writer: Implement xmlTextWriterClose

This function can be used to make sure that closing the output stream
succeeded.

Fixes #513.

testparser.c

@@ -6,6 +6,7 @@
 
 #include <libxml/parser.h>
 #include <libxml/xmlreader.h>
+#include <libxml/xmlwriter.h>
 
 #include <string.h>
 
@@ -203,6 +204,49 @@ testReaderXIncludeError(void) {
 }
 #endif
 
+#ifdef LIBXML_WRITER_ENABLED
+static int
+testWriterIOWrite(void *ctxt, const char *data, int len) {
+    (void) ctxt;
+    (void) data;
+
+    return len;
+}
+
+static int
+testWriterIOClose(void *ctxt) {
+    (void) ctxt;
+
+    return XML_IO_ENAMETOOLONG;
+}
+
+static int
+testWriterClose(void){
+    xmlOutputBufferPtr out;
+    xmlTextWriterPtr writer;
+    int err = 0;
+    int result;
+
+    out = xmlOutputBufferCreateIO(testWriterIOWrite, testWriterIOClose,
+                                  NULL, NULL);
+    writer = xmlNewTextWriter(out);
+    xmlTextWriterStartDocument(writer, "1.0", "UTF-8", NULL);
+    xmlTextWriterStartElement(writer, BAD_CAST "elem");
+    xmlTextWriterEndElement(writer);
+    xmlTextWriterEndDocument(writer);
+    result = xmlTextWriterClose(writer);
+
+    if (result != XML_IO_ENAMETOOLONG) {
+        fprintf(stderr, "xmlTextWriterClose reported wrong error %d\n",
+                result);
+        err = 1;
+    }
+
+    xmlFreeTextWriter(writer);
+    return err;
+}
+#endif
+
 int
 main(void) {
     int err = 0;
@@ -218,6 +262,9 @@ main(void) {
 #if defined(LIBXML_READER_ENABLED) && defined(LIBXML_XINCLUDE_ENABLED)
     err |= testReaderXIncludeError();
 #endif
+#ifdef LIBXML_WRITER_ENABLED
+    err |= testWriterClose();
+#endif
 
     return err;
 }