backend/rest: Ensure base URL ends with slash

This makes it easier for rclone.

doc/100_references.rst

@@ -681,7 +681,7 @@ return JSON. Any different value for this header means API version 1.
 
 The placeholder ``{path}`` in this document is a path to the repository, so
 that multiple different repositories can be accessed. The default path is
-``/``.
+``/``. The path must end with a slash.
 
 POST {path}?create=true
 =======================

internal/backend/rest/config.go

@@ -32,6 +32,10 @@ func ParseConfig(s string) (interface{}, error) {
 	}
 
 	s = s[5:]
+	if !strings.HasSuffix(s, "/") {
+		s += "/"
+	}
+
 	u, err := url.Parse(s)
 
 	if err != nil {

internal/backend/rest/config_test.go

@@ -19,24 +19,34 @@ var configTests = []struct {
 	s   string
 	cfg Config
 }{
-	{"rest:http://localhost:1234", Config{
-		URL:         parseURL("http://localhost:1234"),
+	{
+		s: "rest:http://localhost:1234",
+		cfg: Config{
+			URL:         parseURL("http://localhost:1234/"),
 			Connections: 5,
-	}},
+		},
+	},
+	{
+		s: "rest:http://localhost:1234/",
+		cfg: Config{
+			URL:         parseURL("http://localhost:1234/"),
+			Connections: 5,
+		},
+	},
 }
 
 func TestParseConfig(t *testing.T) {
-	for i, test := range configTests {
+	for _, test := range configTests {
+		t.Run("", func(t *testing.T) {
 			cfg, err := ParseConfig(test.s)
 			if err != nil {
-			t.Errorf("test %d:%s failed: %v", i, test.s, err)
-			continue
+				t.Fatalf("%s failed: %v", test.s, err)
 			}
 
 			if !reflect.DeepEqual(cfg, test.cfg) {
-			t.Errorf("test %d:\ninput:\n  %s\n wrong config, want:\n  %v\ngot:\n  %v",
-				i, test.s, test.cfg, cfg)
-			continue
-		}
+				t.Fatalf("\ninput: %s\n wrong config, want:\n  %v\ngot:\n  %v",
+					test.s, test.cfg, cfg)
+			}
+		})
 	}
 }