Create client transport package

Signed-off-by: Derek McGowan <derek@mcgstyle.net> (github: dmcgowan)

docs/client/transport/http_reader.go

@@ -0,0 +1,164 @@
+package transport
+
+import (
+	"bufio"
+	"bytes"
+	"errors"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"net/http"
+	"os"
+
+	"github.com/docker/distribution"
+)
+
+func NewHTTPReadSeeker(client *http.Client, url string, size int64) distribution.ReadSeekCloser {
+	return &httpReadSeeker{
+		client: client,
+		url:    url,
+		size:   size,
+	}
+}
+
+type httpReadSeeker struct {
+	client *http.Client
+	url    string
+
+	size int64
+
+	rc     io.ReadCloser // remote read closer
+	brd    *bufio.Reader // internal buffered io
+	offset int64
+	err    error
+}
+
+func (hrs *httpReadSeeker) Read(p []byte) (n int, err error) {
+	if hrs.err != nil {
+		return 0, hrs.err
+	}
+
+	rd, err := hrs.reader()
+	if err != nil {
+		return 0, err
+	}
+
+	n, err = rd.Read(p)
+	hrs.offset += int64(n)
+
+	// Simulate io.EOF error if we reach filesize.
+	if err == nil && hrs.offset >= hrs.size {
+		err = io.EOF
+	}
+
+	return n, err
+}
+
+func (hrs *httpReadSeeker) Seek(offset int64, whence int) (int64, error) {
+	if hrs.err != nil {
+		return 0, hrs.err
+	}
+
+	var err error
+	newOffset := hrs.offset
+
+	switch whence {
+	case os.SEEK_CUR:
+		newOffset += int64(offset)
+	case os.SEEK_END:
+		newOffset = hrs.size + int64(offset)
+	case os.SEEK_SET:
+		newOffset = int64(offset)
+	}
+
+	if newOffset < 0 {
+		err = errors.New("cannot seek to negative position")
+	} else {
+		if hrs.offset != newOffset {
+			hrs.reset()
+		}
+
+		// No problems, set the offset.
+		hrs.offset = newOffset
+	}
+
+	return hrs.offset, 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.brd = 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.brd, nil
+	}
+
+	// If the offset is great than or equal to size, return a empty, noop reader.
+	if hrs.offset >= hrs.size {
+		return ioutil.NopCloser(bytes.NewReader([]byte{})), nil
+	}
+
+	req, err := http.NewRequest("GET", hrs.url, nil)
+	if err != nil {
+		return nil, err
+	}
+
+	if hrs.offset > 0 {
+		// TODO(stevvooe): Get this working correctly.
+
+		// If we are at different offset, issue a range request from there.
+		req.Header.Add("Range", "1-")
+		// TODO: get context in here
+		// context.GetLogger(hrs.context).Infof("Range: %s", req.Header.Get("Range"))
+	}
+
+	resp, err := hrs.client.Do(req)
+	if err != nil {
+		return nil, err
+	}
+
+	switch {
+	case resp.StatusCode == 200:
+		hrs.rc = resp.Body
+	default:
+		defer resp.Body.Close()
+		return nil, fmt.Errorf("unexpected status resolving reader: %v", resp.Status)
+	}
+
+	if hrs.brd == nil {
+		hrs.brd = bufio.NewReader(hrs.rc)
+	} else {
+		hrs.brd.Reset(hrs.rc)
+	}
+
+	return hrs.brd, nil
+}