webmail: fix js error rerendering additional headers after updated keywords

i've seen the error a few times:

	msgheaderElem.children[(msgheaderElem.children.length - 1)] is undefined

i've seen it happen after sending a reply (with the "answered" flag added).
the updateKeywords callback would render the message again, but the code for
rendering the "additional headers" table rows again was making invalid
assumptions.

the approach is now changed. the backend now just immediately sends the
additional headers to the frontend. before, the frontend would first render the
base message, then render again once the headers came in for the parsed
message. this also prevents a reflow for the (quite common) case that one of
the additional headers are present in the message.

webmail/webmail.go

@@ -376,7 +376,7 @@ func handle(apiHandler http.Handler, isForwarded bool, accountPath string, w htt
 	// Many of the requests need either a message or a parsed part. Make it easy to
 	// fetch/prepare and cleanup. We only do all the work when the request seems legit
 	// (valid HTTP route and method).
-	xprepare := func() (acc *store.Account, m store.Message, msgr *store.MsgReader, p message.Part, cleanup func(), ok bool) {
+	xprepare := func() (acc *store.Account, moreHeaders []string, m store.Message, msgr *store.MsgReader, p message.Part, cleanup func(), ok bool) {
 		if r.Method != "GET" {
 			http.Error(w, "405 - method not allowed - post required", http.StatusMethodNotAllowed)
 			return
@@ -404,7 +404,17 @@ func handle(apiHandler http.Handler, isForwarded bool, accountPath string, w htt
 		xcheckf(ctx, err, "open account")
 
 		m = store.Message{ID: id}
-		err = acc.DB.Get(ctx, &m)
+		err = acc.DB.Read(ctx, func(tx *bstore.Tx) error {
+			if err := tx.Get(&m); err != nil {
+				return err
+			}
+			s := store.Settings{ID: 1}
+			if err := tx.Get(&s); err != nil {
+				return fmt.Errorf("get settings for more headers: %v", err)
+			}
+			moreHeaders = s.ShowHeaders
+			return nil
+		})
 		if err == bstore.ErrAbsent || err == nil && m.Expunged {
 			http.NotFound(w, r)
 			return
@@ -486,7 +496,7 @@ func handle(apiHandler http.Handler, isForwarded bool, accountPath string, w htt
 
 	switch {
 	case len(t) == 2 && t[1] == "attachments.zip":
-		acc, m, msgr, p, cleanup, ok := xprepare()
+		acc, _, m, msgr, p, cleanup, ok := xprepare()
 		if !ok {
 			return
 		}
@@ -494,7 +504,7 @@ func handle(apiHandler http.Handler, isForwarded bool, accountPath string, w htt
 		state := msgState{acc: acc, m: m, msgr: msgr, part: &p}
 		// note: state is cleared by cleanup
 
-		mi, err := messageItem(log, m, &state)
+		mi, err := messageItem(log, m, &state, nil)
 		xcheckf(ctx, err, "parsing message")
 
 		headers(false, false, false, false)
@@ -605,7 +615,7 @@ func handle(apiHandler http.Handler, isForwarded bool, accountPath string, w htt
 
 	// Raw display of a message, as text/plain.
 	case len(t) == 2 && t[1] == "raw":
-		_, _, msgr, p, cleanup, ok := xprepare()
+		_, _, _, msgr, p, cleanup, ok := xprepare()
 		if !ok {
 			return
 		}
@@ -631,7 +641,7 @@ func handle(apiHandler http.Handler, isForwarded bool, accountPath string, w htt
 		// msg.html has a javascript tag with message data, and javascript to render the
 		// message header like the regular webmail.html and to load the message body in a
 		// separate iframe with a separate request with stronger CSP.
-		acc, m, msgr, p, cleanup, ok := xprepare()
+		acc, _, m, msgr, p, cleanup, ok := xprepare()
 		if !ok {
 			return
 		}
@@ -664,7 +674,7 @@ func handle(apiHandler http.Handler, isForwarded bool, accountPath string, w htt
 		// This is js with data inside instead so we can load it synchronously, which we do
 		// to get a "loaded" event after the page was actually loaded.
 
-		acc, m, msgr, p, cleanup, ok := xprepare()
+		acc, moreHeaders, m, msgr, p, cleanup, ok := xprepare()
 		if !ok {
 			return
 		}
@@ -679,7 +689,8 @@ func handle(apiHandler http.Handler, isForwarded bool, accountPath string, w htt
 
 		m.MsgPrefix = nil
 		m.ParsedBuf = nil
-		mi := MessageItem{m, pm.envelope, pm.attachments, pm.isSigned, pm.isEncrypted, pm.firstLine, false}
+		hl := messageItemMoreHeaders(moreHeaders, pm)
+		mi := MessageItem{m, pm.envelope, pm.attachments, pm.isSigned, pm.isEncrypted, pm.firstLine, false, hl}
 		mijson, err := json.Marshal(mi)
 		xcheckf(ctx, err, "marshal messageitem")
 
@@ -695,7 +706,7 @@ func handle(apiHandler http.Handler, isForwarded bool, accountPath string, w htt
 		// renders just the text content with the same code as webmail.html. Used by the
 		// iframe in the msgtext endpoint. Not used by the regular webmail viewer, it
 		// renders the text itself, with the same shared js code.
-		acc, m, msgr, p, cleanup, ok := xprepare()
+		acc, _, m, msgr, p, cleanup, ok := xprepare()
 		if !ok {
 			return
 		}
@@ -729,7 +740,7 @@ func handle(apiHandler http.Handler, isForwarded bool, accountPath string, w htt
 	case len(t) == 2 && (t[1] == "html" || t[1] == "htmlexternal"):
 		// Returns the first HTML part, with "cid:" URIs replaced with an inlined datauri
 		// if the referenced Content-ID attachment can be found.
-		_, _, _, p, cleanup, ok := xprepare()
+		_, _, _, _, p, cleanup, ok := xprepare()
 		if !ok {
 			return
 		}
@@ -783,7 +794,7 @@ func handle(apiHandler http.Handler, isForwarded bool, accountPath string, w htt
 		// data with a text/plain content-type so the browser will attempt to display it,
 		// and "download" adds a content-disposition header causing the browser the
 		// download the file.
-		_, _, _, p, cleanup, ok := xprepare()
+		_, _, _, _, p, cleanup, ok := xprepare()
 		if !ok {
 			return
 		}