我正在开发一个需要调用休息 API 的应用程序。应用程序需要在执行之前检查是否有互联网连接HttpWebRequest
目前我正在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
}
上面的代码有效，但有时我会收到 HTTP 状态 302（已找到）。
有没有更好的方法来检查互联网连接是否可用？
我会把它作为一个 ping 来做，因为没有歧义。您要么会收到 ping 响应，要么不会。此外，您要花费 32 个字节来检查这一点，而不是获取 Google 的主页，如果您查看源代码，则该主页包含大量数据：
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;
}
编辑
这是一个使用原始低级套接字执行 ping 的类，它在 .NET MF 中工作！
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;
}
}
这是该代码的来源
Use typical try-catch Exception Handling if you dont care for other status such as 503 etc.
try
{
using (WebClient client = new WebClient())
{
string htmlCode = client.DownloadString("https://worldtimeapi.org/api/timezone/EST");
}
}
catch
{
//No Internet
Console.WriteLine("No Internet")
}