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|
package httprange
import (
"context"
"fmt"
"io"
"io/ioutil"
"net/http"
"strconv"
"strings"
"sync/atomic"
)
// Resource represents any HTTP resource that can be read by a GET operation.
// It holds the resource's URL and metadata about it.
type Resource struct {
ETag string
LastModified string
Size int64
url atomic.Value
err atomic.Value
httpClient *http.Client
}
func (r *Resource) URL() string {
url, _ := r.url.Load().(string)
return url
}
func (r *Resource) SetURL(url string) {
if r.URL() == url {
// We want to avoid cache lines invalidation
// on CPU due to value change
return
}
r.url.Store(url)
}
func (r *Resource) Err() error {
err, _ := r.err.Load().(error)
return err
}
func (r *Resource) Valid() bool {
return r.Err() == nil
}
func (r *Resource) setError(err error) {
r.err.Store(err)
}
func (r *Resource) Request() (*http.Request, error) {
req, err := http.NewRequest("GET", r.URL(), nil)
if err != nil {
return nil, err
}
if r.ETag != "" {
req.Header.Set("ETag", r.ETag)
} else if r.LastModified != "" {
// Last-Modified should be a fallback mechanism in case ETag is not present
// https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Last-Modified
req.Header.Set("If-Range", r.LastModified)
}
return req, nil
}
func NewResource(ctx context.Context, url string, httpClient *http.Client) (*Resource, error) {
// the `h.URL` is likely pre-signed URL or a file:// scheme that only supports GET requests
req, err := http.NewRequest("GET", url, nil)
if err != nil {
return nil, err
}
req = req.WithContext(ctx)
// we fetch a single byte and ensure that range requests is additionally supported
req.Header.Set("Range", fmt.Sprintf("bytes=%d-%d", 0, 0))
// nolint: bodyclose
// body will be closed by discardAndClose
res, err := httpClient.Do(req)
if err != nil {
return nil, err
}
defer func() {
io.CopyN(ioutil.Discard, res.Body, 1) // since we want to read a single byte
res.Body.Close()
}()
resource := &Resource{
ETag: res.Header.Get("ETag"),
LastModified: res.Header.Get("Last-Modified"),
httpClient: httpClient,
}
resource.SetURL(url)
switch res.StatusCode {
case http.StatusOK:
resource.Size = res.ContentLength
return resource, nil
case http.StatusPartialContent:
contentRange := res.Header.Get("Content-Range")
ranges := strings.SplitN(contentRange, "/", 2)
if len(ranges) != 2 {
return nil, fmt.Errorf("invalid `Content-Range`: %q", contentRange)
}
resource.Size, err = strconv.ParseInt(ranges[1], 0, 64)
if err != nil {
return nil, fmt.Errorf("invalid `Content-Range`: %q %w", contentRange, err)
}
return resource, nil
case http.StatusRequestedRangeNotSatisfiable:
return nil, ErrRangeRequestsNotSupported
case http.StatusNotFound:
return nil, ErrNotFound
default:
return nil, fmt.Errorf("httprange: new resource %d: %q", res.StatusCode, res.Status)
}
}
|
