gob fetcher for wasm example

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)
+	})
+}