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+# Jason
+
+A blazing fast JSON parser and generator in pure Elixir.
+
+The parser and generator are at least twice as fast as other Elixir/Erlang libraries
+(most notably `Poison`).
+The performance is comparable to `jiffy`, which is implemented in C as a NIF.
+Jason is usually only twice as slow.
+
+Both parser and generator fully conform to
+[RFC 8259](https://tools.ietf.org/html/rfc8259) and
+[ECMA 404](http://www.ecma-international.org/publications/standards/Ecma-404.htm)
+standards. The parser is tested using [JSONTestSuite](https://github.com/nst/JSONTestSuite).
+
+## Installation
+
+The package can be installed by adding `jason` to your list of dependencies
+in `mix.exs`:
+
+```elixir
+def deps do
+  [{:jason, "~> 1.4"}]
+end
+```
+
+## Basic Usage
+
+``` elixir
+iex(1)> Jason.encode!(%{"age" => 44, "name" => "Steve Irwin", "nationality" => "Australian"})
+"{\"age\":44,\"name\":\"Steve Irwin\",\"nationality\":\"Australian\"}"
+
+iex(2)> Jason.decode!(~s({"age":44,"name":"Steve Irwin","nationality":"Australian"}))
+%{"age" => 44, "name" => "Steve Irwin", "nationality" => "Australian"}
+```
+
+Full documentation can be found at [https://hexdocs.pm/jason](https://hexdocs.pm/jason).
+
+## Use with other libraries
+
+### Postgrex
+
+Versions starting at 0.14.0 use `Jason` by default. For earlier versions, please refer to
+[previous versions of this document](https://github.com/michalmuskala/jason/tree/v1.1.2#postgrex).
+
+### Ecto
+
+Versions starting at 3.0.0 use `Jason` by default. For earlier versions, please refer to
+[previous versions of this document](https://github.com/michalmuskala/jason/tree/v1.1.2#ecto).
+
+### Plug (and Phoenix)
+
+Phoenix starting at 1.4.0 uses `Jason` by default. For earlier versions, please refer to
+[previous versions of this document](https://github.com/michalmuskala/jason/tree/v1.1.2#plug-and-phoenix).
+
+### Absinthe
+
+You need to pass the `:json_codec` option to `Absinthe.Plug`
+
+```elixir
+# When called directly:
+plug Absinthe.Plug,
+  schema: MyApp.Schema,
+  json_codec: Jason
+
+# When used in phoenix router:
+forward "/api",
+  to: Absinthe.Plug,
+  init_opts: [schema: MyApp.Schema, json_codec: Jason]
+```
+
+## Benchmarks
+
+Detailed benchmarks (including memory measurements):
+https://gist.github.com/michalmuskala/4d64a5a7696ca84ac7c169a0206640d5
+
+HTML reports for the benchmark (only performance measurements):
+http://michal.muskala.eu/jason/decode.html and http://michal.muskala.eu/jason/encode.html
+
+### Running
+
+Benchmarks against most popular Elixir & Erlang json libraries can be executed after
+going into the `bench/` folder and then executing `mix bench.encode` and `mix bench.decode`.
+A HTML report of the benchmarks (after their execution) can be found in
+`bench/output/encode.html` and `bench/output/decode.html` respectively.
+
+## Differences to Poison
+
+Jason has a couple feature differences compared to Poison.
+
+  * Jason follows the JSON spec more strictly, for example it does not allow
+    unescaped newline characters in JSON strings - e.g. `"\"\n\""` will
+    produce a decoding error.
+  * no support for decoding into data structures (the `as:` option).
+  * no built-in encoders for `MapSet`, `Range` and `Stream`.
+  * no support for encoding arbitrary structs - explicit implementation
+    of the `Jason.Encoder` protocol is always required.
+  * different pretty-printing customisation options (default `pretty: true` works the same)
+
+### Encoders
+
+If you require encoders for any of the unsupported collection types, I suggest
+adding the needed implementations directly to your project:
+
+```elixir
+defimpl Jason.Encoder, for: [MapSet, Range, Stream] do
+  def encode(struct, opts) do
+    Jason.Encode.list(Enum.to_list(struct), opts)
+  end
+end
+```
+
+If you need to encode some struct that does not implement the protocol,
+if you own the struct, you can derive the implementation specifying
+which fields should be encoded to JSON:
+
+```elixir
+@derive {Jason.Encoder, only: [....]}
+defstruct # ...
+```
+
+It is also possible to encode all fields, although this should be
+used carefully to avoid accidentally leaking private information
+when new fields are added:
+
+```elixir
+@derive Jason.Encoder
+defstruct # ...
+```
+
+Finally, if you don't own the struct you want to encode to JSON,
+you may use `Protocol.derive/3` placed outside of any module:
+
+```elixir
+Protocol.derive(Jason.Encoder, NameOfTheStruct, only: [...])
+Protocol.derive(Jason.Encoder, NameOfTheStruct)
+```
+
+## Injecting an already encoded JSON inside a to-be-encoded structure
+
+If parts of the to-be-encoded structure are already JSON-encoded, you can
+use `Jason.Fragment` to mark the parts as already encoded, and avoid a
+decoding/encoding roundtrip.
+
+```elixir
+already_encoded_json = Jason.encode!(%{hello: "world"})
+Jason.encode!(%{foo: Jason.Fragment.new(already_encoded_json)})
+```
+
+This feature is especially useful if you need to cache a part of the JSON,
+or if it is already provided by another system (e.g. `jsonb_agg` with Postgres).
+
+## License
+
+Jason is released under the Apache License 2.0 - see the [LICENSE](LICENSE) file.
+
+Some elements of tests and benchmarks have their origins in the
+[Poison library](https://github.com/devinus/poison) and were initially licensed under [CC0-1.0](https://creativecommons.org/publicdomain/zero/1.0/).