terraform/vendor/github.com/rackspace/gophercloud/pagination/pager.go

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package pagination
import (
"errors"
"fmt"
"net/http"
"reflect"
"strings"
"github.com/rackspace/gophercloud"
)
var (
// ErrPageNotAvailable is returned from a Pager when a next or previous page is requested, but does not exist.
ErrPageNotAvailable = errors.New("The requested page does not exist.")
)
// Page must be satisfied by the result type of any resource collection.
// It allows clients to interact with the resource uniformly, regardless of whether or not or how it's paginated.
// Generally, rather than implementing this interface directly, implementors should embed one of the concrete PageBase structs,
// instead.
// Depending on the pagination strategy of a particular resource, there may be an additional subinterface that the result type
// will need to implement.
type Page interface {
// NextPageURL generates the URL for the page of data that follows this collection.
// Return "" if no such page exists.
NextPageURL() (string, error)
// IsEmpty returns true if this Page has no items in it.
IsEmpty() (bool, error)
// GetBody returns the Page Body. This is used in the `AllPages` method.
GetBody() interface{}
}
// Pager knows how to advance through a specific resource collection, one page at a time.
type Pager struct {
client *gophercloud.ServiceClient
initialURL string
createPage func(r PageResult) Page
Err error
// Headers supplies additional HTTP headers to populate on each paged request.
Headers map[string]string
}
// NewPager constructs a manually-configured pager.
// Supply the URL for the first page, a function that requests a specific page given a URL, and a function that counts a page.
func NewPager(client *gophercloud.ServiceClient, initialURL string, createPage func(r PageResult) Page) Pager {
return Pager{
client: client,
initialURL: initialURL,
createPage: createPage,
}
}
// WithPageCreator returns a new Pager that substitutes a different page creation function. This is
// useful for overriding List functions in delegation.
func (p Pager) WithPageCreator(createPage func(r PageResult) Page) Pager {
return Pager{
client: p.client,
initialURL: p.initialURL,
createPage: createPage,
}
}
func (p Pager) fetchNextPage(url string) (Page, error) {
resp, err := Request(p.client, p.Headers, url)
if err != nil {
return nil, err
}
remembered, err := PageResultFrom(resp)
if err != nil {
return nil, err
}
return p.createPage(remembered), nil
}
// EachPage iterates over each page returned by a Pager, yielding one at a time to a handler function.
// Return "false" from the handler to prematurely stop iterating.
func (p Pager) EachPage(handler func(Page) (bool, error)) error {
if p.Err != nil {
return p.Err
}
currentURL := p.initialURL
for {
currentPage, err := p.fetchNextPage(currentURL)
if err != nil {
return err
}
empty, err := currentPage.IsEmpty()
if err != nil {
return err
}
if empty {
return nil
}
ok, err := handler(currentPage)
if err != nil {
return err
}
if !ok {
return nil
}
currentURL, err = currentPage.NextPageURL()
if err != nil {
return err
}
if currentURL == "" {
return nil
}
}
}
// AllPages returns all the pages from a `List` operation in a single page,
// allowing the user to retrieve all the pages at once.
func (p Pager) AllPages() (Page, error) {
// pagesSlice holds all the pages until they get converted into as Page Body.
var pagesSlice []interface{}
// body will contain the final concatenated Page body.
var body reflect.Value
// Grab a test page to ascertain the page body type.
testPage, err := p.fetchNextPage(p.initialURL)
if err != nil {
return nil, err
}
// Store the page type so we can use reflection to create a new mega-page of
// that type.
pageType := reflect.TypeOf(testPage)
// if it's a single page, just return the testPage (first page)
if _, found := pageType.FieldByName("SinglePageBase"); found {
return testPage, nil
}
// Switch on the page body type. Recognized types are `map[string]interface{}`,
// `[]byte`, and `[]interface{}`.
switch testPage.GetBody().(type) {
case map[string]interface{}:
// key is the map key for the page body if the body type is `map[string]interface{}`.
var key string
// Iterate over the pages to concatenate the bodies.
err := p.EachPage(func(page Page) (bool, error) {
b := page.GetBody().(map[string]interface{})
for k := range b {
// If it's a linked page, we don't want the `links`, we want the other one.
if !strings.HasSuffix(k, "links") {
key = k
}
}
switch keyType := b[key].(type) {
case map[string]interface{}:
pagesSlice = append(pagesSlice, keyType)
case []interface{}:
pagesSlice = append(pagesSlice, b[key].([]interface{})...)
default:
return false, fmt.Errorf("Unsupported page body type: %+v", keyType)
}
return true, nil
})
if err != nil {
return nil, err
}
// Set body to value of type `map[string]interface{}`
body = reflect.MakeMap(reflect.MapOf(reflect.TypeOf(key), reflect.TypeOf(pagesSlice)))
body.SetMapIndex(reflect.ValueOf(key), reflect.ValueOf(pagesSlice))
case []byte:
// Iterate over the pages to concatenate the bodies.
err := p.EachPage(func(page Page) (bool, error) {
b := page.GetBody().([]byte)
pagesSlice = append(pagesSlice, b)
// seperate pages with a comma
pagesSlice = append(pagesSlice, []byte{10})
return true, nil
})
if err != nil {
return nil, err
}
if len(pagesSlice) > 0 {
// Remove the trailing comma.
pagesSlice = pagesSlice[:len(pagesSlice)-1]
}
var b []byte
// Combine the slice of slices in to a single slice.
for _, slice := range pagesSlice {
b = append(b, slice.([]byte)...)
}
// Set body to value of type `bytes`.
body = reflect.New(reflect.TypeOf(b)).Elem()
body.SetBytes(b)
case []interface{}:
// Iterate over the pages to concatenate the bodies.
err := p.EachPage(func(page Page) (bool, error) {
b := page.GetBody().([]interface{})
pagesSlice = append(pagesSlice, b...)
return true, nil
})
if err != nil {
return nil, err
}
// Set body to value of type `[]interface{}`
body = reflect.MakeSlice(reflect.TypeOf(pagesSlice), len(pagesSlice), len(pagesSlice))
for i, s := range pagesSlice {
body.Index(i).Set(reflect.ValueOf(s))
}
default:
return nil, fmt.Errorf("Page body has unrecognized type.")
}
// Each `Extract*` function is expecting a specific type of page coming back,
// otherwise the type assertion in those functions will fail. pageType is needed
// to create a type in this method that has the same type that the `Extract*`
// function is expecting and set the Body of that object to the concatenated
// pages.
page := reflect.New(pageType)
// Set the page body to be the concatenated pages.
page.Elem().FieldByName("Body").Set(body)
// Set any additional headers that were pass along. The `objectstorage` pacakge,
// for example, passes a Content-Type header.
h := make(http.Header)
for k, v := range p.Headers {
h.Add(k, v)
}
page.Elem().FieldByName("Header").Set(reflect.ValueOf(h))
// Type assert the page to a Page interface so that the type assertion in the
// `Extract*` methods will work.
return page.Elem().Interface().(Page), err
}