[Media Router] Parse device description xml in utility process

chrome/utility/media_router/dial_device_description_parser.cc

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "chrome/utility/media_router/dial_device_description_parser.h"
+
+#include <libxml/parser.h>
+#include <libxml/tree.h>
+#include <libxml/xpath.h>
+#include <libxslt/transform.h>
+#include <libxslt/xslt.h>
+#include <libxslt/xsltutils.h>
+
+#include "base/strings/string_util.h"
+#include "third_party/libxml/chromium/libxml_utils.h"
+
+namespace {
+
+constexpr char xslt_text[] =
+    "<?xml version=\"1.0\" encoding=\"utf-8\"?>"
+    "<xsl:stylesheet version=\"1.0\" "
+    "xmlns:t=\"urn:schemas-upnp-org:device-1-0\" "
+    "xmlns:xsl=\"http://www.w3.org/1999/XSL/Transform\">"
+    "<xsl:template match=\"node()|@*\">"
+    "<xsl:copy>"
+    "<xsl:apply-templates select=\"node()|@*\"/>"
+    "</xsl:copy>"
+    "</xsl:template>"
+    "<xsl:template match=\"t:root/t:device/t:UDN/text()\">***</xsl:template>"
+    "<xsl:template "
+    "match=\"t:root/t:device/t:serialNumber/text()\">***</xsl:template>"
+    "</xsl:stylesheet>";
+
+static std::string Validate(
+    const media_router::DialDeviceDescription& description) {
+  if (description.unique_id.empty()) {
+    return "Missing uniqueId";
+  }
+  if (description.friendly_name.empty()) {
+    return "Missing friendlyName";
+  }
+  return "";
+}
+
+}  // namespace
+
+namespace media_router {
+
+DialDeviceDescriptionParser::DialDeviceDescriptionParser() = default;
+DialDeviceDescriptionParser::~DialDeviceDescriptionParser() = default;
+
+bool DialDeviceDescriptionParser::Parse(const std::string& xml) {
+  device_description_ = DialDeviceDescription();
+
+  XmlReader xml_reader;
+  if (!xml_reader.Load(xml))
+    return false;
+
+  while (xml_reader.Read()) {
+    xml_reader.SkipToElement();
+    std::string node_name(xml_reader.NodeName());
+
+    if (node_name == "UDN") {
+      if (!xml_reader.ReadElementContent(&device_description_.unique_id))
+        return false;
+    } else if (node_name == "friendlyName") {
+      if (!xml_reader.ReadElementContent(&device_description_.friendly_name))
+        return false;
+    } else if (node_name == "modelName") {
+      if (!xml_reader.ReadElementContent(&device_description_.model_name))
+        return false;
+    } else if (node_name == "deviceType") {
+      if (!xml_reader.ReadElementContent(&device_description_.device_type))
+        return false;
+    }
+  }
+
+  // If friendly name does not exist, fall back to use model name + last 4
+  // digits of UUID as friendly name.
+  if (device_description_.friendly_name.empty()) {
+    auto model_name = device_description_.model_name;
+    auto unique_id = device_description_.unique_id;
+
+    if (!model_name.empty() && unique_id.length() >= 4) {
+      device_description_.friendly_name =
+          model_name + "[" + unique_id.substr(unique_id.length() - 4) + "]";
+
+      DVLOG(2)
+          << "Fixed device description: created friendlyName from modelName.";

[mark a. foltz, 2017/03/17 19:05:47]

In my opinion, it will be pretty clear from the friendly name that this is what
happened.  Consider removing this log statement.

[zhaobin, 2017/03/18 00:17:39]

Done.

+    }
+  }
+
+  std::string error = Validate(device_description_);
+  if (!error.empty()) {
+    DLOG(WARNING) << "Device description failed to validate: " << error;
+    return false;
+  }
+
+  return true;
+}
+
+std::string DialDeviceDescriptionParser::ScrubXmlForLogging(
+    const std::string& xml) {
+  xmlDocPtr doc = xmlParseMemory(xml.c_str(), xml.size());
+
+  if (doc == NULL) {

[mark a. foltz, 2017/03/17 19:05:47]

s/NULL/nullptr/ assuming doc is a pointer type.

[zhaobin, 2017/03/18 00:17:39]

Done.

+    LOG(WARNING) << "Document not parsed successfully";
+    return "";
+  }
+
+  xmlDocPtr xslt_doc = xmlParseMemory(xslt_text, sizeof(xslt_text));
+  DCHECK(xslt_doc);

[mark a. foltz, 2017/03/17 19:05:47]

Assuming xmlDocPtr is a pointer type, it would be safer to CHECK here to avoid a
null deref later (although xslt_text is under our control).

https://chromium.googlesource.com/chromium/src/+/master/styleguide/c++/c++.md

[zhaobin, 2017/03/18 00:17:39]

Done.

+
+  xsltStylesheetPtr style_ptr = xsltParseStylesheetDoc(xslt_doc);
+  xmlDocPtr res = xsltApplyStylesheet(style_ptr, doc, NULL);
+
+  xmlChar* output;
+  int size;
+  xsltSaveResultToString(&output, &size, res, style_ptr);

[mark a. foltz, 2017/03/17 19:05:47]

I assume this allocates output to be sufficiently sized for the result?

[zhaobin, 2017/03/18 00:17:39]

Seems so. output is allocated inside xsltSaveResultToString().

+
+  std::string logging_xml = std::string(reinterpret_cast<char*>(output));

[mark a. foltz, 2017/03/17 19:05:47]

I'm not an expert in XML APIs to know how safe this is.  Is output guaranteed to
be valid UTF-8 and null-terminated?

[zhaobin, 2017/03/18 00:17:39]

xmlChar is unsigned char, and seems that output is not necessary
null-terminated, so reinterpret_cast is not safe...

+
+  xmlFreeDoc(xslt_doc);
+  xmlFreeDoc(doc);
+
+  xsltCleanupGlobals();
+  xmlCleanupParser();

[mark a. foltz, 2017/03/17 19:05:47]

Who frees output?

[zhaobin, 2017/03/18 00:17:39]

Done.

+
+  return logging_xml;
+}
+
+}  // namespace media_router