Class UsageNormalizer

proxy/model-proxy.js:40–91

* Transform stream that intercepts SSE events and injects missing `usage` * fields. DeepSeek/OpenRouter may omit `usage` in message_start or * message_delta, which crashes Claude Code ("$.input_tokens" is undefined).

 * message_delta, which crashes Claude Code ("$.input_tokens" is undefined).
 */
class UsageNormalizer extends Transform {
    constructor(onUsage) {
        super();
        this._buf = '';
        this._onUsage = onUsage;
        this._inputTokens = 0;
        this._outputTokens = 0;
    }

    _transform(chunk, _enc, cb) {
        this._buf += chunk.toString();
        const parts = this._buf.split('\n\n');
        this._buf = parts.pop();
        for (const part of parts) {
            this.push(this._fix(part) + '\n\n');
        }
        cb();
    }

    _fix(event) {
        const m = event.match(/^data: (.+)$/m);
        if (!m) return event;
        try {
            const d = JSON.parse(m[1]);
            let changed = false;
            if (d.type === 'message_start' && d.message) {
                if (d.message.usage) {
                    this._inputTokens = d.message.usage.input_tokens || 0;
                } else {
                    d.message.usage = { input_tokens: 0, output_tokens: 0 };
                    changed = true;
                }
            }
            if (d.type === 'message_delta') {
                if (d.usage) {
                    this._outputTokens = d.usage.output_tokens || 0;
                } else {
                    d.usage = { output_tokens: 0 };
                    changed = true;
                }
            }
            if (changed) return event.replace(m[1], () => JSON.stringify(d));
        } catch { /* not JSON, pass through */ }
        return event;
    }

    _flush(cb) {
        if (this._buf.trim()) this.push(this._fix(this._buf) + '\n\n');
        if (this._onUsage) this._onUsage(this._inputTokens, this._outputTokens);
        cb();
    }
}

/**
 * For non-streaming JSON responses, ensure `usage` exists.