refactor: add utils responsible for encoding/decoding cursors

internal/domain/utils.go

@@ -1,7 +1,10 @@
 package domain
 
 import (
+	"bytes"
+	"encoding/base64"
 	"net/url"
+	"strings"
 )
 
 func parseURL(rawURL string) (*url.URL, error) {
@@ -14,3 +17,56 @@ func parseURL(rawURL string) (*url.URL, error) {
 
 	return u, nil
 }
+
+const (
+	cursorSeparator         = ","
+	cursorKeyValueSeparator = "="
+)
+
+func encodeCursor(m map[string]string) string {
+	if len(m) == 0 {
+		return ""
+	}
+
+	n := len(cursorSeparator) * (len(m) - 1)
+	for k, v := range m {
+		n += len(k) + len(v) + len(cursorKeyValueSeparator)
+	}
+
+	var b bytes.Buffer
+	b.Grow(n)
+
+	for k, v := range m {
+		if b.Len() > 0 {
+			_, _ = b.WriteString(cursorSeparator)
+		}
+
+		_, _ = b.WriteString(k)
+		_, _ = b.WriteString(cursorKeyValueSeparator)
+		_, _ = b.WriteString(v)
+	}
+
+	return base64.StdEncoding.EncodeToString(b.Bytes())
+}
+
+func decodeCursor(s string) (map[string]string, error) {
+	decodedBytes, err := base64.StdEncoding.DecodeString(s)
+	if err != nil {
+		return nil, ErrInvalidCursor
+	}
+	decoded := string(decodedBytes)
+
+	kvs := strings.Split(decoded, cursorSeparator)
+
+	m := make(map[string]string, len(kvs))
+
+	for _, kv := range kvs {
+		k, v, found := strings.Cut(kv, cursorKeyValueSeparator)
+		if !found {
+			return nil, ErrInvalidCursor
+		}
+		m[k] = v
+	}
+
+	return m, nil
+}

internal/domain/version.go

@@ -1,10 +1,8 @@
 package domain
 
 import (
-	"encoding/base64"
 	"fmt"
 	"net/url"
-	"strings"
 )
 
 const (
@@ -137,18 +135,12 @@ func decodeVersionCursor(encoded string) (VersionCursor, error) {
 		return VersionCursor{}, err
 	}
 
-	decodedBytes, err := base64.StdEncoding.DecodeString(encoded)
+	m, err := decodeCursor(encoded)
 	if err != nil {
-		return VersionCursor{}, ErrInvalidCursor
-	}
-	decoded := string(decodedBytes)
-
-	code, ok := strings.CutPrefix(decoded, "code=")
-	if !ok {
-		return VersionCursor{}, ErrInvalidCursor
+		return VersionCursor{}, err
 	}
 
-	vc, err := NewVersionCursor(code)
+	vc, err := NewVersionCursor(m["code"])
 	if err != nil {
 		return VersionCursor{}, ErrInvalidCursor
 	}
@@ -169,7 +161,9 @@ func (vc VersionCursor) Encode() string {
 		return ""
 	}
 
-	return base64.StdEncoding.EncodeToString([]byte("code=" + vc.code))
+	return encodeCursor(map[string]string{
+		"code": vc.code,
+	})
 }
 
 type ListVersionsParams struct {