Sprheany

Android developer

发表于 更新于 分类于 ，

问题

最近开发了一个 Android 项目，发现第一个接口返回得特别慢，后面的接口就没问题。用浏览器打开链接，访问速度很快，手机连上 Charles 抓包，访问速度也很快。打印 OkHttp 的日志发现第一个接口请求耗时100多秒，后面的接口都只有几十秒，多次实验结果都一样。

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200 OK https://fundgz.1234567.com.cn/js/162605.js (100092ms, unknown-length body)

问题分析

通过查看 OkHttp 源码，发现 OkHttp 默认的连接超时时间是 10 秒。修改 connectTimeout 的值后测试，果然第一个接口返回的时间都是 connectTimeout 的 10 倍。

经过排查后发现是 Dns 的问题。OkHttp 中默认的 Dns 配置代码如下：

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interface Dns {

  @Throws(UnknownHostException::class)
  fun lookup(hostname: String): List<InetAddress>

  companion object {

    @JvmField
    val SYSTEM: Dns = DnsSystem()
    private class DnsSystem : Dns {
      override fun lookup(hostname: String): List<InetAddress> {
        try {
          return InetAddress.getAllByName(hostname).toList()
        } catch (e: NullPointerException) {
          throw UnknownHostException("Broken system behaviour for dns lookup of $hostname").apply {
            initCause(e)
          }
        }
      }
    }
  }
}

加上日志打印出获取到的 IP 地址如下：

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fundgz.1234567.com.cn/2409:8c60:2600:2:0:1:0:16d
fundgz.1234567.com.cn/2409:8c60:2600:2:0:1:0:167
fundgz.1234567.com.cn/2409:8c60:2600:2:0:1:0:16c
fundgz.1234567.com.cn/2409:8c60:2600:2:0:1:0:16b
fundgz.1234567.com.cn/2409:8c60:2600:2:0:1:0:169
fundgz.1234567.com.cn/2409:8c60:2600:2:0:1:0:168
fundgz.1234567.com.cn/2409:8c60:2600:2:0:1:0:16a
fundgz.1234567.com.cn/2409:8c60:2600:2:0:1:0:16f
fundgz.1234567.com.cn/2409:8c60:2600:2:0:1:0:166
fundgz.1234567.com.cn/2409:8c60:2600:2:0:1:0:16e
fundgz.1234567.com.cn/221.178.98.184
fundgz.1234567.com.cn/221.178.98.179
fundgz.1234567.com.cn/221.178.98.188
fundgz.1234567.com.cn/221.178.98.187
fundgz.1234567.com.cn/221.178.98.185
fundgz.1234567.com.cn/221.178.98.182
fundgz.1234567.com.cn/221.178.98.181
fundgz.1234567.com.cn/221.178.98.180
fundgz.1234567.com.cn/221.178.98.183
fundgz.1234567.com.cn/221.178.98.186

可以看到前面 10 个是 IPv6 地址，OkHttp 按顺序一个个解析，IPv6 的都解析超时了，所有请求时间刚好是 connectTimeout 的 10 倍再多一点。

解决问题

我们修改 Dns 的实现为下面的代码，优先解析 IPv4 地址，最后测试问题解决。

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val client = OkHttpClient.Builder()
    .dns(ApiDns())
    .build()

class ApiDns : Dns {
    @Throws(UnknownHostException::class)
    override fun lookup(hostname: String): List<InetAddress> {
        try {
            // IPv4 first
            return InetAddress.getAllByName(hostname).sortedBy {
                Inet6Address::class.java.isInstance(it)
            }
        } catch (e: NullPointerException) {
            throw UnknownHostException("Broken system behaviour for dns lookup of $hostname").apply {
                initCause(e)
            }
        }
    }
}

参考链接

发表于 更新于 分类于 ，

The Nine Patch Generator is an online WYSIWYG tool similar to the one included in Android Studio. The tool lets you create bitmap images that automatically resize to accommodate the contents of the view and the size of the screen. You can scale selected parts of the image horizontally or vertically based on indicators drawn within the image.

Link: https://www.9patch.online

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