Python binding for xmlRegisterInputCallback

It is possible to make xmlIO handle any protocol by means of
xmlRegisterInputCallback(). However, that function is currently only
available in C API. So, the natural solution seems to be implementing Python
bindings for the xmlRegisterInputCallback.

* python/generator.py: skip xmlPopInputCallbacks
* python/libxml.c python/libxml.py python/libxml_wrap.h: implement the
  wrappers
* python/tests/input_callback.py python/tests/Makefile.am: also add a test case

python/tests/input_callback.py

@@ -0,0 +1,128 @@
+#!/usr/bin/python -u
+#
+# This tests custom input callbacks
+#
+import sys
+import StringIO
+import libxml2
+
+# We implement a new scheme, py://strings/ that will reference this dictionary
+pystrings = {
+    'catalogs/catalog.xml' :
+'''<?xml version="1.0" encoding="utf-8"?>
+<!DOCTYPE catalog PUBLIC "-//OASIS//DTD Entity Resolution XML Catalog V1.0//EN" "http://www.oasis-open.org/committees/entity/release/1.0/catalog.dtd">
+<catalog xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog">
+  <rewriteSystem systemIdStartString="http://example.com/dtds/" rewritePrefix="../dtds/"/>
+</catalog>''',
+
+    'xml/sample.xml' :
+'''<?xml version="1.0" encoding="utf-8"?>
+<!DOCTYPE root SYSTEM "http://example.com/dtds/sample.dtd">
+<root>&sample.entity;</root>''',
+
+    'dtds/sample.dtd' :
+'''
+<!ELEMENT root (#PCDATA)>
+<!ENTITY sample.entity "replacement text">'''
+}
+
+def verify_doc(doc):
+    e = doc.getRootElement()
+    if e.name != 'root':
+        raise ValueError("name")
+    if e.content != 'replacement text':
+        raise ValueError("content")
+
+prefix = "py://strings/"
+def my_input_cb(URI):
+    idx = URI.startswith(prefix)
+    if idx == -1:
+        return None
+    path = URI[len(prefix):]
+    if path not in pystrings:
+        print "my_input_cb: path does not exist, '%s'" % path
+        return None
+    print "my_input_cb: loading '%s'" % URI
+    return StringIO.StringIO(pystrings[path])
+
+opts = libxml2.XML_PARSE_DTDLOAD | libxml2.XML_PARSE_NONET | libxml2.XML_PARSE_COMPACT
+startURL = prefix + "xml/sample.xml"
+catURL = prefix + "catalogs/catalog.xml"
+
+# Check that we cannot read custom schema without custom callback
+print
+print "Test 1: Expecting failure to load (custom scheme not handled)"
+try:
+    doc = libxml2.readFile(startURL, None, opts)
+    print "Read custom scheme without registering handler succeeded?"
+    sys.exit(1)
+except libxml2.treeError, e:
+    pass
+
+# Register handler and try to load the same entity
+print
+print "Test 2: Expecting failure to load (no catalog - cannot load DTD)"
+libxml2.registerInputCallback(my_input_cb)
+doc = libxml2.readFile(startURL, None, opts)
+try:
+    verify_doc(doc)
+    print "Doc was loaded?"
+except ValueError, e:
+    if str(e) != "content":
+        print "Doc verify failed"
+doc.freeDoc()
+
+# Register a catalog (also accessible via pystr://) and retry
+print
+print "Test 3: Expecting successful loading"
+parser = libxml2.createURLParserCtxt(startURL, opts)
+parser.addLocalCatalog(catURL)
+parser.parseDocument()
+doc = parser.doc()
+verify_doc(doc)
+doc.freeDoc()
+
+# Unregister custom callback when parser is already created
+print
+print "Test 4: Expect failure to read (custom callback unregistered during read)"
+parser = libxml2.createURLParserCtxt(startURL, opts)
+libxml2.popInputCallbacks()
+parser.addLocalCatalog(catURL)
+parser.parseDocument()
+doc = parser.doc()
+try:
+    verify_doc(doc)
+    print "Doc was loaded?"
+except ValueError, e:
+    if str(e) != "content":
+        print "Doc verify failed"
+doc.freeDoc()
+
+# Try to load the document again
+print
+print "Test 5: Expect failure to load (callback unregistered)"
+try:
+    doc = libxml2.readFile(startURL, None, opts)
+    print "Read custom scheme without registering handler succeeded?"
+    sys.exit(1)
+except libxml2.treeError, e:
+    pass
+
+# But should be able to read standard I/O yet...
+print
+print "Test 6: Expect successful loading using standard I/O"
+doc = libxml2.readFile("tst.xml", None, opts)
+doc.freeDoc()
+
+# Now pop ALL input callbacks, should fail to load even standard I/O
+print
+print "Test 7: Remove all input callbacks, expect failure to load using standard I/O"
+try:
+    while True:
+        libxml2.popInputCallbacks()
+except IndexError, e:
+    print "Popped all input callbacks: " + str(e)
+try:
+    doc = libxml2.readFile("tst.xml", None, opts)
+except libxml2.treeError, e:
+    pass