Add additional xsd schemas with libXml2 - libxml2

Question

I have a xml and schema which I want to validate. I don't want schema to be stored in file, but in database location. I use xmlSchemaNewMemParserCtxt to parse the schema. The problem is that this schema references another schema for basic types: <xs:include schemaLocation="CommonTypes.xsd"/>, which libXml2 searches in the current working directory. Is there any way to supply these additional schemas in memory buffer?

Answer 1

xmlRegisterInputCallbacks is what you're probably looking for.
The advantage, they let you construct some kind of a virtual I/O layer. The disadvantage, inputcallbacks are set globally (there is however xmlPopInputCallbacks and xmlCleanupInputCallbacks).
The code below (built upon code from http://knol2share.blogspot.be) demonstrates the use of xmlRegisterInputCallbacks.
All xml and xsd files are loaded from the file system, except when the URI contains "DataTypes.xsd" the schema is fetched from a string. (since schemaLocation is only a hint one could for example prefix schema's
"test.xsd": the main xml schema (please ignore the reference to peacelane.org, namespaces are from a hobby project, just occurred to me now www.peacelane.org might exist, apparently it does...)
<schema xmlns="http://www.w3.org/2001/XMLSchema"
xmlns:tns="http://peacelane.org/ApplianceType/config/45/LIGHTING1/ARC"
xmlns:dt="http://peacelane.org/ApplianceType/config/45/DataTypes"
targetNamespace="http://peacelane.org/ApplianceType/config/45/LIGHTING1/ARC"
elementFormDefault="qualified">
<import namespace="http://peacelane.org/ApplianceType/config/45/DataTypes" schemaLocation="DataTypes.xsd" />
<complexType name="ConfigType">
<sequence>
<element name="housecode" type="dt:char" />
</sequence>
</complexType>
<element name="Config" type="tns:ConfigType"/>
</schema>
"test.xml": a test xml to validate
<?xml version="1.0"?>
<Config xmlns="http://peacelane.org/ApplianceType/config/45/LIGHTING1/ARC">
<housecode>A</housecode>
</Config>
"main.c": the actual code (update the paths for "XMLFileName" and "XSDFileName")
#define LIBXML_SCHEMAS_ENABLED
#include <libxml/xmlschemastypes.h>
#include <stdio.h>
static const char *databaseSchema =
"<?xml version=\"1.0\" encoding=\"UTF-8\"?>"
" <schema elementFormDefault=\"qualified\" xmlns:tns=\"http://peacelane.org/ApplianceType/config/45/DataTypes\" targetNamespace=\"http://peacelane.org/ApplianceType/config/45/DataTypes\" xmlns=\"http://www.w3.org/2001/XMLSchema\">"
" <simpleType name=\"char\">"
" <restriction base=\"string\">"
" <length value=\"1\" />"
" </restriction>"
" </simpleType>"
" </schema>";
//-----------------------------------------------------------------------------
//-- SQL Callbacks (~ simulated db actions)
//-----------------------------------------------------------------------------
static void* sqlOpen(const char * URI) {
return ((void *) databaseSchema );
}
static int sqlClose(void * context) {
return (0);
}
static int sqlRead(void * context, char * buffer, int len) {
const char* result= (const char *) context;
int rlen = strlen(result);
memcpy(buffer, result, rlen);
return rlen +1;
}
static int sqlMatch(const char * URI) {
if ((URI != NULL )&& (strstr(URI, "DataTypes.xsd") != NULL) )return 1;
return 0;
}
//-----------------------------------------------------------------------------
//-- File callbacks
//-----------------------------------------------------------------------------
static void* fileOpen(const char * URI) {
if (URI == NULL )
return (NULL );
FILE* fh = fopen(URI, "rt");
return ((void *) fh);
}
static int fileClose(void * context) {
FILE* fh = (FILE*) context;
if (fh != NULL )
fclose(fh);
return (0);
}
static int fileRead(void * context, char * buffer, int len) {
FILE* fh = (FILE*) context;
fseek(fh, 0L, SEEK_END);
long flen = ftell(fh);
rewind(fh);
if (buffer != NULL )
fread(buffer, flen, 1, fh);
return flen + 1;
}
static int fileMatch(const char * URI) {
if ((URI != NULL ))
if (strstr(URI, "DataTypes.xsd") == NULL ) {
return (1);
}
return (0);
}
//-----------------------------------------------------------------------------
//-- Main
//-----------------------------------------------------------------------------
int main(int argc, char *argv[]) {
xmlDocPtr doc;
xmlSchemaPtr schema = NULL;
xmlSchemaParserCtxtPtr ctxt;
char *XMLFileName =
"/home/dogguts/Projects/libxml2tests/xsdparse/Debug/test.xml";
char *XSDFileName =
"/home/dogguts/Projects/libxml2tests/xsdparse/Debug/test.xsd";
xmlLineNumbersDefault(1);
if (xmlRegisterInputCallbacks(fileMatch, fileOpen, fileRead, fileClose)
< 0) {
fprintf(stderr, "failed to register File handler\n");
exit(1);
}
if (xmlRegisterInputCallbacks(sqlMatch, sqlOpen, sqlRead, sqlClose) < 0) {
fprintf(stderr, "failed to register SQL handler\n");
exit(1);
}
ctxt = xmlSchemaNewParserCtxt(XSDFileName);
xmlSchemaSetParserErrors(ctxt, (xmlSchemaValidityErrorFunc) fprintf,
(xmlSchemaValidityWarningFunc) fprintf, stderr);
schema = xmlSchemaParse(ctxt);
xmlSchemaFreeParserCtxt(ctxt);
xmlSchemaDump(stdout, schema);
doc = xmlReadFile(XMLFileName, NULL, 0);
if (doc == NULL ) {
fprintf(stderr, "Could not parse %s\n", XMLFileName);
} else {
xmlSchemaValidCtxtPtr ctxt;
int ret;
ctxt = xmlSchemaNewValidCtxt(schema);
xmlSchemaSetValidErrors(ctxt, (xmlSchemaValidityErrorFunc) fprintf,
(xmlSchemaValidityWarningFunc) fprintf, stderr);
ret = xmlSchemaValidateDoc(ctxt, doc);
if (ret == 0) {
printf("%s validates\n", XMLFileName);
} else if (ret > 0) {
printf("%s fails to validate\n", XMLFileName);
} else {
printf("%s validation generated an internal error\n", XMLFileName);
}
xmlSchemaFreeValidCtxt(ctxt);
xmlFreeDoc(doc);
}
if (schema != NULL )
xmlSchemaFree(schema);
xmlSchemaCleanupTypes();
xmlCleanupParser();
xmlMemoryDump();
return (0);
}
Notice that, for brevity, the above code doesnt' perform any checks wether (file, memory,...) operations succeeded.

Answer 2

This is a better example how to do it: io1.c
http://www.xmlsoft.org/examples/
It saves a lot of time when you can find what is good way to return value from Read function.