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// Copyright 2013 Canonical Ltd. This software is licensed under the
// GNU Lesser General Public License version 3 (see the file COPYING).
package gwacl
import (
"fmt"
"time"
)
// Generic poller interface/methods.
// A poller exposes two methods to query a remote server and decide when
// the response given by the server means that the polling is finished.
type poller interface {
poll() (*x509Response, error)
isDone(*x509Response, error) (bool, error)
}
// performPolling calls the poll() method of the given 'poller' object every
// 'interval' until poller.isDone() returns true.
func performPolling(poller poller, interval time.Duration, timeout time.Duration) (*x509Response, error) {
timeoutChannel := time.After(timeout)
ticker := time.Tick(interval)
// Function to do a single poll, checking for timeout. The bool returned
// indicates if polling is finished, one way or another.
poll := func() (bool, *x509Response, error) {
// This may need to tolerate some transient failures, such as network
// failures that may go away after a few retries.
select {
case <-timeoutChannel:
return true, nil, fmt.Errorf("polling timed out waiting for an asynchronous operation")
default:
response, pollerErr := poller.poll()
done, err := poller.isDone(response, pollerErr)
if err != nil {
return true, nil, err
}
if done {
return true, response, nil
}
}
return false, nil, nil
}
// Do an initial poll.
done, response, err := poll()
if done {
return response, err
}
// Poll every interval.
for _ = range ticker {
done, response, err := poll()
if done {
return response, err
}
}
// This code cannot be reached but Go insists on having a return or a panic
// statement at the end of this method. Sigh.
panic("invalid poller state!")
}
// Operation poller structs/methods.
// performOperationPolling calls performPolling on the given arguments and converts
// the returned object into an *Operation.
func performOperationPolling(poller poller, interval time.Duration, timeout time.Duration) (*Operation, error) {
response, err := performPolling(poller, interval, timeout)
if err != nil {
return nil, err
}
operation := Operation{}
err = operation.Deserialize(response.Body)
return &operation, err
}
// operationPoller is an object implementing the poller interface, used to
// poll the Window Azure server until the operation referenced by the given
// operationID is completed.
type operationPoller struct {
api *ManagementAPI
operationID string
}
var _ poller = &operationPoller{}
// newOperationPoller returns a poller object associated with the given
// management API object and the given operationID. It can track (by polling
// the server) the status of the operation associated with the provided
// operationID string.
func newOperationPoller(api *ManagementAPI, operationID string) poller {
return operationPoller{api: api, operationID: operationID}
}
// Poll issues a blocking request to microsoft Azure to fetch the information
// related to the operation associated with the poller.
// See http://msdn.microsoft.com/en-us/library/windowsazure/ee460783.aspx
func (poller operationPoller) poll() (*x509Response, error) {
URI := "operations/" + poller.operationID
return poller.api.session.get(URI, "2009-10-01")
}
// IsDone returns true if the given response has a status code indicating
// success and if the returned XML response corresponds to a valid Operation
// with a status indicating that the operation is completed.
func (poller operationPoller) isDone(response *x509Response, pollerError error) (bool, error) {
// TODO: Add a timeout so that polling won't continue forever if the
// server cannot be reached.
if pollerError != nil {
return true, pollerError
}
if response.StatusCode >= 200 && response.StatusCode < 300 {
operation := Operation{}
err := operation.Deserialize(response.Body)
if err != nil {
return false, err
}
status := operation.Status
done := (status != "" && status != InProgressOperationStatus)
return done, nil
}
return false, nil
}
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