moved server code to internal/server

internal/server/Config.go

@@ -0,0 +1,81 @@
+package server
+
+import (
+	"encoding"
+	"errors"
+	"fmt"
+	"io/fs"
+	"net"
+	"os"
+
+	"github.com/BurntSushi/toml"
+)
+
+type Config struct {
+	Port uint16 `toml:"port"`
+	Ip   IP     `toml:"ip"`
+}
+
+func ReadConfig(path string) (*Config, error) {
+	var config = new(Config)
+	tomlMeta, err := toml.DecodeFile(path, config)
+	if err != nil {
+		return nil, err
+	}
+
+	// check if toml contains unknown keys
+	if undecodedKeys := tomlMeta.Undecoded(); len(undecodedKeys) > 0 {
+		return nil, fmt.Errorf("%s: unknown keys: %v", path, undecodedKeys)
+	}
+
+	return config, nil
+}
+
+func DefaultConfig() *Config {
+	return &Config{
+		Port: 8080,
+		Ip:   IP{net.IPv4(127, 0, 0, 1)},
+	}
+}
+
+func ParseOrCreateConfig(path string) (*Config, error) {
+	config, err := ReadConfig(path)
+	if !errors.Is(err, fs.ErrNotExist) {
+		return config, err // either a parsed config, or a real error
+	}
+	config = DefaultConfig()
+	return config, WriteConfig(config, path)
+}
+
+func WriteConfig(config *Config, path string) (err error) {
+	f, err := os.OpenFile(path, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0o644)
+	if err != nil {
+		return err
+	}
+	defer func() {
+		// Close can report a failed write, so its error matters
+		if closeErr := f.Close(); err == nil {
+			err = closeErr
+		}
+	}()
+	enc := toml.NewEncoder(f)
+	enc.Indent = "    " // 4
+	return enc.Encode(config)
+}
+
+type IP struct {
+	net.IP
+}
+
+var _ encoding.TextUnmarshaler = (*IP)(nil)
+var _ encoding.TextMarshaler = IP{}
+
+func (a *IP) UnmarshalText(text []byte) error {
+	s := string(text)
+	ip := net.ParseIP(s)
+	if ip == nil {
+		return errors.New("can't parse '" + s + "' as IP address")
+	}
+	a.IP = ip
+	return nil
+}