Added maxnum option to limit the number of elements in tables.

README.md

@@ -60,6 +60,7 @@ internal function, but set different options by default:
 * nocode (true/false) -- disable bytecode serialization for easy comparison
 * nohuge (true/false) -- disable checking numbers against undefined and huge values
 * maxlevel (number) -- specify max level up to which to expand nested tables
+* maxnum (number) -- specify max number of elements in a table
 * valignore (table) -- allows to specify a list of values to ignore (as keys)
 * keyallow (table) -- allows to specify the list of keys to be serialized. Any keys not in this list are not included in final output (as keys)
 * valtypeignore (table) -- allows to specify a list of value *types* to ignore (as keys)
@@ -159,6 +160,9 @@ See LICENSE file.
 
 ## History
 
+### v0.25 (Sep 29 2013)
+  - Added `maxnum` option to limit the number of elements in tables.
+
 ### v0.24 (Jun 12 2013)
   - Fixed an issue with missing numerical keys (fixes #8).
   - Fixed an issue with luaffi that returns `getmetatable(ffi.C)` as `true`.

src/serpent.lua

@@ -1,4 +1,4 @@
-local n, v = "serpent", 0.24 -- (C) 2012-13 Paul Kulchenko; MIT License
+local n, v = "serpent", 0.25 -- (C) 2012-13 Paul Kulchenko; MIT License
 local c, d = "Paul Kulchenko", "Lua serializer and pretty printer"
 local snum = {[tostring(1/0)]='1/0 --[[math.huge]]',[tostring(-1/0)]='-1/0 --[[-math.huge]]',[tostring(0/0)]='0/0'}
 local badtype = {thread = true, userdata = true, cdata = true}
@@ -58,6 +58,7 @@ local function s(t, opts)
       for key = 1, maxn do table.insert(o, key) end
       for key in pairs(t) do if not o[key] or key > maxn then table.insert(o, key) end end
       if opts.sortkeys then alphanumsort(o, t, opts.sortkeys) end
+      if opts.maxnum and #o > opts.maxnum then o[opts.maxnum+1] = nil end
       for n, key in ipairs(o) do
         local value, ktype, plainindex = t[key], type(key), n <= maxn and not sparse
         if opts.valignore and opts.valignore[value] -- skip ignored values; do nothing

t/test.lua

@@ -224,4 +224,15 @@ do
   end
 end
 
+-- test maxnum limit
+do
+  local a = {a = {7,6,5,4,3,2,1}, b = {1,2}}
+  local f = assert(loadstring(serpent.dump(a, {maxnum = 3})),
+    "serializing table with numerical keys: failed")
+  local _a = f()
+  assert(#_a.a == 3, "table with maxnum=3 has no more than 3 elements 1/3: failed")
+  assert(_a.a[3] == 5, "table with maxnum=3 has no more than 3 elements 2/3: failed")
+  assert(#_a.b == 2, "table with maxnum=3 has no more than 3 elements 3/3: failed")
+end
+
 print("All tests passed.")