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gecko-dev/js/public/String.h

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/* -*- 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/. */
/* JavaScript string operations. */
#ifndef js_String_h
#define js_String_h
#include "js/shadow/String.h" // JS::shadow::String
#include "mozilla/Assertions.h" // MOZ_ASSERT
#include "mozilla/Attributes.h" // MOZ_ALWAYS_INLINE
#include "mozilla/Likely.h" // MOZ_LIKELY
#include "mozilla/Maybe.h" // mozilla::Maybe
#include "mozilla/Range.h" // mozilla::Range
#include "mozilla/Span.h" // mozilla::Span
// std::tuple
#include <algorithm> // std::copy_n
#include <stddef.h> // size_t
#include <stdint.h> // uint32_t, uint64_t, INT32_MAX
#include "jstypes.h" // JS_PUBLIC_API
#include "js/CharacterEncoding.h" // JS::UTF8Chars, JS::ConstUTF8CharsZ
#include "js/RootingAPI.h" // JS::Handle
#include "js/TypeDecls.h" // JS::Latin1Char
#include "js/UniquePtr.h" // JS::UniquePtr
#include "js/Utility.h" // JS::FreePolicy, JS::UniqueTwoByteChars
#include "js/Value.h" // JS::Value
struct JS_PUBLIC_API JSContext;
class JS_PUBLIC_API JSAtom;
class JSLinearString;
class JS_PUBLIC_API JSString;
namespace JS {
class JS_PUBLIC_API AutoRequireNoGC;
} // namespace JS
extern JS_PUBLIC_API JSString* JS_GetEmptyString(JSContext* cx);
// Don't want to export data, so provide accessors for non-inline Values.
extern JS_PUBLIC_API JS::Value JS_GetEmptyStringValue(JSContext* cx);
/*
* String creation.
*
* NB: JS_NewUCString takes ownership of bytes on success, avoiding a copy;
* but on error (signified by null return), it leaves chars owned by the
* caller. So the caller must free bytes in the error case, if it has no use
* for them. In contrast, all the JS_New*StringCopy* functions do not take
* ownership of the character memory passed to them -- they copy it.
*/
extern JS_PUBLIC_API JSString* JS_NewStringCopyN(JSContext* cx, const char* s,
size_t n);
extern JS_PUBLIC_API JSString* JS_NewStringCopyZ(JSContext* cx, const char* s);
extern JS_PUBLIC_API JSString* JS_NewStringCopyUTF8Z(
JSContext* cx, const JS::ConstUTF8CharsZ s);
extern JS_PUBLIC_API JSString* JS_NewStringCopyUTF8N(JSContext* cx,
const JS::UTF8Chars s);
extern JS_PUBLIC_API JSString* JS_AtomizeStringN(JSContext* cx, const char* s,
size_t length);
extern JS_PUBLIC_API JSString* JS_AtomizeString(JSContext* cx, const char* s);
// Note: unlike the non-pinning JS_Atomize* functions, this can be called
// without entering a realm/zone.
extern JS_PUBLIC_API JSString* JS_AtomizeAndPinStringN(JSContext* cx,
const char* s,
size_t length);
// Note: unlike the non-pinning JS_Atomize* functions, this can be called
// without entering a realm/zone.
extern JS_PUBLIC_API JSString* JS_AtomizeAndPinString(JSContext* cx,
const char* s);
extern JS_PUBLIC_API JSString* JS_NewLatin1String(
JSContext* cx, js::UniquePtr<JS::Latin1Char[], JS::FreePolicy> chars,
size_t length);
extern JS_PUBLIC_API JSString* JS_NewUCString(JSContext* cx,
JS::UniqueTwoByteChars chars,
size_t length);
extern JS_PUBLIC_API JSString* JS_NewUCStringDontDeflate(
JSContext* cx, JS::UniqueTwoByteChars chars, size_t length);
extern JS_PUBLIC_API JSString* JS_NewUCStringCopyN(JSContext* cx,
const char16_t* s, size_t n);
extern JS_PUBLIC_API JSString* JS_NewUCStringCopyZ(JSContext* cx,
const char16_t* s);
extern JS_PUBLIC_API JSString* JS_AtomizeUCStringN(JSContext* cx,
const char16_t* s,
size_t length);
extern JS_PUBLIC_API JSString* JS_AtomizeUCString(JSContext* cx,
const char16_t* s);
extern JS_PUBLIC_API bool JS_CompareStrings(JSContext* cx, JSString* str1,
JSString* str2, int32_t* result);
[[nodiscard]] extern JS_PUBLIC_API bool JS_StringEqualsAscii(
JSContext* cx, JSString* str, const char* asciiBytes, bool* match);
// Same as above, but when the length of asciiBytes (excluding the
// trailing null, if any) is known.
[[nodiscard]] extern JS_PUBLIC_API bool JS_StringEqualsAscii(
JSContext* cx, JSString* str, const char* asciiBytes, size_t length,
bool* match);
template <size_t N>
[[nodiscard]] bool JS_StringEqualsLiteral(JSContext* cx, JSString* str,
const char (&asciiBytes)[N],
bool* match) {
MOZ_ASSERT(asciiBytes[N - 1] == '\0');
return JS_StringEqualsAscii(cx, str, asciiBytes, N - 1, match);
}
extern JS_PUBLIC_API size_t JS_PutEscapedString(JSContext* cx, char* buffer,
size_t size, JSString* str,
char quote);
/*
* Extracting string characters and length.
*
* While getting the length of a string is infallible, getting the chars can
* fail. As indicated by the lack of a JSContext parameter, there are two
* special cases where getting the chars is infallible:
*
* The first case is for strings that have been atomized, e.g. directly by
* JS_AtomizeAndPinString or implicitly because it is stored in a jsid.
*
* The second case is "linear" strings that have been explicitly prepared in a
* fallible context by JS_EnsureLinearString. To catch errors, a separate opaque
* JSLinearString type is returned by JS_EnsureLinearString and expected by
* JS_Get{Latin1,TwoByte}StringCharsAndLength. Note, though, that this is purely
* a syntactic distinction: the input and output of JS_EnsureLinearString are
* the same actual GC-thing. If a JSString is known to be linear,
* JS_ASSERT_STRING_IS_LINEAR can be used to make a debug-checked cast. Example:
*
* // In a fallible context.
* JSLinearString* lstr = JS_EnsureLinearString(cx, str);
* if (!lstr) {
* return false;
* }
* MOZ_ASSERT(lstr == JS_ASSERT_STRING_IS_LINEAR(str));
*
* // In an infallible context, for the same 'str'.
* AutoCheckCannotGC nogc;
* const char16_t* chars = JS::GetTwoByteLinearStringChars(nogc, lstr)
* MOZ_ASSERT(chars);
*
* Note: JS strings (including linear strings and atoms) are not
* null-terminated!
*
* Additionally, string characters are stored as either Latin1Char (8-bit)
* or char16_t (16-bit). Clients can use JS::StringHasLatin1Chars and can then
* call either the Latin1* or TwoByte* functions. Some functions like
* JS_CopyStringChars and JS_GetStringCharAt accept both Latin1 and TwoByte
* strings.
*/
extern JS_PUBLIC_API size_t JS_GetStringLength(JSString* str);
extern JS_PUBLIC_API bool JS_StringIsLinear(JSString* str);
extern JS_PUBLIC_API const JS::Latin1Char* JS_GetLatin1StringCharsAndLength(
JSContext* cx, const JS::AutoRequireNoGC& nogc, JSString* str,
size_t* length);
extern JS_PUBLIC_API const char16_t* JS_GetTwoByteStringCharsAndLength(
JSContext* cx, const JS::AutoRequireNoGC& nogc, JSString* str,
size_t* length);
extern JS_PUBLIC_API bool JS_GetStringCharAt(JSContext* cx, JSString* str,
size_t index, char16_t* res);
extern JS_PUBLIC_API const char16_t* JS_GetTwoByteExternalStringChars(
JSString* str);
extern JS_PUBLIC_API bool JS_CopyStringChars(JSContext* cx,
mozilla::Range<char16_t> dest,
JSString* str);
/**
* Copies the string's characters to a null-terminated char16_t buffer.
*
* Returns nullptr on OOM.
*/
extern JS_PUBLIC_API JS::UniqueTwoByteChars JS_CopyStringCharsZ(JSContext* cx,
JSString* str);
extern JS_PUBLIC_API JSLinearString* JS_EnsureLinearString(JSContext* cx,
JSString* str);
static MOZ_ALWAYS_INLINE JSLinearString* JS_ASSERT_STRING_IS_LINEAR(
JSString* str) {
MOZ_ASSERT(JS_StringIsLinear(str));
return reinterpret_cast<JSLinearString*>(str);
}
static MOZ_ALWAYS_INLINE JSString* JS_FORGET_STRING_LINEARNESS(
JSLinearString* str) {
return reinterpret_cast<JSString*>(str);
}
/*
* Additional APIs that avoid fallibility when given a linear string.
*/
extern JS_PUBLIC_API bool JS_LinearStringEqualsAscii(JSLinearString* str,
const char* asciiBytes);
extern JS_PUBLIC_API bool JS_LinearStringEqualsAscii(JSLinearString* str,
const char* asciiBytes,
size_t length);
template <size_t N>
bool JS_LinearStringEqualsLiteral(JSLinearString* str,
const char (&asciiBytes)[N]) {
MOZ_ASSERT(asciiBytes[N - 1] == '\0');
return JS_LinearStringEqualsAscii(str, asciiBytes, N - 1);
}
extern JS_PUBLIC_API size_t JS_PutEscapedLinearString(char* buffer, size_t size,
JSLinearString* str,
char quote);
/**
* Create a dependent string, i.e., a string that owns no character storage,
* but that refers to a slice of another string's chars. Dependent strings
* are mutable by definition, so the thread safety comments above apply.
*/
extern JS_PUBLIC_API JSString* JS_NewDependentString(JSContext* cx,
JS::Handle<JSString*> str,
size_t start,
size_t length);
/**
* Concatenate two strings, possibly resulting in a rope.
* See above for thread safety comments.
*/
extern JS_PUBLIC_API JSString* JS_ConcatStrings(JSContext* cx,
JS::Handle<JSString*> left,
JS::Handle<JSString*> right);
/**
* For JS_DecodeBytes, set *dstlenp to the size of the destination buffer before
* the call; on return, *dstlenp contains the number of characters actually
* stored. To determine the necessary destination buffer size, make a sizing
* call that passes nullptr for dst.
*
* On errors, the functions report the error. In that case, *dstlenp contains
* the number of characters or bytes transferred so far. If cx is nullptr, no
* error is reported on failure, and the functions simply return false.
*
* NB: This function does not store an additional zero byte or char16_t after
* the transcoded string.
*/
JS_PUBLIC_API bool JS_DecodeBytes(JSContext* cx, const char* src, size_t srclen,
char16_t* dst, size_t* dstlenp);
/**
* Get number of bytes in the string encoding (without accounting for a
* terminating zero bytes. The function returns (size_t) -1 if the string
* can not be encoded into bytes and reports an error using cx accordingly.
*/
JS_PUBLIC_API size_t JS_GetStringEncodingLength(JSContext* cx, JSString* str);
/**
* Encode string into a buffer. The function does not stores an additional
* zero byte. The function returns (size_t) -1 if the string can not be
* encoded into bytes with no error reported. Otherwise it returns the number
* of bytes that are necessary to encode the string. If that exceeds the
* length parameter, the string will be cut and only length bytes will be
* written into the buffer.
*/
[[nodiscard]] JS_PUBLIC_API bool JS_EncodeStringToBuffer(JSContext* cx,
JSString* str,
char* buffer,
size_t length);
/**
* Encode as many scalar values of the string as UTF-8 as can fit
* into the caller-provided buffer replacing unpaired surrogates
* with the REPLACEMENT CHARACTER.
*
* If JS::StringHasLatin1Chars(str) returns true, the function
* is guaranteed to convert the entire string if
* buffer.Length() >= 2 * JS_GetStringLength(str). Otherwise,
* the function is guaranteed to convert the entire string if
* buffer.Length() >= 3 * JS_GetStringLength(str).
*
* This function does not alter the representation of |str| or
* any |JSString*| substring that is a constituent part of it.
* Returns mozilla::Nothing() on OOM, without reporting an error;
* some data may have been written to |buffer| when this happens.
*
* If there's no OOM, returns the number of code units read and
* the number of code units written.
*
* The semantics of this method match the semantics of
* TextEncoder.encodeInto().
*
* The function does not store an additional zero byte.
*/
JS_PUBLIC_API mozilla::Maybe<std::tuple<size_t, size_t>>
JS_EncodeStringToUTF8BufferPartial(JSContext* cx, JSString* str,
mozilla::Span<char> buffer);
namespace JS {
/**
* Maximum length of a JS string. This is chosen so that the number of bytes
* allocated for a null-terminated TwoByte string still fits in int32_t.
*/
static constexpr uint32_t MaxStringLength = (1 << 30) - 2;
static_assert((uint64_t(MaxStringLength) + 1) * sizeof(char16_t) <= INT32_MAX,
"size of null-terminated JSString char buffer must fit in "
"INT32_MAX");
/** Compute the length of a string. */
MOZ_ALWAYS_INLINE size_t GetStringLength(JSString* s) {
return shadow::AsShadowString(s)->length();
}
/** Compute the length of a linear string. */
MOZ_ALWAYS_INLINE size_t GetLinearStringLength(JSLinearString* s) {
return shadow::AsShadowString(s)->length();
}
/** Return true iff the given linear string uses Latin-1 storage. */
MOZ_ALWAYS_INLINE bool LinearStringHasLatin1Chars(JSLinearString* s) {
return shadow::AsShadowString(s)->hasLatin1Chars();
}
/** Return true iff the given string uses Latin-1 storage. */
MOZ_ALWAYS_INLINE bool StringHasLatin1Chars(JSString* s) {
return shadow::AsShadowString(s)->hasLatin1Chars();
}
/**
* Given a linear string known to use Latin-1 storage, return a pointer to that
* storage. This pointer remains valid only as long as no GC occurs.
*/
MOZ_ALWAYS_INLINE const Latin1Char* GetLatin1LinearStringChars(
const AutoRequireNoGC& nogc, JSLinearString* linear) {
return shadow::AsShadowString(linear)->latin1LinearChars();
}
/**
* Given a linear string known to use two-byte storage, return a pointer to that
* storage. This pointer remains valid only as long as no GC occurs.
*/
MOZ_ALWAYS_INLINE const char16_t* GetTwoByteLinearStringChars(
const AutoRequireNoGC& nogc, JSLinearString* linear) {
return shadow::AsShadowString(linear)->twoByteLinearChars();
}
/**
* Given an in-range index into the provided string, return the character at
* that index.
*/
MOZ_ALWAYS_INLINE char16_t GetLinearStringCharAt(JSLinearString* linear,
size_t index) {
shadow::String* s = shadow::AsShadowString(linear);
MOZ_ASSERT(index < s->length());
return s->hasLatin1Chars() ? s->latin1LinearChars()[index]
: s->twoByteLinearChars()[index];
}
/**
* Convert an atom to a linear string. All atoms are linear, so this
* operation is infallible.
*/
MOZ_ALWAYS_INLINE JSLinearString* AtomToLinearString(JSAtom* atom) {
return reinterpret_cast<JSLinearString*>(atom);
}
/**
* If the provided string uses externally-managed storage, return true and set
* |*callbacks| to the external-string callbacks used to create it and |*chars|
* to a pointer to its two-byte storage. (These pointers remain valid as long
* as the provided string is kept alive.)
*/
MOZ_ALWAYS_INLINE bool IsExternalString(
JSString* str, const JSExternalStringCallbacks** callbacks,
const char16_t** chars) {
shadow::String* s = shadow::AsShadowString(str);
if (!s->isExternal()) {
return false;
}
*callbacks = s->externalCallbacks;
*chars = s->nonInlineCharsTwoByte;
return true;
}
namespace detail {
extern JS_PUBLIC_API JSLinearString* StringToLinearStringSlow(JSContext* cx,
JSString* str);
} // namespace detail
/** Convert a string to a linear string. */
MOZ_ALWAYS_INLINE JSLinearString* StringToLinearString(JSContext* cx,
JSString* str) {
if (MOZ_LIKELY(shadow::AsShadowString(str)->isLinear())) {
return reinterpret_cast<JSLinearString*>(str);
}
return detail::StringToLinearStringSlow(cx, str);
}
/** Copy characters in |s[start..start + len]| to |dest[0..len]|. */
MOZ_ALWAYS_INLINE void CopyLinearStringChars(char16_t* dest, JSLinearString* s,
size_t len, size_t start = 0) {
#ifdef DEBUG
size_t stringLen = GetLinearStringLength(s);
MOZ_ASSERT(start <= stringLen);
MOZ_ASSERT(len <= stringLen - start);
#endif
shadow::String* str = shadow::AsShadowString(s);
if (str->hasLatin1Chars()) {
const Latin1Char* src = str->latin1LinearChars();
for (size_t i = 0; i < len; i++) {
dest[i] = src[start + i];
}
} else {
const char16_t* src = str->twoByteLinearChars();
std::copy_n(src + start, len, dest);
}
}
/**
* Copy characters in |s[start..start + len]| to |dest[0..len]|, lossily
* truncating 16-bit values to |char| if necessary.
*/
MOZ_ALWAYS_INLINE void LossyCopyLinearStringChars(char* dest, JSLinearString* s,
size_t len,
size_t start = 0) {
#ifdef DEBUG
size_t stringLen = GetLinearStringLength(s);
MOZ_ASSERT(start <= stringLen);
MOZ_ASSERT(len <= stringLen - start);
#endif
shadow::String* str = shadow::AsShadowString(s);
if (LinearStringHasLatin1Chars(s)) {
const Latin1Char* src = str->latin1LinearChars();
for (size_t i = 0; i < len; i++) {
dest[i] = char(src[start + i]);
}
} else {
const char16_t* src = str->twoByteLinearChars();
for (size_t i = 0; i < len; i++) {
dest[i] = char(src[start + i]);
}
}
}
/**
* Copy characters in |s[start..start + len]| to |dest[0..len]|.
*
* This function is fallible. If you already have a linear string, use the
* infallible |JS::CopyLinearStringChars| above instead.
*/
[[nodiscard]] inline bool CopyStringChars(JSContext* cx, char16_t* dest,
JSString* s, size_t len,
size_t start = 0) {
JSLinearString* linear = StringToLinearString(cx, s);
if (!linear) {
return false;
}
CopyLinearStringChars(dest, linear, len, start);
return true;
}
/**
* Copy characters in |s[start..start + len]| to |dest[0..len]|, lossily
* truncating 16-bit values to |char| if necessary.
*
* This function is fallible. If you already have a linear string, use the
* infallible |JS::LossyCopyLinearStringChars| above instead.
*/
[[nodiscard]] inline bool LossyCopyStringChars(JSContext* cx, char* dest,
JSString* s, size_t len,
size_t start = 0) {
JSLinearString* linear = StringToLinearString(cx, s);
if (!linear) {
return false;
}
LossyCopyLinearStringChars(dest, linear, len, start);
return true;
}
} // namespace JS
/** DO NOT USE, only present for Rust bindings as a temporary hack */
[[deprecated]] extern JS_PUBLIC_API bool JS_DeprecatedStringHasLatin1Chars(
JSString* str);
// JSString* is an aligned pointer, but this information isn't available in the
// public header. We specialize HasFreeLSB here so that JS::Result<JSString*>
// compiles.
namespace mozilla {
namespace detail {
template <>
struct HasFreeLSB<JSString*> {
static constexpr bool value = true;
};
} // namespace detail
} // namespace mozilla
#endif // js_String_h
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