Support for the Location to be a relative URL

The location header value returned by a creation is a URL that
"MAY be absolute or relative" as quoted from the TUS specification:
https://tus.io/protocols/resumable-upload.html#creation

This patch supports the case where the location value is a relative
URL.

client.go

@@ -1,6 +1,7 @@
 package tus
 
 import (
+	"fmt"
 	"io"
 	"io/ioutil"
 	"net/http"
@@ -90,27 +91,18 @@ func (c *Client) CreateUpload(u *Upload) (*Uploader, error) {
 
 	switch res.StatusCode {
 	case 201:
-		url := res.Header.Get("Location")
+		location := res.Header.Get("Location")
 
-		baseUrl, err := netUrl.Parse(c.Url)
+		newURL, err := c.resolveLocationURL(location)
 		if err != nil {
-			return nil, ErrUrlNotRecognized
-		}
-
-		newUrl, err := netUrl.Parse(url)
-		if err != nil {
-			return nil, ErrUrlNotRecognized
-		}
-		if newUrl.Scheme == "" {
-			newUrl.Scheme = baseUrl.Scheme
-			url = newUrl.String()
+			return nil, err
 		}
 
 		if c.Config.Resume {
-			c.Config.Store.Set(u.Fingerprint, url)
+			c.Config.Store.Set(u.Fingerprint, newURL.String())
 		}
 
-		return NewUploader(c, url, u, 0), nil
+		return NewUploader(c, newURL.String(), u, 0), nil
 	case 412:
 		return nil, ErrVersionMismatch
 	case 413:
@@ -120,6 +112,20 @@ func (c *Client) CreateUpload(u *Upload) (*Uploader, error) {
 	}
 }
 
+func (c *Client) resolveLocationURL(location string) (*netUrl.URL, error) {
+	baseURL, err := netUrl.Parse(c.Url)
+	if err != nil {
+		return nil, fmt.Errorf("Invalid URL '%s'", c.Url)
+	}
+
+	locationURL, err := netUrl.Parse(location)
+	if err != nil {
+		return nil, fmt.Errorf("Invalid Location header value for a Creation '%s': %s", location, err.Error())
+	}
+	newURL := baseURL.ResolveReference(locationURL)
+	return newURL, nil
+}
+
 // ResumeUpload resumes the upload if already created, otherwise it will return an error.
 func (c *Client) ResumeUpload(u *Upload) (*Uploader, error) {
 	if u == nil {

client_test.go

@@ -5,7 +5,9 @@ import (
 	"fmt"
 	"net/http"
 	"net/http/httptest"
+	netUrl "net/url"
 	"os"
+	"path"
 	"strings"
 	"sync"
 	"testing"
@@ -325,6 +327,42 @@ func (s *UploadTestSuite) TestResumeUpload() {
 	s.EqualValues(1048576*150, fi.Size)
 }
 
+func (s *UploadTestSuite) TestUploadLocation() {
+	client, err := NewClient(s.url, nil)
+	s.Nil(err)
+	sourceURL, err := netUrl.Parse(s.url)
+	s.Nil(err)
+
+	s.T().Run("Location is a full URL", func(t *testing.T) {
+		location := "https://serveit.com/upload/123"
+		resourceURL, err := client.resolveLocationURL(location)
+		s.Nil(err)
+		s.EqualValues(location, resourceURL.String())
+	})
+
+	s.T().Run("Location is a URL without scheme", func(t *testing.T) {
+		location := "//serveit.com/upload/123"
+		resourceURL, err := client.resolveLocationURL(location)
+		s.Nil(err)
+		s.EqualValues(sourceURL.Scheme+":"+location, resourceURL.String())
+	})
+
+	s.T().Run("Location is an absolute path", func(t *testing.T) {
+		location := "/upload/123"
+		resourceURL, err := client.resolveLocationURL(location)
+		s.Nil(err)
+		s.EqualValues(sourceURL.Scheme+"://"+sourceURL.Host+location, resourceURL.String())
+	})
+
+	s.T().Run("Location is a relative path", func(t *testing.T) {
+		location := "somewhere/123"
+		resourceURL, err := client.resolveLocationURL(location)
+		s.Nil(err)
+		s.EqualValues(sourceURL.Scheme+"://"+sourceURL.Host+path.Join(sourceURL.Path, location), resourceURL.String())
+	})
+
+}
+
 func TestUploadTestSuite(t *testing.T) {
 	suite.Run(t, new(UploadTestSuite))
 }

errors.go

@@ -16,7 +16,6 @@ var (
 	ErrUploadNotFound    = errors.New("upload not found.")
 	ErrResumeNotEnabled  = errors.New("resuming not enabled.")
 	ErrFingerprintNotSet = errors.New("fingerprint not set.")
-	ErrUrlNotRecognized  = errors.New("url not recognized")
 )
 
 type ClientError struct {