Adding upstream version 86.0.1.upstream/86.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 334 insertions, 0 deletions

diff --git a/dom/bindings/DOMString.h b/dom/bindings/DOMString.h
new file mode 100644
index 0000000000..af02dfcffe
--- /dev/null
+++ b/dom/bindings/DOMString.h
@@ -0,0 +1,334 @@
+/* -*- 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 "nsStringBuffer.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/Maybe.h"
+#include "nsDOMString.h"
+#include "nsAtom.h"
+
+namespace mozilla {
+namespace 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 nsStringBuffer, 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 nsStringBuffer with length given by
+  // StringBufferLength() might give you something that is not null-terminated.
+  nsStringBuffer* 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;
+  }
+
+  // Tell the DOMString to relinquish ownership of its nsStringBuffer to the
+  // caller.  Can only be called if HasStringBuffer().
+  void RelinquishBufferOwnership() {
+    MOZ_ASSERT(HasStringBuffer(),
+               "Don't call this if there is no stringbuffer");
+    if (mState == State::OwnedStringBuffer) {
+      // Just hand that ref over.
+      mState = State::UnownedStringBuffer;
+    } else {
+      // Caller should end up holding a ref.
+      mStringBuffer->AddRef();
+    }
+  }
+
+  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;
+  }
+
+  bool HasAtom() 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::UnownedAtom;
+  }
+
+  // Get the atom.  This can only be called if HasAtom() returned true.  If
+  // that's true, it will never return null.
+  nsDynamicAtom* Atom() const {
+    MOZ_ASSERT(HasAtom(), "Don't ask for the atom if we don't have it");
+    MOZ_ASSERT(mAtom, "We better have an atom if we claim to");
+    return mAtom;
+  }
+
+  // Initialize the DOMString to a (nsStringBuffer, length) pair.  The length
+  // does NOT have to be the full length of the (null-terminated) string in the
+  // nsStringBuffer.
+  void SetKnownLiveStringBuffer(nsStringBuffer* 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 nsStringBuffer.
+  void SetStringBuffer(nsStringBuffer* 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()) {
+      nsStringBuffer* buf = nsStringBuffer::FromString(aString);
+      if (buf) {
+        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(!mAtom, "Setting atom twice?");
+    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 {
+        mAtom = aAtom->AsDynamic();
+        mState = State::UnownedAtom;
+      }
+    } 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 nsStringBuffer with aString if the result would not
+      // be null-terminated.
+      nsStringBuffer* buf = StringBuffer();
+      uint32_t len = StringBufferLength();
+      auto chars = static_cast<char16_t*>(buf->Data());
+      if (chars[len] == '\0') {
+        // Safe to share the buffer.
+        buf->ToString(len, aString);
+      } else {
+        // We need to copy, unfortunately.
+        aString.Assign(chars, len);
+      }
+    } else if (HasLiteral()) {
+      aString.AssignLiteral(Literal(), LiteralLength());
+    } else if (HasAtom()) {
+      mAtom->ToString(aString);
+    } else {
+      aString = AsAString();
+    }
+  }
+
+ private:
+  void SetStringBufferInternal(nsStringBuffer* 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).
+    UnownedAtom,  // mAtom is valid and we are not holding a ref.
+    // If we ever add an OwnedAtom state, XPCStringConvert::DynamicAtomToJSVal
+    // will need to grow an out param for whether the atom was shared.
+    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 nsStringBuffer in the OwnedStringBuffer/UnownedStringBuffer cases.
+    nsStringBuffer* 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;
+    // The atom in the UnownedAtom case.
+    nsDynamicAtom* MOZ_UNSAFE_REF(
+        "The ways in which this can be safe are "
+        "documented above and enforced through "
+        "assertions") mAtom;
+  };
+
+  // Length in the stringbuffer and literal cases.
+  uint32_t mLength;
+
+  State mState;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_DOMString_h