Adding namespaces to XML data trees

[syyyr]

Hello,
I'm using libyang to print data trees for NETCONF edit-config. This is kind of a follow up to CESNET/netopeer2#636
I have this schema with a user-ordered list:

module example-schema {
    prefix aha;
    namespace "http://example.com";

    list players {
        key "name";
        ordered-by user;
        leaf name {
            type string;
        }
    }
}

And I want to move /example-schema:players[name='John'] after /example-schema:players[name='Adam']. According to the YANG 1.1 RFC (https://tools.ietf.org/html/rfc7950), I should insert an attribute yang:insert with the value after, and attribute yang:key with the value [aha:name='Adam']. I use this code to create the tree:

#include <libyang/Libyang.hpp>
#include <libyang/Tree_Data.hpp>
#include <iostream>
int main(int argc, char* argv[])
{
    auto ctx = std::make_shared<libyang::Context>();
    ctx->parse_module_path("./example-schema.yang", LYS_IN_YANG);
    auto node = std::make_shared<libyang::Data_Node>(ctx, "/example-schema:players[name='John']", nullptr, LYD_ANYDATA_CONSTSTRING, LYD_PATH_OPT_EDIT);
    node->find_path("/example-schema:players[name='John']")->data().front()->insert_attr(ctx->get_module("yang", nullptr, 0), "insert", "after");
    node->find_path("/example-schema:players[name='John']")->data().front()->insert_attr(ctx->get_module("yang", nullptr, 0), "key", "[aha:name='Adam']");
    std::cout << node->print_mem(LYD_XML, LYP_FORMAT);
    return 0;
}

This code prints this:

<players xmlns="http://example.com" xmlns:yang="urn:ietf:params:xml:ns:yang:1" yang:insert="after" yang:key="[aha:name='Adam']">
  <name>John</name>
</players>

Looking at the example in https://tools.ietf.org/html/rfc7950#page-93, I can see that the key name inside the yang:key attribute should be prefixed with the prefix of my schema (which is "aha"). But, in the example I see one more namespace defined, which seems to be connected to this prefix somehow. So, maybe the XML I want should look like this?

<players xmlns="http://example.com" xmlns:aha="http://example.com" xmlns:yang="urn:ietf:params:xml:ns:yang:1" yang:insert="after" yang:key="[aha:name='Adam']">
  <name>John</name>
</players>

My question is whether the namespace should be defined (as it is in the RFC example), or if it isn't mandatory. And if it is mandatory, then is it possible to tell libyang to insert it?

Thanks for the answer.

[michalvasko]

Hi,
okay, please try again, the XML print should now work. However, it is quite possible something slightly different may again not work because attributes seem not to be used at all, the code I was changing could not have worked and parts of it could have never be executed. But it still comes down to the fact that types implementation in the current libyang is too naive and it should all work properly in libyang version 2 we are working on.

Regards,
Michal

[syyyr]

Okay I tried it again, and it's working, the namespace thingy gets added. Thank you! The key needs to have the module name specified instead of the prefix ("example-schema" instead of "aha"), but the prefix gets added correctly. I'm not sure if this is intentional, but I like this more - it's less work for me (I don't care about prefixes).

[michalvasko]

Hi,
right, sorry, I have forgotten to mention some additional information. Yes, you need to use module names (JSON format prefixes) because those are used in all the other API functions, it is internally transformed as needed. Also, the prefix are mandatory according to specs although completely redundant, strictly speaking, as list keys always belong to the same module as the list itself.

Regards,
Michal