting data out of JSON
values. There are 4 types of basic accessors provided:
- Basic property accessors named after types such as
.string
. These accessors return the underlying value if it matches the type, ornil
if the value is not the right type. For example,.string
returnsString?
. These accessors do not convert between types, e.g.JSON.Int64(42).string
returnsnil
. - Property accessors beginning with the word
as
, such as.asString
. These accessors also return an optional value, but they convert between types if it makes sense to do so. For example,JSON.Int64(42).asString
returns"42"
. - Methods beginnning with
get
, such asgetString()
. These methods return non-optional values, and throwJSONError
s if the value's type does not match. These methods do not convert between types, e.g.try JSON.Int64(42).getString()
throws an error. For every method of this type, there's also a variant ending inOrNil
, such asgetStringOrNil()
, which does return an optional. These methods only returnnil
if the value isnull
, otherwise they throw an error. - Methods beginning with
to
, such astoString()
. These are just like theget
methods except they convert between types when appropriate, using the same rules that theas
methods do, e.g.try JSON.Int64(42).toString()
returns"42"
. Like theget
methods, there are also variants ending inOrNil
.
JSON
also provides both keyed and indexed subscript operators that return a JSON?
, and are always safe to call (even with out-of-bounds indexes). And it provides 2 kinds of subscripting accessors:
- For every basic
get
accessor, there's a variant that takes a key or an index. These are equivalent to subscripting the receiver and invoking theget
accessor on the result, except they produce better errors (and they handle missing keys/out-of-bounds indexes properly). For example,getString("key")
orgetString(index)
. TheOrNil
variants also returnnil
if the key doesn't exist or the index is out-of-bounds. - Similarly, there are subscripting equivalents for the
to
accessors as well.
And finally, the getObject()
and getArray()
accessors provide variants that take a closure. These variants are recommended over the basic accessors as they produce better errors. For example, given the following JSON:
{
"object": {
"elements": [
{
"name": null
}
]
}
}
And the following code:
try json.getObject("object").getArray("elements").getObject(0).getString("name")
The error thrown by this code will have the description "name: expected string, found null"
.
But given the following equivalent code:
try json.getObject("object", { try $0.getArray("elements", { try $0.getObject(0, { try $0.getString("name") }) }) })
The error thrown by this code will have the description "object.elements[0].name: expected string, found null"
.
All of these accessors are also available on the JSONObject
type (which is the type that represents an object).
The last code snippet above looks very verbose, but in practice you don't end up writing code like that. Instead you'll often end up just writing things like
try json.mapArray("elements", Element.init(json:))
The JSON
type has static methods map()
and flatMap()
for working with arrays (since PMJSON does not define its own array type). The benefit of using these methods over using the equivalent SequenceType
methods is the PMJSON static methods produce better errors.
There are also helpers for converting to/from Foundation objects. JSON
offers an initializer init(ns: AnyObject) throws
that converts from any JSON-compatible object to a JSON
. JSON
and JSONObject
both offer the property .ns
, which returns a Foundation object equivalent to the JSON
, and .nsNoNull
which does the same but omits any null
values instead of using NSNull
.
The test suite includes some basic performance tests. Decoding ~70KiB of JSON using PMJSON takes about 2.5-3x the time that NSJSONSerialization
does, though I haven't tested this with different distributions of inputs and it's possible this performance is specific to the characteristics of the test input. However, encoding the same JSON back to a Data
is actually faster with PMJSON, taking around 75% of the time that NSJSONSerialization
does.
Installing as a framework requires a minimum of iOS 8, OS X 10.9, watchOS 2.0, or tvOS 9.0.
After installing with any mechanism, you can use this by adding import PMJSON
to your code.
The Swift Package Manager may be used to install PMJSON by adding it to your dependencies
list:
let package = Package(
name: "YourPackage",
dependencies: [
.Package(url: "https://github.com/postmates/PMJSON.git", majorVersion: 2)
]
)
To install using Carthage, add the following to your Cartfile:
github "postmates/PMJSON" ~> 2.0
This release supports Swift 3. If you want Swift 2.3 support, you can use
github "postmates/PMJSON" ~> 0.9.4
To install using CocoaPods, add the following to your Podfile:
pod 'PMJSON', '~> 2.0'
This release supports Swift 3. If you want Swift 2.3 support, you can use
pod 'PMJSON', '~> 0.9.4'
Licensed under either of
- Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
- MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT) at your option.
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you shall be dual licensed as above, without any additional terms or conditions.
- Add Linux support for
Decimal
(on Swift 3.1 and later). NOTE: Decimal support is still buggy in Swift 3.1, and the workarounds we employ to get the correct values on Apple platforms don't work on Linux. You probably shouldn't rely on this working correctly on Linux until Swift fixes its Decimal implementation. - Add Linux support for decoding from/encoding to
Data
. - Add Linux support for
LocalizedError
on the Error types (only really applies to Swift 3.1 and later). - Fix compilation on Linux using the release configuration.
- Support running the test suite with
swift test
.
- Fix Linux compatibility.
- Add method
JSON.parser(for:options:)
that returns aJSONParser<AnySequence<UnicodeScalar>>
from aData
. LikeJSON.decode(_:options:)
, this method automatically detects UTF-8, UTF-16, or UTF-32 input. - Fix compatibility with Swift Package Manager.
- Add full support for decimal numbers (on supported platforms). This takes the form of a new
JSON
variant.decimal
, any relevant accessors, and full parsing/decoding support with the new option.useDecimals
. With this option, any number that would have been decoded as aDouble
will be decoded as aDecimal
instead. - Add a set of
forEach
accessors for working with arrays, similar to the existingmap
andflatMap
accessors.
- Handle UTF-32 input.
- Detect UTF-16 and UTF-32 input without a BOM.
- Fix bug where we weren't passing decoder options through for UTF-16 input.
- Change how options are provided to the encoder/decoder/parser. All options are now provided in the form of a struct that uses array literal syntax (similar to
OptionSet
s). The old methods that take strict/pretty flags are now marked as deprecated. - Add a new depth limit option to the decoder, with a default of 10,000.
- Implement a new test suite based on JSONTestSuite.
- Fix a crash if the input stream contained a lone trail surrogate without a lead surrogate.
- Fix incorrect parsing of numbers of the form
1e-1
or1e+1
. - When the
strict
option is specified, stop accepting numbers of the form01
or-01
. - Add support for UTF-16 when decoding a
Data
that has a UTF-16 BOM. - Skip a UTF-8 BOM if present when decoding a
Data
.
- Add
Hashable
toJSONEvent
andJSONParserError
. - Make
JSONParserError
conform toCustomNSError
for better Obj-C errors. - Full JSON stream support.
JSONParser
andJSONDecoder
can now both operate in streaming mode, a new typeJSONStreamDecoder
was added as a lazy sequence of JSON values, and a convenience methodJSON.decodeStream(_:)
was added. - Rename
JSONEventGenerator
toJSONEventIterator
andJSONParserGenerator
toJSONParserIterator
. The old names are available (but deprecated) for backwards compatibility. - Add support for pattern matching with
JSONParserError
. It should now work just like any other error, allowing you to say e.g.if case JSONParserError.invalidSyntax = error { … }
.
- Fix CocoaPods.
- Support Swift 3.0.
- Add setters for basic accessors so you can write code like
json["foo"].object?["key"] = "bar"
. - Provide a localized description for errors when bridged to
NSError
. - Add support to
JSONParser
for streams of JSON values (e.g."[1][2]"
).
- Add a set of convenience methods on
JSON
andJSONObject
for mapping arrays returned by subscripting with a key or index:mapArray(_:_:)
,mapArrayOrNil(_:_:)
,flatMapArray(_:_:)
, andflatMapArrayOrNil(_:_:)
. - Add new set of convenience
JSON
initializers. - Change
description
anddebugDescription
forJSON
andJSONObject
to be more useful.description
is now the JSON-encoded string. - Implement
CustomReflectable
forJSON
andJSONObject
.
- CocoaPods support.
- Linux support.
- Swift Package Manager support.
- Rename instances of
plist
in the API tons
. The old names are still available but marked as deprecated. - Support the latest Swift snapshot (2012-02-08).
Initial release.