A first implementation of Unpacker.skip()

Author: jnothman

msgpack/_msgpack.pyx

@@ -200,7 +200,7 @@ cdef extern from "unpack.h":
         PyObject* key
 
     int template_execute(template_context* ctx, const_char_ptr data,
-                         size_t len, size_t* off) except -1
+                         size_t len, size_t* off, bool construct) except -1
     void template_init(template_context* ctx)
     object template_data(template_context* ctx)
 
@@ -246,7 +246,7 @@ def unpackb(object packed, object object_hook=None, object list_hook=None,
         if not PyCallable_Check(list_hook):
             raise TypeError("list_hook must be a callable.")
         ctx.user.list_hook = <PyObject*>list_hook
-    ret = template_execute(&ctx, buf, buf_len, &off)
+    ret = template_execute(&ctx, buf, buf_len, &off, True)
     if ret == 1:
         return template_data(&ctx)
     else:
@@ -440,15 +440,12 @@ cdef class Unpacker(object):
             else:
                 self.file_like = None
 
-    cpdef unpack(self):
-        """unpack one object"""
+    cpdef _unpack(self, bool construct):
         cdef int ret
         while 1:
-            ret = template_execute(&self.ctx, self.buf, self.buf_tail, &self.buf_head)
+            ret = template_execute(&self.ctx, self.buf, self.buf_tail, &self.buf_head, construct)
             if ret == 1:
-                o = template_data(&self.ctx)
-                template_init(&self.ctx)
-                return o
+                return
             elif ret == 0:
                 if self.file_like is not None:
                     self.fill_buffer()
@@ -457,6 +454,18 @@ cdef class Unpacker(object):
             else:
                 raise ValueError("Unpack failed: error = %d" % (ret,))
 
+    cpdef unpack(self):
+        """unpack one object"""
+        self._unpack(True)
+        o = template_data(&self.ctx)
+        template_init(&self.ctx)
+
+
+    cpdef skip(self):
+        """read and ignore one object, returning None"""
+        self._unpack(False)
+        template_init(&self.ctx)
+
     def __iter__(self):
         return self
 

msgpack/unpack_template.h

@@ -95,7 +95,7 @@ msgpack_unpack_func(msgpack_unpack_object, _data)(msgpack_unpack_struct(_context
 }
 
 
-msgpack_unpack_func(int, _execute)(msgpack_unpack_struct(_context)* ctx, const char* data, size_t len, size_t* off)
+msgpack_unpack_func(int, _execute)(msgpack_unpack_struct(_context)* ctx, const char* data, size_t len, size_t* off, bool construct)
 {
 	assert(len >= *off);
 
@@ -117,14 +117,17 @@ msgpack_unpack_func(int, _execute)(msgpack_unpack_struct(_context)* ctx, const c
 
 	int ret;
 
+#define construct_cb(name) \
+    construct && msgpack_unpack_callback(name)
+
 #define push_simple_value(func) \
-	if(msgpack_unpack_callback(func)(user, &obj) < 0) { goto _failed; } \
+	if(construct_cb(func)(user, &obj) < 0) { goto _failed; } \
 	goto _push
 #define push_fixed_value(func, arg) \
-	if(msgpack_unpack_callback(func)(user, arg, &obj) < 0) { goto _failed; } \
+	if(construct_cb(func)(user, arg, &obj) < 0) { goto _failed; } \
 	goto _push
 #define push_variable_value(func, base, pos, len) \
-	if(msgpack_unpack_callback(func)(user, \
+	if(construct_cb(func)(user, \
 		(const char*)base, (const char*)pos, len, &obj) < 0) { goto _failed; } \
 	goto _push
 
@@ -140,9 +143,9 @@ msgpack_unpack_func(int, _execute)(msgpack_unpack_struct(_context)* ctx, const c
 
 #define start_container(func, count_, ct_) \
 	if(top >= MSGPACK_EMBED_STACK_SIZE) { goto _failed; } /* FIXME */ \
-	if(msgpack_unpack_callback(func)(user, count_, &stack[top].obj) < 0) { goto _failed; } \
+	if(construct_cb(func)(user, count_, &stack[top].obj) < 0) { goto _failed; } \
 	if((count_) == 0) { obj = stack[top].obj; \
-		msgpack_unpack_callback(func##_end)(user, &obj); \
+		construct_cb(func##_end)(user, &obj); \
 		goto _push; } \
 	stack[top].ct = ct_; \
 	stack[top].size  = count_; \
@@ -340,10 +343,10 @@ msgpack_unpack_func(int, _execute)(msgpack_unpack_struct(_context)* ctx, const c
 	c = &stack[top-1];
 	switch(c->ct) {
 	case CT_ARRAY_ITEM:
-		if(msgpack_unpack_callback(_array_item)(user, c->count, &c->obj, obj) < 0) { goto _failed; }
+		if(construct_cb(_array_item)(user, c->count, &c->obj, obj) < 0) { goto _failed; }
 		if(++c->count == c->size) {
 			obj = c->obj;
-			msgpack_unpack_callback(_array_end)(user, &obj);
+			construct_cb(_array_end)(user, &obj);
 			--top;
 			/*printf("stack pop %d\n", top);*/
 			goto _push;
@@ -354,10 +357,10 @@ msgpack_unpack_func(int, _execute)(msgpack_unpack_struct(_context)* ctx, const c
 		c->ct = CT_MAP_VALUE;
 		goto _header_again;
 	case CT_MAP_VALUE:
-		if(msgpack_unpack_callback(_map_item)(user, &c->obj, c->map_key, obj) < 0) { goto _failed; }
+		if(construct_cb(_map_item)(user, &c->obj, c->map_key, obj) < 0) { goto _failed; }
 		if(++c->count == c->size) {
 			obj = c->obj;
-			msgpack_unpack_callback(_map_end)(user, &obj);
+			construct_cb(_map_end)(user, &obj);
 			--top;
 			/*printf("stack pop %d\n", top);*/
 			goto _push;
@@ -399,6 +402,7 @@ msgpack_unpack_func(int, _execute)(msgpack_unpack_struct(_context)* ctx, const c
 	*off = p - (const unsigned char*)data;
 
 	return ret;
+#undef construct_cb
 }