Add a parser for Link headers

Source/core/loader/LinkHeader.cpp

+// 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.
+
+#include "config.h"
+#include "core/loader/LinkHeader.h"
+
+#include "platform/ParsingUtilities.h"
+
+namespace blink {
+
+// LWSP definition in https://www.ietf.org/rfc/rfc0822.txt
+template <typename CharType>
+static bool isWhitespace(CharType chr)
+{
+    return (chr == ' ') || (chr == '\t');
+}
+
+template < typename CharType>

[Mike West, 2015/01/30 13:55:13]

Nit: No space after '<'.

+bool LinkHeader::init(CharType* headerValue, unsigned len)
+{
+    CharType* position = headerValue;
+    CharType* headerEnd = headerValue + len;
+
+    skipWhile<CharType, isWhitespace<CharType>>(position, headerEnd);
+
+    if (*position != '<')
+        return false;
+
+    skipWhile<CharType, isWhitespace<CharType>>(++position, headerEnd);
+
+    CharType* urlStart = position;
+    skipUntil<CharType, isWhitespace<CharType>>(position, headerEnd, '>');
+    CharType* urlEnd = position;
+    skipUntil<CharType>(position, headerEnd, '>');
+    ++position;
+    m_url = String(urlStart, urlEnd - urlStart);
+
+    while (position < headerEnd) {
+        skipWhile<CharType, isWhitespace<CharType>>(position, headerEnd);
+        if (*position != ';' && position != headerEnd)
+            return false;
+        skipWhile<CharType, isWhitespace<CharType>>(++position, headerEnd);
+        if (position == headerEnd)
+            return true;
+        CharType* paramStart = position;
+        skipUntil<CharType, isWhitespace<CharType>>(position, headerEnd, '=');
+        CharType* paramEnd = position;
+        skipWhile<CharType, isWhitespace<CharType>>(position, headerEnd);
+        if (*position != '=')
+            return false;
+        skipWhile<CharType, isWhitespace<CharType>>(++position, headerEnd);
+
+        CharType* valueStart = position;
+        skipUntil<CharType, isWhitespace<CharType>>(position, headerEnd, ';');
+        CharType* valueEnd = position;
+        skipWhile<CharType, isWhitespace<CharType>>(position, headerEnd);
+        if ((valueEnd == valueStart) || (*position != ';' && position != headerEnd))
+            return false;
+        if (String(paramStart, paramEnd - paramStart) == "rel")
+            m_rel = String(valueStart, valueEnd - valueStart);

[Mike West, 2015/01/30 13:55:13]

Would you mind adding some comments in here regarding the expectations of the
various pointers? This kind of parsing is tricky enough _with_ comments, and
fairly incomprehensible without.

See the comments before `SubresourceIntegrity::parseAlgorithm` and the related
methods for the kind of thing that I find pretty useful.
(Source/core/frame/SubresourceIntegrity.cpp). CSP has similar.

+    }
+
+    return true;
+}
+
+LinkHeader::LinkHeader(const String& header)
+{
+    if (header.isNull()) {
+        m_isValid = false;
+        return;
+    }
+
+    if (header.is8Bit())
+        m_isValid = init(header.characters8(), header.length());
+    else
+        m_isValid = init(header.characters16(), header.length());
+}
+
+}