/* -*- 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/. */
/** * 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. operatorconst nsString&() = delete; operatorconst 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();
} elseif (!aString.IsEmpty()) { if (mozilla::StringBuffer* buf = aString.GetStringBuffer()) {
SetKnownLiveStringBuffer(buf, aString.Length());
} elseif (aString.IsLiteral()) {
SetLiteralInternal(aString.BeginReading(), aString.Length());
} else {
AsAString() = aString;
}
}
}
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());
}
} elseif (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);
} elseif (IsEmpty()) {
aString.Truncate();
} elseif (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);
}
} elseif (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;
}
enumclass 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
¤ Dauer der Verarbeitung: 0.28 Sekunden
(vorverarbeitet)
¤
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.
