Lua: Add "tonumber" method to NSTime

Absolute and Relative time fields could not be converted to seconds
without converting to string and parsing to number.

Fixed conversion in generated code that was subject to precision loss

Usage:
f=Field.new("frame.delta_time")
delta=f().value:tonumber()

Change-Id: I6ef91c6238a6c2ed9adf6cae03f8913f0a09332e
Reviewed-on: https://code.wireshark.org/review/22316
Petri-Dish: Stig Bjørlykke <stig@bjorlykke.org>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Guy Harris <guy@alum.mit.edu>
(cherry picked from commit 59add43eecfbed3bae5d75dabe6e875b5adefe1b)
Reviewed-on: https://code.wireshark.org/review/22331

3 files changed, 22 insertions, 7 deletions

diff --git a/epan/wslua/make-taps.pl b/epan/wslua/make-taps.pl
index e2d6bd2c91..ef41ba8937 100755
--- a/epan/wslua/make-taps.pl
+++ b/epan/wslua/make-taps.pl
@@ -43,8 +43,8 @@ my %types = %{{
 	'address' => '{ Address a = (Address)g_malloc(sizeof(address)); copy_address(a, &(v->STR)); pushAddress(L,a); }',
 	'address*' => '{ Address a = (Address)g_malloc(sizeof(address)); copy_address(a, v->STR); pushAddress(L,a); }',
 	'int' => 'lua_pushnumber(L,(lua_Number)v->STR);',
-	'nstime_t' => '{ lua_Number t = (lua_Number) v->STR.secs; t += v->STR.nsecs * 1e-9; lua_pushnumber(L,t); }',
-	'nstime_t*' => '{ lua_Number t = (lua_Number) v->STR->secs; t += v->STR->nsecs * 1e-9; lua_pushnumber(L,t); }',
+	'nstime_t' => 'lua_pushnumber(L,(lua_Number)nstime_to_sec(&(v->STR)));',
+	'nstime_t*' => 'lua_pushnumber(L,(lua_Number)nstime_to_sec(v->STR));'
 }};
 
 my %comments = %{{
@@ -164,6 +164,8 @@ print CFILE  <<"HEADER";
 
 #include "wslua.h"
 
+#include <wsutil/nstime.h>
+
 HEADER
 
 print DOCFILE "\n";
diff --git a/epan/wslua/wslua_nstime.c b/epan/wslua/wslua_nstime.c
index e04524151d..f0a87f0595 100644
--- a/epan/wslua/wslua_nstime.c
+++ b/epan/wslua/wslua_nstime.c
@@ -30,7 +30,7 @@
 #include "config.h"
 
 #include "wslua.h"
-
+#include <wsutil/nstime.h>
 
 /* WSLUA_CONTINUE_MODULE Pinfo */
 
@@ -61,6 +61,15 @@ WSLUA_METAMETHOD NSTime__call(lua_State* L) { /* Creates a NSTime object. */
     WSLUA_RETURN(NSTime_new(L)); /* The new NSTime object. */
 }
 
+WSLUA_METHOD NSTime_tonumber(lua_State* L) {
+        /* Returns a Lua number of the `NSTime` representing seconds from epoch
+         *        @since 2.4.0
+         *             */
+        NSTime nstime = checkNSTime(L,1);
+        lua_pushnumber(L, (lua_Number)nstime_to_sec(nstime));
+        WSLUA_RETURN(1); /* The Lua number. */
+}
+
 WSLUA_METAMETHOD NSTime__tostring(lua_State* L) {
     NSTime nstime = checkNSTime(L,1);
     gchar *str;
@@ -174,6 +183,7 @@ WSLUA_ATTRIBUTES NSTime_attributes[] = {
 
 WSLUA_METHODS NSTime_methods[] = {
     WSLUA_CLASS_FNREG(NSTime,new),
+    WSLUA_CLASS_FNREG(NSTime,tonumber),
     { NULL, NULL }
 };
 
diff --git a/test/lua/nstime.lua b/test/lua/nstime.lua
index 65d1b60e93..c8ecdd2d29 100644
--- a/test/lua/nstime.lua
+++ b/test/lua/nstime.lua
@@ -31,7 +31,7 @@ end
 -- note ip only runs 3 times because it gets removed
 -- and bootp only runs twice because the filter makes it run
 -- once and then it gets replaced with a different one for the second time
-local taptests = { [FRAME]=4, [OTHER]=37 }
+local taptests = { [FRAME]=4, [OTHER]=40 }
 local function getResults()
     print("\n-----------------------------\n")
     for k,v in pairs(taptests) do
@@ -132,13 +132,16 @@ test("NSTime.tostring-32", tostring(first) == "0.000000000")
 test("NSTime.tostring-33", tostring(second) == "100.000000100")
 test("NSTime.tostring-34", tostring(third) == "0.000000100")
 
+test("NSTime.tonumber-35", first:tonumber() == 0.0)
+test("NSTime.tonumber-36", second:tonumber() == 100.0000001)
+test("NSTime.tonumber-37", third:tonumber() == 0.0000001)
 
 testing(OTHER,"setters/getters")
 first.secs = 123
 first.nsecs = 100
-test("NSTime.set-35", first == NSTime(123,100))
-test("NSTime.get-36", first.secs == 123)
-test("NSTime.get-37", first.nsecs == 100)
+test("NSTime.set-38", first == NSTime(123,100))
+test("NSTime.get-39", first.secs == 123)
+test("NSTime.get-40", first.nsecs == 100)
 
 
 ----------------------------------