handlers: Handle crash if r.URL.Path is empty. (#3554)

URL paths can be empty and not have preceding separator,
we do not yet know the conditions this can happen inside
Go http server.

This patch is to ensure that we do not crash ourselves
under conditions where r.URL.Path may be empty.

Fixes #3553

cmd/utils_test.go

@@ -220,6 +220,94 @@ func TestMaxPartID(t *testing.T) {
 	}
 }
 
+// Tests extracting bucket and objectname from various types of URL paths.
+func TestURL2BucketObjectName(t *testing.T) {
+	testCases := []struct {
+		u              *url.URL
+		bucket, object string
+	}{
+		// Test case 1 normal case.
+		{
+			u: &url.URL{
+				Path: "/bucket/object",
+			},
+			bucket: "bucket",
+			object: "object",
+		},
+		// Test case 2 where url only has separator.
+		{
+			u: &url.URL{
+				Path: "/",
+			},
+			bucket: "",
+			object: "",
+		},
+		// Test case 3 only bucket is present.
+		{
+			u: &url.URL{
+				Path: "/bucket",
+			},
+			bucket: "bucket",
+			object: "",
+		},
+		// Test case 4 many separators and object is a directory.
+		{
+			u: &url.URL{
+				Path: "/bucket/object/1/",
+			},
+			bucket: "bucket",
+			object: "object/1/",
+		},
+		// Test case 5 object has many trailing separators.
+		{
+			u: &url.URL{
+				Path: "/bucket/object/1///",
+			},
+			bucket: "bucket",
+			object: "object/1///",
+		},
+		// Test case 6 object has only trailing separators.
+		{
+			u: &url.URL{
+				Path: "/bucket/object///////",
+			},
+			bucket: "bucket",
+			object: "object///////",
+		},
+		// Test case 7 object has preceding separators.
+		{
+			u: &url.URL{
+				Path: "/bucket////object////",
+			},
+			bucket: "bucket",
+			object: "///object////",
+		},
+		// Test case 8 url is not allocated.
+		{
+			u:      nil,
+			bucket: "",
+			object: "",
+		},
+		// Test case 9 url path is empty.
+		{
+			u:      &url.URL{},
+			bucket: "",
+			object: "",
+		},
+	}
+
+	// Validate all test cases.
+	for i, testCase := range testCases {
+		bucketName, objectName := urlPath2BucketObjectName(testCase.u)
+		if bucketName != testCase.bucket {
+			t.Errorf("Test %d: failed expected bucket name \"%s\", got \"%s\"", i+1, testCase.bucket, bucketName)
+		}
+		if objectName != testCase.object {
+			t.Errorf("Test %d: failed expected bucket name \"%s\", got \"%s\"", i+1, testCase.object, objectName)
+		}
+	}
+}
+
 // Add tests for starting and stopping different profilers.
 func TestStartProfiler(t *testing.T) {
 	if startProfiler("") != nil {