Re: [xml] userdata for SAX parsing with schema validation

[Nick Wellnhofer <wellnhofer aevum de>]

On 23/12/2021 20:14, Lara Blatchford wrote:
> Hi - I have a simple SAX handler set up, and schema validation errors are 
> being caught by my structured error handler.  So far so good.
>
> It appears that the userdata argument to xmlSAXUserParseMemory /must/ be the 
> xmlSchemaSAXPlugPtr returned by the call to xmlSchemaSAXPlug, and that this 
> pointer is passed as the ctx pointer to the SAX handler callbacks.

This is correct.

> Is there any way for me to make a userdata pointer of my choosing available to 
> my SAX handler callbacks while still getting schema validation?

From a quick look at the code, it seems that you can simply pass your user 
data pointer to xmlSchemaSAXPlug.

>     // userdata arg is set to the pointer to the original SAX user data pointer
>
>     xmlSchemaValidCtxtPtr oldXsdValidCtxt = NULL;;
>
>     void *ctxptr = &oldXsdValidCtxt;
>
>     xmlSchemaSAXPlugPtr saxPlug = xmlSchemaSAXPlug(xsdValidCtxt, 
> &schemaValHandler, &ctxptr );

You should pass your user data pointer here instead of a NULL 
xmlSchemaValidCtxtPtr:

    void *user_data = my_user_data;
    xmlSchemaSAXPlugPtr saxPlug = xmlSchemaSAXPlug(xsdValidCtxt,
        &schemaValHandler, &user_data);

xmlSchemaSAXPlug will then swap the user data pointer with its own one which 
you have to use when calling xmlSAXUserParseMemory. The SAX callbacks, 
however, should receive the original pointer.

Nick