transport: create Client interface (#132)

* plumbing: move plumbing/client package to plumbing/transport.

* transport: create Client interface.

* A Client can instantiate any client transport service.
* InstallProtocol installs a Client for a given protocol,
  instead of just a UploadPackService.
* A Client can open a session for fetch-pack or send-pack
  for a specific Endpoint.
* Adapt ssh and http clients to the new client interface.

* updated doc

1 files changed, 155 insertions, 0 deletions

diff --git a/plumbing/transport/http/fetch_pack.go b/plumbing/transport/http/fetch_pack.go
new file mode 100644
index 0000000..0c32672
--- /dev/null
+++ b/plumbing/transport/http/fetch_pack.go
@@ -0,0 +1,155 @@
+package http
+
+import (
+	"bufio"
+	"bytes"
+	"fmt"
+	"io"
+	"net/http"
+	"strings"
+
+	"gopkg.in/src-d/go-git.v4/plumbing"
+	"gopkg.in/src-d/go-git.v4/plumbing/format/packp/pktline"
+	"gopkg.in/src-d/go-git.v4/plumbing/transport"
+)
+
+type fetchPackSession struct {
+	*session
+}
+
+func newFetchPackSession(c *http.Client,
+	ep transport.Endpoint) transport.FetchPackSession {
+
+	return &fetchPackSession{
+		session: &session{
+			auth:     basicAuthFromEndpoint(ep),
+			client:   c,
+			endpoint: ep,
+		},
+	}
+}
+
+func (s *fetchPackSession) AdvertisedReferences() (*transport.UploadPackInfo,
+	error) {
+
+	url := fmt.Sprintf(
+		"%s/info/refs?service=%s",
+		s.endpoint.String(), transport.UploadPackServiceName,
+	)
+
+	req, err := http.NewRequest(http.MethodGet, url, nil)
+	if err != nil {
+		return nil, err
+	}
+
+	s.applyAuthToRequest(req)
+	s.applyHeadersToRequest(req, nil)
+	res, err := s.client.Do(req)
+	if err != nil {
+		return nil, err
+	}
+
+	defer res.Body.Close()
+	if res.StatusCode == http.StatusUnauthorized {
+		return nil, transport.ErrAuthorizationRequired
+	}
+
+	i := transport.NewUploadPackInfo()
+	return i, i.Decode(res.Body)
+}
+
+func (s *fetchPackSession) FetchPack(r *transport.UploadPackRequest) (io.ReadCloser, error) {
+	url := fmt.Sprintf(
+		"%s/%s",
+		s.endpoint.String(), transport.UploadPackServiceName,
+	)
+
+	res, err := s.doRequest("POST", url, r.Reader())
+	if err != nil {
+		return nil, err
+	}
+
+	reader := newBufferedReadCloser(res.Body)
+	if _, err := reader.Peek(1); err != nil {
+		if err == io.ErrUnexpectedEOF {
+			return nil, transport.ErrEmptyUploadPackRequest
+		}
+
+		return nil, err
+	}
+
+	if err := discardResponseInfo(reader); err != nil {
+		return nil, err
+	}
+
+	return reader, nil
+}
+
+// Close does nothing.
+func (s *fetchPackSession) Close() error {
+	return nil
+}
+
+func discardResponseInfo(r io.Reader) error {
+	s := pktline.NewScanner(r)
+	for s.Scan() {
+		if bytes.Equal(s.Bytes(), []byte{'N', 'A', 'K', '\n'}) {
+			break
+		}
+	}
+
+	return s.Err()
+}
+
+func (s *fetchPackSession) doRequest(method, url string, content *strings.Reader) (*http.Response, error) {
+	var body io.Reader
+	if content != nil {
+		body = content
+	}
+
+	req, err := http.NewRequest(method, url, body)
+	if err != nil {
+		return nil, plumbing.NewPermanentError(err)
+	}
+
+	s.applyHeadersToRequest(req, content)
+	s.applyAuthToRequest(req)
+
+	res, err := s.client.Do(req)
+	if err != nil {
+		return nil, plumbing.NewUnexpectedError(err)
+	}
+
+	if err := NewErr(res); err != nil {
+		_ = res.Body.Close()
+		return nil, err
+	}
+
+	return res, nil
+}
+
+func (s *fetchPackSession) applyHeadersToRequest(req *http.Request, content *strings.Reader) {
+	req.Header.Add("User-Agent", "git/1.0")
+	req.Header.Add("Host", "github.com")
+
+	if content == nil {
+		req.Header.Add("Accept", "*/*")
+	} else {
+		req.Header.Add("Accept", "application/x-git-upload-pack-result")
+		req.Header.Add("Content-Type", "application/x-git-upload-pack-request")
+		req.Header.Add("Content-Length", string(content.Len()))
+	}
+}
+
+type bufferedReadCloser struct {
+	*bufio.Reader
+	closer io.Closer
+}
+
+func newBufferedReadCloser(r io.ReadCloser) *bufferedReadCloser {
+	return &bufferedReadCloser{bufio.NewReader(r), r}
+}
+
+func (r *bufferedReadCloser) Close() error {
+	return r.closer.Close()
+}