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| 1 // Copyright 2016 The Chromium Authors. All rights reserved. |
| 2 // Use of this source code is governed by a BSD-style license that can be |
| 3 // found in the LICENSE file. |
| 4 |
| 5 #ifndef HTMLParserReentryPermit_h |
| 6 #define HTMLParserReentryPermit_h |
| 7 |
| 8 #include "base/macros.h" |
| 9 #include "wtf/PassRefPtr.h" |
| 10 #include "wtf/RefCounted.h" |
| 11 |
| 12 namespace blink { |
| 13 |
| 14 // The HTML spec for parsing controls reentering the parser from |
| 15 // script with the "parser pause flag" and "script nesting level." |
| 16 // |
| 17 // The parser pause flag puts a brake on whether the tokenizer will |
| 18 // produce more tokens. When the parser is paused, nested invocations |
| 19 // of the tokenizer unwind. |
| 20 // |
| 21 // The script nesting level is incremented and decremented any time |
| 22 // the parser causes script to run. The script nesting level: |
| 23 // |
| 24 // - May prevent document.open from blowing away the document. |
| 25 // |
| 26 // - Governs whether a script element becomes the "pending |
| 27 // parsing-blocking script." The pending parsing-blocking script in |
| 28 // turn affects whether document.write reenters the parser. |
| 29 // |
| 30 // Clearing the parser pause flag is simple: Whenever the script |
| 31 // nesting level hits zero, the parser pause flag is cleared. However |
| 32 // setting the parser pause flag is subtle. |
| 33 // |
| 34 // Processing a typical script end tag, or running a chain of pending |
| 35 // parser-blocking scripts after that, does not set the parser pause |
| 36 // flag. However recursively parsing end script tags, or running |
| 37 // custom element constructors, does set the parser pause flag. |
| 38 class HTMLParserReentryPermit final : public RefCounted<HTMLParserReentryPermit>
{ |
| 39 public: |
| 40 static PassRefPtr<HTMLParserReentryPermit> create(); |
| 41 ~HTMLParserReentryPermit() = default; |
| 42 |
| 43 unsigned scriptNestingLevel() const { return m_scriptNestingLevel; } |
| 44 bool parserPauseFlag() const { return m_parserPauseFlag; } |
| 45 void pause() |
| 46 { |
| 47 CHECK(m_scriptNestingLevel); |
| 48 m_parserPauseFlag = true; |
| 49 } |
| 50 |
| 51 class ScriptNestingLevelIncrementer final { |
| 52 STACK_ALLOCATED(); |
| 53 public: |
| 54 explicit ScriptNestingLevelIncrementer(HTMLParserReentryPermit* permit) |
| 55 : m_permit(permit) |
| 56 { |
| 57 m_permit->m_scriptNestingLevel++; |
| 58 } |
| 59 |
| 60 ScriptNestingLevelIncrementer(ScriptNestingLevelIncrementer&&) |
| 61 = default; |
| 62 |
| 63 ~ScriptNestingLevelIncrementer() |
| 64 { |
| 65 m_permit->m_scriptNestingLevel--; |
| 66 if (!m_permit->m_scriptNestingLevel) |
| 67 m_permit->m_parserPauseFlag = false; |
| 68 } |
| 69 |
| 70 private: |
| 71 HTMLParserReentryPermit* m_permit; |
| 72 |
| 73 DISALLOW_COPY_AND_ASSIGN(ScriptNestingLevelIncrementer); |
| 74 }; |
| 75 |
| 76 ScriptNestingLevelIncrementer incrementScriptNestingLevel() |
| 77 { |
| 78 return ScriptNestingLevelIncrementer(this); |
| 79 } |
| 80 |
| 81 private: |
| 82 HTMLParserReentryPermit(); |
| 83 |
| 84 // https://html.spec.whatwg.org/#script-nesting-level |
| 85 unsigned m_scriptNestingLevel; |
| 86 |
| 87 // https://html.spec.whatwg.org/#parser-pause-flag |
| 88 bool m_parserPauseFlag; |
| 89 |
| 90 DISALLOW_COPY_AND_ASSIGN(HTMLParserReentryPermit); |
| 91 }; |
| 92 |
| 93 } // namespace blink |
| 94 |
| 95 #endif // HTMLParserReentryPermit_h |
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