WIP: Add support for logging errors

Author: FranklinWaller

src/services/VirtualFsService.ts

@@ -0,0 +1,37 @@
+import { WasmFs } from '@wasmer/wasmfs';
+
+const CONSOLE_FDS = [0, 1, 2];
+
+class VirtualFs {
+    private logs?: string = undefined;
+
+    constructor(private wasmFs: WasmFs) {}
+
+    getFs() {
+        const fs = this.wasmFs.fs;
+
+        const originalWriteSync = fs.writeSync;
+        fs.writeSync = (...args: any[]) => {
+            const fd = args[0];
+
+            if (CONSOLE_FDS.includes(fd)) {
+                if (this.logs) {
+                    this.logs += new TextDecoder().decode(args[1]);
+                } else {
+                    this.logs = new TextDecoder().decode(args[1]);
+                }
+            }
+
+            // @ts-ignore
+            return originalWriteSync(...args);
+        }
+
+        return fs;
+    } 
+
+    getLogOutput(): string[] {
+        return this.logs?.split('\n') ?? [];
+    }
+}
+
+export default VirtualFs;

src/services/VirtualMachineService.ts

@@ -5,6 +5,7 @@ import { alea } from 'seedrandom';
 import { VmContext } from "../models/Context";
 import { ExecuteResult } from '../models/ExecuteResult';
 import { generateFixedBuffer } from './CryptoService';
+import VirtualFs from './VirtualFsService';
 import WasmImports from './WasmImports';
 
 const metering = require('wasm-metering');
@@ -19,6 +20,7 @@ export function prepareWasmBinary(binary: Uint8Array): Uint8Array {
 
 export async function executeWasm(context: VmContext): Promise<ExecuteResult> {
     const wasmFs = new WasmFs();
+    const virtualFs = new VirtualFs(wasmFs);
 
     try {
         const random = alea(context.randomSeed);
@@ -27,7 +29,7 @@ export async function executeWasm(context: VmContext): Promise<ExecuteResult> {
             env: context.env,
             bindings: {
                 ...WASIBindings,
-                fs: wasmFs.fs,
+                fs: virtualFs.getFs(),
                 hrtime: () => BigInt(context.timestamp),
                 randomFillSync: (buffer: any, offset, size) => {
                     const randomBuffer = generateFixedBuffer(random.int32().toString(), size ?? buffer.length - offset);
@@ -46,25 +48,15 @@ export async function executeWasm(context: VmContext): Promise<ExecuteResult> {
         wasmImports.setMemory(instance.exports.memory as WebAssembly.Memory);
         wasi.start(instance);
 
-        const logs = [];
-        const stdout = await wasmFs.getStdOut() as string;
-
-        if (stdout) {
-            logs.push(...stdout.split("\n"));
-        }
+        const logs = virtualFs.getLogOutput();
 
         return {
             code: 0,
             logs,
             gasUsed: context.gasUsed.toString(),
         }
     } catch(error: any) {
-        const stdout = await wasmFs.getStdOut();
-        const logs = [];
-
-        if (stdout) {
-            logs.push(stdout);
-        }
+        const logs = virtualFs.getLogOutput();
 
         logs.push(error?.message);