RouteSelector.kt

/*
 * Copyright (C) 2012 Square, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package okhttp3.internal.connection

import java.io.IOException
import java.net.InetAddress
import java.net.InetSocketAddress
import java.net.Proxy
import java.net.SocketException
import java.net.UnknownHostException
import java.util.NoSuchElementException
import okhttp3.Address
import okhttp3.HttpUrl
import okhttp3.Route
import okhttp3.internal.canParseAsIpAddress
import okhttp3.internal.immutableListOf
import okhttp3.internal.toImmutableList

/**
 * Selects routes to connect to an origin server. Each connection requires a choice of proxy server,
 * IP address, and TLS mode. Connections may also be recycled.
 */
class RouteSelector(
  private val address: Address,
  private val routeDatabase: RouteDatabase,
  private val connectionUser: ConnectionUser,
  private val fastFallback: Boolean,
) {
  // State for negotiating the next proxy to use.
  private var proxies = emptyList<Proxy>()
  private var nextProxyIndex: Int = 0

  // State for negotiating the next socket address to use.
  private var inetSocketAddresses = emptyList<InetSocketAddress>()

  // State for negotiating failed routes
  private val postponedRoutes = mutableListOf<Route>()

  init {
    resetNextProxy(address.url, address.proxy)
  }

  /**
   * Returns true if there's another set of routes to attempt. Every address has at least one route.
   */
  operator fun hasNext(): Boolean = hasNextProxy() || postponedRoutes.isNotEmpty()

  @Throws(IOException::class)
  operator fun next(): Selection {
    if (!hasNext()) throw NoSuchElementException()

    // Compute the next set of routes to attempt.
    val routes = mutableListOf<Route>()
    while (hasNextProxy()) {
      // Postponed routes are always tried last. For example, if we have 2 proxies and all the
      // routes for proxy1 should be postponed, we'll move to proxy2. Only after we've exhausted
      // all the good routes will we attempt the postponed routes.
      val proxy = nextProxy()
      for (inetSocketAddress in inetSocketAddresses) {
        val route = Route(address, proxy, inetSocketAddress)
        if (routeDatabase.shouldPostpone(route)) {
          postponedRoutes += route
        } else {
          routes += route
        }
      }

      if (routes.isNotEmpty()) {
        break
      }
    }

    if (routes.isEmpty()) {
      // We've exhausted all Proxies so fallback to the postponed routes.
      routes += postponedRoutes
      postponedRoutes.clear()
    }

    return Selection(routes)
  }

  /** Prepares the proxy servers to try. */
  private fun resetNextProxy(
    url: HttpUrl,
    proxy: Proxy?,
  ) {
    fun selectProxies(): List<Proxy> {
      // If the user specifies a proxy, try that and only that.
      if (proxy != null) return listOf(proxy)

      // If the URI lacks a host (as in "http://</"), don't call the ProxySelector.
      val uri = url.toUri()
      if (uri.host == null) return immutableListOf(Proxy.NO_PROXY)

      // Try each of the ProxySelector choices until one connection succeeds.
      val proxiesOrNull = address.proxySelector.select(uri)
      if (proxiesOrNull.isNullOrEmpty()) return immutableListOf(Proxy.NO_PROXY)

      return proxiesOrNull.toImmutableList()
    }

    connectionUser.proxySelectStart(url)
    proxies = selectProxies()
    nextProxyIndex = 0
    connectionUser.proxySelectEnd(url, proxies)
  }

  /** Returns true if there's another proxy to try. */
  private fun hasNextProxy(): Boolean = nextProxyIndex < proxies.size

  /** Returns the next proxy to try. May be PROXY.NO_PROXY but never null. */
  @Throws(IOException::class)
  private fun nextProxy(): Proxy {
    if (!hasNextProxy()) {
      throw SocketException(
        "No route to ${address.url.host}; exhausted proxy configurations: $proxies",
      )
    }
    val result = proxies[nextProxyIndex++]
    resetNextInetSocketAddress(result)
    return result
  }

  /** Prepares the socket addresses to attempt for the current proxy or host. */
  @Throws(IOException::class)
  private fun resetNextInetSocketAddress(proxy: Proxy) {
    // Clear the addresses. Necessary if getAllByName() below throws!
    val mutableInetSocketAddresses = mutableListOf<InetSocketAddress>()
    inetSocketAddresses = mutableInetSocketAddresses

    val socketHost: String
    val socketPort: Int
    if (proxy.type() == Proxy.Type.DIRECT || proxy.type() == Proxy.Type.SOCKS) {
      socketHost = address.url.host
      socketPort = address.url.port
    } else {
      val proxyAddress = proxy.address()
      require(proxyAddress is InetSocketAddress) {
        "Proxy.address() is not an InetSocketAddress: ${proxyAddress.javaClass}"
      }
      socketHost = proxyAddress.socketHost
      socketPort = proxyAddress.port
    }

    if (socketPort !in 1..65535) {
      throw SocketException("No route to $socketHost:$socketPort; port is out of range")
    }

    if (proxy.type() == Proxy.Type.SOCKS) {
      mutableInetSocketAddresses += InetSocketAddress.createUnresolved(socketHost, socketPort)
    } else {
      val addresses =
        if (socketHost.canParseAsIpAddress()) {
          listOf(InetAddress.getByName(socketHost))
        } else {
          connectionUser.dnsStart(socketHost)

          val result = address.dns.lookup(socketHost)
          if (result.isEmpty()) {
            throw UnknownHostException("${address.dns} returned no addresses for $socketHost")
          }

          connectionUser.dnsEnd(socketHost, result)
          result
        }

      // Try each address for best behavior in mixed IPv4/IPv6 environments.
      val orderedAddresses =
        when {
          fastFallback -> reorderForHappyEyeballs(addresses)
          else -> addresses
        }

      for (inetAddress in orderedAddresses) {
        mutableInetSocketAddresses += InetSocketAddress(inetAddress, socketPort)
      }
    }
  }

  /** A set of selected Routes. */
  class Selection(val routes: List<Route>) {
    private var nextRouteIndex = 0

    operator fun hasNext(): Boolean = nextRouteIndex < routes.size

    operator fun next(): Route {
      if (!hasNext()) throw NoSuchElementException()
      return routes[nextRouteIndex++]
    }
  }

  companion object {
    /** Obtain a host string containing either an actual host name or a numeric IP address. */
    val InetSocketAddress.socketHost: String get() {
      // The InetSocketAddress was specified with a string (either a numeric IP or a host name). If
      // it is a name, all IPs for that name should be tried. If it is an IP address, only that IP
      // address should be tried.
      val address = address ?: return hostName

      // The InetSocketAddress has a specific address: we should only try that address. Therefore we
      // return the address and ignore any host name that may be available.
      return address.hostAddress
    }
  }
}