Blocking APIs may be inefficient because you hold a thread idle while waiting on the network. Threads are expensive because they have both a memory overhead and a context-switching overhead.

#### Framed protocols

        }

        if (connectResult.isSuccess) {
          // We have a connected TCP connection. Cancel and defer the racing connects that all lost.
          cancelInFlightConnects()

          // Finish connecting. We won't have to if the winner is from the connection pool.
          if (!connectResult.plan.isReady) {

        // Something was parsed. It's possible the entire string was not consumed but we ignore
        // that. If any of the BROWSER_COMPATIBLE_DATE_FORMAT_STRINGS ended in "'GMT'" we'd have
        // to also check that position.getIndex() == value.length() otherwise parsing might have
        // terminated early, ignoring things like "+01:00". Leaving this as != 0 means that any
        // trailing junk is ignored.
        return result
      }
    }

      "method.isEmpty() == true"
    }
    if (body == null) {
      require(!HttpMethod.requiresRequestBody(method)) {
        "method $method must have a request body."
      }
    } else {
      require(HttpMethod.permitsRequestBody(method)) {
        "method $method must not have a request body."
      }
    }
    this.method = method
    this.body = body
  }

fun <T : Any> Request.Builder.commonTag(

  private val provider: Provider = org.openjsse.net.ssl.OpenJSSE()

  // Selects TLSv1.3 so we are specific about our intended version ranges (not just 1.3)
  // and because it's a common pattern for VMs to have differences between supported and
  // defaulted versions for TLS based on what is requested.
  override fun newSSLContext(): SSLContext = SSLContext.getInstance("TLSv1.3", provider)

received followed by a cache hit or miss.  Critically in the cache hit scenario the server won’t send the response body.

The response will have non-null `cacheResponse` and `networkResponse`. The cacheResponse will be used as the top level
response only if the response code is HTTP/1.1 304 Not Modified.
 
 - CallStart
 - **CacheConditionalHit**
 - ConnectionAcquired

  @Override public void log(String message) {
    Timber.tag("OkHttp").d(message);
  }
});
```

**Warning**: The logs generated by this interceptor when using the `HEADERS` or `BODY` levels have
the potential to leak sensitive information such as "Authorization" or "Cookie" headers and the
contents of request and response bodies. This data should only be logged in a controlled way or in
a non-production environment.

Some requests will have a cached response. When this cached response isn’t fresh, OkHttp can do a _conditional GET_ to download an updated response if it’s newer than what’s cached. This requires headers like `If-Modified-Since` and `If-None-Match` to be added.

  /**
   * Load cookies from the jar for an HTTP request to [url]. This method returns a possibly
   * empty list of cookies for the network request.
   *
   * Simple implementations will return the accepted cookies that have not yet expired and that
   * [match][Cookie.matches] [url].
   */
  fun loadForRequest(url: HttpUrl): List<Cookie>

  companion object {
    /** A cookie jar that never accepts any cookies. */
    @JvmField

    // 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()