clients: support async page fetching

An async fetch replaces a section of the page with content without full
page reload. Example syntax:

--form--
type="action" value="/remote/resource"
type="submit" label="Submit Invoice"
type="asynctarget" value="section_one"
--/form--

--section id=section_one --
--/section--

When the form is submitted, brclient/bruig fetches the contents of
/remote/resource, then replaces everything inside #section_one with it.

Sections and forms should not be nested (that is unsupported).

brclient/appstate.go

@@ -1281,9 +1281,8 @@ func (as *appState) findPagesChatWindow(sessID clientintf.PagesSessionID) *chatW
 	return nil
 }
 
-func (as *appState) findOrNewPagesChatWindow(sessID clientintf.PagesSessionID) *chatWindow {
+func (as *appState) findOrNewPagesChatWindow(sessID clientintf.PagesSessionID) (cw *chatWindow, isNew bool) {
 	as.chatWindowsMtx.Lock()
-	var cw *chatWindow
 	for i, acw := range as.chatWindows {
 		if acw.isPage && acw.pageSess == sessID {
 			if i != as.activeCW {
@@ -1303,10 +1302,11 @@ func (as *appState) findOrNewPagesChatWindow(sessID clientintf.PagesSessionID) *
 		}
 		as.chatWindows = append(as.chatWindows, cw)
 		as.updatedCW[len(as.chatWindows)-1] = false
+		isNew = true
 	}
 	as.chatWindowsMtx.Unlock()
 	as.footerInvalidate()
-	return cw
+	return
 }
 
 // markWindowUpdated marks the window as updated.
@@ -2447,7 +2447,7 @@ func (as *appState) downloadEmbed(source clientintf.UserID, embedded mdembeds.Em
 
 // fetchPage requests the given page from the user.
 func (as *appState) fetchPage(uid clientintf.UserID, pagePath string, session,
-	parent clientintf.PagesSessionID, form *formEl) error {
+	parent clientintf.PagesSessionID, form *formEl, asyncTargetId string) error {
 	if len(pagePath) < 1 {
 		return fmt.Errorf("page path is empty")
 	}
@@ -2498,14 +2498,15 @@ func (as *appState) fetchPage(uid clientintf.UserID, pagePath string, session,
 		return err
 	}
 
-	tag, err := as.c.FetchResource(uid, path, nil, session, parent, data)
+	tag, err := as.c.FetchResource(uid, path, nil, session, parent, data,
+		asyncTargetId)
 	if err != nil {
 		return err
 	}
 
 	// Mark session making a new request (if it already exists).
 	cw := as.findPagesChatWindow(session)
-	if cw != nil {
+	if cw != nil && asyncTargetId == "" {
 		cw.Lock()
 		cw.pageRequested = &path
 		cw.Unlock()
@@ -2514,6 +2515,9 @@ func (as *appState) fetchPage(uid clientintf.UserID, pagePath string, session,
 			// Initialize the page spinner.
 			as.sendMsg(msgActiveCWRequestedPage{[]tea.Cmd{cw.pageSpinner.Tick}})
 		}
+	} else if cw != nil && asyncTargetId != "" {
+		cw.replaceAsyncTargetWithLoading(asyncTargetId)
+		as.repaintIfActive(cw)
 	}
 
 	as.diagMsg("Attempting to fetch %s from %s (session %s, tag %s)",
@@ -3183,8 +3187,22 @@ func newAppState(sendMsg func(tea.Msg), lndLogLines *sloglinesbuffer.Buffer,
 			return
 		}
 
-		cw := as.findOrNewPagesChatWindow(fr.SessionID)
-		cw.replacePage(nick, fr)
+		cw, isNew := as.findOrNewPagesChatWindow(fr.SessionID)
+
+		// When this is the response to an async request and this is the
+		// first time this page is opened, load the entire history of
+		// the page and its async requests.
+		var history []*clientdb.FetchedResource
+		if isNew && fr.AsyncTargetID != "" {
+			history, err = as.c.LoadFetchedResource(uid, fr.SessionID, fr.ParentPage)
+			if err != nil {
+				as.diagMsg("Error loading history for page %s/%s: %v",
+					fr.SessionID, fr.ParentPage, err)
+				return
+			}
+		}
+
+		cw.replacePage(nick, fr, history)
 		sendMsg(msgPageFetched{
 			uid:  uid,
 			nick: nick,

brclient/chatwindow.go

@@ -189,6 +189,20 @@ type formEl struct {
 	fields []*formField
 }
 
+// asyncTarget returns the id of the target when the form has an asynctarget
+// field.
+func (f *formEl) asyncTarget() string {
+	for _, ff := range f.fields {
+		if ff.typ == "asynctarget" && ff.value != nil {
+			if target, ok := ff.value.(string); ok {
+				return target
+			}
+		}
+	}
+
+	return ""
+}
+
 func (f *formEl) action() string {
 	for _, ff := range f.fields {
 		if ff.typ == "action" && ff.value != nil {
@@ -215,6 +229,10 @@ func (f *formEl) toJson() (json.RawMessage, error) {
 	return json.RawMessage(res), nil
 }
 
+type sectionEl struct {
+	id string
+}
+
 // chatMsgEl is one element of a chat msg AST.
 type chatMsgEl struct {
 	text      string
@@ -407,6 +425,11 @@ func parseMsgLine(line string, mention string) *chatMsgElLine {
 	return res
 }
 
+var (
+	sectionStartRegexp = regexp.MustCompile(`--section id=([\w]+) --`)
+	sectionEndRegexp   = regexp.MustCompile(`--/section--`)
+)
+
 func parseMsgIntoElements(msg string, mention string) []*chatMsgElLine {
 	// First, break into lines.
 	lines := strings.Split(msg, "\n")
@@ -418,6 +441,10 @@ func parseMsgIntoElements(msg string, mention string) []*chatMsgElLine {
 			form = &formEl{}
 		case line == "--/form--":
 			form = nil
+		case sectionStartRegexp.MatchString(line):
+			// Skip section start line
+		case sectionEndRegexp.MatchString(line):
+			// Skip section end line
 		case form != nil:
 			ff := parseFormField(line)
 			if ff != nil {
@@ -429,6 +456,7 @@ func parseMsgIntoElements(msg string, mention string) []*chatMsgElLine {
 				el.PushBack(msgEl)
 				res = append(res, el)
 			}
+
 		default:
 			res = append(res, parseMsgLine(line, mention))
 		}
@@ -564,7 +592,54 @@ func (cw *chatWindow) newRecvdMsg(from, msg string, fromUID *zkidentity.ShortID,
 	return m
 }
 
-func (cw *chatWindow) replacePage(nick string, fr clientdb.FetchedResource) {
+func (cw *chatWindow) replaceAsyncTargetWithLoading(asyncTargetID string) {
+	cw.Lock()
+	defer cw.Unlock()
+
+	if len(cw.msgs) == 0 {
+		return
+	}
+	if cw.page == nil {
+		return
+	}
+
+	data := cw.page.Response.Data
+
+	reStartPattern := `--section id=` + asyncTargetID + ` --\n`
+	reStart, err := regexp.Compile(reStartPattern)
+	if err != nil {
+		// Skip invalid ids.
+		return
+	}
+
+	startPos := reStart.FindIndex(data)
+	if startPos == nil {
+		// Did not find the target location.
+		return
+	}
+
+	endPos := sectionEndRegexp.FindIndex(data[startPos[1]:])
+	if endPos == nil {
+		// Unterminated section.
+		return
+	}
+	endPos[0] += startPos[1] // Convert to absolute index
+
+	// Copy the rest of the string to an aux buffer.
+	aux := append([]byte(nil), data[endPos[0]:]...)
+
+	// Create the new buffer, replacing the contents inside
+	// the section with this response.
+	data = data[0:startPos[1]]
+	data = append(data, []byte("(⏳ Loading response)\n")...)
+	data = append(data, aux...)
+
+	msg := cw.msgs[0]
+	msg.elements = parseMsgIntoElements(string(data), "")
+	cw.page.Response.Data = data
+}
+
+func (cw *chatWindow) replacePage(nick string, fr clientdb.FetchedResource, history []*clientdb.FetchedResource) {
 	cw.Lock()
 	var msg *chatMsg
 	if len(cw.msgs) == 0 {
@@ -573,10 +648,70 @@ func (cw *chatWindow) replacePage(nick string, fr clientdb.FetchedResource) {
 	} else {
 		msg = cw.msgs[0]
 	}
-	msg.elements = parseMsgIntoElements(string(fr.Response.Data), "")
+
+	// Replace async targets.
+	var data, aux []byte
+	if len(history) > 0 || fr.AsyncTargetID != "" {
+		// If there is history, this is loading from disk, so use only
+		// whats in the slice. Otherwise, replace the response data.
+		var toProcess []*clientdb.FetchedResource
+		if len(history) > 0 {
+			data = history[0].Response.Data
+			toProcess = history[1:]
+		} else {
+			data = cw.page.Response.Data
+			toProcess = []*clientdb.FetchedResource{&fr}
+		}
+
+		// Process the async targets.
+		for _, asyncRes := range toProcess {
+			reStartPattern := `--section id=` + asyncRes.AsyncTargetID + ` --\n`
+			reStart, err := regexp.Compile(reStartPattern)
+			if err != nil {
+				// Skip invalid ids.
+				continue
+			}
+
+			startPos := reStart.FindIndex(data)
+			if startPos == nil {
+				// Did not find the target location.
+				continue
+			}
+
+			endPos := sectionEndRegexp.FindIndex(data[startPos[1]:])
+			if endPos == nil {
+				// Unterminated section.
+				continue
+			}
+			endPos[0] += startPos[1] // Convert to absolute index
+
+			// Copy the rest of the string to an aux buffer.
+			aux = append(aux, data[endPos[0]:]...)
+
+			// Create the new buffer, replacing the contents inside
+			// the section with this response.
+			data = data[0:startPos[1]]
+			data = append(data, asyncRes.Response.Data...)
+			data = append(data, aux...)
+			aux = aux[:0]
+		}
+	} else {
+		data = fr.Response.Data
+	}
+
+	msg.elements = parseMsgIntoElements(string(data), "")
 	msg.fromUID = &fr.UID
-	cw.page = &fr
-	cw.selElIndex = 0
+	if len(history) > 0 {
+		cw.page = history[0]
+	} else if fr.AsyncTargetID == "" {
+		cw.page = &fr
+	}
+	cw.page.Response.Data = data
+	if history != nil || fr.AsyncTargetID == "" {
+		// Only reset the selected element index when replacing the
+		// entire page.
+		cw.selElIndex = 0
+	}
 	cw.pageRequested = nil
 	cw.alias = fmt.Sprintf("%v/%v", nick, strings.Join(fr.Request.Path, "/"))
 	cw.Unlock()

brclient/commands.go

@@ -3113,7 +3113,7 @@ var pagesCommands = []tuicmd{
 			if len(args) > 1 {
 				pagePath = strings.TrimSpace(args[1])
 			}
-			return as.fetchPage(uid, pagePath, nextSess, 0, nil)
+			return as.fetchPage(uid, pagePath, nextSess, 0, nil, "")
 		},
 		completer: func(args []string, arg string, as *appState) []string {
 			if len(args) == 0 {
@@ -3135,7 +3135,7 @@ var pagesCommands = []tuicmd{
 			// Always use the same session ID for convenience when
 			// fetching a local page.
 			nextSess := clientintf.PagesSessionID(0)
-			return as.fetchPage(as.c.PublicID(), pagePath, nextSess, 0, nil)
+			return as.fetchPage(as.c.PublicID(), pagePath, nextSess, 0, nil, "")
 		},
 	},
 }

brclient/mainwindow.go

@@ -299,7 +299,7 @@ func (mws mainWindowState) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 					// Navigate to other page.
 					uid := cw.page.UID
 					err := mws.as.fetchPage(uid, *cw.selEl.link,
-						cw.page.SessionID, cw.page.PageID, nil)
+						cw.page.SessionID, cw.page.PageID, nil, "")
 					if err != nil {
 						mws.as.diagMsg("Unable to fetch page: %v", err)
 					}
@@ -316,7 +316,8 @@ func (mws mainWindowState) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 					action := cw.selEl.form.action()
 
 					err := mws.as.fetchPage(uid, action,
-						cw.page.SessionID, cw.page.PageID, cw.selEl.form)
+						cw.page.SessionID, cw.page.PageID,
+						cw.selEl.form, cw.selEl.form.asyncTarget())
 					if err != nil {
 						mws.as.diagMsg("Unable to fetch page: %v", err)
 					}
@@ -509,7 +510,7 @@ func (mws mainWindowState) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 			// Navigate to other page.
 			uid := cw.page.UID
 			err := mws.as.fetchPage(uid, *cw.selEl.link,
-				cw.page.SessionID, cw.page.PageID, nil)
+				cw.page.SessionID, cw.page.PageID, nil, "")
 			if err != nil {
 				mws.as.diagMsg("Unable to fetch page: %v", err)
 			}
@@ -525,7 +526,8 @@ func (mws mainWindowState) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 			// }
 
 			err := mws.as.fetchPage(uid, action,
-				cw.page.SessionID, cw.page.PageID, cw.selEl.form)
+				cw.page.SessionID, cw.page.PageID, cw.selEl.form,
+				cw.selEl.form.asyncTarget())
 			if err != nil {
 				mws.as.diagMsg("Unable to fetch page: %v", err)
 			}

bruig/flutterui/bruig/lib/components/md_elements.dart

@@ -357,7 +357,7 @@ class MarkdownArea extends StatelessWidget {
     var parentPageID = pageSource?.pageID ?? 0;
     try {
       await resources.fetchPage(
-          uid, parsed.pathSegments, sessionID, parentPageID, null);
+          uid, parsed.pathSegments, sessionID, parentPageID, null, "");
     } catch (exception) {
       snackbar.error("Unable to fetch page: $exception");
     }