Go app framework

pkg/config/config.go

@@ -0,0 +1,69 @@
+package config
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"os"
+	"runtime/debug"
+
+	"github.com/caarlos0/env/v9"
+	"gopkg.in/yaml.v3"
+)
+
+// To be set by ldflags in go build command or
+// retrieved from build meta below
+var Version = "(devel)"
+
+// Calling this will try to load from config if -config is
+// provided as a file, and will apply any environment overrides
+// on-top of configuration defaults.
+// Config is stored in returned context, and can be retrieved
+// using config.FromCtx(ctx)
+func LoadConfig(ctx context.Context) (context.Context, error) {
+	configPath := flag.String("config", "", "Path to the configuration file")
+	flag.Parse()
+
+	// Start with defaults
+	// Load from config if provided
+	// Layer on environment
+	cfg, err := loadConfig(*configPath)
+	if err != nil {
+		return ctx, err
+	}
+
+	// Add config to context, and return
+	// an updated context
+	ctx = cfg.AddToCtx(ctx)
+	return ctx, nil
+}
+
+func loadConfig(configPath string) (*AppConfig, error) {
+	cfg := newAppConfig()
+
+	if configPath != "" {
+		file, err := os.Open(configPath)
+		if err != nil {
+			return nil, fmt.Errorf("could not open config file: %w", err)
+		}
+		defer file.Close()
+
+		decoder := yaml.NewDecoder(file)
+		if err := decoder.Decode(cfg); err != nil {
+			return nil, fmt.Errorf("could not decode config file: %w", err)
+		}
+	}
+
+	if err := env.Parse(cfg); err != nil {
+		return nil, fmt.Errorf("could not parse environment variables: %w", err)
+	}
+
+	return cfg, nil
+}
+
+func getVersion() string {
+	if info, ok := debug.ReadBuildInfo(); ok && info.Main.Version != "(devel)" {
+		return info.Main.Version
+	}
+	return Version
+}

pkg/config/ctx.go

@@ -0,0 +1,36 @@
+package config
+
+import (
+	"context"
+	"errors"
+)
+
+type appConfigKey uint8
+
+const appConfigCtxKey appConfigKey = iota
+
+func (a *AppConfig) AddToCtx(ctx context.Context) context.Context {
+	return context.WithValue(ctx, appConfigCtxKey, a)
+}
+
+func MustFromCtx(ctx context.Context) *AppConfig {
+	cfg, err := FromCtx(ctx)
+	if err != nil {
+		panic(err)
+	}
+	return cfg
+}
+
+func FromCtx(ctx context.Context) (*AppConfig, error) {
+	ctxData := ctx.Value(appConfigCtxKey)
+	if ctxData == nil {
+		return nil, errors.New("no config found in context")
+	}
+
+	cfg, ok := ctxData.(*AppConfig)
+	if !ok {
+		return nil, errors.New("invalid config stored in context")
+	}
+
+	return cfg, nil
+}

pkg/config/types.go

@@ -0,0 +1,70 @@
+package config
+
+func newAppConfig() *AppConfig {
+	return &AppConfig{
+		Version: getVersion(),
+		Logging: &LogConfig{},
+		HTTP:    &HTTPConfig{},
+		OTEL:    &OTELConfig{},
+	}
+}
+
+type AppConfig struct {
+	Name        string `yaml:"name" env:"APP_NAME" envDefault:"go-http-server-with-otel"`
+	Environment string `yaml:"environment" env:"APP_ENVIRONMENT" envDefault:"development"`
+	// This should either be set by ldflags, such as with
+	// go build -ldflags "-X gitea.libretechconsulting.com/rmcguire/go-app/pkg/config.Version=$(VERSION)"
+	// or allow this to use build meta. Will default to (devel)
+	Version string      `yaml:"version" env:"APP_VERSION"`
+	Logging *LogConfig  `yaml:"logging"`
+	HTTP    *HTTPConfig `yaml:"http"`
+	OTEL    *OTELConfig `yaml:"otel"`
+}
+
+// Logging Configuration
+type LogConfig struct {
+	Enabled    bool       `yaml:"enabled" env:"APP_LOG_ENABLED" envDefault:"true"`
+	Level      string     `yaml:"level" env:"APP_LOG_LEVEL" envDefault:"info"`
+	Format     LogFormat  `yaml:"format" env:"APP_LOG_FORMAT" envDefault:"json"`
+	Output     LogOutput  `yaml:"output" env:"APP_LOG_OUTPUT" envDefault:"stderr"`
+	TimeFormat TimeFormat `yaml:"timeFormat" env:"APP_LOG_TIME_FORMAT" envDefault:"short"`
+}
+
+type LogFormat string
+
+const (
+	LogFormatConsole LogFormat = "console"
+	LogFormatJSON    LogFormat = "json"
+)
+
+type TimeFormat string
+
+const (
+	TimeFormatShort   TimeFormat = "short"
+	TimeFormatLong    TimeFormat = "long"
+	TimeFormatUnix    TimeFormat = "unix"
+	TimeFormatRFC3339 TimeFormat = "rfc3339"
+	TimeFormatOff     TimeFormat = "off"
+)
+
+type LogOutput string
+
+const (
+	LogOutputStdout LogOutput = "stdout"
+	LogOutputStderr LogOutput = "stderr"
+)
+
+// HTTP Configuration
+type HTTPConfig struct {
+	Listen         string `yaml:"listen" env:"APP_HTTP_LISTEN" envDefault:"127.0.0.1:8080"`
+	RequestTimeout int    `yaml:"requestTimeout" env:"APP_HTTP_REQUEST_TIMEOUT" envDefault:"30"`
+}
+
+// OTEL Configuration
+type OTELConfig struct {
+	Enabled            bool   `yaml:"enabled" env:"APP_OTEL_ENABLED" envDefault:"true"`
+	PrometheusEnabled  bool   `yaml:"prometheusEnabled" env:"APP_OTEL_PROMETHEUS_ENABLED" envDefault:"true"`
+	PrometheusPath     string `yaml:"prometheusPath" env:"APP_OTEL_PROMETHEUS_PATH" envDefault:"/metrics"`
+	StdoutEnabled      bool   `yaml:"stdoutEnabled" env:"APP_OTEL_STDOUT_ENABLED" envDefault:"false"`
+	MetricIntervalSecs int    `yaml:"metricIntervalSecs" env:"APP_OTEL_METRIC_INTERVAL_SECS" envDefault:"15"`
+}