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) // 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 } } pagesSlice = append(pagesSlice, b[key].([]interface{})...) 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 }