From e7958936e4cce981a25ea8072f33b61d209573df Mon Sep 17 00:00:00 2001
From: mizho <mizuho128@gmail.com>
Date: Wed, 16 Oct 2024 01:05:22 +0900
Subject: [PATCH] Subject mime decode functions and test

---
 store/search.go      | 60 ++++++++++++++++++++++++++++++++++++++++++++
 store/search_test.go | 38 ++++++++++++++++++++++++++++
 2 files changed, 98 insertions(+)
 create mode 100644 store/search_test.go

diff --git a/store/search.go b/store/search.go
index ec4858adde..10a396391c 100644
--- a/store/search.go
+++ b/store/search.go
@@ -2,13 +2,21 @@ package store
 
 import (
 	"bytes"
+	"encoding/base64"
+	"fmt"
 	"io"
+	"regexp"
 	"strings"
 	"unicode"
 	"unicode/utf8"
 
 	"github.com/mjl-/mox/message"
 	"github.com/mjl-/mox/mlog"
+
+	"golang.org/x/text/encoding"
+	"golang.org/x/text/encoding/japanese"
+	encUnicode "golang.org/x/text/encoding/unicode"
+	"golang.org/x/text/transform"
 )
 
 // WordSearch holds context for a search, with scratch buffers to prevent
@@ -193,3 +201,55 @@ func toLower(buf []byte) []byte {
 	}
 	return r
 }
+
+func decodeRFC2047(encoded string) (string, error) {
+	// match e.g. =?(iso-2022-jp)?(B)?(Rnc6...)?=
+	r := regexp.MustCompile(`=\?([^?]+)\?([BQ])\?([^?]+)\?=`)
+	matches := r.FindAllStringSubmatch(encoded, -1)
+
+	if len(matches) == 0 { // no match. Looks ASCII.
+		return encoded, nil
+	}
+
+	var decodedStrings []string
+	for _, match := range matches {
+		charset := match[1]
+		encodingName := match[2]
+		encodedText := match[3]
+
+		// Decode Base64 or Quoted-Printable
+		var decodedBytes []byte
+		var err error
+		if encodingName == "B" {
+			decodedBytes, err = base64.StdEncoding.DecodeString(encodedText)
+			if err != nil {
+				return "", fmt.Errorf("Base64 decode error: %w", err)
+			}
+		} else {
+			return "", fmt.Errorf("not supported encoding: %s", encodingName)
+		}
+
+		// Select charset
+		var enc encoding.Encoding
+		switch strings.ToLower(charset) {
+		case "iso-2022-jp":
+			enc = japanese.ISO2022JP
+		case "utf-8":
+			enc = encUnicode.UTF8
+		default:
+			return "", fmt.Errorf("not supported charset: %s", charset)
+		}
+
+		// Decode with charset
+		reader := transform.NewReader(strings.NewReader(string(decodedBytes)), enc.NewDecoder())
+		decodedText, err := io.ReadAll(reader)
+		if err != nil {
+			return "", err
+		}
+
+		decodedStrings = append(decodedStrings, string(decodedText))
+	}
+
+	// Concat multiple strings
+	return strings.Join(decodedStrings, ""), nil
+}
diff --git a/store/search_test.go b/store/search_test.go
new file mode 100644
index 0000000000..995bb05663
--- /dev/null
+++ b/store/search_test.go
@@ -0,0 +1,38 @@
+package store
+
+import (
+	"fmt"
+	"testing"
+)
+
+func TestSubjectMatch(t *testing.T) {
+	// Auto detect subject text encoding and decode
+
+	//log := mlog.New("search", nil)
+
+	originalSubject := `テストテキスト Abc 123...`
+	asciiSubject := "test text Abc 123..."
+
+	encodedSubjectUTF8 := `=?UTF-8?B?44OG44K544OI44OG44Kt44K544OIIEFiYyAxMjMuLi4=?=`
+	encodedSubjectISO2022 := `=?iso-2022-jp?B?GyRCJUYlOSVIJUYlLSU5JUgbKEIgQWJjIDEyMy4uLg==?=`
+	encodedSubjectUTF8 = encodedSubjectUTF8 + " \n " + encodedSubjectUTF8
+	encodedSubjectISO2022 = encodedSubjectISO2022 + " \n " + encodedSubjectISO2022
+	originalSubject = originalSubject + originalSubject
+
+	encodedTexts := map[string]string{encodedSubjectUTF8: originalSubject, encodedSubjectISO2022: originalSubject, asciiSubject: asciiSubject}
+
+	for encodedSubject, originalSubject := range encodedTexts {
+
+		// Autodetect & decode
+		decodedSubject, err := decodeRFC2047(encodedSubject)
+
+		fmt.Printf("decoded text:%s\n", decodedSubject)
+		if err != nil {
+			t.Fatalf("Decode error: %v", err)
+		}
+
+		if originalSubject != decodedSubject {
+			t.Fatalf("Decode mismatch %s != %s", originalSubject, decodedSubject)
+		}
+	}
+}