thedotmack/claude-mem · error

sync hub push: response is not JSON

Error message

sync hub push: response is not JSON

What it means

Thrown when the push POST returned OK but response.json() threw — a 200 with a non-JSON body. The push contract requires the hub to return a JSON object ({ acked, head_seq, projected_seq }) on success, so a non-JSON 200 is a protocol violation.

Source

Thrown at src/services/sync/CloudSync.ts:975

    // paths would keep hammering the socket through an incident.
    // Asymmetric on purpose (SyncClient.onSyncModeHint contract): header
    // PRESENCE is emitted regardless of status; header ABSENCE is only
    // emitted (as null = "cleared") from an OK response — absence on an
    // error response is ambiguous (a degraded auth upstream 503s without
    // the funnel) and must not read as "switch cleared".
    const syncMode = res.headers.get('X-Sync-Mode');
    if (syncMode !== null || res.ok) {
      this.emitSyncMode(syncMode);
    }
    if (!res.ok) {
      const body = (await res.text().catch(() => '')).slice(0, 200);
      throw new Error(`sync hub push ${res.status}: ${body}`);
    }
    let parsed: unknown;
    try {
      parsed = await res.json();
    } catch {
      throw new Error('sync hub push: response is not JSON');
    }
    const acked = (parsed as { acked?: unknown } | null)?.acked;
    if (!Array.isArray(acked)) {
      throw new Error('sync hub push: response missing acked array');
    }
    const headSeq = (parsed as { head_seq?: unknown }).head_seq;
    const projectedSeq = (parsed as { projected_seq?: unknown }).projected_seq;
    if (typeof headSeq !== 'string' || typeof projectedSeq !== 'string') {
      throw new Error('sync hub push: response requires decimal-string head_seq/projected_seq');
    }
    assertCanonicalDecimal(headSeq);
    assertCanonicalDecimal(projectedSeq);
    const validatedAcked = acked.map((value, index): AckedOp => {
      if (!value || typeof value !== 'object' || Array.isArray(value)) {
        throw new Error(`sync hub push: acked[${index}] must be an object`);
      }
      const item = value as Record<string, unknown>;
      if (

View on GitHub (pinned to d768ba3643)

Solutions

1. Capture the raw response body and Content-Type for the push to identify what was returned.
2. Verify hubUrl/routes the POST to the real sync hub push endpoint.
3. Bypass or fix any proxy returning HTML on a 200.
4. If the hub itself is non-JSON on 200, report it — the push contract requires JSON.
5. Retry once in case of a transient mid-body truncation.

Example fix

// before: hubUrl points at a server that acks pushes with an empty 200
hubUrl = 'https://example.com';
// after: hubUrl points at the sync hub that returns JSON acks
hubUrl = 'https://sync.example.com'; // POST /v1/sync/ops -> {"acked":[...],"head_seq":"...",...}

function isPushNotJson(e: unknown): boolean {
  return e instanceof Error && /sync hub push: response is not JSON/i.test(e.message);
}

try { await cloudSync.pushOps(ops); }
catch (e) { if (isPushNotJson(e)) { markHubMisconfigured(e.message); return; } throw e; }

When it happens

Trigger: Hub returned 200 with HTML/empty/truncated body; a proxy rewrote the response; the endpoint routed to a static server; the connection dropped mid-body so json() failed.

Common situations: Reverse proxy/CDN returning an HTML page with 200; hub misconfigured to acknowledge pushes without a JSON body; middlebox truncation; pointing hubUrl at the wrong host.

Related errors

• sync hub status: response is not JSON
• sync hub status: response must be an object
• sync hub push: response missing acked array
• sync hub status: response requires decimal-string epoch/head
• sync hub push ${res.status}: ${body}

AI-assisted analysis of thedotmack/claude-mem@d768ba3643 (2026-08-12). Data as JSON: /api/errors/71340f66efa54e49. Report an issue: GitHub.