| Andrew Cooke | Contents | Latest | RSS | Twitter | Previous | Next

C[omp]ute

Welcome to my blog, which was once a mailing list of the same name and is still generated by mail. Please reply via the "comment" links.

Always interested in offers/projects/new ideas. Eclectic experience in fields like: numerical computing; Python web; Java enterprise; functional languages; GPGPU; SQL databases; etc. Based in Santiago, Chile; telecommute worldwide. CV; email.

Personal Projects

Lepl parser for Python.

Colorless Green.

Photography around Santiago.

SVG experiment.

Professional Portfolio

Calibration of seismometers.

Data access via web services.

Cache rewrite.

Extending OpenSSH.

C-ORM: docs, API.

Last 100 entries

Enrique Ferrari - Argentine Author; Transcript of German Scientists on Learning of Hiroshima; Calvert Journal; Telephone System Quotes for Cat Soft LLC; Owen Jones on Twitter; Telephone System Quotes for Cat Soft LLC; Possible Japanese Authors; Complex American Literature; Chutney v5; Weird Componentized Virus; Interesting Argentinian Author - Antonio Di Benedetto; Useful Thread on MetaPhysics; RAND on fighting online anarchy (2001); Now Is Cat Soft LLC's Chance To Save Up To 32% On Mail; NSA Hacked; Call Center Services for Cat Soft LLC; Very Good LRB Article on Brexit; Nussbaum on Anger; Credit Card Processing for Cat Soft LLC; Discover new movies on demand in our online cinema; Tasting; Credit Card Processing for Cat Soft LLC; Apple + Kiwi Jam; Hit Me; Increase Efficiency with GPS Vehicle Tracking for Cat Soft LLC; Sudoku - CSP + Chaos; Recycling Electronics In Santiago; Vector Displays in OpenGL; Call Center Services for Cat Soft LLC; And Anti-Aliased; OpenGL - Render via Intermediate Texture; And Garmin Connect; Using Garmin Forerunner 230 With Linux; Payroll Service Quotes for Cat Soft LLC; (Beating Dead Horse) StackOverflow; Current State of Justice in China; Now Is Cat Soft LLC's Chance To Save Up To 32% On Mail; Axiom of Determinacy; Ewww; Fee Chaos Book; Course on Differential Geometry; Increase Efficiency with GPS Vehicle Tracking for Cat Soft LLC; Okay, but...; Sparse Matrices, Deep Learning; Sounds Bad; Applebaum Rape; Tomato Chutney v4; Have to add...; Culturally Liberal and Nothing More; Weird Finite / Infinite Result; Your diamond is a beaten up mess; Maths Books; Good Bike Route from Providencia / Las Condes to Panul\; Iain Pears (Author of Complex Plots); Plum Jam; Excellent; More Recently; For a moment I forgot StackOverflow sucked; A Few Weeks On...; Chilean Book Recommendations; How To Write Shared Libraries; Jenny Erpenbeck (Author); Dijkstra, Coins, Tables; Python libraries error on OpenSuse; Deserving Trump; And Smugness; McCloskey Economics Trilogy; cmocka - Mocks for C; Concept Creep (Americans); Futhark - OpenCL Language; Moved / Gone; Fan and USB issues; Burgers in Santiago; The Origin of Icosahedral Symmetry in Viruses; autoenum on PyPI; Jars Explains; Tomato Chutney v3; REST; US Elections and Gender: 24 Point Swing; PPPoE on OpenSuse Leap 42.1; SuperMicro X10SDV-TLN4F/F with Opensuse Leap 42.1; Big Data AI Could Be Very Bad Indeed....; Cornering; Postcapitalism (Paul Mason); Black Science Fiction; Git is not a CDN; Mining of Massive Data Sets; Rachel Kaadzi Ghansah; How great republics meet their end; Raspberry, Strawberry and Banana Jam; Interesting Dead Areas of Math; Later Taste; For Sale; Death By Bean; It's Good!; Tomato Chutney v2; Time ATAC MX 2 Pedals - First Impressions; Online Chilean Crafts; Intellectual Variety; Taste + Texture; Time Invariance and Gauge Symmetry

© 2006-2015 Andrew Cooke (site) / post authors (content).

libxml2: Creating XML and Validating with Schema

From: andrew cooke <andrew@...>

Date: Thu, 14 Jul 2011 16:57:48 -0400

I need to create a document for a horribly complicated schema in XML, from C,
using libxml2.  Since the document has a schema I am bootstrapping myself by
creating an empty document, testing it, and then adding elements etc as needed
until it validates.  At that point, hopefully, I will (1) have a good starting
point and (2) understand libxml2 much more than I do right now.

But anyway, just to get there has taken fair amount of effort, so here's the
code, in case it will help anyone else (some parts removed to protect the
innocent - mainly logging).  Also, logging and handling of failures is
incomplete.

Andrew

PS This is on CentOS 5.4, although I had to install libxml from
https://github.com/projecthydra/libxml2 to handle my particular schema.


#include <stdio.h>

// do not simply append libxml2 here - it will not work
// see http://bugs.centos.org/view.php?id=1340 for solution
#include <libxml/parser.h>
#include <libxml/xmlschemas.h>

// elided imports

// first, two callbacks that display errors - you could probably use
// fprintf instead.

static void xmlSchemaValidityErrorFunc_impl(void __attribute__((unused)) *ctx,
const char *msg, ...) {
    static char buffer[5000];
    va_list argp;
    va_start(argp, msg);
    vsprintf(buffer, msg, argp);
    va_end(argp);
    // elided logging of errors
}


static void xmlSchemaValidityWarningFunc_impl(void __attribute__((unused))
*ctx, const char *msg, ...) {
    static char buffer[5000];
    va_list argp;
    va_start(argp, msg);
    vsprintf(buffer, msg, argp);
    va_end(argp);
    // elided logging of warnings
}


/**
 * See http://wiki.njh.eu/XML-Schema_validation_with_libxml2
 */
static int validate(xmlDocPtr doc, const char *schema_path) {

    int status = ...;
    const char *schema_path;
    xmlDocPtr schema_doc = NULL;
    xmlSchemaParserCtxtPtr parser_ctxt = NULL;
    xmlSchemaPtr schema = NULL;
    xmlSchemaValidCtxtPtr valid_ctxt = NULL;

    if (! (schema_doc = xmlReadFile(schema_path, NULL, XML_PARSE_NONET))) {
       status = ...;
       goto exit;
    }

    if (! (parser_ctxt = xmlSchemaNewDocParserCtxt(schema_doc))) {
       status = ...;
       goto exit;
    }

    if (! (schema = xmlSchemaParse(parser_ctxt))) {
       status = ...;
       goto exit;
    }

    if (! (valid_ctxt = xmlSchemaNewValidCtxt(schema))) {
       status = ...;
       goto exit;
    }

    xmlSchemaSetValidErrors(valid_ctxt, &xmlSchemaValidityErrorFunc_impl,
       &xmlSchemaValidityWarningFunc_impl, NULL);

    if (xmlSchemaValidateDoc(valid_ctxt, doc)) {
       ssi_chan_log("error", "Document is invalid");
       status = ...;
       goto exit;
    }

exit:
    if (valid_ctxt) xmlSchemaFreeValidCtxt(valid_ctxt);
    if (schema) xmlSchemaFree(schema);
    if (parser_ctxt) xmlSchemaFreeParserCtxt(parser_ctxt);
    if (schema_doc) xmlFreeDoc(schema_doc);

    return status;
}


int new_document(const char* path, configuration *conf) {

    int status = ..;
    xmlDocPtr doc = NULL;
    xmlNodePtr root_node = NULL;
    xmlNsPtr ns = NULL;

    char *namespace = "http://...";

    LIBXML_TEST_VERSION; // checks link against compilation

    // probably need more tests/error handling here
    doc = xmlNewDoc(BAD_CAST "1.0"); // XML version
    ns = xmlNewNs(NULL, BAD_CAST namespace, BAD_CAST "foo");
    root_node = xmlNewNode(ns, BAD_CAST "MyRoot");
    xmlDocSetRootElement(doc, root_node);

    if ((status = validate(doc, conf->schema_path))) goto exit;

    if (-1 == xmlSaveFormatFileEnc(path, doc, "UTF-8", 1)) {
        status = ...;
        goto exit;
    }

exit:
    if (ns) xmlFreeNs(ns);
    if (doc) xmlFreeDoc(doc);
    xmlCleanupParser();
    xmlMemoryDump();

    return status;
}

Comment on this post