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// Copyright 2016 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 HTMLParserReentryPermit_h
#define HTMLParserReentryPermit_h
#include "base/macros.h"
#include "wtf/PassRefPtr.h"
#include "wtf/RefCounted.h"
namespace blink {
// The HTML spec for parsing controls reentering the parser from
// script with the "parser pause flag" and "script nesting level."
//
// The parser pause flag puts a brake on whether the tokenizer will
// produce more tokens. When the parser is paused, nested invocations
// of the tokenizer unwind.
//
// The script nesting level is incremented and decremented any time
// the parser causes script to run. The script nesting level:
//
// - May prevent document.open from blowing away the document.
//
// - Governs whether a script element becomes the "pending
// parsing-blocking script." The pending parsing-blocking script in
// turn affects whether document.write reenters the parser.
//
// Clearing the parser pause flag is simple: Whenever the script
// nesting level hits zero, the parser pause flag is cleared. However
// setting the parser pause flag is subtle.
//
// Processing a typical script end tag, or running a chain of pending
// parser-blocking scripts after that, does not set the parser pause
// flag. However recursively parsing end script tags, or running
// custom element constructors, does set the parser pause flag.
class HTMLParserReentryPermit final
: public RefCounted<HTMLParserReentryPermit> {
public:
static PassRefPtr<HTMLParserReentryPermit> create();
~HTMLParserReentryPermit() = default;
unsigned scriptNestingLevel() const { return m_scriptNestingLevel; }
bool parserPauseFlag() const { return m_parserPauseFlag; }
void pause() {
CHECK(m_scriptNestingLevel);
m_parserPauseFlag = true;
}
class ScriptNestingLevelIncrementer final {
STACK_ALLOCATED();
public:
explicit ScriptNestingLevelIncrementer(HTMLParserReentryPermit* permit)
: m_permit(permit) {
m_permit->m_scriptNestingLevel++;
}
ScriptNestingLevelIncrementer(ScriptNestingLevelIncrementer&&) = default;
~ScriptNestingLevelIncrementer() {
m_permit->m_scriptNestingLevel--;
if (!m_permit->m_scriptNestingLevel)
m_permit->m_parserPauseFlag = false;
}
private:
HTMLParserReentryPermit* m_permit;
DISALLOW_COPY_AND_ASSIGN(ScriptNestingLevelIncrementer);
};
ScriptNestingLevelIncrementer incrementScriptNestingLevel() {
return ScriptNestingLevelIncrementer(this);
}
private:
HTMLParserReentryPermit();
// https://html.spec.whatwg.org/#script-nesting-level
unsigned m_scriptNestingLevel;
// https://html.spec.whatwg.org/#parser-pause-flag
bool m_parserPauseFlag;
DISALLOW_COPY_AND_ASSIGN(HTMLParserReentryPermit);
};
} // namespace blink
#endif // HTMLParserReentryPermit_h
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