gob fetcher for wasm example

go/cmd/examples/go-wasm-web/README.md

@@ -16,10 +16,19 @@ go run ./server            # codegen + SSR + hot reload at http://localhost:8085
 ```
 
 Open http://localhost:8085. `/` and `/about` use the light **public** layout;
-`/chart`, `/server`, and **`/kit`** (a UI-kit "kitchen-sink" demo of the webui
-components) use the dark **app** layout. Edit any `.go` file and the browser
-hot-swaps the new wasm **without a full reload or a flash**, preserving page
-state; a build failure shows the Go compiler output as an overlay.
+`/chart`, `/server`, **`/data`** (client-side fetching), and **`/kit`** (a UI-kit
+"kitchen-sink" demo of the webui components) use the dark **app** layout. Edit
+any `.go` file and the browser hot-swaps the new wasm **without a full reload or
+a flash**, preserving page state; a build failure shows the Go compiler output
+as an overlay.
+
+**Data fetching** (`/data`) shows both directions of `kjol/httputil`: the server
+answers `/api/quotes` with `httputil.RespondGob([]Quote)` and the client decodes
+it straight back into `[]Quote` with `httputil.FetchGob` (the same Go type on
+both ends — no JSON); and a **user-entered** GitHub repo (`owner/name`) is
+fetched with `httputil.FetchJSON` into a tagged Go struct. The client HTTP
+transport is `wasmruntime.FetchBytes`, injected once via
+`httputil.SetClientTransport`.
 
 Styling is **Tailwind**: the dev server (and `build.sh`) run `kjol/cmd/twcss`,
 which scans the Go markup + the `webui` kit for utility classes and compiles
@@ -41,6 +50,7 @@ app/                the application — neutral, standalone functions (no centra
   pages.go            Deps + Shell + App/Public layouts + nav + Counter + pages
   chart.go            Chart page (go-chart, renders on both sides)
   kit.go              /kit — UI-kit demo page showcasing kjol/webui components
+  data.go             /data — client fetch: gob from /api/quotes + third-party JSON
   server_counter.go   //gowasm:server component (server-only; clicks-over-time chart)
   *.gen.go            GENERATED by kjol/cmd/wasmgen (routes, layout dispatch, stubs)
 css/app.css         Tailwind entry (@import "tailwindcss" + @theme tokens)
@@ -57,6 +67,7 @@ wwwroot/            wasmboot.js (+ generated app.css, wasm_exec.js, app.wasm)
 | `kjol/wasmruntime` | wasm client runtime: reconcile, `Run`/`Hydrate`, router, fetch, HMR state | `wasm/main.go` calls `Hydrate`/`Run` |
 | `kjol/rsc` | stateless server components over HTTP (gob) | `//gowasm:server` + the generated client stub |
 | `kjol/wasmdevserver` | reusable dev server: SSR, `/rsc`, hot reload, error overlay | `server/main.go` fills a `wasmdevserver.Config` |
+| `kjol/httputil` | gob/JSON responders + typed client fetch (`RespondGob`, `FetchGob`, `FetchJSON`) | the `/data` page + the `/api/quotes` handler |
 | `kjol/cmd/wasmgen` | directive codegen → `app/*.gen.go` | run by `buildWasm` and `//go:generate` |
 
 The **golden rule** holds: `wasmdevserver` imports no app code. The app injects

go/cmd/examples/go-wasm-web/app/data.go

@@ -0,0 +1,147 @@
+package app
+
+import (
+	"strconv"
+	"strings"
+
+	"kjol/httputil"
+	. "kjol/vdom"
+	ui "kjol/webui"
+)
+
+// Quote is the payload the /api/quotes endpoint returns. The server encodes a
+// []Quote with httputil.RespondGob; the client decodes it straight back into
+// []Quote — the SAME Go type, no JSON, no hand-written unmarshalling.
+type Quote struct {
+	Author string
+	Text   string
+}
+
+// repoInfo is a subset of GitHub's repo JSON (a third-party API), tagged for
+// json decoding.
+type repoInfo struct {
+	FullName    string `json:"full_name"`
+	Description string `json:"description"`
+	Stars       int    `json:"stargazers_count"`
+}
+
+//gowasm:page /data layout=app
+func DataPage(d Deps) func() *VNode {
+	// (1) gob from our own server via httputil.RespondGob / FetchGob.
+	quotes := NewSignal([]Quote{})
+	qLoading := NewSignal(true)
+	qErr := NewSignal("")
+	// (2) JSON from a third-party API (GitHub), for a user-entered repo.
+	repo := NewSignal(repoInfo{})
+	rLoading := NewSignal(true)
+	rErr := NewSignal("")
+	repoQuery := NewSignal("golang/go")
+	started := false
+
+	// fetchRepo loads owner/name from the GitHub API into the repo signal.
+	fetchRepo := func(q string) {
+		q = strings.Trim(strings.TrimSpace(q), "/")
+		if q == "" {
+			rErr.Set("enter a repo as owner/name")
+			rLoading.Set(false)
+			return
+		}
+		rErr.Set("")
+		rLoading.Set(true)
+		httputil.FetchJSON("https://api.github.com/repos/"+q, func(r repoInfo, err error) {
+			if err != nil {
+				rErr.Set(err.Error())
+			} else {
+				repo.Set(r)
+			}
+			rLoading.Set(false)
+		})
+	}
+
+	return func() *VNode {
+		// Fire the initial fetches once, on the client (no transport on the server,
+		// so SSR ships the loading state and the client takes over).
+		if !started {
+			started = true
+			httputil.FetchGob("/api/quotes", func(qs []Quote, err error) {
+				if err != nil {
+					qErr.Set(err.Error())
+				} else {
+					quotes.Set(qs)
+				}
+				qLoading.Set(false)
+			})
+			fetchRepo(repoQuery.Get())
+		}
+
+		return Div(Attr("class", "space-y-8"),
+			Div(
+				H2(Attr("class", "text-2xl font-semibold tracking-tight text-text-heading"), Text("Data fetching")),
+				P(Attr("class", "mt-1 text-neutral-500"), Text("Two client-side fetches: gob from our own server, and JSON from a third-party API you choose.")),
+			),
+
+			ui.Card("",
+				ui.CardHeader("", Text("gob — from our server")),
+				P(Attr("class", "mb-3 text-sm text-neutral-500"),
+					Text("The client GETs /api/quotes; the server responds with httputil.RespondGob "+
+						"(a gob-encoded []Quote) and httputil.FetchGob decodes it straight into []Quote — "+
+						"the same Go type on both ends, no JSON.")),
+				quotesBody(qLoading.Get(), qErr.Get(), quotes.Get()),
+			),
+
+			ui.Card("",
+				ui.CardHeader("", Text("JSON — from a third-party API")),
+				P(Attr("class", "mb-3 text-sm text-neutral-500"),
+					Text("Enter a GitHub repo; the client GETs api.github.com and httputil.FetchJSON "+
+						"decodes the response into a Go struct with `json:\"…\"` tags.")),
+				row("mb-4 flex items-end gap-2",
+					row("flex grow flex-col gap-1 max-w-sm",
+						ui.FormLabel(ui.FormLabelProps{}, Text("GitHub repo (owner/name)")),
+						ui.FormInput(ui.FormInputProps{
+							Value:       repoQuery.Get(),
+							Placeholder: "golang/go",
+							OnInput:     func(v string) { repoQuery.Set(v) },
+						}),
+					),
+					ui.Button(ui.ButtonProps{Color: ui.ButtonPrimary, Text: "Fetch", OnClick: func() { fetchRepo(repoQuery.Get()) }}),
+				),
+				repoBody(rLoading.Get(), rErr.Get(), repo.Get()),
+			),
+		)
+	}
+}
+
+func quotesBody(loading bool, failed string, quotes []Quote) *VNode {
+	switch {
+	case failed != "":
+		return ui.Alert(ui.AlertRed, "Fetch failed", Text(failed))
+	case loading:
+		return ui.Loader()
+	default:
+		cards := make([]*VNode, 0, len(quotes))
+		for _, q := range quotes {
+			cards = append(cards, ui.BorderCard("",
+				P(Attr("class", "text-neutral-800"), Text("“"+q.Text+"”")),
+				P(Attr("class", "mt-2 text-sm text-neutral-500"), Text("— "+q.Author)),
+			))
+		}
+		return row("grid gap-3 sm:grid-cols-2", cards...)
+	}
+}
+
+func repoBody(loading bool, failed string, r repoInfo) *VNode {
+	switch {
+	case failed != "":
+		return ui.Alert(ui.AlertRed, "Fetch failed", Text(failed))
+	case loading:
+		return ui.Loader()
+	default:
+		return ui.BorderCard("",
+			row("flex items-center gap-2",
+				Strong(Attr("class", "text-neutral-800"), Text(r.FullName)),
+				ui.Badge(ui.BadgeProps{Color: ui.BadgeAmber}, Text("★ "+strconv.Itoa(r.Stars))),
+			),
+			P(Attr("class", "mt-2 text-sm text-neutral-600"), Text(r.Description)),
+		)
+	}
+}

go/cmd/examples/go-wasm-web/app/pages.go

@@ -81,6 +81,7 @@ func AppLayout(d Deps, content *VNode) *VNode {
 				Ul(Attr("class", "ml-4 flex items-center gap-1"),
 					navItem(d, "/chart", "Chart", true),
 					navItem(d, "/server", "Server", true),
+					navItem(d, "/data", "Data", true),
 					navItem(d, "/kit", "UI Kit", true)),
 				Ul(Attr("class", "ml-auto flex items-center"),
 					navItem(d, "/", "Home", true)),

go/cmd/examples/go-wasm-web/app/routes.gen.go

@@ -9,6 +9,7 @@ func Routes(d Deps) map[string]func() *vdom.VNode {
 		"/":       HomePage(d),
 		"/about":  AboutPage(d),
 		"/chart":  ChartPage(d),
+		"/data":   DataPage(d),
 		"/kit":    KitPage(d),
 		"/server": ServerPage(d),
 	}
@@ -26,6 +27,7 @@ var RouteLayout = map[string]string{
 	"/":       "public",
 	"/about":  "public",
 	"/chart":  "app",
+	"/data":   "app",
 	"/kit":    "app",
 	"/server": "app",
 }

go/cmd/examples/go-wasm-web/server/main.go

@@ -12,10 +12,12 @@ package main
 import (
 	"flag"
 	"log"
+	"net/http"
 	"os"
 	"os/exec"
 	"path/filepath"
 
+	"kjol/httputil"
 	"kjol/vdom"
 	"kjol/wasmdevserver"
 
@@ -35,9 +37,28 @@ func main() {
 		Build:     buildWasm,
 		Render:    render,
 		Document:  document,
+		Handle:    apiRoutes,
 	}))
 }
 
+// apiRoutes registers the example's API endpoints. /api/quotes responds with a
+// gob-encoded []app.Quote (via httputil.RespondGob) — the /data page fetches and
+// decodes it on the client with encoding/gob (Go types end to end, no JSON).
+func apiRoutes(mux *http.ServeMux) {
+	mux.HandleFunc("GET /api/quotes", func(w http.ResponseWriter, r *http.Request) {
+		httputil.RespondGob(w, http.StatusOK, sampleQuotes())
+	})
+}
+
+func sampleQuotes() []app.Quote {
+	return []app.Quote{
+		{Author: "Rob Pike", Text: "A little copying is better than a little dependency."},
+		{Author: "Rob Pike", Text: "Don't communicate by sharing memory; share memory by communicating."},
+		{Author: "Ken Thompson", Text: "When in doubt, use brute force."},
+		{Author: "Alan Kay", Text: "The best way to predict the future is to invent it."},
+	}
+}
+
 // render SSRs a static route's #app inner HTML; ok=false ships an empty #app
 // (client-rendered). It's the same neutral render the client runs, so the client
 // hydrates it.

go/cmd/examples/go-wasm-web/wasm/main.go

@@ -6,6 +6,7 @@ package main
 
 import (
 	"gowasmweb/app"
+	"kjol/httputil"
 	"kjol/vdom"
 	"kjol/wasmruntime"
 )
@@ -15,6 +16,7 @@ func main() {
 	// across an in-place hot swap. On a normal load RestoreState is nil (fresh
 	// state); after a dev hot-reload it carries the previous instance's values,
 	// which NewSignal restores by creation order.
+	httputil.SetClientTransport(wasmruntime.FetchBytes) // typed gob/json fetches for app pages
 	collector := vdom.BeginCollect(wasmruntime.RestoreState())
 	router := wasmruntime.NewRouter()
 	deps := app.Deps{Path: router.Path, Navigate: router.Navigate}

go/httputil/fetch.go

@@ -0,0 +1,66 @@
+package httputil
+
+import (
+	"bytes"
+	"encoding/gob"
+	"encoding/json"
+	"errors"
+)
+
+// Client-side fetch helpers — the counterparts to RespondGob / RespondJSON. In a
+// gowasm app the server and the WebAssembly client share the same Go types, so
+// the server encodes with RespondGob(data) and the client decodes straight back
+// into that type with FetchGob — no JSON, no hand-written unmarshalling. These
+// are neutral (they only touch encoding/*), so app code can call them while
+// staying SSR-able; the actual HTTP transport is client-only and injected at
+// startup by the wasm runtime (SetClientTransport), the inversion vdom.Schedule
+// uses.
+
+// clientTransport does an HTTP GET returning the raw body; nil on the server.
+var clientTransport func(url string) ([]byte, error)
+
+// SetClientTransport installs the HTTP GET used by FetchGob / FetchJSON. The
+// wasm client runtime calls this at startup with wasmruntime.FetchBytes.
+func SetClientTransport(get func(url string) ([]byte, error)) { clientTransport = get }
+
+func fetchInto[T any](url string, cb func(T, error), decode func([]byte, *T) error) {
+	go func() {
+		var out T
+		if clientTransport == nil {
+			cb(out, errors.New("httputil: no client transport installed (client-only)"))
+			return
+		}
+		body, err := clientTransport(url)
+		if err != nil {
+			cb(out, err)
+			return
+		}
+		if err := decode(body, &out); err != nil {
+			cb(out, err)
+			return
+		}
+		cb(out, nil)
+	}()
+}
+
+// FetchGob GETs url and gob-decodes the body into T (pair with RespondGob), then
+// calls cb(result, err) on a background goroutine — safe to call from a render
+// or event handler; set the result into a signal in the callback. T is inferred
+// from the callback:
+//
+//	httputil.FetchGob("/api/quotes", func(qs []Quote, err error) {
+//	    if err != nil { /* … */ } else { quotes.Set(qs) }
+//	})
+func FetchGob[T any](url string, cb func(T, error)) {
+	fetchInto(url, cb, func(b []byte, out *T) error {
+		return gob.NewDecoder(bytes.NewReader(b)).Decode(out)
+	})
+}
+
+// FetchJSON GETs url and json-decodes the body into T — for third-party JSON
+// APIs (or your own RespondJSON). Same callback/goroutine shape as FetchGob.
+func FetchJSON[T any](url string, cb func(T, error)) {
+	fetchInto(url, cb, func(b []byte, out *T) error {
+		return json.Unmarshal(b, out)
+	})
+}

go/httputil/respond.go

@@ -1,6 +1,7 @@
 package httputil
 
 import (
+	"encoding/gob"
 	"encoding/json"
 	"net/http"
 )
@@ -11,6 +12,12 @@ func RespondJSON(w http.ResponseWriter, statusCode int, data any) {
 	json.NewEncoder(w).Encode(data)
 }
 
+func RespondGob(w http.ResponseWriter, statusCode int, data any) {
+	w.Header().Set("Content-Type", "application/gob")
+	w.WriteHeader(statusCode)
+	gob.NewEncoder(w).Encode(data)
+}
+
 func RespondError(w http.ResponseWriter, statusCode int, message string) {
 	RespondJSON(w, statusCode, map[string]string{"error": message})
 }

go/wasmdevserver/devserver.go

@@ -40,6 +40,7 @@ type Config struct {
 	Build     func() ([]byte, error)                    // (re)build the wasm bundle; combined output on failure
 	Render    func(path string) (inner string, ok bool) // SSR the #app inner HTML for a route (ok=false => client-rendered)
 	Document  func(inner string) string                 // wrap #app inner HTML in a full HTML document
+	Handle    func(mux *http.ServeMux)                  // optional: register extra routes (e.g. app API endpoints)
 }
 
 // Serve builds once (in watch mode), wires the routes, and blocks serving.
@@ -70,6 +71,9 @@ func Serve(cfg Config) error {
 	}
 
 	mux.HandleFunc("POST /rsc", rsc.Handler) // server components
+	if cfg.Handle != nil {
+		cfg.Handle(mux) // app-registered routes (API endpoints, etc.)
+	}
 	mux.HandleFunc("/", rootHandler(cfg))
 
 	log.Printf("serving %q on http://localhost%s", cfg.Dir, cfg.Addr)

go/wasmruntime/fetch.go

@@ -5,10 +5,22 @@ package wasmruntime
 import (
 	"errors"
 	"fmt"
+	"strings"
 	"sync"
 	"syscall/js"
 )
 
+// absURL resolves a relative path against the current origin (a browser resolves
+// relative fetch URLs itself, but building the absolute URL keeps behavior
+// uniform — and lets non-browser hosts, e.g. tests, fetch too).
+func absURL(url string) string {
+	if strings.HasPrefix(url, "http://") || strings.HasPrefix(url, "https://") {
+		return url
+	}
+	loc := js.Global().Get("location")
+	return loc.Get("protocol").String() + "//" + loc.Get("host").String() + url
+}
+
 // Fetch performs an HTTP GET via the browser Fetch API and returns the response
 // body as a string. It bridges a JS Promise into Go: it registers then/catch
 // callbacks and blocks the calling goroutine on a channel until the request
@@ -67,7 +79,7 @@ func Fetch(url string) (string, error) {
 		return nil
 	})
 
-	js.Global().Call("fetch", url).Call("then", onResp).Call("catch", onErr)
+	js.Global().Call("fetch", absURL(url)).Call("then", onResp).Call("catch", onErr)
 
 	<-done
 	onResp.Release()
@@ -75,3 +87,63 @@ func Fetch(url string) (string, error) {
 	onErr.Release()
 	return body, ferr
 }
+
+// FetchBytes is like Fetch but returns the raw response body as bytes (via
+// resp.arrayBuffer()), for binary payloads such as gob (Fetch's resp.text()
+// would corrupt non-UTF-8 data). It blocks the calling goroutine the same way —
+// call it from a goroutine and write the result into signals when it returns.
+func FetchBytes(url string) ([]byte, error) {
+	var (
+		once                 sync.Once
+		done                 = make(chan struct{})
+		body                 []byte
+		ferr                 error
+		onResp, onBuf, onErr js.Func
+	)
+	finish := func() { once.Do(func() { close(done) }) }
+
+	onErr = js.FuncOf(func(this js.Value, args []js.Value) any {
+		msg := "fetch error"
+		if len(args) > 0 && args[0].Truthy() {
+			e := args[0]
+			if m := e.Get("message"); m.Truthy() {
+				msg = m.String()
+			} else {
+				msg = e.Call("toString").String()
+			}
+		}
+		ferr = errors.New(msg)
+		finish()
+		return nil
+	})
+
+	onBuf = js.FuncOf(func(this js.Value, args []js.Value) any {
+		if len(args) > 0 {
+			arr := js.Global().Get("Uint8Array").New(args[0])
+			b := make([]byte, arr.Get("length").Int())
+			js.CopyBytesToGo(b, arr)
+			body = b
+		}
+		finish()
+		return nil
+	})
+
+	onResp = js.FuncOf(func(this js.Value, args []js.Value) any {
+		resp := args[0]
+		if !resp.Get("ok").Bool() {
+			ferr = fmt.Errorf("HTTP %d", resp.Get("status").Int())
+			finish()
+			return nil
+		}
+		resp.Call("arrayBuffer").Call("then", onBuf).Call("catch", onErr)
+		return nil
+	})
+
+	js.Global().Call("fetch", absURL(url)).Call("then", onResp).Call("catch", onErr)
+
+	<-done
+	onResp.Release()
+	onBuf.Release()
+	onErr.Release()
+	return body, ferr
+}