Function Flags support (no-writes, no-cluster, allow-state, allow-oom) (#10066)

# Redis Functions Flags

Following the discussion on #10025 Added Functions Flags support.
The PR is divided to 2 sections:
* Add named argument support to `redis.register_function` API.
* Add support for function flags

## `redis.register_function` named argument support

The first part of the PR adds support for named argument on `redis.register_function`, example:
```
redis.register_function{
    function_name='f1',
    callback=function()
        return 'hello'
    end,
    description='some desc'
}
```

The positional arguments is also kept, which means that it still possible to write:
```
redis.register_function('f1', function() return 'hello' end)
```

But notice that it is no longer possible to pass the optional description argument on the positional
argument version. Positional argument was change to allow passing only the mandatory arguments
(function name and callback). To pass more arguments the user must use the named argument version.

As with positional arguments, the `function_name` and `callback` is mandatory and an error will be
raise if those are missing. Also, an error will be raise if an unknown argument name is given or the
arguments type is wrong.

Tests was added to verify the new syntax.

## Functions Flags

The second part of the PR is adding functions flags support.
Flags are given to Redis when the engine calls `functionLibCreateFunction`, supported flags are:

* `no-writes` - indicating the function perform no writes which means that it is OK to run it on:
   * read-only replica
   * Using FCALL_RO
   * If disk error detected
   
   It will not be possible to run a function in those situations unless the function turns on the `no-writes` flag

* `allow-oom` - indicate that its OK to run the function even if Redis is in OOM state, if the function will
  not turn on this flag it will not be possible to run it if OOM reached (even if the function declares `no-writes`
  and even if `fcall_ro` is used). If this flag is set, any command will be allow on OOM (even those that is
  marked with CMD_DENYOOM). The assumption is that this flag is for advance users that knows its
  meaning and understand what they are doing, and Redis trust them to not increase the memory usage.
  (e.g. it could be an INCR or a modification on an existing key, or a DEL command)

* `allow-state` - indicate that its OK to run the function on stale replica, in this case we will also make
  sure the function is only perform `stale` commands and raise an error if not.

* `no-cluster` - indicate to disallow running the function if cluster is enabled.

Default behaviure of functions (if no flags is given):
1. Allow functions to read and write
2. Do not run functions on OOM
3. Do not run functions on stale replica
4. Allow functions on cluster

### Lua API for functions flags

On Lua engine, it is possible to give functions flags as `flags` named argument:

```
redis.register_function{function_name='f1', callback=function() return 1 end, flags={'no-writes', 'allow-oom'}, description='description'}
```

The function flags argument must be a Lua table that contains all the requested flags, The following
will result in an error:
* Unknown flag
* Wrong flag type

Default behaviour is the same as if no flags are used.

Tests were added to verify all flags functionality

## Additional changes
* mark FCALL and FCALL_RO with CMD_STALE flag (unlike EVAL), so that they can run if the function was
  registered with the `allow-stale` flag.
* Verify `CMD_STALE` on `scriptCall` (`redis.call`), so it will not be possible to call commands from script while
  stale unless the command is marked with the `CMD_STALE` flags. so that even if the function is allowed while
  stale we do not allow it to bypass the `CMD_STALE` flag of commands.
* Flags section was added to `FUNCTION LIST` command to provide the set of flags for each function:
```
> FUNCTION list withcode
1)  1) "library_name"
    2) "test"
    3) "engine"
    4) "LUA"
    5) "description"
    6) (nil)
    7) "functions"
    8) 1) 1) "name"
          2) "f1"
          3) "description"
          4) (nil)
          5) "flags"
          6) (empty array)
    9) "library_code"
   10) "redis.register_function{function_name='f1', callback=function() return 1 end}"
```
* Added API to get Redis version from within a script, The redis version can be provided using:
   1. `redis.REDIS_VERSION` - string representation of the redis version in the format of MAJOR.MINOR.PATH
   2. `redis.REDIS_VERSION_NUM` - number representation of the redis version in the format of `0x00MMmmpp`
      (`MM` - major, `mm` - minor,  `pp` - patch). The number version can be used to check if version is greater or less 
      another version. The string version can be used to return to the user or print as logs.

   This new API is provided to eval scripts and functions, it also possible to use this API during functions loading phase.

5 files changed, 271 insertions, 37 deletions

diff --git a/tests/cluster/tests/00-base.tcl b/tests/cluster/tests/00-base.tcl
index e731bf6a3..6ff043497 100644
--- a/tests/cluster/tests/00-base.tcl
+++ b/tests/cluster/tests/00-base.tcl
@@ -62,3 +62,9 @@ test "Sanity for CLUSTER COUNTKEYSINSLOT" {
 test "It is possible to write and read from the cluster" {
     cluster_write_test 0
 }
+
+test "Function no-cluster flag" {
+    R 1 function load lua test {redis.register_function('f1', function() return 'hello' end, {'no-cluster'})}
+    catch {R 1 fcall f1 0} e
+    assert_match {*Can not run function on cluster, 'no-cluster' flag is set*} $e
+}
diff --git a/tests/integration/redis-cli.tcl b/tests/integration/redis-cli.tcl
index 9cbec3f96..88b189ac0 100644
--- a/tests/integration/redis-cli.tcl
+++ b/tests/integration/redis-cli.tcl
@@ -338,7 +338,7 @@ if {!$::tls} { ;# fake_redis_node doesn't support TLS
         assert_equal "OK" [r function load lua should_not_exist_func "redis.register_function('should_not_exist_func', function() return 456 end)"]
         assert_equal "OK" [r debug reload nosave]
         assert_equal {} [r get should-not-exist]
-        assert_equal {{library_name lib1 engine LUA description {} functions {{name func1 description {}}}}} [r function list]
+        assert_equal {{library_name lib1 engine LUA description {} functions {{name func1 description {} flags {}}}}} [r function list]
         if {$functions_only} {
             assert_equal 0 [r dbsize]
         } else {
diff --git a/tests/unit/cluster.tcl b/tests/unit/cluster.tcl
index d1c02a7c5..99925688c 100644
--- a/tests/unit/cluster.tcl
+++ b/tests/unit/cluster.tcl
@@ -199,13 +199,13 @@ start_server [list overrides $base_conf] {
         }
 
         # make sure 'test' function was added to the new node
-        assert_equal {{library_name TEST engine LUA description {} functions {{name test description {}}}}} [$node4_rd FUNCTION LIST]
+        assert_equal {{library_name TEST engine LUA description {} functions {{name test description {} flags {}}}}} [$node4_rd FUNCTION LIST]
 
         # add function to node 5
         assert_equal {OK} [$node5_rd FUNCTION LOAD LUA TEST {redis.register_function('test', function() return 'hello' end)}]
 
         # make sure functions was added to node 5
-        assert_equal {{library_name TEST engine LUA description {} functions {{name test description {}}}}} [$node5_rd FUNCTION LIST]
+        assert_equal {{library_name TEST engine LUA description {} functions {{name test description {} flags {}}}}} [$node5_rd FUNCTION LIST]
 
         # adding node 5 to the cluster should failed because it already contains the 'test' function
         catch {
diff --git a/tests/unit/functions.tcl b/tests/unit/functions.tcl
index 84f9154e5..48f846e20 100644
--- a/tests/unit/functions.tcl
+++ b/tests/unit/functions.tcl
@@ -2,6 +2,10 @@ proc get_function_code {args} {
     return [format "redis.register_function('%s', function(KEYS, ARGV)\n %s \nend)" [lindex $args 0] [lindex $args 1]]
 }
 
+proc get_no_writes_function_code {args} {
+    return [format "redis.register_function{function_name='%s', callback=function(KEYS, ARGV)\n %s \nend, flags={'no-writes'}}" [lindex $args 0] [lindex $args 1]]
+}
+
 start_server {tags {"scripting"}} {
     test {FUNCTION - Basic usage} {
         r function load LUA test [get_function_code test {return 'hello'}]
@@ -68,7 +72,7 @@ start_server {tags {"scripting"}} {
     test {FUNCTION - test description argument} {
         r function load LUA test DESCRIPTION {some description} [get_function_code test {return 'hello'}]
         r function list
-    } {{library_name test engine LUA description {some description} functions {{name test description {}}}}}
+    } {{library_name test engine LUA description {some description} functions {{name test description {} flags {}}}}}
 
     test {FUNCTION - test fcall bad arguments} {
         catch {
@@ -122,7 +126,7 @@ start_server {tags {"scripting"}} {
         assert_match "*Error trying to load the RDB*" $e
         r debug reload noflush merge
         r function list
-    } {{library_name test engine LUA description {some description} functions {{name test description {}}}}} {needs:debug}
+    } {{library_name test engine LUA description {some description} functions {{name test description {} flags {}}}}} {needs:debug}
 
     test {FUNCTION - test debug reload with nosave and noflush} {
         r function delete test
@@ -141,7 +145,7 @@ start_server {tags {"scripting"}} {
         r flushall
         r flushdb
         r function list
-    } {{library_name test engine LUA description {} functions {{name test description {}}}}}
+    } {{library_name test engine LUA description {} functions {{name test description {} flags {}}}}}
 
     test {FUNCTION - test function dump and restore} {
         r function flush
@@ -151,7 +155,7 @@ start_server {tags {"scripting"}} {
         assert_match {} [r function list]
         r function restore $e
         r function list
-    } {{library_name test engine LUA description {some description} functions {{name test description {}}}}}
+    } {{library_name test engine LUA description {some description} functions {{name test description {} flags {}}}}}
 
     test {FUNCTION - test function dump and restore with flush argument} {
         set e [r function dump]
@@ -159,7 +163,7 @@ start_server {tags {"scripting"}} {
         assert_match {} [r function list]
         r function restore $e FLUSH
         r function list
-    } {{library_name test engine LUA description {some description} functions {{name test description {}}}}}
+    } {{library_name test engine LUA description {some description} functions {{name test description {} flags {}}}}}
 
     test {FUNCTION - test function dump and restore with append argument} {
         set e [r function dump]
@@ -193,7 +197,7 @@ start_server {tags {"scripting"}} {
         catch {r function restore bad_payload} e
         assert_match {*payload version or checksum are wrong*} $e
         r function list
-    } {{library_name test engine LUA description {some description} functions {{name test description {}}}}}
+    } {{library_name test engine LUA description {some description} functions {{name test description {} flags {}}}}}
 
     test {FUNCTION - test function restore with wrong number of arguments} {
         catch {r function restore arg1 args2 arg3} e
@@ -201,13 +205,13 @@ start_server {tags {"scripting"}} {
     } {*wrong number of arguments*}
 
     test {FUNCTION - test fcall_ro with write command} {
-        r function load lua test REPLACE [get_function_code test {return redis.call('set', 'x', '1')}]
+        r function load lua test REPLACE [get_no_writes_function_code test {return redis.call('set', 'x', '1')}]
         catch { r fcall_ro test 0 } e
         set _ $e
     } {*Write commands are not allowed from read-only scripts*}
 
     test {FUNCTION - test fcall_ro with read only commands} {
-        r function load lua test REPLACE [get_function_code test {return redis.call('get', 'x')}]
+        r function load lua test REPLACE [get_no_writes_function_code test {return redis.call('get', 'x')}]
         r set x 1
         r fcall_ro test 0
     } {1}
@@ -271,17 +275,17 @@ start_server {tags {"scripting"}} {
 
     test {FUNCTION - test function flush} {
         r function load lua test REPLACE [get_function_code test {local a = 1 while true do a = a + 1 end}]
-        assert_match {{library_name test engine LUA description {} functions {{name test description {}}}}} [r function list]
+        assert_match {{library_name test engine LUA description {} functions {{name test description {} flags {}}}}} [r function list]
         r function flush
         assert_match {} [r function list]
 
         r function load lua test REPLACE [get_function_code test {local a = 1 while true do a = a + 1 end}]
-        assert_match {{library_name test engine LUA description {} functions {{name test description {}}}}} [r function list]
+        assert_match {{library_name test engine LUA description {} functions {{name test description {} flags {}}}}} [r function list]
         r function flush async
         assert_match {} [r function list]
 
         r function load lua test REPLACE [get_function_code test {local a = 1 while true do a = a + 1 end}]
-        assert_match {{library_name test engine LUA description {} functions {{name test description {}}}}} [r function list]
+        assert_match {{library_name test engine LUA description {} functions {{name test description {} flags {}}}}} [r function list]
         r function flush sync
         assert_match {} [r function list]
     }
@@ -308,9 +312,9 @@ start_server {tags {"scripting repl external:skip"}} {
         }
 
         test {FUNCTION - creation is replicated to replica} {
-            r function load LUA test DESCRIPTION {some description} [get_function_code test {return 'hello'}]
-            wait_for_condition 50 100 {
-                [r -1 function list] eq {{library_name test engine LUA description {some description} functions {{name test description {}}}}}
+            r function load LUA test DESCRIPTION {some description} [get_no_writes_function_code test {return 'hello'}]
+            wait_for_condition 50 100 {    
+                [r -1 function list] eq {{library_name test engine LUA description {some description} functions {{name test description {} flags no-writes}}}}
             } else {
                 fail "Failed waiting for function to replicate to replica"
             }
@@ -333,7 +337,7 @@ start_server {tags {"scripting repl external:skip"}} {
             assert_equal [r function restore $e] {OK}
 
             wait_for_condition 50 100 {
-                [r -1 function list] eq {{library_name test engine LUA description {some description} functions {{name test description {}}}}}
+                [r -1 function list] eq {{library_name test engine LUA description {some description} functions {{name test description {} flags no-writes}}}}
             } else {
                 fail "Failed waiting for function to replicate to replica"
             }
@@ -351,7 +355,7 @@ start_server {tags {"scripting repl external:skip"}} {
         test {FUNCTION - flush is replicated to replica} {
             r function load LUA test DESCRIPTION {some description} [get_function_code test {return 'hello'}]
             wait_for_condition 50 100 {
-                [r -1 function list] eq {{library_name test engine LUA description {some description} functions {{name test description {}}}}}
+                [r -1 function list] eq {{library_name test engine LUA description {some description} functions {{name test description {} flags {}}}}}
             } else {
                 fail "Failed waiting for function to replicate to replica"
             }
@@ -367,7 +371,7 @@ start_server {tags {"scripting repl external:skip"}} {
             r -1 slaveof no one
             # creating a function after disconnect to make sure function
             # is replicated on rdb phase
-            r function load LUA test DESCRIPTION {some description} [get_function_code test {return 'hello'}]
+            r function load LUA test DESCRIPTION {some description} [get_no_writes_function_code test {return 'hello'}]
 
             # reconnect the replica
             r -1 slaveof [srv 0 host] [srv 0 port]
@@ -385,7 +389,7 @@ start_server {tags {"scripting repl external:skip"}} {
 
         test "FUNCTION - test replication to replica on rdb phase info command" {
             r -1 function list
-        } {{library_name test engine LUA description {some description} functions {{name test description {}}}}}
+        } {{library_name test engine LUA description {some description} functions {{name test description {} flags no-writes}}}}
 
         test "FUNCTION - create on read only replica" {
             catch {
@@ -417,7 +421,7 @@ start_server {tags {"scripting repl external:skip"}} {
                 r -1 fcall test 0
             } e
             set _ $e
-        } {*can't write against a read only replica*}
+        } {*Can not run a function with write flag on readonly replica*}
     }
 }
 
@@ -430,7 +434,7 @@ test {FUNCTION can processes create, delete and flush commands in AOF when doing
         r slaveof 127.0.0.1 0
         r debug loadaof
         r slaveof no one
-        assert_equal [r function list] {{library_name test engine LUA description {} functions {{name test description {}}}}}
+        assert_equal [r function list] {{library_name test engine LUA description {} functions {{name test description {} flags {}}}}}
 
         r FUNCTION DELETE test
 
@@ -474,15 +478,13 @@ start_server {tags {"scripting"}} {
                 'f1',
                 function(keys, args)
                     return add1(1)
-                end,
-                'f1 description'
+                end
             )
             redis.register_function(
                 'f2',
                 function(keys, args)
                     return add1(2)
-                end,
-                'f2 description'
+                end
             )
         }
         assert_equal [r fcall f1 0] {2}
@@ -565,12 +567,12 @@ start_server {tags {"scripting"}} {
             }
         } e
         set _ $e
-    } {*wrong number of arguments to redis.register_function*}
+    } {*calling redis.register_function with a single argument is only applicable to Lua table*}
 
     test {LIBRARIES - test registration with to many arguments} {
         catch {
             r function load LUA lib2 replace {
-                redis.register_function('f1', function() return 1 end, 'description', 'extra arg')
+                redis.register_function('f1', function() return 1 end, {}, 'description', 'extra arg')
             }
         } e
         set _ $e
@@ -741,6 +743,104 @@ start_server {tags {"scripting"}} {
         set _ $e
     } {*attempted to create global variable 'a'*}
 
+    test {LIBRARIES - named arguments} {
+        r function load LUA lib {
+            redis.register_function{
+                function_name='f1',
+                callback=function()
+                    return 'hello'
+                end,
+                description='some desc'
+            }
+        }
+        r function list
+    } {{library_name lib engine LUA description {} functions {{name f1 description {some desc} flags {}}}}}
+
+    test {LIBRARIES - named arguments, bad function name} {
+        catch {
+            r function load LUA lib replace {
+                redis.register_function{
+                    function_name=function() return 1 end,
+                    callback=function()
+                        return 'hello'
+                    end,
+                    description='some desc'
+                }
+            }
+        } e
+        set _ $e
+    } {*function_name argument given to redis.register_function must be a string*}
+
+    test {LIBRARIES - named arguments, bad callback type} {
+        catch {
+            r function load LUA lib replace {
+                redis.register_function{
+                    function_name='f1',
+                    callback='bad',
+                    description='some desc'
+                }
+            }
+        } e
+        set _ $e
+    } {*callback argument given to redis.register_function must be a function*}
+
+    test {LIBRARIES - named arguments, bad description} {
+        catch {
+            r function load LUA lib replace {
+                redis.register_function{
+                    function_name='f1',
+                    callback=function()
+                        return 'hello'
+                    end,
+                    description=function() return 1 end
+                }
+            }
+        } e
+        set _ $e
+    } {*description argument given to redis.register_function must be a string*}
+
+    test {LIBRARIES - named arguments, unknown argument} {
+        catch {
+            r function load LUA lib replace {
+                redis.register_function{
+                    function_name='f1',
+                    callback=function()
+                        return 'hello'
+                    end,
+                    description='desc',
+                    some_unknown='unknown'
+                }
+            }
+        } e
+        set _ $e
+    } {*unknown argument given to redis.register_function*}
+
+    test {LIBRARIES - named arguments, missing function name} {
+        catch {
+            r function load LUA lib replace {
+                redis.register_function{
+                    callback=function()
+                        return 'hello'
+                    end,
+                    description='desc'
+                }
+            }
+        } e
+        set _ $e
+    } {*redis.register_function must get a function name argument*}
+
+    test {LIBRARIES - named arguments, missing callback} {
+        catch {
+            r function load LUA lib replace {
+                redis.register_function{
+                    function_name='f1',
+                    description='desc'
+                }
+            }
+        } e
+        set _ $e
+    } {*redis.register_function must get a callback argument*}
+
     test {FUNCTION - test function restore with function name collision} {
         r function flush
         r function load lua lib1 {
@@ -821,12 +921,12 @@ start_server {tags {"scripting"}} {
         r function flush
         r function load lua library1 {redis.register_function('f6', function(keys, args) return 7 end)}
         r function list withcode
-    } {{library_name library1 engine LUA description {} functions {{name f6 description {}}} library_code {redis.register_function('f6', function(keys, args) return 7 end)}}}
+    } {{library_name library1 engine LUA description {} functions {{name f6 description {} flags {}}} library_code {redis.register_function('f6', function(keys, args) return 7 end)}}}
 
     test {FUNCTION - test function list with pattern} {
         r function load lua lib1 {redis.register_function('f7', function(keys, args) return 7 end)}
         r function list libraryname library*
-    } {{library_name library1 engine LUA description {} functions {{name f6 description {}}}}}
+    } {{library_name library1 engine LUA description {} functions {{name f6 description {} flags {}}}}}
 
     test {FUNCTION - test function list wrong argument} {
         catch {r function list bad_argument} e
@@ -864,4 +964,135 @@ start_server {tags {"scripting"}} {
 
         r config set maxmemory 0
     }
+
+    test {FUNCTION - verify allow-omm allows running any command} {
+        r FUNCTION load lua f1 replace { redis.register_function{
+            function_name='f1',
+            callback=function() return redis.call('set', 'x', '1') end,
+            flags={'allow-oom'}
+        }}
+
+        r config set maxmemory 1
+
+        assert_match {OK} [r fcall f1 1 k]
+        assert_match {1} [r get x]
+
+        r config set maxmemory 0
+    }
+}
+
+start_server {tags {"scripting"}} {
+    test {FUNCTION - wrong flags type named arguments} {
+        catch {r function load lua test replace {redis.register_function{
+            function_name = 'f1',
+            callback = function() return 1 end,
+            flags = 'bad flags type'
+        }}} e
+        set _ $e
+    } {*flags argument to redis.register_function must be a table representing function flags*}
+
+    test {FUNCTION - wrong flag type} {
+        catch {r function load lua test replace {redis.register_function{
+            function_name = 'f1',
+            callback = function() return 1 end,
+            flags = {function() return 1 end}
+        }}} e
+        set _ $e
+    } {*unknown flag given*}
+
+    test {FUNCTION - unknown flag} {
+        catch {r function load lua test replace {redis.register_function{
+            function_name = 'f1',
+            callback = function() return 1 end,
+            flags = {'unknown'}
+        }}} e
+        set _ $e
+    } {*unknown flag given*}
+
+    test {FUNCTION - write script on fcall_ro} {
+        r function load lua test replace {redis.register_function{
+            function_name = 'f1',
+            callback = function() return redis.call('set', 'x', 1) end
+        }}
+        catch {r fcall_ro f1 0} e
+        set _ $e
+    } {*Can not execute a function with write flag using fcall_ro*}
+
+    test {FUNCTION - write script with no-writes flag} {
+        r function load lua test replace {redis.register_function{
+            function_name = 'f1',
+            callback = function() return redis.call('set', 'x', 1) end,
+            flags = {'no-writes'}
+        }}
+        catch {r fcall f1 0} e
+        set _ $e
+    } {*Write commands are not allowed from read-only scripts*}
+
+    test {FUNCTION - deny oom} {
+        r FUNCTION load lua test replace { redis.register_function('f1', function() return redis.call('set', 'x', '1') end) }
+
+        r config set maxmemory 1
+
+        catch {[r fcall f1 1 k]} e
+        assert_match {*can not run it when used memory > 'maxmemory'*} $e
+
+        r config set maxmemory 0
+    }
+
+    test {FUNCTION - deny oom on no-writes function} {
+        r FUNCTION load lua test replace {redis.register_function{function_name='f1', callback=function() return 'hello' end, flags={'no-writes'}}}
+
+        r config set maxmemory 1
+
+        catch {r fcall f1 1 k} e
+        assert_match {*can not run it when used memory > 'maxmemory'*} $e
+
+        catch {r fcall_ro f1 1 k} e
+        assert_match {*can not run it when used memory > 'maxmemory'*} $e
+
+        r config set maxmemory 0
+    }
+
+    test {FUNCTION - allow stale} {
+        r FUNCTION load lua test replace { 
+            redis.register_function{function_name='f1', callback=function() return 'hello' end, flags={'no-writes'}}
+            redis.register_function{function_name='f2', callback=function() return 'hello' end, flags={'allow-stale', 'no-writes'}}
+            redis.register_function{function_name='f3', callback=function() return redis.call('get', 'x') end, flags={'allow-stale', 'no-writes'}}
+            redis.register_function{function_name='f4', callback=function() return redis.call('info', 'server') end, flags={'allow-stale', 'no-writes'}}
+        }
+        
+        r config set replica-serve-stale-data no
+        r replicaof 127.0.0.1 1
+
+        catch {[r fcall f1 0]} e
+        assert_match {*'allow-stale' flag is not set on the function*} $e
+
+        assert_equal {hello} [r fcall f2 0]
+
+        catch {[r fcall f3 0]} e
+        assert_match {*Can not execute the command on a stale replica*} $e
+
+        assert_match {*redis_version*} [r fcall f4 0]
+
+        r replicaof no one
+        r config set replica-serve-stale-data yes
+        set _ {}
+    } {} {external:skip}
+
+    test {FUNCTION - redis version api} {
+        r FUNCTION load lua test replace { 
+            local version = redis.REDIS_VERSION_NUM
+
+            redis.register_function{function_name='get_version_v1', callback=function()
+              return string.format('%s.%s.%s',
+                                    bit.band(bit.rshift(version, 4), 0x000000ff),
+                                    bit.band(bit.rshift(version, 2), 0x000000ff),
+                                    bit.band(version, 0x000000ff))
+            end}
+            redis.register_function{function_name='get_version_v2', callback=function() return redis.REDIS_VERSION end}
+        }
+
+        catch {[r fcall f1 0]} e
+        assert_equal  [r fcall get_version_v1 0] [r fcall get_version_v2 0]
+    }
 }
diff --git a/tests/unit/scripting.tcl b/tests/unit/scripting.tcl
index 96511bad5..312557283 100644
--- a/tests/unit/scripting.tcl
+++ b/tests/unit/scripting.tcl
@@ -19,7 +19,7 @@ if {$is_eval == 1} {
         r fcall test {*}[lrange $args 1 end]
     }
     proc run_script_ro {args} {
-        r function load LUA test replace [format "redis.register_function('test', function(KEYS, ARGV)\n %s \nend)" [lindex $args 0]]
+        r function load LUA test replace [format "redis.register_function{function_name='test', callback=function(KEYS, ARGV)\n %s \nend, flags={'no-writes'}}" [lindex $args 0]]
         r fcall_ro test {*}[lrange $args 1 end]
     }
     proc run_script_on_connection {args} {
@@ -36,19 +36,16 @@ if {$is_eval == 1} {
 
 start_server {tags {"scripting"}} {
 
+    if {$is_eval eq 1} {
     test {Script - disallow write on OOM} {
-        r FUNCTION load lua f1 replace { redis.register_function('f1', function() return redis.call('set', 'x', '1') end) }
-
         r config set maxmemory 1
 
-        catch {[r fcall f1 1 k]} e
-        assert_match {*command not allowed when used memory*} $e
-
         catch {[r eval "redis.call('set', 'x', 1)" 0]} e
         assert_match {*command not allowed when used memory*} $e
 
         r config set maxmemory 0
     }
+    } ;# is_eval
 
     test {EVAL - Does Lua interpreter replies to our requests?} {
         run_script {return 'hello'} 0