Major refactoring and extension

.travis.yml

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+language: elm
+elm:
+  - "0.19.0"

LICENSE

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+Copyright (c) 2018, Erik Timmers
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+* Redistributions of source code must retain the above copyright notice, this
+  list of conditions and the following disclaimer.
+
+* Redistributions in binary form must reproduce the above copyright notice,
+  this list of conditions and the following disclaimer in the documentation
+  and/or other materials provided with the distribution.
+
+* Neither the name of the copyright holder nor the names of its
+  contributors may be used to endorse or promote products derived from
+  this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

README.md

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+# Protocol Buffers [![Build Status](https://travis-ci.org/eriktim/elm-protocol-buffers.svg?branch=master)](https://travis-ci.org/eriktim/elm-protocol-buffers)
+
+This package lets you create encoders and decoders for working with
+[ProtoBuf](https://developers.google.com/protocol-buffers) messages. Typically,
+**you should not use this package directly** as the encoder and decoders can be
+generated directly from `.proto` specification files.
+
+## Motivation
+
+> Protocol buffers are Google's language-neutral, platform-neutral, extensible
+> mechanism for serializing structured data – think XML, but smaller, faster,
+> and simpler. You define how you want your data to be structured once, then
+> you can use special generated source code to easily write and read your
+> structured data to and from a variety of data streams and using a variety of
+> languages.
+
+As Evan explained in his vision on
+[data interchange](https://gist.github.com/evancz/1c5f2cf34939336ecb79b97bb89d9da6),
+there are many ways to send information between clients and servers, like JSON
+(optionally according to a specfication, like OpenAPI), GraphQL and the one
+this package provides: **ProtoBuf**.
+
+Where Elm spoils us with an excellent type system, we lose this safety at the
+edges of our application when talking to servers. ProtoBuf requires you to
+specify the interchange format explicity up front, making it **type-safe**. It
+also:
+
+* makes you **decouple code** for data exchange from your business logic,
+  enabling your application to evolve over time;
+* makes you send **fewer bytes** over the wire;
+* allows you to **generate code** using the same data interchange format for
+  your backend as well!
+* is Google's **_lingua franca_** for data
+
+This package provides an API to help converting between Elm values and bytes by
+implementing the ProtoBuf specification. Ultimately, nobody should be writing
+these encoders and decoders directly as the required code can be generated
+automatically from `.proto` files. This is still a _work-in-progress_. Also
+implementing [gRPC](https://grpc.io/docs/guides/index.html) could be an
+interesting next step.
+
+## Example
+
+Given a ProtoBuf `.proto` file
+
+```protobuf
+message Person {
+  required string name = 1;
+  required int32 id = 2;
+  optional string email = 3;
+
+  enum PhoneType {
+    MOBILE = 0;
+    HOME = 1;
+    WORK = 2;
+  }
+
+  message PhoneNumber {
+    required string number = 1;
+    optional PhoneType type = 2 [default = HOME];
+  }
+
+  repeated PhoneNumber phone = 4;
+}
+```
+
+this package handles converting between `Person` and `Bytes` values:
+
+```elm
+import ProtoBuf.Decode as Decode
+import ProtoBuf.Encode as Encode
+
+
+
+-- MODEL
+
+
+type alias Person =
+    { name : String
+    , id : Int
+    , email : String
+    , phone : List PhoneNumber
+    }
+
+
+type alias PhoneNumber =
+    { number : String
+    , type_ : PhoneType
+    }
+
+
+type PhoneType
+    = Mobile
+    | Home
+    | Work
+
+
+
+-- ENCODE
+
+
+encodePerson : Person -> Encode.Encoder
+encodePerson person =
+    Encode.message
+        [ ( 1, Encode.string person.name )
+        , ( 2, Encode.int32 person.id )
+        , ( 3, Encode.string person.email )
+        , ( 4, Encode.list encodePhoneNumber person.phone )
+        ]
+
+
+encodePhoneNumber : PhoneNumber -> Encode.Encoder
+encodePhoneNumber phoneNumber =
+    Encode.message
+        [ ( 1, Encode.string phoneNumber.number )
+        , ( 2, encodePhoneType phoneNumber.type_ )
+        ]
+
+
+encodePhoneType : PhoneType -> Encode.Encoder
+encodePhoneType phoneType =
+    case phoneType of
+        Mobile ->
+            Encode.int32 0
+
+        Home ->
+            Encode.int32 1
+
+        Work ->
+            Encode.int32 2
+
+
+
+-- DECODE
+
+
+personDecoder : Decode.Decoder Person
+personDecoder =
+    Decode.message Person
+        |> Decode.required 1 Decode.string
+        |> Decode.required 2 Decode.int32
+        |> Decode.optional 3 Decode.string ""
+        |> Decode.repeated 4 phoneNumberDecoder
+
+
+phoneNumberDecoder : Decode.Decoder PhoneNumber
+phoneNumberDecoder =
+    Decode.message PhoneNumber
+        |> Decode.required 1 Decode.string
+        |> Decode.optional 2 phoneTypeDecoder Home
+
+
+phoneTypeDecoder : Decode.Decoder PhoneType
+phoneTypeDecoder =
+    Decode.int32
+        |> Decode.map
+            (\value ->
+                case value of
+                    0 ->
+                        Mobile
+
+                    1 ->
+                        Home
+
+                    2 ->
+                        Work
+
+                    _ ->
+                        Home
+            )
+```
+
+## Known limitations
+
+This packages aims to support both `proto2` and `proto3`. However, there are
+some limitations.
+
+* JavaScript uses 64-bit floating point
+  [numbers](https://tc39.github.io/ecma262/#sec-ecmascript-language-types-number-type)
+  for both integers and floats. Integers are only considered safe to use up to
+  about 54 bits. Therefore all 64-bit integer variants are not supported by
+  this package.
+
+* Unknown fields are well-formed protocol buffer serialized data representing
+  fields that the decoder does not recognize (for example when the field is
+  removed from the `.proto` file but the server is not yet updated). Currently,
+  these fields are ignored and hence are lost when re-serializing messages.
+
+* The [any](https://developers.google.com/protocol-buffers/docs/proto3#any)
+  type is currently not supported.
+