internal/warpc: Improve the JS plugin API

* Move the error handling into commons and make sure the error returned also returns message errors
* Make the protocol version an int so it can be more easily compared

internal/warpc/js/common.js

@@ -41,13 +41,21 @@ export function readInput(handle) {
 			if (currentLine[i] === 10) {
 				const chunk = currentLine.splice(j, i + 1);
 				const arr = new Uint8Array(chunk);
-				let json;
+				let message;
 				try {
-					json = JSON.parse(new TextDecoder().decode(arr));
+					message = JSON.parse(new TextDecoder().decode(arr));
 				} catch (e) {
 					throw new Error(`Error parsing JSON '${new TextDecoder().decode(arr)}' from stdin: ${e.message}`);
 				}
-				handle(json);
+
+				try {
+					handle(message);
+				} catch (e) {
+					let header = message.header;
+					header.err = e.message;
+					writeOutput({ header: header });
+				}
+
 				j = i + 1;
 			}
 		}

internal/warpc/js/renderkatex.js

@@ -6,13 +6,9 @@ const render = function (input) {
 	const expression = data.expression;
 	const options = data.options;
 	const header = input.header;
-	try {
-		const output = katex.renderToString(expression, options);
-		writeOutput({ header: header, data: { output: output } });
-	} catch (e) {
-		header.err = e.message;
-		writeOutput({ header: header });
-	}
+	// Any error thrown here will be caught by the common.js readInput function.
+	const output = katex.renderToString(expression, options);
+	writeOutput({ header: header, data: { output: output } });
 };
 
 readInput(render);

internal/warpc/warpc.go

@@ -35,15 +35,19 @@ import (
 	"github.com/tetratelabs/wazero/imports/wasi_snapshot_preview1"
 )
 
-const currentVersion = "v1"
+const currentVersion = 1
 
 //go:embed wasm/quickjs.wasm
 var quickjsWasm []byte
 
 // Header is in both the request and response.
 type Header struct {
-	Version string `json:"version"`
-	ID      uint32 `json:"id"`
+	// Major version of the protocol.
+	Version uint16 `json:"version"`
+
+	// Unique ID for the request.
+	// Note that this only needs to be unique within the current request set time window.
+	ID uint32 `json:"id"`
 
 	// Set in the response if there was an error.
 	Err string `json:"err"`
@@ -150,7 +154,11 @@ func (p *dispatcherPool[Q, R]) Execute(ctx context.Context, q Message[Q]) (Messa
 		return d.zero, call.err
 	}
 
-	return call.response, p.Err()
+	resp, err := call.response, p.Err()
+	if err == nil && resp.Header.Err != "" {
+		err = errors.New(resp.Header.Err)
+	}
+	return resp, err
 }
 
 func (d *dispatcher[Q, R]) newCall(q Message[Q]) (*call[Q, R], error) {

internal/warpc/warpc_test.go

@@ -45,28 +45,44 @@ func TestKatex(t *testing.T) {
 
 	defer d.Close()
 
-	ctx := context.Background()
+	runExpression := func(c *qt.C, id uint32, expression string) (Message[KatexOutput], error) {
+		c.Helper()
 
-	input := KatexInput{
-		Expression: "c = \\pm\\sqrt{a^2 + b^2}",
-		Options: KatexOptions{
-			Output:      "html",
-			DisplayMode: true,
-		},
-	}
+		ctx := context.Background()
+
+		input := KatexInput{
+			Expression: expression,
+			Options: KatexOptions{
+				Output:       "html",
+				DisplayMode:  true,
+				ThrowOnError: true,
+			},
+		}
+
+		message := Message[KatexInput]{
+			Header: Header{
+				Version: currentVersion,
+				ID:      uint32(id),
+			},
+			Data: input,
+		}
 
-	message := Message[KatexInput]{
-		Header: Header{
-			Version: currentVersion,
-			ID:      uint32(32),
-		},
-		Data: input,
+		return d.Execute(ctx, message)
 	}
 
-	result, err := d.Execute(ctx, message)
-	c.Assert(err, qt.IsNil)
+	c.Run("Simple", func(c *qt.C) {
+		id := uint32(32)
+		result, err := runExpression(c, id, "c = \\pm\\sqrt{a^2 + b^2}")
+		c.Assert(err, qt.IsNil)
+		c.Assert(result.GetID(), qt.Equals, id)
+	})
 
-	c.Assert(result.GetID(), qt.Equals, message.GetID())
+	c.Run("Invalid expression", func(c *qt.C) {
+		id := uint32(32)
+		result, err := runExpression(c, id, "c & \\foo\\")
+		c.Assert(err, qt.IsNotNil)
+		c.Assert(result.GetID(), qt.Equals, id)
+	})
 }
 
 func TestGreet(t *testing.T) {

tpl/transform/transform.go

@@ -235,7 +235,7 @@ func (ns *Namespace) ToMath(ctx context.Context, args ...any) (types.Result[temp
 		_, r, err := fileCache.GetOrCreate(key, func() (io.ReadCloser, error) {
 			message := warpc.Message[warpc.KatexInput]{
 				Header: warpc.Header{
-					Version: "v1",
+					Version: 1,
 					ID:      ns.id.Add(1),
 				},
 				Data: katexInput,
@@ -249,9 +249,6 @@ func (ns *Namespace) ToMath(ctx context.Context, args ...any) (types.Result[temp
 			if err != nil {
 				return nil, err
 			}
-			if result.Header.Err != "" {
-				return nil, errors.New(result.Header.Err)
-			}
 			return hugio.NewReadSeekerNoOpCloserFromString(result.Data.Output), nil
 		})
 		if err != nil {