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httpreadat.go
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httpreadat.go
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// Package httpreadat provides an io.ReaderAt for http requests using the Range header.
package httpreadat
import (
"errors"
"fmt"
"io"
"io/ioutil"
"net/http"
"strconv"
"strings"
)
type RangeReader struct {
url string
roundTripper http.RoundTripper
cacheHandler CacheHandler
}
func New(url string, opts ...Option) *RangeReader {
rr := RangeReader{
url: url,
}
for _, opt := range opts {
opt.set(&rr)
}
return &rr
}
func (rr *RangeReader) rawReadAt(p []byte, off int64) (n int, err error) {
fetchSize := len(p)
req, err := http.NewRequest("GET", rr.url, nil)
if err != nil {
return 0, err
}
req.Header.Add("Range", fmt.Sprintf("bytes=%d-%d", off, off+int64(fetchSize-1)))
resp, err := rr.client().Do(req)
if err != nil {
return 0, err
}
defer resp.Body.Close()
n, err = io.ReadFull(resp.Body, p)
if err == io.ErrUnexpectedEOF {
return n, io.EOF
} else if err != nil {
return n, err
}
return n, nil
}
func (rr *RangeReader) ReadAt(p []byte, off int64) (n int, err error) {
rawFetcher := readerAt{
readAt: rr.rawReadAt,
}
cacheHandler := rr.cacheHandler
if cacheHandler == nil {
cacheHandler = &nopCacheHandler{}
}
return cacheHandler.Get(p, off, rawFetcher)
}
func (rr *RangeReader) client() *http.Client {
if rr.roundTripper == nil {
return http.DefaultClient
}
return &http.Client{
Transport: rr.roundTripper,
}
}
func (rr *RangeReader) Size() (n int64, err error) {
req, err := http.NewRequest("GET", rr.url, nil)
if err != nil {
return 0, err
}
req.Header.Set("Range", "bytes=0-0")
resp, err := rr.client().Do(req)
if err != nil {
return 0, err
}
io.Copy(ioutil.Discard, resp.Body)
resp.Body.Close()
rangeHeader := resp.Header.Get("Content-Range")
rangeFields := strings.Fields(rangeHeader)
if len(rangeFields) != 2 {
return 0, invalidContentRangeErr
}
if strings.ToLower(rangeFields[0]) != "bytes" {
return 0, invalidContentRangeErr
}
amts := strings.Split(rangeFields[1], "/")
if len(amts) != 2 {
return 0, invalidContentRangeErr
}
if amts[1] == "*" {
return 0, invalidContentRangeErr
}
n, err = strconv.ParseInt(amts[1], 10, 64)
if err != nil {
return 0, invalidContentRangeErr
}
return n, nil
}
type nopCacheHandler struct {
}
func (h *nopCacheHandler) Get(p []byte, off int64, fetcher io.ReaderAt) (int, error) {
return fetcher.ReadAt(p, off)
}
type readerAt struct {
readAt func(p []byte, off int64) (n int, err error)
}
func (r readerAt) ReadAt(p []byte, off int64) (n int, err error) {
return r.readAt(p, off)
}
var invalidContentRangeErr = errors.New("invalid Content-Range response")