fix(*) correct error message from bn:mod_sqr and pkey (#233)

- pkey.lua: use builtin tostring (not the file-local __tostring
  serializer) and preserve the original padding value in the
  "invalid padding" error message.
- bn.lua: fix copy-paste mistakes in error reporting — mod_sqr now
  tags check_args as "mod_sqr" (was "mod_sub"), and __shr reports
  "BN_rshift() failed" (was "BN_lshift() failed").

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: perfgao

lib/resty/openssl/bn.lua

@@ -371,7 +371,7 @@ for _, op in ipairs({ "add", "sub" , "mul", "exp" }) do
 end
 
 function _M.mod_sqr(...)
-  local r, a, m = check_args("mod_sub", ...)
+  local r, a, m = check_args("mod_sqr", ...)
   if C.BN_mod_sqr(r.ctx, a, m, bn_ctx_tmp) == 0 then
     error("BN_mod_sqr() failed")
   end
@@ -401,7 +401,7 @@ _M.lshift = mt.__shl
 function mt.__shr(a, b)
   local r, a = check_args("rshift", a)
   if C.BN_rshift(r.ctx, a, b) == 0 then
-    error("BN_lshift() failed")
+    error("BN_rshift() failed")
   end
   return r
 end

lib/resty/openssl/pkey.lua

@@ -738,10 +738,11 @@ local function asymmetric_routine(self, s, op, padding, opts)
 
   if self.key_type == evp_macro.EVP_PKEY_RSA then
     if padding then
-      padding = tonumber(padding)
-      if not padding then
-        return nil, "invalid padding: " .. __tostring(padding)
+      local p = tonumber(padding)
+      if not p then
+        return nil, "invalid padding: " .. tostring(padding)
       end
+      padding = p
     else
       padding = rsa_macro.paddings.RSA_PKCS1_PADDING
     end

t/openssl/bn.t

@@ -592,3 +592,23 @@ true
 "
 --- no_error_log
 [error]
+
+
+
+=== TEST: mod_sqr: error message names the correct op
+--- http_config eval: $::HttpConfig
+--- config
+    location =/t {
+        content_by_lua_block {
+            local bn = require("resty.openssl.bn")
+            local a = myassert(bn.new(3))
+            local ok, err = pcall(function() return bn.mod_sqr(a, "not-a-bn", 5) end)
+            ngx.say(ok)
+            ngx.say(err)
+        }
+    }
+--- request
+    GET /t
+--- response_body_like: mod_sqr
+--- no_error_log
+[error]

t/openssl/pkey.t

@@ -1493,3 +1493,27 @@ default
 "
 --- no_error_log
 [error]
+
+
+
+=== TEST: encryption: invalid padding error message preserves user input
+--- http_config eval: $::HttpConfig
+--- config
+    location =/t {
+        content_by_lua_block {
+            local privkey = myassert(require("resty.openssl.pkey").new())
+            local pubkey = myassert(require("resty.openssl.pkey").new(assert(privkey:to_PEM("public"))))
+
+            local ok, err = pubkey:encrypt("23333", "bad_pad")
+            ngx.say(ok)
+            ngx.say(err)
+        }
+    }
+--- request
+    GET /t
+--- response_body eval
+"nil
+invalid padding: bad_pad
+"
+--- no_error_log
+[error]