Service Client: add HEAD method (gophercloud#876)

* service client: add HEAD method

* use the new HEAD() function in all HEAD calls

* fix error

Author: zhangzujian

Diff for: openstack/identity/v3/tokens/requests.go

@@ -133,7 +133,7 @@ func Get(c *gophercloud.ServiceClient, token string) (r GetResult) {
 
 // Validate determines if a specified token is valid or not.
 func Validate(c *gophercloud.ServiceClient, token string) (bool, error) {
-	resp, err := c.Request("HEAD", tokenURL(c), &gophercloud.RequestOpts{
+	resp, err := c.Head(tokenURL(c), &gophercloud.RequestOpts{
 		MoreHeaders: subjectTokenHeaders(c, token),
 		OkCodes:     []int{200, 204, 404},
 	})

Diff for: openstack/identity/v3/users/requests.go

@@ -272,7 +272,7 @@ func AddToGroup(client *gophercloud.ServiceClient, groupID, userID string) (r Ad
 func IsMemberOfGroup(client *gophercloud.ServiceClient, groupID, userID string) (r IsMemberOfGroupResult) {
 	url := isMemberOfGroupURL(client, groupID, userID)
 	var response *http.Response
-	response, r.Err = client.Request("HEAD", url, &gophercloud.RequestOpts{
+	response, r.Err = client.Head(url, &gophercloud.RequestOpts{
 		OkCodes: []int{204, 404},
 	})
 	if r.Err == nil && response != nil {

Diff for: openstack/objectstorage/v1/accounts/requests.go

@@ -35,7 +35,7 @@ func Get(c *gophercloud.ServiceClient, opts GetOptsBuilder) (r GetResult) {
 			h[k] = v
 		}
 	}
-	resp, err := c.Request("HEAD", getURL(c), &gophercloud.RequestOpts{
+	resp, err := c.Head(getURL(c), &gophercloud.RequestOpts{
 		MoreHeaders: h,
 		OkCodes:     []int{204},
 	})

Diff for: openstack/objectstorage/v1/containers/requests.go

@@ -180,7 +180,7 @@ func Update(c *gophercloud.ServiceClient, containerName string, opts UpdateOptsB
 // the custom metadata, pass the GetResult response to the ExtractMetadata
 // function.
 func Get(c *gophercloud.ServiceClient, containerName string) (r GetResult) {
-	resp, err := c.Request("HEAD", getURL(c, containerName), &gophercloud.RequestOpts{
+	resp, err := c.Head(getURL(c, containerName), &gophercloud.RequestOpts{
 		OkCodes: []int{200, 204},
 	})
 	if resp != nil {

Diff for: openstack/objectstorage/v1/objects/requests.go

@@ -344,7 +344,7 @@ func Get(c *gophercloud.ServiceClient, containerName, objectName string, opts Ge
 		}
 		url += query
 	}
-	resp, err := c.Request("HEAD", url, &gophercloud.RequestOpts{
+	resp, err := c.Head(url, &gophercloud.RequestOpts{
 		OkCodes: []int{200, 204},
 	})
 	if resp != nil {

Diff for: service_client.go

@@ -112,6 +112,15 @@ func (client *ServiceClient) Delete(url string, opts *RequestOpts) (*http.Respon
 	return client.Request("DELETE", url, opts)
 }
 
+// Head calls `Request` with the "HEAD" HTTP verb.
+func (client *ServiceClient) Head(url string, opts *RequestOpts) (*http.Response, error) {
+	if opts == nil {
+		opts = new(RequestOpts)
+	}
+	client.initReqOpts(url, nil, nil, opts)
+	return client.Request("HEAD", url, opts)
+}
+
 func (client *ServiceClient) setMicroversionHeader(opts *RequestOpts) {
 	switch client.Type {
 	case "compute":