Add optional C extension wrapper for Python JSON parsing

The pure Python in-tree JSON parser is *much* slower than the
in-tree C JSON parser. A local test parsing a 100Mb JSON file
showed the Python version taking 270 seconds. With the C wrapper,
it took under 4 seconds.

The C extension will be used automatically if it can be built. If
the extension fails to build, a warning is displayed and the build
is restarted without the extension.

The Serializer class is replaced with Python's built-in
JSON library since the ability to process chunked data is not
needed in that case.

The extension should work with both Python 2.7 and Python 3.3+.

Signed-off-by: Terry Wilson <twilson@redhat.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>

4 files changed, 331 insertions, 2 deletions

diff --git a/python/automake.mk b/python/automake.mk
index dc6242232..ecad39d35 100644
--- a/python/automake.mk
+++ b/python/automake.mk
@@ -46,6 +46,9 @@ EXTRA_DIST += \
 	python/README.rst \
 	python/setup.py
 
+# C extension support.
+EXTRA_DIST += python/ovs/_json.c
+
 PYFILES = $(ovs_pyfiles) python/ovs/dirs.py $(ovstest_pyfiles)
 EXTRA_DIST += $(PYFILES)
 PYCOV_CLEAN_FILES += $(PYFILES:.py=.py,cover)
diff --git a/python/ovs/_json.c b/python/ovs/_json.c
new file mode 100644
index 000000000..c4e2af33f
--- /dev/null
+++ b/python/ovs/_json.c
@@ -0,0 +1,268 @@
+#include "Python.h"
+#include <openvswitch/lib/json.h>
+#include "structmember.h"
+
+#if PY_MAJOR_VERSION >= 3
+#define IS_PY3K
+#endif
+
+typedef struct {
+    PyObject_HEAD
+    struct json_parser *_parser;
+} json_ParserObject;
+
+static void
+Parser_dealloc(json_ParserObject * p)
+{
+    json_parser_abort(p->_parser);
+    Py_TYPE(p)->tp_free(p);
+}
+
+static PyObject *
+Parser_new(PyTypeObject * type, PyObject * args, PyObject * kwargs)
+{
+    json_ParserObject *self;
+    static char *kwlist[] = { "check_trailer", NULL };
+    PyObject *check_trailer = NULL;
+    int ct_int = 0;
+
+    if (!PyArg_ParseTupleAndKeywords(args, kwargs, "|O", kwlist,
+                                     &check_trailer)) {
+        return NULL;
+    }
+
+    if (check_trailer != NULL) {
+        ct_int = PyObject_IsTrue(check_trailer);
+        if (ct_int < 0) {
+            return NULL;
+        } else if (ct_int) {
+            ct_int = JSPF_TRAILER;
+        }
+    }
+
+    self = (json_ParserObject *) type->tp_alloc(type, 0);
+    if (self != NULL) {
+        self->_parser = json_parser_create(ct_int);
+    }
+
+    return (PyObject *) self;
+}
+
+static PyObject *
+Parser_feed(json_ParserObject * self, PyObject * args)
+{
+    Py_ssize_t input_sz;
+    PyObject *input;
+    size_t rd;
+    char *input_str;
+
+    if (self->_parser == NULL) {
+        return NULL;
+    }
+
+    if (!PyArg_UnpackTuple(args, "input", 1, 1, &input)) {
+        return NULL;
+    }
+#ifdef IS_PY3K
+    if ((input_str = PyUnicode_AsUTF8AndSize(input, &input_sz)) == NULL) {
+#else
+    if (PyString_AsStringAndSize(input, &input_str, &input_sz) < 0) {
+#endif
+        return NULL;
+    }
+
+    rd = json_parser_feed(self->_parser, input_str, (size_t) input_sz);
+
+#ifdef IS_PY3K
+    return PyLong_FromSize_t(rd);
+#else
+    return PyInt_FromSize_t(rd);
+#endif
+}
+
+static PyObject *
+Parser_is_done(json_ParserObject * self)
+{
+    if (self->_parser == NULL) {
+        return NULL;
+    }
+    return PyBool_FromLong(json_parser_is_done(self->_parser));
+}
+
+static PyObject *
+json_to_python(struct json *json)
+{
+    switch (json->type) {
+    case JSON_NULL:
+        Py_RETURN_NONE;
+    case JSON_FALSE:
+        Py_RETURN_FALSE;
+    case JSON_TRUE:
+        Py_RETURN_TRUE;
+    case JSON_OBJECT:{
+            struct shash_node *node;
+            PyObject *dict = PyDict_New();
+
+            if (dict == NULL) {
+                return PyErr_NoMemory();
+            }
+            SHASH_FOR_EACH(node, json->u.object) {
+                PyObject *key = PyUnicode_FromString(node->name);
+                PyObject *val = json_to_python(node->data);
+
+                if (!(key && val) || PyDict_SetItem(dict, key, val)) {
+                    Py_XDECREF(key);
+                    Py_XDECREF(val);
+                    Py_XDECREF(dict);
+                    return NULL;
+                }
+
+                Py_XDECREF(key);
+                Py_XDECREF(val);
+            }
+            return dict;
+        }
+    case JSON_ARRAY:{
+            int i;
+            PyObject *arr = PyList_New(json->u.array.n);
+
+            if (arr == NULL) {
+                return PyErr_NoMemory();
+            }
+            for (i = 0; i < json->u.array.n; i++) {
+                PyObject *item = json_to_python(json->u.array.elems[i]);
+
+                if (!item || PyList_SetItem(arr, i, item)) {
+                    Py_XDECREF(arr);
+                    return NULL;
+                }
+            }
+            return arr;
+        }
+    case JSON_REAL:
+        if (json->u.real != 0) {
+            return PyFloat_FromDouble(json->u.real);
+        } /* fall through to treat 0 as int */
+    case JSON_INTEGER:
+#ifdef IS_PY3K
+        return PyLong_FromLong((long) json->u.integer);
+#else
+        return PyInt_FromLong((long) json->u.integer);
+#endif
+
+    case JSON_STRING:
+        return PyUnicode_FromString(json->u.string);
+    default:
+        return NULL;
+    }
+}
+
+static PyObject *
+Parser_finish(json_ParserObject * self)
+{
+    struct json *json;
+    PyObject *obj;
+
+    if (self->_parser == NULL) {
+        return NULL;
+    }
+
+    json = json_parser_finish(self->_parser);
+    self->_parser = NULL;
+    obj = json_to_python(json);
+    return obj;
+}
+
+static PyMethodDef Parser_methods[] = {
+    {"feed", (PyCFunction) Parser_feed, METH_VARARGS,
+     "Feed data to the parser and return the index of the last object."},
+    {"is_done", (PyCFunction) Parser_is_done, METH_NOARGS,
+     "Whether the parser has finished decoding an object."},
+    {"finish", (PyCFunction) Parser_finish, METH_NOARGS,
+     "Finish parsing and return Python object parsed."},
+    {NULL},
+};
+
+static PyTypeObject json_ParserType = {
+    PyVarObject_HEAD_INIT(NULL, 0)
+        "ovs._json.Parser",     /* tp_name */
+    sizeof (json_ParserObject), /* tp_basicsize */
+    0,                          /* tp_itemsize */
+    (destructor) Parser_dealloc,        /* tp_dealloc */
+    0,                          /* tp_print */
+    0,                          /* tp_getattr */
+    0,                          /* tp_setattr */
+    0,                          /* tp_compare */
+    0,                          /* tp_repr */
+    0,                          /* tp_as_number */
+    0,                          /* tp_as_sequence */
+    0,                          /* tp_as_mapping */
+    0,                          /* tp_hash */
+    0,                          /* tp_call */
+    0,                          /* tp_str */
+    0,                          /* tp_getattro */
+    0,                          /* tp_setattro */
+    0,                          /* tp_as_buffer */
+    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,   /* tp_flags */
+    "Parser objects",           /* tp_doc */
+    0,                          /* tp_traverse */
+    0,                          /* tp_clear */
+    0,                          /* tp_richcompare */
+    0,                          /* tp_weaklistoffset */
+    0,                          /* tp_iter */
+    0,                          /* tp_iternext */
+    Parser_methods,             /* tp_methods */
+    0,                          /* tp_members */
+    0,                          /* tp_getset */
+    0,                          /* tp_base */
+    0,                          /* tp_dict */
+    0,                          /* tp_descr_get */
+    0,                          /* tp_descr_set */
+    0,                          /* tp_dictoffset */
+    0,                          /* tp_init */
+    0,                          /* tp_alloc */
+    Parser_new,                 /* tp_new */
+};
+
+#ifdef IS_PY3K
+static struct PyModuleDef moduledef = {
+    PyModuleDef_HEAD_INIT,
+    "ovs._json",                /* m_name */
+    "OVS JSON Parser module",   /* m_doc */
+    0,                          /* m_size */
+    0,                          /* m_methods */
+    0,                          /* m_slots */
+    0,                          /* m_traverse */
+    0,                          /* m_clear */
+    0,                          /* m_free */
+};
+
+#define INITERROR return NULL
+#else /* !IS_PY3K */
+#define INITERROR return
+#endif
+
+PyMODINIT_FUNC
+#ifdef IS_PY3K
+PyInit__json(void)
+#else
+init_json(void)
+#endif
+{
+    PyObject *m;
+
+    if (PyType_Ready(&json_ParserType) < 0) {
+        INITERROR;
+    }
+#ifdef IS_PY3K
+    m = PyModule_Create(&moduledef);
+#else
+    m = Py_InitModule3("ovs._json", NULL, "OVS JSON Parser module");
+#endif
+
+    Py_INCREF(&json_ParserType);
+    PyModule_AddObject(m, "Parser", (PyObject *) & json_ParserType);
+#ifdef IS_PY3K
+    return m;
+#endif
+}
diff --git a/python/ovs/json.py b/python/ovs/json.py
index ff986eab9..ea0400ab8 100644
--- a/python/ovs/json.py
+++ b/python/ovs/json.py
@@ -18,6 +18,11 @@ import sys
 import six
 from six.moves import range
 
+try:
+    import ovs._json
+except ImportError:
+    pass
+
 __pychecker__ = 'no-stringiter'
 
 escapes = {ord('"'): u"\\\"",
@@ -165,6 +170,12 @@ class Parser(object):
     # Maximum height of parsing stack. #
     MAX_HEIGHT = 1000
 
+    def __new__(cls, *args, **kwargs):
+        try:
+            return ovs._json.Parser(*args, **kwargs)
+        except NameError:
+            return super(Parser, cls).__new__(cls)
+
     def __init__(self, check_trailer=False):
         self.check_trailer = check_trailer
 
diff --git a/python/setup.py b/python/setup.py
index 49c8c4e6f..19c1f18d2 100644
--- a/python/setup.py
+++ b/python/setup.py
@@ -13,6 +13,10 @@
 from __future__ import print_function
 import sys
 
+from distutils.command.build_ext import build_ext
+from distutils.errors import CCompilerError, DistutilsExecError, \
+    DistutilsPlatformError
+
 import setuptools
 
 VERSION = "unknown"
@@ -25,8 +29,33 @@ except IOError:
           file=sys.stderr)
     sys.exit(-1)
 
+ext_errors = (CCompilerError, DistutilsExecError, DistutilsPlatformError)
+if sys.platform == 'win32':
+    ext_errors += (IOError, ValueError)
+
+
+class BuildFailed(Exception):
+    pass
+
+
+class try_build_ext(build_ext):
+    # This class allows C extension building to fail
+    # NOTE: build_ext is not a new-style class
+
+    def run(self):
+        try:
+            build_ext.run(self)
+        except DistutilsPlatformError:
+            raise BuildFailed()
 
-setuptools.setup(
+    def build_extension(self, ext):
+        try:
+            build_ext.build_extension(self, ext)
+        except ext_errors:
+            raise BuildFailed()
+
+
+setup_args = dict(
     name='ovs',
     description='Open vSwitch library',
     version=VERSION,
@@ -46,5 +75,23 @@ setuptools.setup(
         'Programming Language :: Python :: 2.7',
         'Programming Language :: Python :: 3',
         'Programming Language :: Python :: 3.4',
-    ]
+    ],
+    ext_modules=[setuptools.Extension("ovs._json", sources=["ovs/_json.c"],
+                                      libraries=['openvswitch'])],
+    cmdclass={'build_ext': try_build_ext},
 )
+
+try:
+    setuptools.setup(**setup_args)
+except BuildFailed:
+    BUILD_EXT_WARNING = ("WARNING: The C extension could not be compiled, "
+                         "speedups are not enabled.")
+    print("*" * 75)
+    print(BUILD_EXT_WARNING)
+    print("Failure information, if any, is above.")
+    print("Retrying the build without the C extension.")
+    print("*" * 75)
+
+    del(setup_args['cmdclass'])
+    del(setup_args['ext_modules'])
+    setuptools.setup(**setup_args)