jackwener/OpenCLI · error · CommandExecutionError

${label} returned malformed JSON: ${err?.message ?? err}

Error message

${label} returned malformed JSON: ${err?.message ?? err}

What it means

restCountriesFetch throws CommandExecutionError when resp.json() fails, i.e. the HTTP 200 body is not parseable JSON. The library expects REST Countries to always return JSON on success, so a non-JSON body indicates the response was intercepted or corrupted.

Source

Thrown at clis/rest-countries/utils.js:77

            `${label} request failed: ${err?.message ?? err}`,
            'Check that restcountries.com is reachable from this network.',
        );
    }
    if (resp.status === 404) {
        throw new EmptyResultError(label, `REST Countries returned 404 for ${url}.`);
    }
    if (resp.status === 429) {
        throw new CommandExecutionError(`${label} returned HTTP 429 (rate limited)`);
    }
    if (!resp.ok) {
        throw new CommandExecutionError(`${label} returned HTTP ${resp.status}`);
    }
    let body;
    try {
        body = await resp.json();
    }
    catch (err) {
        throw new CommandExecutionError(`${label} returned malformed JSON: ${err?.message ?? err}`);
    }
    return body;
}

/** Convert REST Countries' `{cur: {name, symbol}}` map to a comma-joined list. */
export function joinCurrencies(currencies) {
    if (!currencies || typeof currencies !== 'object') return '';
    return Object.entries(currencies)
        .map(([code, info]) => {
            const name = info && typeof info.name === 'string' ? info.name : '';
            return name ? `${code} (${name})` : code;
        })
        .join(', ');
}

/** Convert `{eng: 'English', fra: 'French'}` map to a comma-joined list of language names. */
export function joinLanguages(languages) {
    if (!languages || typeof languages !== 'object') return '';

View on GitHub (pinned to 49907e53dc)

Solutions

  1. Retry the request — truncation/corruption is often transient
  2. Check whether a proxy, VPN, or captive portal is rewriting responses (fetch the URL in a browser and inspect the body)
  3. Disable intercepting extensions or exclusion-list restcountries.com
  4. Report a bug if the API persistently returns non-JSON
Defensive patterns

Strategy: try-catch

Validate before calling

null

Type guard

null

Try / catch

try {
  await restCountriesCommand(args);
} catch (e) {
  if (String(e.message).includes('malformed JSON')) {
    // likely a proxy/captive portal; surface network context to the user
    throw new Error('Non-JSON response from restcountries.com — check proxy/VPN/network', { cause: e });
  }
  throw e;
}

Prevention

When it happens

Trigger: The API returns status 200 but the body is HTML (captive portal, proxy block page, Cloudflare interstitial), a truncated body, or empty content, causing JSON.parse inside resp.json() to reject.

Common situations: Corporate proxy or Wi-Fi captive portal replacing the response with an HTML page; aggressive ad-blockers/privacy tools intercepting the request; network interruption truncating the body; REST Countries serving an error page with a 200 status.

Understand the failure class

Related errors

AI-assisted analysis of jackwener/OpenCLI@49907e53dc (2026-08-29). Data as JSON: /api/errors/e3a155ba287c8e96. Report an issue: GitHub.