Quelle DOMString.h Sprache: C

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef mozilla_dom_DOMString_h
#define mozilla_dom_DOMString_h

#include "nsString.h"
#include "mozilla/Assertions.h"
#include "mozilla/Attributes.h"
#include "mozilla/Maybe.h"
#include "mozilla/StringBuffer.h"
#include "nsDOMString.h"
#include "nsAtom.h"

namespace mozilla::dom {

/**
* A class for representing string return values.  This can be either passed to
* callees that have an nsString or nsAString out param or passed to a callee
* that actually knows about this class and can work with it.  Such a callee may
* call these setters:
*
*   SetKnownLiveStringBuffer
*   SetStringBuffer
*   SetKnownLiveString
*   SetKnownLiveAtom
*   SetNull
*
* to assign a value to the DOMString without instantiating an actual nsString
* in the process, or use AsAString() to instantiate an nsString and work with
* it.  These options are mutually exclusive!  Don't do more than one of them.
*
* It's only OK to call
* SetKnownLiveStringBuffer/SetKnownLiveString/SetKnownLiveAtom if the caller of
* the method in question plans to keep holding a strong ref to the stringbuffer
* involved, whether it's a raw mozilla::StringBuffer, or stored inside the
* string or atom being passed.  In the string/atom cases that means the caller
* must own the string or atom, and not mutate it (in the string case) for the
* lifetime of the DOMString.
*
* The proper way to extract a value is to check IsNull().  If not null, then
* check IsEmpty().  If neither of those is true, check HasStringBuffer().  If
* that's true, call StringBuffer()/StringBufferLength().  If HasStringBuffer()
* returns false, check HasLiteral, and if that returns true call
* Literal()/LiteralLength().  If HasLiteral() is false, call AsAString() and
* get the value from that.
*/
class MOZ_STACK_CLASS DOMString {
public:
  DOMString() : mStringBuffer(nullptr), mLength(0), mState(State::Empty) {}
  ~DOMString() {
    MOZ_ASSERT(!mString || !mStringBuffer, "Shouldn't have both present!");
    if (mState == State::OwnedStringBuffer) {
      MOZ_ASSERT(mStringBuffer);
      mStringBuffer->Release();
    }
  }

  operator nsString&() { return AsAString(); }

  // It doesn't make any sense to convert a DOMString to a const nsString or
  // nsAString reference; this class is meant for outparams only.
  operator const nsString&() = delete;
  operator const nsAString&() = delete;

  nsString& AsAString() {
    MOZ_ASSERT(mState == State::Empty || mState == State::String,
               "Moving from nonempty state to another nonempty state?");
    MOZ_ASSERT(!mStringBuffer, "We already have a stringbuffer?");
    if (!mString) {
      mString.emplace();
      mState = State::String;
    }
    return *mString;
  }

  bool HasStringBuffer() const {
    MOZ_ASSERT(!mString || !mStringBuffer, "Shouldn't have both present!");
    MOZ_ASSERT(mState > State::Null,
               "Caller should have checked IsNull() and IsEmpty() first");
    return mState >= State::OwnedStringBuffer;
  }

  // Get the stringbuffer.  This can only be called if HasStringBuffer()
  // returned true.  If that's true, it will never return null.  Note that
  // constructing a string from this mozilla::StringBuffer with length given by
  // StringBufferLength() might give you something that is not null-terminated.
  mozilla::StringBuffer* StringBuffer() const {
    MOZ_ASSERT(HasStringBuffer(),
               "Don't ask for the stringbuffer if we don't have it");
    MOZ_ASSERT(mStringBuffer, "We better have a stringbuffer if we claim to");
    return mStringBuffer;
  }

  // Get the length of the stringbuffer.  Can only be called if
  // HasStringBuffer().
  uint32_t StringBufferLength() const {
    MOZ_ASSERT(HasStringBuffer(),
               "Don't call this if there is no stringbuffer");
    return mLength;
  }

  bool HasLiteral() const {
    MOZ_ASSERT(!mString || !mStringBuffer, "Shouldn't have both present!");
    MOZ_ASSERT(mState > State::Null,
               "Caller should have checked IsNull() and IsEmpty() first");
    return mState == State::Literal;
  }

  // Get the literal string.  This can only be called if HasLiteral()
  // returned true.  If that's true, it will never return null.
  const char16_t* Literal() const {
    MOZ_ASSERT(HasLiteral(), "Don't ask for the literal if we don't have it");
    MOZ_ASSERT(mLiteral, "We better have a literal if we claim to");
    return mLiteral;
  }

  // Get the length of the literal.  Can only be called if HasLiteral().
  uint32_t LiteralLength() const {
    MOZ_ASSERT(HasLiteral(), "Don't call this if there is no literal");
    return mLength;
  }

  // Initialize the DOMString to a (mozilla::StringBuffer, length) pair.  The
  // length does NOT have to be the full length of the (null-terminated) string
  // in the mozilla::StringBuffer.
  void SetKnownLiveStringBuffer(mozilla::StringBuffer* aStringBuffer,
                                uint32_t aLength) {
    MOZ_ASSERT(mState == State::Empty, "We're already set to a value");
    if (aLength != 0) {
      SetStringBufferInternal(aStringBuffer, aLength);
      mState = State::UnownedStringBuffer;
    }
    // else nothing to do
  }

  // Like SetKnownLiveStringBuffer, but holds a reference to the
  // mozilla::StringBuffer.
  void SetStringBuffer(mozilla::StringBuffer* aStringBuffer, uint32_t aLength) {
    MOZ_ASSERT(mState == State::Empty, "We're already set to a value");
    if (aLength != 0) {
      SetStringBufferInternal(aStringBuffer, aLength);
      aStringBuffer->AddRef();
      mState = State::OwnedStringBuffer;
    }
    // else nothing to do
  }

  void SetKnownLiveString(const nsAString& aString) {
    MOZ_ASSERT(mString.isNothing(), "We already have a string?");
    MOZ_ASSERT(mState == State::Empty, "We're already set to a value");
    MOZ_ASSERT(!mStringBuffer, "Setting stringbuffer twice?");
    if (MOZ_UNLIKELY(aString.IsVoid())) {
      SetNull();
    } else if (!aString.IsEmpty()) {
      if (mozilla::StringBuffer* buf = aString.GetStringBuffer()) {
        SetKnownLiveStringBuffer(buf, aString.Length());
      } else if (aString.IsLiteral()) {
        SetLiteralInternal(aString.BeginReading(), aString.Length());
      } else {
        AsAString() = aString;
      }
    }
  }

  enum NullHandling { eTreatNullAsNull, eTreatNullAsEmpty, eNullNotExpected };

  void SetKnownLiveAtom(nsAtom* aAtom, NullHandling aNullHandling) {
    MOZ_ASSERT(mString.isNothing(), "We already have a string?");
    MOZ_ASSERT(mState == State::Empty, "We're already set to a value");
    MOZ_ASSERT(aAtom || aNullHandling != eNullNotExpected);
    if (aNullHandling == eNullNotExpected || aAtom) {
      if (aAtom->IsStatic()) {
        // Static atoms are backed by literals.  Explicitly call AsStatic() here
        // to avoid the extra IsStatic() checks in nsAtom::GetUTF16String().
        SetLiteralInternal(aAtom->AsStatic()->GetUTF16String(),
                           aAtom->GetLength());
      } else {
        SetKnownLiveStringBuffer(aAtom->AsDynamic()->StringBuffer(),
                                 aAtom->GetLength());
      }
    } else if (aNullHandling == eTreatNullAsNull) {
      SetNull();
    }
  }

  void SetNull() {
    MOZ_ASSERT(!mStringBuffer, "Should have no stringbuffer if null");
    MOZ_ASSERT(mString.isNothing(), "Should have no string if null");
    MOZ_ASSERT(mState == State::Empty, "Already set to a value?");
    mState = State::Null;
  }

  bool IsNull() const {
    MOZ_ASSERT(!mStringBuffer || mString.isNothing(),
               "How could we have a stringbuffer and a nonempty string?");
    return mState == State::Null || (mString && mString->IsVoid());
  }

  bool IsEmpty() const {
    MOZ_ASSERT(!mStringBuffer || mString.isNothing(),
               "How could we have a stringbuffer and a nonempty string?");
    // This is not exact, because we might still have an empty XPCOM string.
    // But that's OK; in that case the callers will try the XPCOM string
    // themselves.
    return mState == State::Empty;
  }

  void ToString(nsAString& aString) {
    if (IsNull()) {
      SetDOMStringToNull(aString);
    } else if (IsEmpty()) {
      aString.Truncate();
    } else if (HasStringBuffer()) {
      // Don't share the mozilla::StringBuffer with aString if the result would
      // not be null-terminated.
      mozilla::StringBuffer* buf = StringBuffer();
      uint32_t len = StringBufferLength();
      auto chars = static_cast<char16_t*>(buf->Data());
      if (chars[len] == '\0') {
        // Safe to share the buffer.
        aString.Assign(buf, len);
      } else {
        // We need to copy, unfortunately.
        aString.Assign(chars, len);
      }
    } else if (HasLiteral()) {
      aString.AssignLiteral(Literal(), LiteralLength());
    } else {
      aString = AsAString();
    }
  }

private:
  void SetStringBufferInternal(mozilla::StringBuffer* aStringBuffer,
                               uint32_t aLength) {
    MOZ_ASSERT(mString.isNothing(), "We already have a string?");
    MOZ_ASSERT(mState == State::Empty, "We're already set to a value");
    MOZ_ASSERT(!mStringBuffer, "Setting stringbuffer twice?");
    MOZ_ASSERT(aStringBuffer, "Why are we getting null?");
    MOZ_ASSERT(aLength != 0, "Should not have empty string here");
    mStringBuffer = aStringBuffer;
    mLength = aLength;
  }

  void SetLiteralInternal(const char16_t* aLiteral, uint32_t aLength) {
    MOZ_ASSERT(!mLiteral, "What's going on here?");
    mLiteral = aLiteral;
    mLength = aLength;
    mState = State::Literal;
  }

  enum class State : uint8_t {
    Empty,  // An empty string.  Default state.
    Null,   // Null (not a string at all)

    // All states that involve actual string data should come after
    // Empty and Null.

    String,               // An XPCOM string stored in mString.
    Literal,              // A string literal (static lifetime).
    OwnedStringBuffer,    // mStringBuffer is valid and we have a ref to it.
    UnownedStringBuffer,  // mStringBuffer is valid; we are not holding a ref.
    // The two string buffer values must come last.  This lets us avoid doing
    // two tests to figure out whether we have a stringbuffer.
  };

  // We need to be able to act like a string as needed
  Maybe<nsAutoString> mString;

  union {
    // The mozilla::StringBuffer in the OwnedStringBuffer/UnownedStringBuffer
    // cases.
    mozilla::StringBuffer* MOZ_UNSAFE_REF(
        "The ways in which this can be safe are "
        "documented above and enforced through "
        "assertions") mStringBuffer;
    // The literal in the Literal case.
    const char16_t* mLiteral;
  };

  // Length in the stringbuffer and literal cases.
  uint32_t mLength;

  State mState;
};

}  // namespace mozilla::dom

#endif  // mozilla_dom_DOMString_h

quality100%

¤ Dauer der Verarbeitung: 0.1 Sekunden (vorverarbeitet) ¤

Wurzel

Suchen

Beweissystem der NASA

Beweissystem Isabelle

NIST Cobol Testsuite

Cephes Mathematical Library

Wiener Entwicklungsmethode

Haftungshinweis

Die Informationen auf dieser Webseite wurden nach bestem Wissen sorgfältig zusammengestellt. Es wird jedoch weder Vollständigkeit, noch Richtigkeit, noch Qualität der bereit gestellten Informationen zugesichert.

Bemerkung:

Die farbliche Syntaxdarstellung ist noch experimentell.