teach Download() how to follow hypermedia

Author: technoweenie

hawser/client.go

@@ -14,15 +14,20 @@ import (
 	"net/http"
 	"os"
 	"path/filepath"
+	"strings"
 )
 
 const (
 	// Legacy type
 	gitMediaType = "application/vnd.git-media"
 
+	// The main type, sub type, and suffix.  Use this when ensuring the type from
+	// an HTTP response is correct.
+	gitMediaMetaTypePrefix = gitMediaType + "+json"
+
 	// Adds the extra mime params.  Use this when sending the type in an HTTP
 	// request.
-	gitMediaMetaType = gitMediaType + "+json; charset=utf-8"
+	gitMediaMetaType = gitMediaMetaTypePrefix + "; charset=utf-8"
 )
 
 func Download(oidPath string) (io.ReadCloser, int64, *WrappedError) {
@@ -46,6 +51,47 @@ func Download(oidPath string) (io.ReadCloser, int64, *WrappedError) {
 		return nil, 0, wErr
 	}
 
+	if strings.HasPrefix(contentType, gitMediaMetaTypePrefix) {
+		obj := &objectResource{}
+		err := json.NewDecoder(res.Body).Decode(obj)
+		res.Body.Close()
+		if err != nil {
+			wErr := Error(err)
+			setErrorResponseContext(wErr, res)
+			return nil, 0, wErr
+		}
+
+		dlReq, err := obj.NewRequest("download", "GET")
+		if err != nil {
+			wErr := Error(err)
+			setErrorResponseContext(wErr, res)
+			return nil, 0, wErr
+		}
+
+		dlCreds, err := setRequestHeaders(dlReq)
+		if err != nil {
+			return nil, 0, Errorf(err, "Error attempting to GET %s", oidPath)
+		}
+
+		dlRes, err := DoHTTP(Config, dlReq)
+		if err != nil {
+			wErr := Error(err)
+			setErrorResponseContext(wErr, res)
+			return nil, 0, wErr
+		}
+
+		saveCredentials(dlCreds, dlRes)
+
+		contentType := dlRes.Header.Get("Content-Type")
+		if contentType == "" {
+			wErr = Error(errors.New("Empty Content-Type"))
+			setErrorResponseContext(wErr, res)
+			return nil, 0, wErr
+		}
+
+		res = dlRes
+	}
+
 	ok, headerSize, wErr := validateMediaHeader(contentType, res.Body)
 	if !ok {
 		setErrorResponseContext(wErr, res)

hawser/client_download_test.go

@@ -1,6 +1,7 @@
 package hawser
 
 import (
+	"encoding/json"
 	"io/ioutil"
 	"net/http"
 	"net/http/httptest"
@@ -49,6 +50,77 @@ func TestDownload(t *testing.T) {
 	}
 }
 
+func TestDownloadFromMeta(t *testing.T) {
+	mux := http.NewServeMux()
+	server := httptest.NewServer(mux)
+	tmp := tempdir(t)
+	defer server.Close()
+	defer os.RemoveAll(tmp)
+
+	// simulates an endpoint that returns the meta data for every request.
+	// this way downloads keep working with the older prototype server during
+	// the pre-release.
+	mux.HandleFunc("/media/objects/oid", func(w http.ResponseWriter, r *http.Request) {
+		if r.Method != "GET" {
+			w.WriteHeader(405)
+			return
+		}
+
+		obj := &objectResource{
+			Oid:  "oid",
+			Size: 4,
+			Links: map[string]*linkRelation{
+				"download": &linkRelation{
+					Href: server.URL + "/media/download/oid",
+				},
+			},
+		}
+
+		by, err := json.Marshal(obj)
+		if err != nil {
+			t.Errorf("Error marshaling json: %s", err)
+		}
+
+		head := w.Header()
+		head.Set("Content-Type", "application/vnd.git-media+json")
+		w.WriteHeader(200)
+		w.Write(by)
+	})
+
+	mux.HandleFunc("/media/download/oid", func(w http.ResponseWriter, r *http.Request) {
+		if r.Method != "GET" {
+			w.WriteHeader(405)
+			return
+		}
+
+		head := w.Header()
+		head.Set("Content-Type", "application/octet-stream")
+		head.Set("Content-Length", "4")
+		w.WriteHeader(200)
+		w.Write([]byte("test"))
+	})
+
+	Config.SetConfig("hawser.url", server.URL+"/media")
+	reader, size, wErr := Download("whatever/oid")
+	if wErr != nil {
+		t.Fatalf("unexpected error: %s", wErr)
+	}
+	defer reader.Close()
+
+	if size != 4 {
+		t.Errorf("unexpected size: %d", size)
+	}
+
+	by, err := ioutil.ReadAll(reader)
+	if err != nil {
+		t.Fatalf("unexpected error: %s", err)
+	}
+
+	if body := string(by); body != "test" {
+		t.Errorf("unexpected body: %s", body)
+	}
+}
+
 func TestDownloadWithRedirect(t *testing.T) {
 	mux := http.NewServeMux()
 	server := httptest.NewServer(mux)