bootstrap.go

// Copyright (c) 2014 Ashley Jeffs
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, sub to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

package service

import (
	"encoding/json"
	"flag"
	"fmt"
	"io/ioutil"
	"os"
	"path/filepath"

	"gopkg.in/yaml.v2"
)

//------------------------------------------------------------------------------

var (
	version        string
	dateBuilt      string
	showVersion    *bool
	showConfigJSON *bool
	showConfigYAML *bool
	configPath     *string
)

func init() {
	showVersion = flag.Bool("version", false, "Display version info, then exit")
	showConfigJSON = flag.Bool("print-json", false, "Print loaded configuration as JSON, then exit")
	showConfigYAML = flag.Bool("print-yaml", false, "Print loaded configuration as YAML, then exit")
	configPath = flag.String("c", "", "Path to a configuration file")
}

//------------------------------------------------------------------------------

func readConfig(path string, config interface{}) error {
	configBytes, err := ioutil.ReadFile(path)
	if err != nil {
		return err
	}
	ext := filepath.Ext(path)
	if ".js" == ext || ".json" == ext {
		if err = json.Unmarshal(configBytes, config); err != nil {
			return err
		}
	} else if ".yml" == ext || ".yaml" == ext {
		if err = yaml.Unmarshal(configBytes, config); err != nil {
			return err
		}
	} else {
		return fmt.Errorf("config file extension not recognised: %v", path)
	}
	return nil
}

// Bootstrap bootstraps the configuration loading, parsing and reporting for a
// service through cmd flags. The argument configPtr should be a pointer to a
// serializable configuration object with all default values.
//
// configPtr should be a pointer to a config struct, which contains default
// values and should be populated with a users config values if applicable. For
// an example look at the stats and logger files.
//
// defaultConfigPaths should contain any known standard configuration paths, if
// the user neglects to specify a config then bootstrap will iterate these paths
// and read the first one that exists, if any.
//
// Bootstrap allows a user to do the following:
// - Print version and build info and exit
// - Load an optional configuration file (supports JSON, YAML)
// - Print the config file (supports JSON, YAML) and exit
//
// NOTE: The user may request a version and build time stamp, in which case
// Bootstrap will print the values of util.Version and util.DateBuilt. To
// populate those values you must run go build with the following:
//
// -ldflags "-X github.com/jeffail/benthos/lib/util/service.version $(VERSION) \
//   -X github.com/jeffail/benthos/lib/util/service.dateBuilt $(DATE)"
//
// Returns a flag indicating whether the service should continue or not.
func Bootstrap(configPtr interface{}, defaultConfigPaths ...string) bool {
	// Ensure that cmd flags are parsed.
	if !flag.Parsed() {
		flag.Parse()
	}

	// If the user wants the version we print it.
	if *showVersion {
		fmt.Printf("Version: %v\nDate: %v\n", version, dateBuilt)
		return false
	}

	if len(*configPath) > 0 {
		if err := readConfig(*configPath, configPtr); err != nil {
			fmt.Fprintf(os.Stderr, "Configuration file read error: %v\n", err)
			return false
		}
	} else {
		// Iterate default config paths
		for _, path := range defaultConfigPaths {
			if _, err := os.Stat(path); err == nil {
				fmt.Fprintf(os.Stderr, "Config file not specified, reading from %v\n", path)

				if err = readConfig(path, configPtr); err != nil {
					fmt.Fprintf(os.Stderr, "Configuration file read error: %v\n", err)
					return false
				}
				break
			}
		}
	}

	// If the user wants the configuration to be printed we do so and then exit.
	if *showConfigJSON {
		if configJSON, err := json.MarshalIndent(configPtr, "", "\t"); err == nil {
			fmt.Println(string(configJSON))
		} else {
			fmt.Fprintln(os.Stderr, fmt.Sprintf("Configuration marshal error: %v", err))
		}
		return false
	} else if *showConfigYAML {
		if configYAML, err := yaml.Marshal(configPtr); err == nil {
			fmt.Println(string(configYAML))
		} else {
			fmt.Fprintln(os.Stderr, fmt.Sprintf("Configuration marshal error: %v", err))
		}
		return false
	}
	return true
}

//------------------------------------------------------------------------------