Convert from BoltDB to Maildir storage for emails

internal/imap/uidlist/header.go

@@ -0,0 +1,131 @@
+package uidlist
+
+import (
+	"crypto/rand"
+	"encoding/hex"
+	"errors"
+	"fmt"
+	"strconv"
+	"strings"
+	"time"
+)
+
+const (
+	HeaderTemplate = "%d V%d N%d G%s"
+)
+
+type Header struct {
+	Version     uint64
+	UIDValidity uint64
+	NextUID     uint64
+	GUID        string
+	Extra       map[string][]string
+}
+
+func setUint64(s string, out *uint64) error {
+	num, err := strconv.ParseUint(s, 10, 64)
+	if err != nil {
+		return err
+	}
+
+	*out = uint64(num)
+	return nil
+}
+
+// GenerateHeader produces a valid verison 3 dovecot-uidlist header line, using
+// the time for UIDValidity and a random string for the GUID.
+func GenerateHeader() (Header, error) {
+	// A GUID is a random 128-bit number
+	guidBytes := make([]byte, 16)
+	_, err := rand.Read(guidBytes)
+	if err != nil {
+		return Header{}, err
+	}
+
+	// ...hex-encoded
+	guidString := hex.EncodeToString(guidBytes)
+
+	return Header{
+		Version:     uint64(3),
+		UIDValidity: uint64(time.Now().Unix()),
+		NextUID:     uint64(1),
+		GUID:        guidString,
+		Extra:       make(map[string][]string),
+	}, nil
+}
+
+// ParseHeader breaks a dovecot-uidlist header line into its constituent parts
+func ParseHeader(line string) (Header, error) {
+	var seenUIDValidity bool
+	var seenNextUID bool
+	var seenGUID bool
+
+	out := Header{}
+	parts := strings.Split(strings.TrimSpace(line), " ")
+	if len(parts) < 4 {
+		return out, errors.New("Short header")
+	}
+
+	if err := setUint64(parts[0], &out.Version); err != nil {
+		return out, err
+	}
+
+	out.Extra = make(map[string][]string)
+	for _, part := range parts[1:] {
+		part = strings.TrimSpace(part)
+
+		if len(part) == 0 {
+			continue
+		}
+
+		key := part[0:1]
+		value := part[1:]
+		switch key {
+		case "V":
+			if seenUIDValidity {
+				return out, errors.New("UIDVALIDITY specified twice")
+			}
+			seenUIDValidity = true
+
+			if err := setUint64(value, &out.UIDValidity); err != nil {
+				return out, err
+			}
+		case "N":
+			if seenNextUID {
+				return out, errors.New("NEXTUID specified twice")
+			}
+			seenNextUID = true
+
+			if err := setUint64(value, &out.NextUID); err != nil {
+				return out, err
+			}
+		case "G":
+			if seenGUID {
+				return out, errors.New("GUID specified twice")
+			}
+			seenGUID = true
+
+			out.GUID = value
+		default:
+			out.Extra[key] = append(out.Extra[key], value)
+		}
+	}
+
+	return out, nil
+}
+
+func (h Header) String() string {
+	var sb strings.Builder
+
+	fmt.Fprintf(
+		&sb,
+		HeaderTemplate,
+		h.Version, h.UIDValidity, h.NextUID, h.GUID,
+	)
+
+	for k, v := range h.Extra {
+		fmt.Fprintf(&sb, " %s%s", k, v)
+	}
+
+	return sb.String()
+}