lib: add ability to decode from lua scripts

This implements the ability to get results out from lua scripts after
they've run.

For each C type we support passing to Lua, there is a corresponding
`struct frrscript_codec`. This struct contains a typename field - just a
string identifying the type - and two function pointers. The first
function pointer, encode, takes a lua_State and a pointer to the C value
and pushes some corresponding Lua representation onto the stack. The
second, decode, assumes there is some Lua value on the stack and decodes
it into the corresponding C value.

Each supported type's `struct frrscript_codec` is registered with the
scripting stuff in the library, which creates a mapping between the type
name (string) and the `struct frrscript_codec`. When calling a script,
you specify arguments by passing an array of `struct frrscript_env`.
Each of these structs has a void *, a type name, and a desired binding
name. The type names are used to look up the appropriate function to
encode the pointed-at value onto the Lua stack, then bind the pushed
value to the provided binding name, so that the converted value is
accessible by that name within the script.

Results work in a similar way. After a script runs, call
frrscript_get_result() with the script and a `struct frrscript_env`.
The typename and name fields are used to fetch the Lua value from the
script's environment and use the registered decoder for the typename to
convert the Lua value back into a C value, which is returned from the
function. The caller is responsible for freeing these.

frrscript_call()'s macro foo has been stripped, as the underlying
function now takes fixed arrays. varargs have awful performance
characteristics, they're hard to read, and structs are more defined than
an order sensitive list.

Signed-off-by: Quentin Young <qlyoung@nvidia.com>

1 files changed, 73 insertions, 11 deletions

diff --git a/lib/frrlua.h b/lib/frrlua.h
index f9ab5509a6..a105bd069d 100644
--- a/lib/frrlua.h
+++ b/lib/frrlua.h
@@ -33,42 +33,104 @@ extern "C" {
 #endif
 
 /*
- * Pushes a new table containing relevant fields from a prefix structure.
+ * Converts a prefix to a Lua value and pushes it on the stack.
  */
 void lua_pushprefix(lua_State *L, const struct prefix *prefix);
 
 /*
- * Pushes a new table containing relevant fields from an interface structure.
+ * Converts the Lua value at idx to a prefix.
+ *
+ * Returns:
+ *    struct prefix allocated with MTYPE_TMP
+ */
+void *lua_toprefix(lua_State *L, int idx);
+
+/*
+ * Converts an interface to a Lua value and pushes it on the stack.
  */
 void lua_pushinterface(lua_State *L, const struct interface *ifp);
 
 /*
- * Pushes a new table containing both numeric and string representations of an
- * in_addr to the stack.
+ * Converts the Lua value at idx to an interface.
+ *
+ * Returns:
+ *    struct interface allocated with MTYPE_TMP. This interface is not hooked
+ *    to anything, nor is it inserted in the global interface tree.
+ */
+void *lua_tointerface(lua_State *L, int idx);
+
+/*
+ * Converts an in_addr to a Lua value and pushes it on the stack.
  */
 void lua_pushinaddr(lua_State *L, const struct in_addr *addr);
 
 /*
- * Pushes a new table containing both numeric and string representations of an
- * in6_addr to the stack.
+ * Converts the Lua value at idx to an in_addr.
+ *
+ * Returns:
+ *    struct in_addr allocated with MTYPE_TMP.
+ */
+void *lua_toinaddr(lua_State *L, int idx);
+
+/*
+ * Converts an in6_addr to a Lua value and pushes it on the stack.
  */
 void lua_pushin6addr(lua_State *L, const struct in6_addr *addr);
 
 /*
- * Pushes a time_t to the stack.
+ * Converts the Lua value at idx to an in6_addr.
+ *
+ * Returns:
+ *    struct in6_addr allocated with MTYPE_TMP.
+ */
+void *lua_toin6addr(lua_State *L, int idx);
+
+/*
+ * Converts a time_t to a Lua value and pushes it on the stack.
  */
 void lua_pushtimet(lua_State *L, const time_t *time);
 
 /*
- * Pushes a table representing a sockunion to the stack.
+ * Converts the Lua value at idx to a time_t.
+ *
+ * Returns:
+ *    time_t allocated with MTYPE_TMP.
+ */
+void *lua_totimet(lua_State *L, int idx);
+
+/*
+ * Converts a sockunion to a Lua value and pushes it on the stack.
  */
 void lua_pushsockunion(lua_State *L, const union sockunion *su);
 
 /*
- * Push integer. This just wraps lua_pushinteger(), but it takes a pointer, so
- * as to be compatible with the encoder_func signature.
+ * Converts the Lua value at idx to a sockunion.
+ *
+ * Returns:
+ *    sockunion allocated with MTYPE_TMP.
+ */
+void *lua_tosockunion(lua_State *L, int idx);
+
+/*
+ * Converts an int to a Lua value and pushes it on the stack.
+ */
+void lua_pushintegerp(lua_State *L, const long long *num);
+
+/*
+ * Converts the Lua value at idx to an int.
+ *
+ * Returns:
+ *    int allocated with MTYPE_TMP.
+ */
+void *lua_tointegerp(lua_State *L, int idx);
+
+/*
+ * Pop string.
+ *
+ * Sets *string to a copy of the string at the top of the stack. The copy is
+ * allocated with MTYPE_TMP and the caller is responsible for freeing it.
  */
-void lua_pushintegerp(lua_State *L, const int *num);
+void *lua_tostringp(lua_State *L, int idx);
 
 /*
  * Retrieve an integer from table on the top of the stack.