Add Protocol Buffer Message Generation to Types Plugin (#211)

* types: add Protocol Buffer message generation

* remove unused timestamp import logic

---------

Co-authored-by: Marco Colletti <m.colletti@ips-intelligence.com>

Author: ilCollez

types/README.md

@@ -1,8 +1,8 @@
 # Types Plugin
 
 The `types` plugin is a [Goa](https://github.com/goadesign/goa/tree/v3) plugin
-that generates Go data types and validation functions for all user types defined
-in a Goa design package.
+that generates Go data types, validation functions, and Protocol Buffer message
+definitions for all user types defined in a Goa design package.
 
 Given the following design:
 
@@ -17,7 +17,9 @@ var _ = Type("MyType", func() {
 })
 ```
 
-The plugin generates the file `gen/types/types.go` with the  following code:
+The plugin generates two files:
+
+## Generated Go Code (`gen/types/types.go`)
 
 ```go
 package types
@@ -43,6 +45,24 @@ func ValidateMyType(v *MyType) (err error) {
 }
 ```
 
+## Generated Protocol Buffer Definitions (`gen/types/types.proto`)
+
+```proto
+syntax = "proto3";
+
+package types;
+
+option go_package = "<your-module>/types";
+
+// My type
+message MyType {
+  // Age
+  int32 age = 1;
+  // Name
+  string name = 2;
+}
+```
+
 ## Usage Pattern
 
 This plugin makes it possible to share data types between Goa microservices and
@@ -53,6 +73,12 @@ generated by the `types` plugin to decode and validate messages. The adapter can
 then make requests to a Goa microservice whose design package imports the
 original design package defining the data types thus guaranteeing compatibility.
 
+The protobuf definitions enable:
+- Cross-language compatibility with protobuf-based systems
+- Efficient binary serialization
+- gRPC service integration
+- Schema evolution with backwards compatibility
+
 ## Enabling the Plugin
 
 To enable the plugin simply import both the `types` package as follows:
@@ -71,5 +97,107 @@ necessary as the package is imported solely for its side-effects
 ## Effects on Code Generation
 
 Enabling the plugin changes the behavior of the `gen` command of the `goa` tool.
-The command generates an additional `types/types.go` file under the `gen` folder
-containing the type definitions and validations.
+The command generates two additional files under the `gen/types` folder:
+- `types.go` - containing the Go type definitions and validations
+- `types.proto` - containing the Protocol Buffer message definitions
+
+## Type Mappings
+
+The plugin maps Goa types to both Go and Protocol Buffer types:
+
+| Goa Type   | Go Type    | Proto Type               |
+|------------|------------|--------------------------|
+| Boolean    | bool       | bool                     |
+| Int        | int        | int32                    |
+| Int32      | int32      | int32                    |
+| Int64      | int64      | int64                    |
+| UInt       | uint       | uint32                   |
+| UInt32     | uint32     | uint32                   |
+| UInt64     | uint64     | uint64                   |
+| Float32    | float32    | float                    |
+| Float64    | float64    | double                   |
+| String     | string     | string                   |
+| Bytes      | []byte     | bytes                    |
+| Any        | interface{}| google.protobuf.Any      |
+| ArrayOf(T) | []T        | repeated T               |
+| MapOf(K,V) | map[K]V    | map<K, V>                |
+
+## Features
+
+### Arrays and Nested Types
+
+The plugin handles complex nested structures:
+
+```go
+var _ = Type("Order", func() {
+    Attribute("items", ArrayOf("OrderItem"))
+})
+
+var _ = Type("OrderItem", func() {
+    Attribute("name", String)
+    Attribute("quantity", Int)
+})
+```
+
+Generates:
+
+```proto
+message OrderItem {
+  string name = 1;
+  int32 quantity = 2;
+}
+
+message Order {
+  repeated OrderItem items = 1;
+}
+```
+
+### Maps
+
+The plugin supports map types:
+
+```go
+var _ = Type("Config", func() {
+    Attribute("settings", MapOf(String, String))
+})
+```
+
+Generates:
+
+```proto
+message Config {
+  map<string, string> settings = 1;
+}
+```
+
+### Any Type Support
+
+The plugin supports the `Any` type for dynamic content:
+
+```go
+var _ = Type("Envelope", func() {
+    Attribute("metadata", MapOf(String, Any))
+})
+```
+
+Generates:
+
+```proto
+import "google/protobuf/any.proto";
+
+message Envelope {
+  map<string, google.protobuf.Any> metadata = 1;
+}
+```
+
+## Compiling Protocol Buffers
+
+To compile the generated `.proto` files to Go code, use the Protocol Buffer compiler:
+
+```bash
+protoc --go_out=. --go_opt=paths=source_relative \
+    gen/types/types.proto
+```
+
+This generates `gen/types/types.pb.go` which can be used alongside the Goa-generated
+`gen/types/types.go` for maximum interoperability.

types/generate.go

@@ -25,6 +25,7 @@ const Gendir = "types"
 // init registers the plugin generator function.
 func init() {
 	codegen.RegisterPlugin("types", "gen", nil, Generate)
+	codegen.RegisterPlugin("types-proto", "gen", nil, GenerateProto)
 }
 
 // Generate produces the documentation JSON file.