Fix a regression in xmlGetDocCompressMode()

The switch to xzlib had for consequence that the compression
level of the input was not gathered anymore in ctxt->input->buf,
then the parser compression flags was left to -1 and propagated
to the resulting document.
Fix the I/O layer to get compression detection in xzlib,
then carry it in the input buffer and the resulting document

  This should fix
    https://lsbbugs.linuxfoundation.org/show_bug.cgi?id=3456

parser.c

@@ -10681,6 +10681,10 @@ xmlParseDocument(xmlParserCtxtPtr ctxt) {
         ctxt->sax->startDocument(ctxt->userData);
     if (ctxt->instate == XML_PARSER_EOF)
 	return(-1);
+    if ((ctxt->myDoc != NULL) && (ctxt->input != NULL) &&
+        (ctxt->input->buf != NULL) && (ctxt->input->buf->compressed >= 0)) {
+	ctxt->myDoc->compression = ctxt->input->buf->compressed;
+    }
 
     /*
      * The Misc part of the Prolog

xmlIO.c

@@ -2668,6 +2668,12 @@ __xmlParserInputBufferCreateFilename(const char *URI, xmlCharEncoding enc) {
 	    }
 #endif
 	}
+#endif
+#ifdef HAVE_LZMA_H
+	if ((xmlInputCallbackTable[i].opencallback == xmlXzfileOpen) &&
+		(strcmp(URI, "-") != 0)) {
+            ret->compressed = __libxml2_xzcompressed(context);
+	}
 #endif
     }
     else
@@ -3325,6 +3331,17 @@ xmlParserInputBufferGrow(xmlParserInputBufferPtr in, int len) {
     if (res < 0) {
 	return(-1);
     }
+
+    /*
+     * try to establish compressed status of input if not done already
+     */
+    if (in->compressed == -1) {
+#ifdef HAVE_LZMA_H
+	if (in->readcallback == xmlXzfileRead)
+            in->compressed = __libxml2_xzcompressed(in->context);
+#endif
+    }
+
     len = res;
     if (in->encoder != NULL) {
         unsigned int use;

xzlib.c

@@ -182,12 +182,37 @@ xz_open(const char *path, int fd, const char *mode ATTRIBUTE_UNUSED)
     return (xzFile) state;
 }
 
+static int
+xz_compressed(xzFile f) {
+    xz_statep state;
+
+    if (f == NULL)
+        return(-1);
+    state = (xz_statep) f;
+    if (state->init <= 0)
+        return(-1);
+
+    switch (state->how) {
+        case COPY:
+	    return(0);
+	case GZIP:
+	case LZMA:
+	    return(1);
+    }
+    return(-1);
+}
+
 xzFile
 __libxml2_xzopen(const char *path, const char *mode)
 {
     return xz_open(path, -1, mode);
 }
 
+int
+__libxml2_xzcompressed(xzFile f) {
+    return xz_compressed(f);
+}
+
 xzFile
 __libxml2_xzdopen(int fd, const char *mode)
 {

xzlib.h

@@ -15,4 +15,5 @@ xzFile __libxml2_xzopen(const char *path, const char *mode);
 xzFile __libxml2_xzdopen(int fd, const char *mode);
 int __libxml2_xzread(xzFile file, void *buf, unsigned len);
 int __libxml2_xzclose(xzFile file);
+int __libxml2_xzcompressed(xzFile f);
 #endif /* LIBXML2_XZLIB_H */