poseidon/config/config.go

package config

import (
	"crypto/tls"
	"errors"
	"flag"
	"fmt"
	"gitlab.hpi.de/codeocean/codemoon/poseidon/logging"
	"gopkg.in/yaml.v3"
	"net/url"
	"os"
	"reflect"
	"strconv"
	"strings"
)

// Config contains the default configuration of Poseidon.
var (
	Config = &configuration{
		Server: server{
			Address: "127.0.0.1",
			Port:     3000,
			Token:    "",
			TLS:      false,
			CertFile: "",
			KeyFile:  "",
		},
		Nomad: nomad{
			Address: "",
			Port:    4646,
			Token:   "",
			TLS:     false,
		},
		Logger: logger{
			Level: "INFO",
		},
	}
	configurationFilePath    = "./configuration.yaml"
	configurationInitialized = false
	log                      = logging.GetLogger("config")
	TLSConfig                = &tls.Config{
		MinVersion:               tls.VersionTLS13,
		CurvePreferences:         []tls.CurveID{tls.CurveP521, tls.CurveP384, tls.CurveP256},
		PreferServerCipherSuites: true,
	}
)

// server configures the Poseidon webserver.
type server struct {
	Address  string
	Port     int
	Token    string
	TLS      bool
	CertFile string
	KeyFile  string
}

// nomad configures the used Nomad cluster.
type nomad struct {
	Address string
	Port    int
	Token   string
	TLS     bool
}

// logger configures the used logger.
type logger struct {
	Level string
}

// configuration contains the complete configuration of Poseidon.
type configuration struct {
	Server server
	Nomad  nomad
	Logger logger
}

// InitConfig merges configuration options from environment variables and
// a configuration file into the default configuration. Calls of InitConfig
// after the first call have no effect and return an error. InitConfig
// should be called directly after starting the program.
func InitConfig() error {
	if configurationInitialized {
		return errors.New("configuration is already initialized")
	}
	configurationInitialized = true
	content := readConfigFile()
	Config.mergeYaml(content)
	Config.mergeEnvironmentVariables()
	return nil
}

func (c *configuration) NomadAPIURL() *url.URL {
	return parseURL(Config.Nomad.Address, Config.Nomad.Port, Config.Nomad.TLS)
}

func (c *configuration) PoseidonAPIURL() *url.URL {
	return parseURL(Config.Server.Address, Config.Server.Port, false)
}

func parseURL(address string, port int, tls bool) *url.URL {
	scheme := "http"
	if tls {
		scheme = "https"
	}
	return &url.URL{
		Scheme: scheme,
		Host:   fmt.Sprintf("%s:%d", address, port),
	}
}

func readConfigFile() []byte {
	parseFlags()
	data, err := os.ReadFile(configurationFilePath)
	if err != nil {
		log.WithError(err).Info("Using default configuration...")
	}
	return data
}

func parseFlags() {
	if flag.Lookup("config") == nil {
		flag.StringVar(&configurationFilePath, "config", configurationFilePath, "path of the yaml config file")
	}
	flag.Parse()
}

func (c *configuration) mergeYaml(content []byte) {
	if err := yaml.Unmarshal(content, c); err != nil {
		log.WithError(err).Fatal("Could not parse configuration file")
	}
}

func (c *configuration) mergeEnvironmentVariables() {
	readFromEnvironment("POSEIDON", reflect.ValueOf(c).Elem())
}

func readFromEnvironment(prefix string, value reflect.Value) {
	logEntry := log.WithField("prefix", prefix)
	// if value was not derived from a pointer, it is not possible to alter its contents
	if !value.CanSet() {
		logEntry.Warn("Cannot overwrite struct field that can not be set")
		return
	}

	if value.Kind() != reflect.Struct {
		content, ok := os.LookupEnv(prefix)
		if !ok {
			return
		}
		logEntry = logEntry.WithField("content", content)

		switch value.Kind() {
		case reflect.String:
			value.SetString(content)
		case reflect.Int:
			integer, err := strconv.Atoi(content)
			if err != nil {
				logEntry.Warn("Could not parse environment variable as integer")
				return
			}
			value.SetInt(int64(integer))
		case reflect.Bool:
			boolean, err := strconv.ParseBool(content)
			if err != nil {
				logEntry.Warn("Could not parse environment variable as boolean")
				return
			}
			value.SetBool(boolean)
		default:
			// ignore this field
			logEntry.WithField("type", value.Type().Name()).Warn("Setting configuration option via environment variables is not supported")
		}
	} else {
		for i := 0; i < value.NumField(); i++ {
			fieldName := value.Type().Field(i).Name
			newPrefix := fmt.Sprintf("%s_%s", prefix, strings.ToUpper(fieldName))
			readFromEnvironment(newPrefix, value.Field(i))
		}
	}
}