dotnet/runtime · error · Error

Failed on mono_wasm_get_dbg_command_info

Error message

Failed on mono_wasm_get_dbg_command_info

What it means

Thrown by `mono_wasm_get_dbg_command_info` when the bootstrap command (keyed under id `0`) returns `res_ok === false`. This call fetches initial debugger bookkeeping from the native runtime; failure means the debugger handshake could not complete.

Solutions

1. Only call `mono_wasm_get_dbg_command_info` after `runtimeHelpers.mono_wasm_runtime_is_ready` is true.
2. Ensure the runtime was built with the debugger enabled (not a stripped release build).
3. Avoid calling it after the debugger has been detached; re-attach first if needed.
4. Match the debugger proxy build to the runtime build.

Example fix

// before: queried before runtime ready
mono_wasm_get_dbg_command_info(); // throws

// after: wait for runtime readiness, then query
await runtimeReadyPromise;
mono_wasm_get_dbg_command_info();

function canQueryCommandInfo () {
  return !!runtimeHelpers.mono_wasm_runtime_is_ready;
}
if (canQueryCommandInfo()) mono_wasm_get_dbg_command_info();

function isRuntimeReadyForDebugger (): boolean {
  return !!runtimeHelpers.mono_wasm_runtime_is_ready;
}

try {
  return mono_wasm_get_dbg_command_info();
} catch (e) {
  if (e instanceof Error && /Failed on mono_wasm_get_dbg_command_info/.test(e.message)) {
    // runtime not ready or debugger detached; defer and retry once
    setTimeout(() => mono_wasm_get_dbg_command_info(), 100);
    return;
  }
  throw e;
}

When it happens

Trigger: Calling `mono_wasm_get_dbg_command_info()` (debug.ts:105) before the runtime has fully initialised its debugger, or after the debugger was detached. The native side returns a failing response for id 0 because no command info is available.

Common situations: Invoking the function during startup before `mono_wasm_runtime_ready`; calling it after `mono_wasm_detach_debugger`; runtime build with the debugger stubbed out (release build) that always responds with res_ok=false.

Related errors

• Failed on mono_wasm_send_dbg_command
• Failed on mono_wasm_send_dbg_command_with_parms
• args must be an object, but got
• event.eventName is a required parameter, in event
• event must be an object, but got

AI-assisted analysis of dotnet/runtime@60108ba66e (2026-08-10). Data as JSON: /api/errors/2bc853c7d792e3e5. Report an issue: GitHub.

Appendix: source

Thrown at src/mono/browser/runtime/debug.ts:109

export function mono_wasm_send_dbg_command (id: number, command_set: number, command: number, command_parameters: string): CommandResponseResult {
    forceThreadMemoryViewRefresh();

    mono_wasm_malloc_and_set_debug_buffer(command_parameters);
    cwraps.mono_wasm_send_dbg_command(id, command_set, command, _debugger_buffer, command_parameters.length);

    const { res_ok, res } = commands_received.remove(id);

    if (!res_ok)
        throw new Error("Failed on mono_wasm_send_dbg_command");
    return res;

}

export function mono_wasm_get_dbg_command_info (): CommandResponseResult {
    const { res_ok, res } = commands_received.remove(0);

    if (!res_ok)
        throw new Error("Failed on mono_wasm_get_dbg_command_info");
    return res;
}

export function mono_wasm_debugger_resume (): void {
    forceThreadMemoryViewRefresh();
}

export function mono_wasm_detach_debugger (): void {
    forceThreadMemoryViewRefresh();
    cwraps.mono_wasm_set_is_debugger_attached(false);
}

export function mono_wasm_change_debugger_log_level (level: number): void {
    forceThreadMemoryViewRefresh();
    cwraps.mono_wasm_change_debugger_log_level(level);
}

/**

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