fix(gmail): land charset fallback note (#428) (thanks @WinnCook)

CHANGELOG.md

@@ -19,6 +19,7 @@
 - Auth: keep Keep-only service-account fallback isolated to Keep commands so other Google services do not accidentally pick it up. (#414) — thanks @jgwesterlund.
 - Contacts: send the required `copyMask` when deleting "other contacts", avoiding People API 400 errors. (#384) — thanks @rbansal42.
 - Calendar: hide cancelled/deleted events from `calendar events` list output by explicitly setting `showDeleted=false`. (#362) — thanks @sharukh010.
+- Gmail: fall back to `MimeType` charset hints when `Content-Type` headers are missing so GBK/GB2312 message bodies decode correctly. (#428) — thanks @WinnCook.
 - Gmail: add a fetch delay in `watch serve` so History API reads don't race message indexing. (#397) — thanks @salmonumbrella.
 - Gmail: allow Workspace-managed send-as aliases with empty verification status in `send` and `drafts create`. (#407) — thanks @salmonumbrella.
 - Gmail: preserve the selected `--client` during `watch serve` push handling instead of falling back to the default client. (#411) — thanks @chrysb.

internal/cmd/gmail_thread.go

@@ -462,7 +462,11 @@ func decodePartBody(p *gmail.MessagePart) (string, error) {
 		decoded = decodeTransferEncoding(decoded, cte)
 	}
 
-	if contentType := strings.TrimSpace(headerValue(p, "Content-Type")); contentType != "" {
+	contentType := strings.TrimSpace(headerValue(p, "Content-Type"))
+	if contentType == "" {
+		contentType = strings.TrimSpace(p.MimeType)
+	}
+	if contentType != "" {
 		decoded = decodeBodyCharset(decoded, contentType)
 	}
 

internal/cmd/gmail_thread_helpers_test.go

@@ -7,7 +7,9 @@ import (
 	"path/filepath"
 	"testing"
 
+	"golang.org/x/text/encoding/ianaindex"
 	"golang.org/x/text/encoding/japanese"
+	"golang.org/x/text/encoding/simplifiedchinese"
 	"google.golang.org/api/gmail/v1"
 )
 
@@ -297,6 +299,40 @@ func TestDecodeBodyCharset_ISO2022JP_TruncatedEscapeSequence(t *testing.T) {
 	}
 }
 
+func TestDecodeBodyCharset_GBK(t *testing.T) {
+	source := "您的阿里云账户已欠费即将停服提醒"
+	enc, err := ianaindex.MIME.Encoding("gbk")
+	if err != nil || enc == nil {
+		t.Fatalf("lookup gbk encoding: %v", err)
+	}
+	encoded, err := enc.NewEncoder().Bytes([]byte(source))
+	if err != nil {
+		t.Fatalf("encode gbk: %v", err)
+	}
+	got := decodeBodyCharset(encoded, "text/plain; charset=gbk")
+	if string(got) != source {
+		t.Fatalf("unexpected decoded charset: expected %q, got %q", source, string(got))
+	}
+}
+
+func TestFindPartBody_UsesMimeTypeCharsetWhenHeaderMissing(t *testing.T) {
+	source := "您的阿里云账户已欠费即将停服提醒"
+	encodedBody, err := simplifiedchinese.GBK.NewEncoder().Bytes([]byte(source))
+	if err != nil {
+		t.Fatalf("encode gb2312: %v", err)
+	}
+	part := &gmail.MessagePart{
+		MimeType: "text/plain; charset=gb2312",
+		Body: &gmail.MessagePartBody{
+			Data: base64.RawURLEncoding.EncodeToString(encodedBody),
+		},
+	}
+	got := findPartBody(part, "text/plain")
+	if got != source {
+		t.Fatalf("unexpected decoded body: expected %q, got %q", source, got)
+	}
+}
+
 func TestMimeTypeMatches(t *testing.T) {
 	if !mimeTypeMatches("Text/Plain; charset=UTF-8", "text/plain") {
 		t.Fatalf("expected mime match")