public static EntityTag Parse(string original)
{
string s = original;
EntityTag tag = new EntityTag();
if (s.StartsWithInvariant("W/"))
{
tag.IsWeak = true;
s = s.Substring(2);
}
if (s == "*")
{
tag.Tag = "*";
}
else if (!s.StartsWithInvariant("\"") && !s.EndsWithInvariant("\""))
{
tag.Tag = s;
}
else if (s.Length < 2 || !s.StartsWithInvariant("\"") || !s.EndsWithInvariant("\""))
{
throw new ArgumentOutOfRangeException(s);
}
else
{
tag.Tag = s.Substring(1, s.Length - 2);
}
return tag;
}
public void StartPolling(Uri uri, EntityTag etag, DateTime? lastModifiedTime)
{
if (this.HttpClient == null)
{
throw new InvalidOperationException("The http client to use for polling is not specified.");
}
lock (thisLock)
{
if (this.isBusy)
{
throw new InvalidOperationException("Polling has already started");
}
this.isBusy = true;
}
this.uri = uri ?? this.HttpClient.BaseAddress;
this.etag = etag;
this.lastModifiedTime = lastModifiedTime;
this.timer = new Timer(this.PollingInterval.TotalMilliseconds);
this.timer.AutoReset = true;
this.syncContext = SynchronizationContext.Current;
this.timer.Elapsed += this.TimerElapsed;
this.timer.Enabled = true;
this.timer.Start();
}
public DateOrEntityTag(EntityTag entityTag)
{
this.EntityTag = entityTag;
}
void TimerElapsed(object sender, ElapsedEventArgs e)
{
if (!this.isBusy)
{
return;
}
if (!this.IgnoreExpiresHeader)
{
// Since Expires is a static guess by the server, use Expires only when the server did
// not send back any Etag or LastModifiedTime, which makes conditional GET impossible
if (this.etag == null && this.lastModifiedTime == null && this.expires != null && (DateTime.UtcNow < this.expires.Value.ToUniversalTime()))
{
return;
}
}
this.expires = null;
HttpRequestMessage request = new HttpRequestMessage("GET", this.uri);
if (this.etag != null)
{
var ifNoneMatch = new HeaderValues<EntityTag>();
ifNoneMatch.Add(this.etag);
request.Headers.IfNoneMatch = ifNoneMatch;
}
request.Headers.IfModifiedSince = this.lastModifiedTime;
bool stopTimer = false;
try
{
HttpResponseMessage response = null;
try
{
response = this.HttpClient.Send(request);
}
catch (Exception ex)
{
if (!this.IgnoreSendErrors)
{
stopTimer = InvokeHandler(ex);
}
if (response != null)
{
response.Dispose();
}
return;
}
using (response)
{
switch (response.StatusCode)
{
case HttpStatusCode.NotModified:
// the resource has not been modified
response.Dispose();
break;
case HttpStatusCode.OK:
// the resource has been modified. Fire the event, along with the response message
this.etag = response.Headers.ETag;
this.expires = response.Headers.Expires;
this.lastModifiedTime = response.Headers.LastModified;
try
{
stopTimer = InvokeHandler(response);
}
finally
{
response.Dispose();
}
break;
default:
// this is an unexpected error. Fire the event, if errors are not to be suppressed
try
{
if (!this.IgnoreNonOKStatusCodes)
{
stopTimer = InvokeHandler(response);
}
}
finally
{
response.Dispose();
}
break;
}
}
}
finally
{
if (stopTimer)
{
StopPolling();
}
}
}
public DateOrEntityTag(EntityTag entityTag)
{
this.EntityTag = entityTag;
}
