--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/cmd/sievemgr/internal/config/config.go	Tue Nov 03 23:44:45 2020 +0100
@@ -0,0 +1,105 @@
+// Copyright (C) 2020 Guido Berhoerster <guido+sievemgr@berhoerster.name>
+//
+// 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, subject 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 config
+
+import (
+	"bufio"
+	"bytes"
+	"fmt"
+	"os"
+	"path/filepath"
+)
+
+const bom = '\ufeff'
+
+type ParserError struct {
+	Message string
+	LineNo  int
+}
+
+func (e *ParserError) Error() string {
+	if e.LineNo > 0 {
+		return fmt.Sprintf("error in line %d: %s", e.LineNo, e.Message)
+	}
+	return e.Message
+}
+
+func NewParserError(message string, lineNo int) *ParserError {
+	return &ParserError{message, lineNo}
+}
+
+type Configuration struct {
+	Accounts []*Account
+	Default  *Account
+}
+
+type Account struct {
+	Name     string
+	Host     string
+	Port     string
+	User     string
+	Password string
+	Insecure bool
+}
+
+func Parse(data []byte, conf *Configuration) error {
+	rd := bytes.NewReader(data)
+	s := newScanner(bufio.NewReader(rd))
+	p := &parser{s: s}
+	return p.parse(conf)
+}
+
+func DefaultFilename() (string, error) {
+	dir, err := os.UserConfigDir()
+	if err != nil {
+		return "", fmt.Errorf("failed to determine the name of the configuration file: %s", err)
+	}
+	return filepath.Join(dir, "sievemgr", "sievemgr.conf"), nil
+}
+
+func ParseFile(filename string, conf *Configuration) error {
+	f, err := os.Open(filename)
+	if os.IsNotExist(err) {
+		return nil
+	} else if err != nil {
+		return fmt.Errorf("failed to open configuration file: %s", err)
+	}
+	defer f.Close()
+
+	// configutaion file must be a regular file with no more than 0600
+	// permissions
+	info, err := f.Stat()
+	if err != nil {
+		return fmt.Errorf("failed to stat configuration file: %s", err)
+	}
+	mode := info.Mode()
+	if !mode.IsRegular() {
+		return fmt.Errorf("configuration file is not a regular file")
+	}
+	if perm := mode.Perm(); perm&0077 != 0 {
+		return fmt.Errorf("permissions %04o on configuration file are too open", perm)
+	}
+
+	s := newScanner(bufio.NewReader(f))
+	p := &parser{s: s}
+	return p.parse(conf)
+}