debian-mirror-gitlab/workhorse/internal/httprs/httprs.go
2022-07-23 20:15:48 +02:00

216 lines
5.4 KiB
Go

/*
Package httprs provides a ReadSeeker for http.Response.Body.
Usage :
resp, err := http.Get(url)
rs := httprs.NewHttpReadSeeker(resp)
defer rs.Close()
io.ReadFull(rs, buf) // reads the first bytes from the response body
rs.Seek(1024, 0) // moves the position, but does no range request
io.ReadFull(rs, buf) // does a range request and reads from the response body
If you want use a specific http.Client for additional range requests :
rs := httprs.NewHttpReadSeeker(resp, client)
*/
package httprs
import (
"context"
"errors"
"fmt"
"io"
"net/http"
"github.com/mitchellh/copystructure"
)
const shortSeekBytes = 1024
// A HttpReadSeeker reads from a http.Response.Body. It can Seek
// by doing range requests.
type HttpReadSeeker struct {
c *http.Client
req *http.Request
res *http.Response
ctx context.Context
r io.ReadCloser
pos int64
Requests int
}
var _ io.ReadCloser = (*HttpReadSeeker)(nil)
var _ io.Seeker = (*HttpReadSeeker)(nil)
var (
// ErrNoContentLength is returned by Seek when the initial http response did not include a Content-Length header
ErrNoContentLength = errors.New("header Content-Length was not set")
// ErrRangeRequestsNotSupported is returned by Seek and Read
// when the remote server does not allow range requests (Accept-Ranges was not set)
ErrRangeRequestsNotSupported = errors.New("range requests are not supported by the remote server")
// ErrInvalidRange is returned by Read when trying to read past the end of the file
ErrInvalidRange = errors.New("invalid range")
// ErrContentHasChanged is returned by Read when the content has changed since the first request
ErrContentHasChanged = errors.New("content has changed since first request")
)
// NewHttpReadSeeker returns a HttpReadSeeker, using the http.Response and, optionaly, the http.Client
// that needs to be used for future range requests. If no http.Client is given, http.DefaultClient will
// be used.
//
// res.Request will be reused for range requests, headers may be added/removed
func NewHttpReadSeeker(res *http.Response, client ...*http.Client) *HttpReadSeeker {
r := &HttpReadSeeker{
req: res.Request,
ctx: res.Request.Context(),
res: res,
r: res.Body,
}
if len(client) > 0 {
r.c = client[0]
} else {
r.c = http.DefaultClient
}
return r
}
// Clone clones the reader to enable parallel downloads of ranges
func (r *HttpReadSeeker) Clone() (*HttpReadSeeker, error) {
req, err := copystructure.Copy(r.req)
if err != nil {
return nil, err
}
return &HttpReadSeeker{
req: req.(*http.Request),
res: r.res,
r: nil,
c: r.c,
}, nil
}
// Read reads from the response body. It does a range request if Seek was called before.
//
// May return ErrRangeRequestsNotSupported, ErrInvalidRange or ErrContentHasChanged
func (r *HttpReadSeeker) Read(p []byte) (n int, err error) {
if r.r == nil {
err = r.rangeRequest()
}
if r.r != nil {
n, err = r.r.Read(p)
r.pos += int64(n)
}
return
}
// ReadAt reads from the response body starting at offset off.
//
// May return ErrRangeRequestsNotSupported, ErrInvalidRange or ErrContentHasChanged
func (r *HttpReadSeeker) ReadAt(p []byte, off int64) (n int, err error) {
var nn int
r.Seek(off, 0)
for n < len(p) && err == nil {
nn, err = r.Read(p[n:])
n += nn
}
return
}
// Close closes the response body
func (r *HttpReadSeeker) Close() error {
if r.r != nil {
return r.r.Close()
}
return nil
}
// Seek moves the reader position to a new offset.
//
// It does not send http requests, allowing for multiple seeks without overhead.
// The http request will be sent by the next Read call.
//
// May return ErrNoContentLength or ErrRangeRequestsNotSupported
func (r *HttpReadSeeker) Seek(offset int64, whence int) (int64, error) {
var err error
switch whence {
case 0:
case 1:
offset += r.pos
case 2:
if r.res.ContentLength <= 0 {
return 0, ErrNoContentLength
}
offset = r.res.ContentLength - offset
}
if r.r != nil {
// Try to read, which is cheaper than doing a request
if r.pos < offset && offset-r.pos <= shortSeekBytes {
_, err := io.CopyN(io.Discard, r, offset-r.pos)
if err != nil {
return 0, err
}
}
if r.pos != offset {
err = r.r.Close()
r.r = nil
}
}
r.pos = offset
return r.pos, err
}
func cloneHeader(h http.Header) http.Header {
h2 := make(http.Header, len(h))
for k, vv := range h {
vv2 := make([]string, len(vv))
copy(vv2, vv)
h2[k] = vv2
}
return h2
}
func (r *HttpReadSeeker) newRequest() *http.Request {
newreq := r.req.WithContext(r.ctx) // includes shallow copies of maps, but okay
if r.req.ContentLength == 0 {
newreq.Body = nil // Issue 16036: nil Body for http.Transport retries
}
newreq.Header = cloneHeader(r.req.Header)
return newreq
}
func (r *HttpReadSeeker) rangeRequest() error {
r.req = r.newRequest()
r.req.Header.Set("Range", fmt.Sprintf("bytes=%d-", r.pos))
etag, last := r.res.Header.Get("ETag"), r.res.Header.Get("Last-Modified")
switch {
case last != "":
r.req.Header.Set("If-Range", last)
case etag != "":
r.req.Header.Set("If-Range", etag)
}
r.Requests++
res, err := r.c.Do(r.req)
if err != nil {
return err
}
switch res.StatusCode {
case http.StatusRequestedRangeNotSatisfiable:
return ErrInvalidRange
case http.StatusOK:
// some servers return 200 OK for bytes=0-
if r.pos > 0 ||
(etag != "" && etag != res.Header.Get("ETag")) {
return ErrContentHasChanged
}
fallthrough
case http.StatusPartialContent:
r.r = res.Body
return nil
}
return ErrRangeRequestsNotSupported
}