Custom preprocess (#3)

* add ability to implement custom preprocessors

* update readme

* syntax highlight in readme for protobuf

* Preprocess not generated if unused

* update custom example

README.md

@@ -6,13 +6,13 @@ We have variety of validators for protobuf, however sometimes we need to pre-pro
 
 ### Example
 
-```proto
+```protobuf
 syntax = "proto3";
 
 import "github.com/infobloxopen/protoc-gen-preprocess/options/preprocess.proto";
 
 message Demo {
-   string preprocessedField = 1 [(preprocess.field).string.trim_space = true ];
+   string preprocessedField = 1 [(preprocess.field).string.trim_space = true];
    repeated string preprocessedRepeatedField = 2 [(preprocess.field).string.trim_space = true ];
    string untouched = 3;
 }
@@ -74,12 +74,8 @@ func runService() {
 ### Installation
 
 ```sh
-# get repo
-go get -d github.com/infobloxopen/protoc-gen-preprocess
-
-# build
-make install
-
+# get repo and install
+go get github.com/infobloxopen/protoc-gen-preprocess
 ```
 
 ### Running Demo

example/demo.proto

@@ -1,5 +1,5 @@
 syntax = "proto3";
-
+package proto;
 import "github.com/infobloxopen/protoc-gen-preprocess/options/preprocess.proto";
 import "google/api/annotations.proto";
 
@@ -10,6 +10,10 @@ message Demo {
    int32 ignored = 4  [(preprocess.field).string.trim_space = true ];
 }
 
+message Custom {
+    string doItYourself = 1;
+}
+
 service DemoService {
     rpc Echo(Demo) returns (Demo){
         option (google.api.http) = {

example/proto/demo.pb.custom.preprocess.go

@@ -0,0 +1,7 @@
+package proto
+
+// Preprocess will be called by interceptor
+func (m *Custom) Preprocess() error {
+	m.DoItYourself = "Changed Internals"
+	return nil
+}

preprocess/preprocess.go

@@ -10,7 +10,8 @@ import (
 type preprocessor struct {
 	*generator.Generator
 	generator.PluginImports
-	stringsPkg generator.Single
+	packageName string
+	stringsPkg  generator.Single
 }
 
 func NewPreprocessor() *preprocessor {
@@ -30,7 +31,9 @@ func (p *preprocessor) Generate(file *generator.FileDescriptor) {
 	p.PluginImports = generator.NewPluginImports(p.Generator)
 	p.stringsPkg = p.NewImport("strings")
 	for _, message := range file.Messages() {
-		p.generateProto3Message(file, message)
+		if containsPreprocessOptions(message) {
+			p.generateProto3Message(message)
+		}
 	}
 }
 
@@ -53,7 +56,7 @@ func getFieldOptions(field *descriptor.FieldDescriptorProto) *prep.PreprocessFie
 	return opts
 }
 
-func (p *preprocessor) generateProto3Message(file *generator.FileDescriptor, message *generator.Descriptor) {
+func (p *preprocessor) generateProto3Message(message *generator.Descriptor) {
 	ccTypeName := generator.CamelCaseSlice(message.TypeName())
 	p.P(`func (m *`, ccTypeName, `) Preprocess() error {`)
 	p.In()
@@ -94,3 +97,13 @@ func (p *preprocessor) generateStringValidator(variableName string, ccTypeName s
 		}
 	}
 }
+
+func containsPreprocessOptions(message *generator.Descriptor) bool {
+	for _, field := range message.Field {
+		fieldOptions := getFieldOptions(field)
+		if fieldOptions != nil {
+			return true
+		}
+	}
+	return false
+}