forked from jeffallen/seekinghttp
/
seekinghttp.go
301 lines (255 loc) · 6.72 KB
/
seekinghttp.go
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package seekinghttp
import (
"bytes"
"io"
"net/http"
"net/url"
"os"
"strconv"
"strings"
"github.com/pkg/errors"
)
type HttpClient interface {
Do(req *http.Request) (*http.Response, error)
}
type Logger interface {
Infof(format string, args ...interface{})
Debugf(format string, args ...interface{})
}
// SeekingHTTP uses a series of HTTP GETs with Range headers to implement
// io.ReadSeeker and io.ReaderAt.
//
// NOTE: SeekingHTTP is NOT concurrency safe!
type SeekingHTTP struct {
URL string
MinFetch int64
KnownSize *int64
Logger Logger
Client HttpClient
url *url.URL
offset int64
last *bytes.Buffer
lastOffset int64
}
// _ is a type assertion
var (
_ io.ReadSeeker = (*SeekingHTTP)(nil)
_ io.ReaderAt = (*SeekingHTTP)(nil)
)
// New initializes a SeekingHTTP for the given URL.
func New(url string) *SeekingHTTP {
return NewWithClient(url, http.DefaultClient)
}
// NewWithClient initializes a SeekingHTTP for the given URL with a client..
func NewWithClient(url string, client HttpClient) *SeekingHTTP {
return &SeekingHTTP{URL: url, Client: client, MinFetch: 1024 * 1024}
}
func (s *SeekingHTTP) SetLogger(logger Logger) {
s.Logger = logger
}
func (s *SeekingHTTP) newReq() (*http.Request, error) {
var err error
if s.url == nil {
s.url, err = url.Parse(s.URL)
if err != nil {
return nil, err
}
}
return http.NewRequest("GET", s.url.String(), nil)
}
func fmtRange(from, l int64) string {
var to int64
if l == 0 {
to = from
} else {
to = from + (l - 1)
}
var sb strings.Builder
sb.Grow(24)
_, _ = sb.WriteString("bytes=")
_, _ = sb.WriteString(strconv.FormatInt(from, 10))
_, _ = sb.WriteString("-")
_, _ = sb.WriteString(strconv.FormatInt(to, 10))
return sb.String()
}
// ReadAt reads len(buf) bytes into buf starting at offset off.
// Returns the length read into buf.
func (s *SeekingHTTP) ReadAt(buf []byte, off int64) (n int, err error) {
n, err = s.ReadAtWithLength(buf, off, int64(len(buf)))
n = min(len(buf), n)
if n != len(buf) && err == nil {
// ReadAt must always return len(buf), nil
err = io.EOF
}
return n, err
}
// ReadAtWithLength reads length bytes into buf starting at offset off.
// If the buffer is short, reads the full length & copies the beginning to the buffer.
// The minimum read size is controlled by MinFetch.
// Returns min(full length read, length) (may be larger than len(buf))
func (s *SeekingHTTP) ReadAtWithLength(buf []byte, off, length int64) (n int, err error) {
if s.Logger != nil {
s.Logger.Debugf("ReadAt len %v off %v", length, off)
}
if off < 0 {
return 0, io.EOF
}
// Set the length to be at least MinFetch if set.
if s.MinFetch != 0 {
length = max(length, s.MinFetch)
}
// If the size is known, cap the length to the size.
if s.KnownSize != nil {
length = min(*s.KnownSize-off, length)
if length < 0 {
return 0, io.EOF
}
}
if s.last != nil && off >= s.lastOffset {
end := off + length
if end <= s.lastOffset+int64(s.last.Len()) {
start := off - s.lastOffset
if s.Logger != nil {
s.Logger.Debugf("cache hit: range (%v-%v) is within cache (%v-%v)", off, off+length, s.lastOffset, s.lastOffset+int64(s.last.Len()))
}
copy(buf, s.last.Bytes()[start:end-s.lastOffset])
return min(len(buf), int(length)), nil
}
}
if s.Logger != nil {
if s.last != nil {
s.Logger.Debugf("cache miss: range (%v-%v) is NOT within cache (%v-%v)", off, off+length, s.lastOffset, s.lastOffset+int64(s.last.Len()))
} else {
s.Logger.Debugf("cache miss: cache empty")
}
}
req, err := s.newReq()
if err != nil {
return 0, err
}
rng := fmtRange(off, length)
req.Header.Add("Range", rng)
if s.Logger != nil {
s.Logger.Infof("Start HTTP GET with Range: %s", rng)
}
resp, err := s.Client.Do(req)
if err != nil {
return 0, err
}
// body needs to be closed, even if responses that aren't 200 or 206
defer func(body io.ReadCloser) {
_, cErr := io.Copy(io.Discard, body)
if cErr == nil {
cErr = body.Close()
} else {
_ = body.Close()
}
if err == nil && cErr != nil {
err = cErr
}
}(resp.Body)
if s.Logger != nil {
s.Logger.Infof("Response status: %v", resp.StatusCode)
}
if resp.StatusCode == http.StatusOK || resp.StatusCode == http.StatusPartialContent {
s.lastOffset = off
if s.last == nil {
// Cache does not exist yet. So make it.
s.last = &bytes.Buffer{}
} else {
// Cache is getting replaced. Bring it back to zero bytes, but
// keep the underlying []byte, since we'll reuse it right away.
s.last.Reset()
}
n, err := s.last.ReadFrom(resp.Body)
if err != nil {
return 0, err
}
contentLength := resp.ContentLength
if contentLength == 0 {
// for some reason the content length header was not set
contentLength = n
} else if n != contentLength {
return 0, errors.Errorf("read %d bytes but content length indicated %d", n, contentLength)
} else if resp.StatusCode == http.StatusOK && s.KnownSize == nil {
// status 200 = this is the full file, set the size.
size := contentLength
s.KnownSize = &size
}
if s.Logger != nil {
s.Logger.Debugf("loaded %d bytes into last", contentLength)
}
n = min(contentLength, length)
bufN := min(int(n), len(buf))
copy(buf, s.last.Bytes())
return bufN, err
}
return 0, io.EOF
}
func (s *SeekingHTTP) Read(buf []byte) (int, error) {
if s.Logger != nil {
s.Logger.Debugf("got read len %v", len(buf))
}
n, err := s.ReadAt(buf, s.offset)
if err == nil {
s.offset += int64(n)
}
return n, err
}
// Seek sets the offset for the next Read.
func (s *SeekingHTTP) Seek(offset int64, whence int) (int64, error) {
if s.Logger != nil {
s.Logger.Debugf("got seek %v %v", offset, whence)
}
switch whence {
case io.SeekStart:
s.offset = offset
case io.SeekCurrent:
s.offset += offset
case io.SeekEnd:
var length int64
if s.KnownSize != nil {
length = *s.KnownSize
} else {
var err error
length, err = s.Size()
if err != nil {
return 0, err
}
}
s.offset = length + offset
if s.offset > length || s.offset < 0 {
return 0, io.EOF
}
default:
return 0, os.ErrInvalid
}
return s.offset, nil
}
// Size uses an HTTP HEAD to find out how many bytes are available in total.
func (s *SeekingHTTP) Size() (int64, error) {
if s.KnownSize != nil {
return *s.KnownSize, nil
}
req, err := s.newReq()
if err != nil {
return 0, err
}
req.Method = "HEAD"
resp, err := s.Client.Do(req)
if err != nil {
return 0, err
}
if resp.ContentLength < 0 {
return 0, errors.New("no content length for Size()")
}
length := resp.ContentLength
if s.Logger != nil {
s.Logger.Debugf("url: %v, size %v", req.URL.String(), length)
}
if length < 0 {
return 0, errors.New("invalid negative content legnth returned")
}
s.KnownSize = &length
return resp.ContentLength, nil
}