loci: add a function to parse messages without allocating memory

This will be used by the Indigo connection manager to parse messages directly
from the read buffer, saving three allocations and a memcpy.
diff --git a/c_gen/templates/locitest/test_utils.c b/c_gen/templates/locitest/test_utils.c
index bcd4194..563f510 100644
--- a/c_gen/templates/locitest/test_utils.c
+++ b/c_gen/templates/locitest/test_utils.c
@@ -118,10 +118,32 @@
     return TEST_PASS;
 }
 
+static int
+test_of_object_new_from_message_preallocated(void)
+{
+    /* v1 OFPT_HELLO, xid=0x12345678 */
+    uint8_t buf[] = { 0x01, 0x00, 0x00, 0x08, 0x12, 0x34, 0x56, 0x78 };
+
+    of_object_storage_t storage;
+    of_object_t *obj = of_object_new_from_message_preallocated(
+        &storage, buf, sizeof(buf));
+
+    TEST_ASSERT(obj != NULL);
+    TEST_ASSERT(obj->version = OF_VERSION_1_0);
+    TEST_ASSERT(obj->object_id = OF_HELLO);
+
+    uint32_t xid;
+    of_hello_xid_get(obj, &xid);
+    TEST_ASSERT(xid == 0x12345678);
+
+    return TEST_PASS;
+}
+
 int
 run_utility_tests(void)
 {
     RUN_TEST(has_outport);
+    RUN_TEST(of_object_new_from_message_preallocated);
     RUN_TEST(dump_objs);
 
     return TEST_PASS;
diff --git a/c_gen/templates/of_object.c b/c_gen/templates/of_object.c
index 005965e..8fd0aab 100644
--- a/c_gen/templates/of_object.c
+++ b/c_gen/templates/of_object.c
@@ -180,6 +180,54 @@
 }
 
 /**
+ * Parse a message without allocating memory
+ *
+ * @param storage Pointer to an uninitialized of_object_storage_t
+ * @param buf Pointer to the buffer
+ * @param length Length of buf
+ * @returns Pointer to an initialized of_object_t
+ *
+ * The lifetime of the returned object is the minimum of the lifetimes of
+ * 'buf' and 'storage'.
+ */
+
+of_object_t *
+of_object_new_from_message_preallocated(of_object_storage_t *storage,
+                                        uint8_t *buf, int len)
+{
+    of_object_t *obj = &storage->obj;
+    of_wire_buffer_t *wbuf = &storage->wbuf;
+    of_message_t msg = buf;
+    of_version_t version;
+    of_object_id_t object_id;
+
+    memset(storage, 0, sizeof(*storage));
+
+    version = of_message_version_get(msg);
+    if (!OF_VERSION_OKAY(version)) {
+        return NULL;
+    }
+
+    if (of_validate_message(msg, len) != 0) {
+        LOCI_LOG_ERROR("message validation failed\n");
+        return NULL;
+    }
+
+    object_id = of_message_to_object_id(msg, len);
+    /* Already validated */
+    LOCI_ASSERT(object_id != OF_OBJECT_INVALID);
+
+    of_object_init_map[object_id](obj, version, len, 0);
+
+    obj->wire_object.wbuf = wbuf;
+    wbuf->buf = msg;
+    wbuf->alloc_bytes = len;
+    wbuf->current_bytes = len;
+
+    return obj;
+}
+
+/**
  * Bind an existing buffer to an LOCI object
  *
  * @param obj Pointer to the object to be updated
diff --git a/c_gen/templates/of_object.h b/c_gen/templates/of_object.h
index 0e761fd..3172ad1 100644
--- a/c_gen/templates/of_object.h
+++ b/c_gen/templates/of_object.h
@@ -122,6 +122,11 @@
 
 extern of_object_t *of_object_new_from_message(of_message_t msg, int len);
 
+typedef struct of_object_storage_s of_object_storage_t;
+
+of_object_t *of_object_new_from_message_preallocated(
+    of_object_storage_t *storage, uint8_t *buf, int len);
+
 /* Delete an OpenFlow object without reference to its type */
 extern void of_object_delete(of_object_t *obj);
 
@@ -169,4 +174,9 @@
     uint64_t metadata[(OF_OBJECT_METADATA_BYTES + 7) / 8];
 };
 
+struct of_object_storage_s {
+    of_object_t obj;
+    of_wire_buffer_t wbuf;
+};
+
 #endif /* _OF_OBJECT_H_ */