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http_reader.go
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http_reader.go
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package transport
import (
"errors"
"fmt"
"io"
"net/http"
"os"
"regexp"
"strconv"
)
var (
contentRangeRegexp = regexp.MustCompile(`bytes ([0-9]+)-([0-9]+)/([0-9]+|\\*)`)
// ErrWrongCodeForByteRange is returned if the client sends a request
// with a Range header but the server returns a 2xx or 3xx code other
// than 206 Partial Content.
ErrWrongCodeForByteRange = errors.New("expected HTTP 206 from byte range request")
)
// ReadSeekCloser combines io.ReadSeeker with io.Closer.
type ReadSeekCloser interface {
io.ReadSeeker
io.Closer
}
// NewHTTPReadSeeker handles reading from an HTTP endpoint using a GET
// request. When seeking and starting a read from a non-zero offset
// the a "Range" header will be added which sets the offset.
// TODO(dmcgowan): Move this into a separate utility package
func NewHTTPReadSeeker(client *http.Client, url string, errorHandler func(*http.Response) error) ReadSeekCloser {
return &httpReadSeeker{
client: client,
url: url,
errorHandler: errorHandler,
}
}
type httpReadSeeker struct {
client *http.Client
url string
// errorHandler creates an error from an unsuccessful HTTP response.
// This allows the error to be created with the HTTP response body
// without leaking the body through a returned error.
errorHandler func(*http.Response) error
size int64
// rc is the remote read closer.
rc io.ReadCloser
// readerOffset tracks the offset as of the last read.
readerOffset int64
// seekOffset allows Seek to override the offset. Seek changes
// seekOffset instead of changing readOffset directly so that
// connection resets can be delayed and possibly avoided if the
// seek is undone (i.e. seeking to the end and then back to the
// beginning).
seekOffset int64
err error
}
func (hrs *httpReadSeeker) Read(p []byte) (n int, err error) {
if hrs.err != nil {
return 0, hrs.err
}
// If we sought to a different position, we need to reset the
// connection. This logic is here instead of Seek so that if
// a seek is undone before the next read, the connection doesn't
// need to be closed and reopened. A common example of this is
// seeking to the end to determine the length, and then seeking
// back to the original position.
if hrs.readerOffset != hrs.seekOffset {
hrs.reset()
}
hrs.readerOffset = hrs.seekOffset
rd, err := hrs.reader()
if err != nil {
return 0, err
}
n, err = rd.Read(p)
hrs.seekOffset += int64(n)
hrs.readerOffset += int64(n)
return n, err
}
func (hrs *httpReadSeeker) Seek(offset int64, whence int) (int64, error) {
if hrs.err != nil {
return 0, hrs.err
}
lastReaderOffset := hrs.readerOffset
if whence == os.SEEK_SET && hrs.rc == nil {
// If no request has been made yet, and we are seeking to an
// absolute position, set the read offset as well to avoid an
// unnecessary request.
hrs.readerOffset = offset
}
_, err := hrs.reader()
if err != nil {
hrs.readerOffset = lastReaderOffset
return 0, err
}
newOffset := hrs.seekOffset
switch whence {
case os.SEEK_CUR:
newOffset += offset
case os.SEEK_END:
if hrs.size < 0 {
return 0, errors.New("content length not known")
}
newOffset = hrs.size + offset
case os.SEEK_SET:
newOffset = offset
}
if newOffset < 0 {
err = errors.New("cannot seek to negative position")
} else {
hrs.seekOffset = newOffset
}
return hrs.seekOffset, err
}
func (hrs *httpReadSeeker) Close() error {
if hrs.err != nil {
return hrs.err
}
// close and release reader chain
if hrs.rc != nil {
hrs.rc.Close()
}
hrs.rc = nil
hrs.err = errors.New("httpLayer: closed")
return nil
}
func (hrs *httpReadSeeker) reset() {
if hrs.err != nil {
return
}
if hrs.rc != nil {
hrs.rc.Close()
hrs.rc = nil
}
}
func (hrs *httpReadSeeker) reader() (io.Reader, error) {
if hrs.err != nil {
return nil, hrs.err
}
if hrs.rc != nil {
return hrs.rc, nil
}
req, err := http.NewRequest("GET", hrs.url, nil)
if err != nil {
return nil, err
}
if hrs.readerOffset > 0 {
// If we are at different offset, issue a range request from there.
req.Header.Add("Range", fmt.Sprintf("bytes=%d-", hrs.readerOffset))
// TODO: get context in here
// context.GetLogger(hrs.context).Infof("Range: %s", req.Header.Get("Range"))
}
req.Header.Add("Accept-Encoding", "identity")
resp, err := hrs.client.Do(req)
if err != nil {
return nil, err
}
// Normally would use client.SuccessStatus, but that would be a cyclic
// import
if resp.StatusCode >= 200 && resp.StatusCode <= 399 {
if hrs.readerOffset > 0 {
if resp.StatusCode != http.StatusPartialContent {
return nil, ErrWrongCodeForByteRange
}
contentRange := resp.Header.Get("Content-Range")
if contentRange == "" {
return nil, errors.New("no Content-Range header found in HTTP 206 response")
}
submatches := contentRangeRegexp.FindStringSubmatch(contentRange)
if len(submatches) < 4 {
return nil, fmt.Errorf("could not parse Content-Range header: %s", contentRange)
}
startByte, err := strconv.ParseUint(submatches[1], 10, 64)
if err != nil {
return nil, fmt.Errorf("could not parse start of range in Content-Range header: %s", contentRange)
}
if startByte != uint64(hrs.readerOffset) {
return nil, fmt.Errorf("received Content-Range starting at offset %d instead of requested %d", startByte, hrs.readerOffset)
}
endByte, err := strconv.ParseUint(submatches[2], 10, 64)
if err != nil {
return nil, fmt.Errorf("could not parse end of range in Content-Range header: %s", contentRange)
}
if submatches[3] == "*" {
hrs.size = -1
} else {
size, err := strconv.ParseUint(submatches[3], 10, 64)
if err != nil {
return nil, fmt.Errorf("could not parse total size in Content-Range header: %s", contentRange)
}
if endByte+1 != size {
return nil, fmt.Errorf("range in Content-Range stops before the end of the content: %s", contentRange)
}
hrs.size = int64(size)
}
} else if resp.StatusCode == http.StatusOK {
hrs.size = resp.ContentLength
} else {
hrs.size = -1
}
hrs.rc = resp.Body
} else {
defer resp.Body.Close()
if hrs.errorHandler != nil {
return nil, hrs.errorHandler(resp)
}
return nil, fmt.Errorf("unexpected status resolving reader: %v", resp.Status)
}
return hrs.rc, nil
}