jackwener/OpenCLI · error · CommandExecutionError

coingecko exchanges returned malformed JSON: ${err?.message

Error message

coingecko exchanges returned malformed JSON: ${err?.message ?? err}

What it means

The library calls resp.json() on the CoinGecko exchanges response; if the body is not valid JSON (HTML error pages from proxies/Cloudflare, truncated responses, empty bodies), json() throws and this CommandExecutionError wraps that parse failure with the underlying SyntaxError message.

Source

Thrown at clis/coingecko/exchanges.js:58

        }
        catch (err) {
            throw new CommandExecutionError(`coingecko exchanges request failed: ${err?.message ?? err}`);
        }
        if (resp.status === 429) {
            throw new CommandExecutionError(
                'coingecko returned HTTP 429 (rate limited)',
                'Free tier allows ~30 calls/min. Wait and retry.',
            );
        }
        if (!resp.ok) {
            throw new CommandExecutionError(`coingecko exchanges returned HTTP ${resp.status}`);
        }
        let data;
        try {
            data = await resp.json();
        }
        catch (err) {
            throw new CommandExecutionError(`coingecko exchanges returned malformed JSON: ${err?.message ?? err}`);
        }
        if (!Array.isArray(data) || !data.length) {
            throw new EmptyResultError('coingecko exchanges', 'CoinGecko returned no exchange data.');
        }
        return data.map((ex, i) => ({
            rank: (page - 1) * limit + i + 1,
            id: String(ex.id ?? ''),
            name: String(ex.name ?? ''),
            trustScore: ex.trust_score != null ? Number(ex.trust_score) : null,
            volume24hBtc: ex.trade_volume_24h_btc != null ? Number(ex.trade_volume_24h_btc) : null,
            country: String(ex.country ?? ''),
            yearEstablished: ex.year_established != null ? Number(ex.year_established) : null,
            url: String(ex.url ?? ''),
        }));
    },
});

View on GitHub (pinned to 49907e53dc)

Solutions

Inspect the raw body with `curl -s https://api.coingecko.com/api/v3/exchanges?per_page=20&page=1 | head` to see what is actually returned (HTML challenge vs JSON).
If Cloudflare/proxy HTML is the cause, retry from a different network or use a proper API key plan that avoids challenge pages.
Retry the request — truncated bodies from flaky connections are usually transient.
Check for proxies (HTTP_PROXY/HTTPS_PROXY, corporate MITM) interfering with the response encoding.

Defensive patterns

Strategy: try-catch

Try / catch

try {
  await exchanges.func({ page: 1 });
} catch (e) {
  if (/malformed JSON/.test(e.message)) {
    // body was HTML/truncated: verify raw response, retry or switch network
    const raw = await fetch('https://api.coingecko.com/api/v3/exchanges?per_page=5&page=1').then(r => r.text());
    if (raw.trimStart().startsWith('<')) handleCloudflareChallenge();
  } else throw e;
}

Prevention

Spot-check raw responses with curl when behind unfamiliar networks.
Disable or correctly configure proxies that rewrite HTML into responses.
Treat JSON parse failures on 2xx as a proxy/Cloudflare symptom, not a code bug.
Retry truncated responses — they are usually transient.

When it happens

Trigger: The HTTP request succeeded (2xx) but resp.json() throws: response body is HTML (Cloudflare challenge page, captive portal), response is truncated, Content-Encoding mismatch (e.g. broken gzip via a proxy), or an empty body.

Common situations: Corporate proxies injecting HTML login pages, Cloudflare bot-challenge interstitials returned with a 200, flaky mobile/VPN connections truncating the body, or misconfigured local MITM proxies.

Understand the failure class

Background: "Invalid JSON response" and "Failed to parse response" errors: when an API answers 200 but the body isn't the JSON your library expected — this error's family across 28 libraries.

Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

AI-assisted analysis of jackwener/OpenCLI@49907e53dc (2026-08-29). Data as JSON: /api/errors/f4175a3e23f55a93. Report an issue: GitHub.