Question

我正在开发一个需要调用rest API的应用程序。在执行HttpWebRequest之前，应用程序需要检查是否存在互联网连接目前，我使用以下代码检查互联网是否可用：

var request = (HttpWebRequest) WebRequest.Create("http://www.google.co.uk");
response = (HttpWebResponse) request.GetResponse();
if (response.StatusCode == HttpStatusCode.OK)
{

   //there is internet

}

以上代码可以正常运行，但有时候我的HTTP状态为302（已找到）。

有没有更好的方法来检查互联网连接是否可用？

Answer 1

我会这样做，因为没有歧义。您将获得ping响应或不响应。此外，你花了32个字节来检查这个，而不是获得谷歌的主页，如果你查看源代码，那么主页就是很多：

public bool IsOnline() {
    var ping = new Ping();
    string host = "google.com";
    byte[] buffer = new byte[32];
    int timeout = 1000;
    var pingOptions = new PingOptions();
    PingReply reply = ping.Send(host, timeout, buffer, pingOptions);
    if (reply.Status == IPStatus.Success) {
      return true;
    }
    return false;
}

修改

这是一个使用原始低级套接字执行ping的类，它可以在.NET MF中使用！

public class RawSocketPing { public Socket pingSocket; // Raw socket handle public int pingTtl; // Time-to-live value to set on ping public ushort pingId; // ID value to set in ping packet public ushort pingSequence; // Current sending sequence number public int pingPayloadLength; // Size of the payload in ping packet public int pingCount; // Number of times to send ping request public int pingReceiveTimeout; // Timeout value to wait for ping response private IPEndPoint destEndPoint; // Destination being pinged public IPEndPoint responseEndPoint; // Contains the source address of the ping response public EndPoint castResponseEndPoint; // Simple cast time used for the responseEndPoint private byte[] pingPacket; // Byte array of ping packet built private byte[] pingPayload; // Payload in the ping packet private byte[] receiveBuffer; // Buffer used to receive ping response private IcmpHeader icmpHeader; // ICMP header built (for IPv4) private DateTime pingSentTime; // Timestamp of when ping request was sent /// <summary> /// Base constructor that initializes the member variables to default values. It also /// creates the events used and initializes the async callback function. /// </summary> public RawSocketPing() { pingSocket = null; pingTtl = 8; pingPayloadLength = 8; pingSequence = 0; pingReceiveTimeout = 2000; destEndPoint = new IPEndPoint(IPAddress.Loopback, 0); icmpHeader = null; } /// <summary> /// Constructor that overrides several members of the ping packet such as TTL, /// payload length, ping ID, etc. /// </summary> /// <param name="af">Indicates whether we're doing IPv4 or IPv6 ping</param> /// <param name="ttlValue">Time-to-live value to set on ping packet</param> /// <param name="payloadSize">Number of bytes in ping payload</param> /// <param name="sendCount">Number of times to send a ping request</param> /// <param name="idValue">ID value to put into ping header</param> public RawSocketPing( int ttlValue, int payloadSize, int sendCount, ushort idValue ) : this() { pingTtl = ttlValue; pingPayloadLength = payloadSize; pingCount = sendCount; pingId = idValue; } /// <summary> /// This routine is called when the calling application is done with the ping class. /// This routine closes any open resource such as socket handles. /// </summary> public void Close() { try { if (pingSocket != null) { pingSocket.Close(); pingSocket = null; } } catch (Exception err) { throw; } } /// <summary> /// Since ICMP raw sockets don't care about the port (as the ICMP protoocl has no port /// field), we require the caller to just update the IPAddress of the destination /// although internally we keep it as an IPEndPoint since the SendTo method requires /// that (and the port is simply set to zero). /// </summary> public IPAddress PingAddress { get { return destEndPoint.Address; } set { destEndPoint = new IPEndPoint(value, 0); } } /// <summary> /// This routine initializes the raw socket, sets the TTL, allocates the receive /// buffer, and sets up the endpoint used to receive any ICMP echo responses. /// </summary> public void InitializeSocket() { IPEndPoint localEndPoint = new IPEndPoint(IPAddress.Any, 0); // Create the raw socket pingSocket = new Socket(AddressFamily.InterNetwork, SocketType.Raw, ProtocolType.Icmp); // Socket must be bound locally before socket options can be applied pingSocket.Bind(localEndPoint); pingSocket.SetSocketOption( SocketOptionLevel.IP, SocketOptionName.IpTimeToLive, pingTtl ); // Allocate the buffer used to receive the response pingSocket.ReceiveTimeout = pingReceiveTimeout; receiveBuffer = new byte[540]; responseEndPoint = new IPEndPoint(IPAddress.Any, 0); castResponseEndPoint = (EndPoint)responseEndPoint; } /// <summary> /// This routine builds the appropriate ICMP echo packet depending on the /// protocol family requested. /// </summary> public void BuildPingPacket() { // Initialize the socket if it hasn't already been done if (pingSocket == null) { InitializeSocket(); } // Create the ICMP header and initialize the members icmpHeader = new IcmpHeader() { Id = pingId, Sequence = pingSequence, Type = IcmpHeader.EchoRequestType, Code = IcmpHeader.EchoRequestCode }; // Build the data payload of the ICMP echo request pingPayload = new byte[pingPayloadLength]; for (int i = 0; i < pingPayload.Length; i++) { pingPayload[i] = (byte)'e'; } } /// <summary> /// This function performs the actual ping. It sends the ping packets created to /// the destination /// </summary> public bool DoPing() { bool success = false; // Send an echo request while (pingCount > 0) { try { pingCount--; // Increment the sequence count in the ICMP header icmpHeader.Sequence = (ushort)(icmpHeader.Sequence + (ushort)1); // Build the byte array representing the ping packet. This needs to be done // before ever send because we change the sequence number (which will affect // the calculated checksum). pingPacket = icmpHeader.BuildPacket(pingId, pingPayload); // Mark the time we sent the packet pingSentTime = DateTime.Now; // Send the echo request pingSocket.SendTo(pingPacket, destEndPoint); int Brecieved = pingSocket.ReceiveFrom( receiveBuffer, 0, receiveBuffer.Length, SocketFlags.None, ref castResponseEndPoint ); //IF you get to here, then you got a response. success = true; break; } catch (SocketException err) { //PING FAILED, try it again for remaining ping counts } } return success; } }

以下是该代码的source

Answer 2

如果您不关心其他状态（例如 503 等），请使用典型的 try-catch 异常处理。

        try
        {
            using (WebClient client = new WebClient())
            {
                string htmlCode = client.DownloadString("https://worldtimeapi.org/api/timezone/EST");                    
            }
        }
        catch
        {
            //No Internet 
            Console.WriteLine("No Internet")
        }

使用HttpWebRequest检查Internet连接

2 个答案: