Fix exception when decoded value is too large by doubling buffer

tests/test_main.py

@@ -29,13 +29,7 @@ def test_long_random():
 def test_decode_error():
     with pytest.raises(xdelta3.XDeltaError) as exc_info:
         xdelta3.decode(expected_delta, value_one)
-    assert exc_info.value.args[0] == 'Error occur executing xdelta3: XD3_INVALID_INPUT'
-
-
-def test_no_delta():
-    with pytest.raises(xdelta3.NoDeltaFound) as exc_info:
-        xdelta3.encode(b'hello', b'goodbye')
-    assert exc_info.value.args[0] == 'No delta found shorter than the input value'
+    assert exc_info.value.args[0] == 'Error occurred executing xdelta3: XD3_INVALID_INPUT'
 
 
 def test_different_compression():
@@ -57,6 +51,14 @@ def test_version():
     xdelta3.print_version()
 
 
+def test_huge_output():
+    b1 = b''
+    b2 = b't' * 10000  # 10K same characters
+    d = xdelta3.encode(b1, b2)
+    assert len(d) < 100  # 0 bytes + very small delta = big output
+    assert xdelta3.decode(b1, d) == b2
+
+
 def test_readme():
     value_one = b'wonderful string to demonstrate xdelta3, much of these two strings is the same.'
     value_two = b'different string to demonstrate xdelta3, much of these two strings is the same.'

xdelta3/_xdelta3.c

@@ -7,7 +7,7 @@
 static PyObject *NoDeltaFound;
 static PyObject *XDeltaError;
 
-static PyObject * xdelta3_execute(PyObject *self, PyObject *args)
+static PyObject * _xdelta3_execute(PyObject *self, PyObject *args, int buffer_double_cnt)
 {
   uint8_t *input_bytes = NULL, *source_bytes = NULL, *output_buf = NULL;
   int input_len, source_len, flags, action, result;
@@ -21,13 +21,13 @@ static PyObject * xdelta3_execute(PyObject *self, PyObject *args)
 
   if (action == 0) {
     // if the output would be longer than the input itself, there's no point using delta encoding
-    output_alloc = input_size;
+    output_alloc = input_size << buffer_double_cnt;
     output_buf = main_malloc(output_alloc);
     result = xd3_encode_memory(input_bytes, input_size, source_bytes, source_size,
         output_buf, &output_size, output_alloc, flags);
   } else {
     // output shouldn't be bigger than the original plus the delta, but give a little leeway
-    output_alloc = input_size + source_size * 11 / 10;
+    output_alloc = (input_size + source_size * 11 / 10) << buffer_double_cnt;
     output_buf = main_malloc(output_alloc);
     result = xd3_decode_memory(input_bytes, input_size, source_bytes, source_size,
         output_buf, &output_size, output_alloc, flags);
@@ -39,23 +39,31 @@ static PyObject * xdelta3_execute(PyObject *self, PyObject *args)
     return ret;
   }
 
-  if(result == ENOSPC) {
-    if (action == 0) {
-      // all is well, just not efficient delta could be found
-      PyErr_SetString(NoDeltaFound, "No delta found shorter than the input value");
-    } else {
+  if (result == ENOSPC) {
+    // Leave some leeway before we overflow int. This is a bad way, the better way would be to
+    // check above when we left shift.
+    if (buffer_double_cnt < sizeof(int) - 4) {
       PyErr_SetString(XDeltaError, "Output of decoding delta longer than expected");
+    } else {
+      main_free(output_buf);
+      return _xdelta3_execute(self, args, buffer_double_cnt + 1);
     }
   } else {
     char exc_str[80];
-    sprintf(exc_str, "Error occur executing xdelta3: %s", xd3_strerror(result));
+    snprintf(exc_str, sizeof(exc_str) / sizeof(exc_str[0]),
+      "Error occurred executing xdelta3: %s", xd3_strerror(result));
     PyErr_SetString(XDeltaError, exc_str);
 
   }
   main_free(output_buf);
   return NULL;
 }
 
+static PyObject * xdelta3_execute(PyObject *self, PyObject *args)
+{
+  return _xdelta3_execute(self, args, 1);
+}
+
 static PyObject * xdelta3_version(PyObject *self, PyObject *args)
 {
   int result = main_version();
@@ -88,8 +96,5 @@ PyMODINIT_FUNC PyInit__xdelta3(void) {
   Py_INCREF(XDeltaError);
   PyModule_AddObject(m, "XDeltaError", XDeltaError);
 
-  NoDeltaFound = PyErr_NewException("xdelta3.NoDeltaFound", NULL, NULL);
-  Py_INCREF(NoDeltaFound);
-  PyModule_AddObject(m, "NoDeltaFound", NoDeltaFound);
   return m;
 }

xdelta3/main.py

@@ -2,12 +2,11 @@
 from enum import IntEnum
 
 import _xdelta3
-from _xdelta3 import NoDeltaFound, XDeltaError  # noqa
+from _xdelta3 import XDeltaError  # noqa
 
 from .version import VERSION
 
 __all__ = [
-    'NoDeltaFound',
     'XDeltaError',
     'Flags',
     'encode',