protoc-gen-preprocess

Purpose

We have variety of validators for protobuf, however sometimes we need to pre-process incoming data. This protobuf plugin helps to generate preprocessing methods for incoming messages.

Example

syntax = "proto3";

import "github.com/infobloxopen/protoc-gen-preprocess/options/preprocess.proto";

message Demo {
    // Options specified at message level are applied for each field (in this case of type string)
    option (preprocess.each).string = {
        methods: [trim]
    };
    // Also it is possible to specify additional method on field level
    string preprocessedField = 1 [(preprocess.field).string.methods = lower];
    // Preprocessor automatically checks if field is repeated and generates methods accordingly
    repeated string preprocessedRepeatedField = 2;
    // If a field does not fit preprocess method, it is just ignored
    int32 ignored = 3 [(preprocess.field).string = {methods:[lower]}];
}

will generate:

import proto "github.com/gogo/protobuf/proto"
import fmt "fmt"
import math "math"
import _ "github.com/infobloxopen/protoc-gen-preprocess/options"

// Reference imports to suppress errors if they are not otherwise used.
var _ = proto.Marshal
var _ = fmt.Errorf
var _ = math.Inf

func (m *Demo) Preprocess() error {

    m.PreprocessedField = strings.TrimSpace(m.PreprocessedField)
    m.PreprocessedField = strings.ToLower(m.PreprocessedField)

    for i, s := range m.PreprocessedRepeatedField {
        m.PreprocessedRepeatedField[i] = strings.TrimSpace(s)
    }

    return nil
}

Usage

It is best to use this plugin as a middleware as shown in example application:

package main

import (
...
    grpc_preprocessor "github.com/infobloxopen/protoc-gen-preprocess/middleware"
...
)

func runService() {
...
// Middleware chain.
    interceptors := []grpc.UnaryServerInterceptor{
...
        grpc_preprocessor.UnaryServerInterceptor(), // preprocessing middleware
...
    }
    server := grpc.NewServer(grpc.UnaryInterceptor(grpc_middleware.ChainUnaryServer(interceptors...)))
...
}

Installation

# get repo and install
go get github.com/infobloxopen/protoc-gen-preprocess

Running Demo

# build demo
make demo

# run example application
go run example/main.go

This will launch a server with our demo service. To check functionality of demo application send following request:

curl -X POST -i http://localhost:8080/echo --data '{"preprocessedField": "     Those spaces will be trimmed    ","untouched": " Notice how those spaces will be left as is    "}'

Supported Field Types

For now following list of fields supported:

• String:
  • trim_space - Will trim leading and following spaces
  • upper - Will convert to upper
  • lower - Will convert to lower
  • clear - Will clear all previous options either inherited from message level or previous items in list.