cacheResponseAge()

cacheResponseAge()

/**
 * Returns the current age of the response, in milliseconds. The calculation is specified by RFC
 * 7234, 4.2.3 Calculating Age.
 */
private fun cacheResponseAge(): Long {
    val servedDate = this.servedDate
    val apparentReceivedAge = if (servedDate != null) {
        maxOf(0, receivedResponseMillis - servedDate.time)
    } else {
        0
    }

    val receivedAge = if (ageSeconds != -1) {
        maxOf(apparentReceivedAge, SECONDS.toMillis(ageSeconds.toLong()))
    } else {
        apparentReceivedAge
    }

    val responseDuration = receivedResponseMillis - sentRequestMillis
    val residentDuration = nowMillis - receivedResponseMillis
    return receivedAge + responseDuration + residentDuration
}

上述计算规则实际是按照RFC 2616 13.2.3 Age Calculations实现的， 而且查看history:ResponseStrategy.java 发现，从最开始就是这个写法。

apparent_age = max(0, response_time - date_value);
corrected_received_age = max(apparent_age, age_value);
response_delay = response_time - request_time;
corrected_initial_age = corrected_received_age + response_delay;
resident_time = now - response_time;
current_age   = corrected_initial_age + resident_time;

// 变形1
current_age   = corrected_received_age + response_delay + resident_time;

// 最终变形
current_age   = max(apparent_age, age_value) + response_delay + resident_time;

并不是按照rfc 7234 4.2.3 Calculating Age来写的，但是研究发现，上述

// 原始公式
current_age = corrected_initial_age + resident_time;

// 变形
current_age = max(apparent_age, corrected_age_value) + resident_time;

// 最终变形
current_age = max(apparent_age, age_value + response_delay) + resident_time;