# Module issue in pengines **URL:** \ **Category:** Help!\ **Created:** [August 10, 2024, 7:17am UTC](https://swi-prolog.discourse.group/t/module-issue-in-pengines/7676 "2024-08-10T07:17:24Z")\ **Posts on this page:** 16\ **Page:** 1
**Author:** ![Gauntlet173](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/gauntlet173/32/3778_2.png) [@Gauntlet173](https://swi-prolog.discourse.group/u/Gauntlet173)\ **Post date:** [August 10, 2024, 7:17am UTC](https://swi-prolog.discourse.group/t/module-issue-in-pengines/7676/1 "2024-08-10T07:17:24Z")
I’m using pengines from Python, and getting syntax errors that suggest a malformed query, when the query is not malformed. It only happens when I call something that tries to use sCASP to prove a goal defined in the source text parameter. If I call the same predicate and have it use sCASP to prove a predicate defined in the modules that are loaded by the pengines server, the problem doesn’t happen. I suspect that it is a whitelisting issue, and to test that theory I would like to temporarily disable the sandbox restrictions and see if it goes away. The documentation says that it’s possible, but I can’t see where it indicates how to do it. How is that done? Thanks in advance. ---
**Author:** ![jan](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/jan/32/4_2.png) [@jan](https://swi-prolog.discourse.group/u/jan)\ **Post date:** [August 10, 2024, 9:41am UTC](https://swi-prolog.discourse.group/t/module-issue-in-pengines/7676/2 "2024-08-10T09:41:23Z")
> [@Gauntlet173](#): > > How is that done? I doubt this is the problem. More looks like a module issue. See the SWISH sources for adding sCASP to the system (in config-available). To disable the sandbox, see `pengines.pl`. There are two hooks: authentication\_hook/3 that allows connecting an HTTP request to a user and not\_sandboxed/2 that allows disabling the sandbox for a particular application and user. You can make that as (un)safe as you like, ranging from demanding proper HTTPS authentication to just claim any request comes from a particular user without any verification and allow that user to do anything. ---
**Author:** ![Gauntlet173](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/gauntlet173/32/3778_2.png) [@Gauntlet173](https://swi-prolog.discourse.group/u/Gauntlet173)\ **Post date:** [August 10, 2024, 5:08pm UTC](https://swi-prolog.discourse.group/t/module-issue-in-pengines/7676/3 "2024-08-10T17:08:52Z")
Thanks, I’ll try that, but honestly I feel like I don’t understand pengines well enough at this point to imagine how to use those predicates. The only thing I’m doing right now is starting the server, and calling that goal when I run SWIPL. Is there an example somewhere? Also what do you mean by module problem? Do I need to call user-specified predicates in “source\_txt” with a module name in the “ask” parameter, or something? ---
**Author:** ![Gauntlet173](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/gauntlet173/32/3778_2.png) [@Gauntlet173](https://swi-prolog.discourse.group/u/Gauntlet173)\ **Post date:** [August 11, 2024, 12:11am UTC](https://swi-prolog.discourse.group/t/module-issue-in-pengines/7676/4 "2024-08-11T00:11:32Z")
I have not been able to figure out how to disable the sandbox, but I suspect you were right that there is a module problem. After fighting with it for another couple of hours, here’s the problem I’m having in detail: This is the code that is being loaded when swipl runs, with the goal of server(8080). ```prolog % scasp_server.pl :- use_module(library(http/http_server)). :- use_module(library(pengines)). :- use_module(library(sandbox)). :- use_module(library(scasp)). :- use_module(aggregates). :- use_module(dates). :- use_module(events). :- use_module(ldap). :- use_module(passthrough). :- use_module(library(scasp/output)). blawxrun(Query, Tree, Model, Attributes) :- scasp(Query, [tree(Tree), model(Model), source(false)]), ovar_analyze_term(t(Query, Tree, Model), [name_constraints(true), name_prefix('Var_')]), ( term_attvars(t(Query, Tree, Model), []) -> Attributes = [] ; copy_term(t(Query, Tree, Model), _, Attributes) ). server(Port) :- http_server([port(Port)]). ``` I then run swipl, run `use_module(library(pengines)).` and run the following three queries: ```prolog ?- pengine_rpc('http://localhost:8080', winner(X,Y),[src_text("winner(test,jason).")]). X = test, Y = jason. ?- pengine_rpc('http://localhost:8080', blawxrun(true,A,B,C),[src_text("winner(test,jason).")]). A = query-[], B = C, C = []. ?- pengine_rpc('http://localhost:8080', blawxrun(winner(X,Y),A,B,C),[src_text("winner(test,jason).")]). ERROR: scasp_predicate `'user:winner'/2' does not exist ERROR: In: ERROR: [18] throw(error(existence_error(scasp_predicate,...),_121072)) ERROR: [13] setup_call_catcher_cleanup(pengines:pengine_create(...),pengines:wait_event(...,...,...),_121106,pengines:pengine_destroy_and_wait(...,'fb2e42ea-55d2-4390-9b33-d32645b9b22d',_121146)) at /usr/lib/swipl/boot/init.pl:678 ERROR: [11] toplevel_call(user:user: ...) at /usr/lib/swipl/boot/toplevel.pl:1318 ERROR: ERROR: Note: some frames are missing due to last-call optimization. ERROR: Re-run your program in debug mode (:- debug.) to get more detail. ``` I have no idea why, if both blawxrun and winner are available in the default module, blawxrun can’t find winner. I wonder if this line from the error message gives a clue: `ERROR: [11] toplevel_call(user:user: ...) at /usr/lib/swipl/boot/toplevel.pl:1318`. I don’t think `user:user` is what we want, there, is it? ---
**Author:** ![jan](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/jan/32/4_2.png) [@jan](https://swi-prolog.discourse.group/u/jan)\ **Post date:** [August 11, 2024, 9:58am UTC](https://swi-prolog.discourse.group/t/module-issue-in-pengines/7676/5 "2024-08-11T09:58:06Z")
The mistake (I think) you are making is that Pengines do not inherit from `user`, but from the “Pengine application” module, `pengine_sandbox` (by default). So, to load sCASP you need to do :- use\_module(pengine\_sandbox:library(scasp)). All the other code you want to be available to Pengines must be loaded into the `pengine_sandbox` module. Typically you do that by implementing a module and load it as above. You can also add stuff to thie module directly using this syntax: ``` pengine_sandbox:mypred(...) :- ... ``` As for using the hooks, you use ``` :- multifile pengines:not_sandboxed/2. not_sandboxed(_,_). ``` and something similar for the authentication hook. But again, s(CASP) does not need to lift the sandbox AFAIK and for security reasons you better do not 🙂 ---
**Author:** ![Gauntlet173](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/gauntlet173/32/3778_2.png) [@Gauntlet173](https://swi-prolog.discourse.group/u/Gauntlet173)\ **Post date:** [August 12, 2024, 4:37am UTC](https://swi-prolog.discourse.group/t/module-issue-in-pengines/7676/6 "2024-08-12T04:37:26Z")
That’s extremely helpful, @jan, thank you. I’ll give it another shot later tonight, but that makes a lot of sense. ---
**Author:** ![Gauntlet173](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/gauntlet173/32/3778_2.png) [@Gauntlet173](https://swi-prolog.discourse.group/u/Gauntlet173)\ **Post date:** [August 12, 2024, 6:57am UTC](https://swi-prolog.discourse.group/t/module-issue-in-pengines/7676/7 "2024-08-12T06:57:10Z")
With your help I was able to confirm that it’s not a sandboxing issue, it’s a module problem. But following the instructions you gave, I still have the same module issue. I’m loading the following file: ```prolog % scasp_server.pl :- use_module(library(http/http_server)). :- use_module(library(pengines)). :- use_module(library(sandbox)). :- use_module(pengine_sandbox:blawx). server(Port) :- http_server([port(Port)]). ``` And blawx.pl is defined as follows: ```prolog :- module(blawx,[blawxrun/4]). :- use_module(library(scasp)). :- use_module(library(scasp/human)). :- use_module(library(scasp/output)). :- use_module(aggregates). :- use_module(dates). :- use_module(events). :- use_module(ldap). :- use_module(passthrough). blawxrun(Query, Tree, Model, Attributes) :- scasp(Query, [tree(Tree), model(Model), source(false)]), ovar_analyze_term(t(Query, Tree, Model), [name_constraints(true), name_prefix('Var_')]), ( term_attvars(t(Query, Tree, Model), []) -> Attributes = [] ; copy_term(t(Query, Tree, Model), _, Attributes) ). ``` Running the commands described above, I’m still getting the same error message, except that it is looking for winner/2 inside `blawx` instead of inside `user`. If I eliminate everything in blawxrun/4 except for the scasp line, I’m still getting the same error message. ---
**Author:** ![jan](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/jan/32/4_2.png) [@jan](https://swi-prolog.discourse.group/u/jan)\ **Post date:** [August 12, 2024, 7:20am UTC](https://swi-prolog.discourse.group/t/module-issue-in-pengines/7676/8 "2024-08-12T07:20:58Z")
You’re moving in the right direction. However, your scasp program will be loaded into the `pengine_sandbox` module, while you try to run everything from blawx. So, you must at least load scasp in the pengine\_sandbox module. Next, you can make the scasp call from blawx to the pengine\_sandbox module or, probably simpler, load all code into the penfgine\_sandbox module. Simplest way to get there is probably to remove the module header from blawx and use ``` :- ensure_loaded(pengine_sandbox:blawx). ``` If that doesn’t work, I’ll give it a try … Note that the scasp package also contains an HTTP server that works without Pengines. That is a way simpler way to use scasp over HTTP. ---
**Author:** ![Gauntlet173](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/gauntlet173/32/3778_2.png) [@Gauntlet173](https://swi-prolog.discourse.group/u/Gauntlet173)\ **Post date:** [August 13, 2024, 1:02am UTC](https://swi-prolog.discourse.group/t/module-issue-in-pengines/7676/9 "2024-08-13T01:02:13Z")
> [@jan](#): > > So, you must at least load scasp in the pengine\_sandbox module. Next, you can make the scasp call from blawx to the pengine\_sandbox module or, probably simpler, load all code into the penfgine\_sandbox module. > > Simplest way to get there is probably to remove the module header from blawx and use > > ```prolog > :- ensure_loaded(pengine_sandbox:blawx). > > ``` I’m sorry, I don’t know if you’re saying that I need to do `:- ensure_loaded(pengine_sandbox:blawx).` in the main scasp\_server.pl file, and remove the `module` entry from blawx.pl, or if you are saying I need to do those two things AND add `pengine_sandbox:` before the scasp `use_module` command in blawx.pl? But I have tried both, and I have tried adding `pengine_sandbox:` in front of everything loaded inside blawx.pl. Nothing changes the result, it just changes the module in which it complains it cannot find winner/2. Now pengine\_sandbox:winner/2 doesn’t exist. I am very much in the dark, despite my best efforts. It doesn’t make any sense to me that calling a query inside the blawxrun predicate in the blawx module is “running it from blawx”, but that doing a use\_module in the same file is somehow going to result in it being loaded into pengine\_sandbox. I’m happy to try something simpler if it’s actually simpler, but none of this makes any sense to me, and so if this is close to working, I’d rather not change bucking horses mid tsunami. If you could give this a quick try and let me know what you had to do to make the third query work, that would be GREATLY appreciated. ---
**Author:** ![jan](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/jan/32/4_2.png) [@jan](https://swi-prolog.discourse.group/u/jan)\ **Post date:** [August 13, 2024, 7:08am UTC](https://swi-prolog.discourse.group/t/module-issue-in-pengines/7676/10 "2024-08-13T07:08:58Z")
Can you make the whole thing (i.e., enough to reproduce) available, including something (e.g., a curl request) to test it? I think it is minor to fix it, but I don’t like reproducing the whole setup from this discussion. ---
**Author:** ![Gauntlet173](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/gauntlet173/32/3778_2.png) [@Gauntlet173](https://swi-prolog.discourse.group/u/Gauntlet173)\ **Post date:** [August 13, 2024, 1:18pm UTC](https://swi-prolog.discourse.group/t/module-issue-in-pengines/7676/11 "2024-08-13T13:18:56Z")
Of course. I’ll get back to you. ---
**Author:** ![Gauntlet173](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/gauntlet173/32/3778_2.png) [@Gauntlet173](https://swi-prolog.discourse.group/u/Gauntlet173)\ **Post date:** [August 18, 2024, 3:03am UTC](https://swi-prolog.discourse.group/t/module-issue-in-pengines/7676/12 "2024-08-18T03:03:12Z")
> [@Gauntlet173](#): > > `?- pengine_rpc('http://localhost:8080', blawxrun(winner(X,Y),A,B,C),[src_text("winner(test,jason).")]).` WIth my thanks for your patience, here’s a little github repo with as clean an example as I can generate. > **[GitHub - Gauntlet173/swipl\_pengine\_example](https://github.com/Gauntlet173/swipl_pengine_example)** > > Contribute to Gauntlet173/swipl\_pengine\_example development by creating an account on GitHub. . ---
**Author:** ![jan](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/jan/32/4_2.png) [@jan](https://swi-prolog.discourse.group/u/jan)\ **Post date:** [August 18, 2024, 8:40am UTC](https://swi-prolog.discourse.group/t/module-issue-in-pengines/7676/13 "2024-08-18T08:40:50Z")
Seems all that is needed is ``` :- meta_predicate blawxrun(0, -, -, -). ``` above the definition of the predicate. After all, this _is_ a meta predicate. Thanks for the clear reproducible case. That makes helping people a lot easier 🙂 ---
**Author:** ![Gauntlet173](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/gauntlet173/32/3778_2.png) [@Gauntlet173](https://swi-prolog.discourse.group/u/Gauntlet173)\ **Post date:** [August 18, 2024, 1:41pm UTC](https://swi-prolog.discourse.group/t/module-issue-in-pengines/7676/14 "2024-08-18T13:41:14Z")
> [@jan](#): > > `blawxrun` Thank you. Could you give me some intuition as to why it is required, and what it is doing? In the hopes I might avoid or at least recognized similar problems in future? ---
**Author:** ![jan](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/jan/32/4_2.png) [@jan](https://swi-prolog.discourse.group/u/jan)\ **Post date:** [August 18, 2024, 3:19pm UTC](https://swi-prolog.discourse.group/t/module-issue-in-pengines/7676/15 "2024-08-18T15:19:55Z")
> [@Gauntlet173](#): > > Could you give me some intuition as to why it is required, and what it is doing? Roughly, in good old plain Prolog, a term f(…) refers to the predicate (procedure) f/n. Given a module system, each module potentially defines its own f/n, denoted m:f/n. Now, if we pass winner(X,Y) to a predicate that must find a predicate from this term, such as sCASP, it needs to know into which module it must resolve winner/2. The meta\_predicate/1 declaration tells the system which arguments must be annotated with the current module. These are the arguments annotated as 0…9, `:` or `//`. They all do the same: you pass winner(X,Y) and the called predicate is passed pengine\_sandbox:winner(X,Y). The difference only affects the cross-referencing tools: 0 means it is a simple call. 1…9 means 1…9 arguments will be added before it is translated into a call. `:` means the target wants to know the module, but it will not call the result. Finally, `//` means the argument is a DCG goal (this is a SWI-Prolog extension). ---
**Author:** ![Gauntlet173](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/gauntlet173/32/3778_2.png) [@Gauntlet173](https://swi-prolog.discourse.group/u/Gauntlet173)\ **Post date:** [August 18, 2024, 4:05pm UTC](https://swi-prolog.discourse.group/t/module-issue-in-pengines/7676/16 "2024-08-18T16:05:55Z")
Gotcha, thanks!