Introduce 'url::Origin'.

url/origin.h

+// Copyright 2015 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.
+
+#ifndef URL_ORIGIN_H_
+#define URL_ORIGIN_H_
+
+#include <string>
+
+#include "base/strings/string16.h"
+#include "url/scheme_host_port.h"
+#include "url/third_party/mozilla/url_parse.h"
+#include "url/url_canon.h"
+#include "url/url_constants.h"
+#include "url/url_export.h"
+
+class GURL;
+
+namespace url {
+
+// An Origin is a tuple of (scheme, host, port), as described in RFC 6454.
+//
+// TL;DR: If you need to make a security-relevant decision, use 'url::Origin'.
+// If you only need to extract the bits of a URL which are relevant for a
+// network connection, use 'url::SchemeHostPort'.
+//
+// STL;SDR: If you're not working in //url or //net, use 'url::Origin'.

[Ryan Sleevi, 2015/07/17 19:48:18]

:(

This feels like a layering violation to discuss higher-level components and
their usages. I defer to Brett here, but when reviewing comments, I prefer
they're treated like code - that is, observe the same knowledge of "Talk about
what you use and how to use things, but not about how you're _used_". I know
Blink is more... inconsistent... in this respect.

[Mike West, 2015/07/20 08:46:10]

Rephrased. I still think giving advice about how to use things _is_ giving
advice about how the thing is _used_. And that that's good. Perhaps you're happy
with the new sentence?
You mean "Awesomer", right?

+//
+// 'Origin', like 'SchemeHostPort', is composed of a tuple of (scheme, host,
+// port), but contains a number of additional concepts which make it appropriate
+// for use as a security boundary and access control mechanism between contexts.
+//
+// This class ought to be used when code needs to determine if two resources
+// are "same-origin", and when a canonical serialization of an origin is
+// required. Note that some origins are "unique", meaning that they are not
+// same-origin with any other origin (including themselves).
+//
+// There are a few subtleties to note:
+//
+// * Invalid and non-standard GURLs are parsed as unique origins. This includes
+//   non-hierarchical URLs like 'data:text/html,...' and 'javascript:alert(1)'.
+//
+// * GURLs with schemes of 'filesystem' or 'blob' parse the origin out of the
+//   internals of the URL. That is, 'filesystem:https://example.com/temporary/f'
+//   is parsed as ('https', 'example.com', 443).
+//
+// * Unique origins all serialize to the string "null"; this means that the
+//   serializations of two unique origins are identical to each other, though
+//   the origins themselves are not "the same". This means that origins'
+//   serializations must not be relied upon for security checks.
+//
+// * GURLs with a 'file' scheme are tricky. They are parsed as ('file', '', 0),
+//   but their behavior may differ from embedder to embedder.
+//
+// * The host component of an IPv6 address includes brackets, just like the URL
+//   representation.
+//
+// Usage:
+//
+// * Origins are generally constructed from an already-canonicalized GURL:
+//
+//     GURL url("https://example.com/");
+//     url::Origin origin(url);
+//     origin.scheme(); // "https"
+//     origin.host(); // "example.com"
+//     origin.port(); // 443
+//     origin.IsUnique(); // false
+//
+// * To answer the question "Are |this| and |that| "same-origin" with each
+//   other?", use |Origin::IsSameOriginWith|:
+//
+//     if (this.IsSameOriginWith(that)) {
+//       // Amazingness goes here.
+//     }
+class URL_EXPORT Origin {
+ public:
+  // Creates a unique Origin.
+  Origin();
+
+  // Creates an Origin from |url|, as described at
+  // https://url.spec.whatwg.org/#origin, with the following additions:
+  //
+  // 1. If |url| is invalid or non-standard, a unique Origin is constructed.
+  // 2. 'filesystem' URLs behave as 'blob' URLs (that is, the origin is parsed
+  //    out of everything in the URL which follows the scheme).
+  // 3. 'file' URLs all parse as ("file", "", 0).
+  Origin(const GURL& url);
+
+  ~Origin();
+
+  std::string scheme() const { return tuple_.scheme(); }
+  std::string host() const { return tuple_.host(); }

[Ryan Sleevi, 2015/07/17 19:48:18]

Bummer! I was asleep at the wheel on url::SchemeHostPort!

Both it, and this, should preferably be using "const std::string&" as their
return types, rather than making a full copy of the string.

Before you can fix this, you'd have to fix url::SchemeHostPort.

[Mike West, 2015/07/20 08:46:10]

I think you're right. Oops! Will fix in a followup CL:
https://codereview.chromium.org/1229003007

+  uint16 port() const { return tuple_.port(); }
+
+  bool unique() const { return unique_; }
+
+  // An ASCII serialization of the Origin as per Section 6.2 of RFC 6454, with
+  // the addition that all Origins with a 'file' scheme serialize to "file://".
+  std::string Serialize() const;
+
+  // Two Origins are "same-origin" iff their schemes, hosts, and ports are exact
+  // matches; and neither is unique.
+  bool IsSameOriginWith(const Origin& other) const;
+
+  // Allows SchemeHostPort to used as a key in STL (for example, a std::set or
+  // std::map).
+  bool operator<(const Origin& other) const;
+
+ private:
+  url::SchemeHostPort tuple_;
+  bool unique_;
+
+  DISALLOW_COPY_AND_ASSIGN(Origin);
+};
+
+}  // namespace url
+
+#endif  // URL_SCHEME_HOST_PORT_H_