throw better errors when app errors and fix hang (#294)

* throw better errors when app errors

* small improvements

* show nice errors in more places

* add back mark_displayed!

src/HTTPServer/helper.jl

@@ -12,15 +12,16 @@ function response_404(body="Not Found")
     ], body=body)
 end
 
-function response_500(exception)
-    body = sprint(io-> Base.showerror(io, exception))
+function response_500(html)
     return HTTP.Response(404, [
         "Content-Type" => "text/html",
         "charset" => "utf-8",
         # Avoids throwing lots of errors in the devtools console when
         # VSCode tries to load non-existent resources from the plots pane.
         "Access-Control-Allow-Origin" => "*",
-    ], body=body)
+        ];
+        body=html,
+    )
 end
 
 # TODO, how to do this without pircay? THis happens inside HTTP, so we can't just use try & catch in our own code

src/HTTPServer/implementation.jl

@@ -88,6 +88,58 @@ function apply_handler(chain::Tuple, context, args...)
     return apply_handler(Base.tail(chain), context, result...)
 end
 
+function linkify_stacktrace(bt::String)
+    lines = split(bt, '\n'; keepempty=false)  # Split stack trace into lines
+    elements = []
+
+    for line in lines
+        # Match both Windows (C:\path\file.jl:123) and Unix (/path/file.jl:123) paths
+        m = match(r"^(.*?)([A-Za-z]:[\\/][^\s]+\.jl|\.[\\/][^\s]+\.jl):(\d+)(.*)", line)
+        if m !== nothing
+            prefix, file, line_num, suffix = m.captures
+            normalized_file = replace(file, "\\" => "/")  # Convert Windows paths to `/`
+            vscode_url = "vscode://file/" * normalized_file * ":" * line_num  # VS Code link
+            push!(
+                elements,
+                DOM.span(
+                    String(prefix),
+                    DOM.a(file * ":" * line_num; href=vscode_url),
+                    String(suffix),
+                ),
+                DOM.br(),
+            )
+        else
+            m2 = match(r"^(.*?)(\[\d+\])", line)
+            if !isnothing(m2)
+                prefix, suffix = m2.captures
+                push!(
+                    elements,
+                    DOM.span(String(line); style="color: darkred; font-weight: bold;"),
+                    DOM.br(),
+                )  # Normal line
+            else
+                push!(elements, DOM.span(String(line)), DOM.br())  # Normal line
+            end
+        end
+    end
+    return DOM.pre(
+        elements...; class="backtrace", style="white-space: nowrap; overflow-x: auto;"
+    )
+end
+
+function err_to_html(err, stacktrace)
+    error_msg = sprint() do io
+        Base.showerror(io, err)
+    end
+    stacktrace_msg = sprint() do io
+        iol = IOContext(io, :stacktrace_types_limited => Base.RefValue(true))
+        Base.show_backtrace(iol, stacktrace)
+    end
+    return DOM.div(
+        DOM.h1(error_msg; style="color: red;"), linkify_stacktrace(stacktrace_msg)
+    )
+end
+
 function delegate(routes::Routes, application, request::Request, args...)
     try
         for (pattern, f) in routes.table
@@ -107,9 +159,14 @@ function delegate(routes::Routes, application, request::Request, args...)
         # What a classic this response!
         return response_404("Didn't find route for $(request.target)")
     catch e
-        err = CapturedException(e, Base.catch_backtrace())
+        stacktrace = Base.catch_backtrace()
+        err = CapturedException(e, stacktrace)
         Base.showerror(stderr, err)
-        return response_500(err)
+        html = err_to_html(e, stacktrace)
+        html_str = sprint() do io
+            Bonito.print_as_page(io,  html)
+        end
+        return response_500(html_str)
     end
 end
 

src/app.jl

@@ -34,11 +34,17 @@ function update_app!(parent::Session, new_app::App)
     update_session_dom!(parent, "subsession-application-dom", new_app)
 end
 
+
 function rendered_dom(session::Session, app::App, target=HTTP.Request())
     app.session[] = session
     session.current_app[] = app
-    dom = Base.invokelatest(app.handler, session, target)
-    return jsrender(session, dom)
+    try
+        dom = Base.invokelatest(app.handler, session, target)
+        return jsrender(session, dom)
+    catch err
+        html = HTTPServer.err_to_html(err, Base.catch_backtrace())
+        return jsrender(session, html)
+    end
 end
 
 function bind_global(session::Session, var::AbstractObservable{T}) where T
@@ -57,9 +63,8 @@ function serve_app(app, context)
     html_str = sprint() do io
         page_html(io, session, html_dom)
     end
-    response = html(html_str)
     mark_displayed!(session)
-    return response
+    return html(html_str)
 end
 
 # Enable route!(server, "/" => app)
@@ -161,5 +166,7 @@ end
 function wait_for_ready(app::App; timeout=100)
     wait_for(()-> !isnothing(app.session[]); timeout=timeout)
     isclosed(app.session[]) && return nothing
-    wait_for(()-> isready(app.session[]); timeout=timeout)
+    wait_for(timeout=timeout) do
+        isready(app.session[]) || isclosed(app.session[])
+    end
 end