Adding upstream version 1:115.7.0.upstream/1%115.7.0upstream

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

1 files changed, 1358 insertions, 0 deletions

diff --git a/intl/Encoding.h b/intl/Encoding.h
new file mode 100644
index 0000000000..3b5639e431
--- /dev/null
+++ b/intl/Encoding.h
@@ -0,0 +1,1358 @@
+// Copyright 2015-2016 Mozilla Foundation. See the COPYRIGHT
+// file at the top-level directory of this distribution.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Adapted from third_party/rust/encoding_c/include/encoding_rs_cpp.h, so the
+// "top-level directory" in the above notice refers to
+// third_party/rust/encoding_c/.
+
+#ifndef mozilla_Encoding_h
+#define mozilla_Encoding_h
+
+#include "mozilla/CheckedInt.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/NotNull.h"
+#include "mozilla/Span.h"
+#include "nsString.h"
+
+#include <tuple>
+
+namespace mozilla {
+class Encoding;
+class Decoder;
+class Encoder;
+};  // namespace mozilla
+
+#define ENCODING_RS_ENCODING mozilla::Encoding
+#define ENCODING_RS_NOT_NULL_CONST_ENCODING_PTR \
+  mozilla::NotNull<const mozilla::Encoding*>
+#define ENCODING_RS_ENCODER mozilla::Encoder
+#define ENCODING_RS_DECODER mozilla::Decoder
+
+#include "encoding_rs.h"
+
+extern "C" {
+
+nsresult mozilla_encoding_decode_to_nsstring(mozilla::Encoding const** encoding,
+                                             uint8_t const* src, size_t src_len,
+                                             nsAString* dst);
+
+nsresult mozilla_encoding_decode_to_nsstring_with_bom_removal(
+    mozilla::Encoding const* encoding, uint8_t const* src, size_t src_len,
+    nsAString* dst);
+
+nsresult mozilla_encoding_decode_to_nsstring_without_bom_handling(
+    mozilla::Encoding const* encoding, uint8_t const* src, size_t src_len,
+    nsAString* dst);
+
+nsresult
+mozilla_encoding_decode_to_nsstring_without_bom_handling_and_without_replacement(
+    mozilla::Encoding const* encoding, uint8_t const* src, size_t src_len,
+    nsAString* dst);
+
+nsresult mozilla_encoding_encode_from_utf16(mozilla::Encoding const** encoding,
+                                            char16_t const* src, size_t src_len,
+                                            nsACString* dst);
+
+nsresult mozilla_encoding_decode_to_nscstring(
+    mozilla::Encoding const** encoding, nsACString const* src, nsACString* dst);
+
+nsresult mozilla_encoding_decode_to_nscstring_with_bom_removal(
+    mozilla::Encoding const* encoding, nsACString const* src, nsACString* dst);
+
+nsresult mozilla_encoding_decode_to_nscstring_without_bom_handling(
+    mozilla::Encoding const* encoding, nsACString const* src, nsACString* dst);
+
+nsresult mozilla_encoding_decode_from_slice_to_nscstring_without_bom_handling(
+    mozilla::Encoding const* encoding, uint8_t const* src, size_t src_len,
+    nsACString* dst, size_t already_validated);
+
+nsresult
+mozilla_encoding_decode_to_nscstring_without_bom_handling_and_without_replacement(
+    mozilla::Encoding const* encoding, nsACString const* src, nsACString* dst);
+
+nsresult mozilla_encoding_encode_from_nscstring(
+    mozilla::Encoding const** encoding, nsACString const* src, nsACString* dst);
+
+}  // extern "C"
+
+namespace mozilla {
+
+/**
+ * Return value from `Decoder`/`Encoder` to indicate that input
+ * was exhausted.
+ */
+const uint32_t kInputEmpty = INPUT_EMPTY;
+
+/**
+ * Return value from `Decoder`/`Encoder` to indicate that output
+ * space was insufficient.
+ */
+const uint32_t kOutputFull = OUTPUT_FULL;
+
+/**
+ * An encoding as defined in the Encoding Standard
+ * (https://encoding.spec.whatwg.org/).
+ *
+ * See https://docs.rs/encoding_rs/ for the Rust API docs.
+ *
+ * An _encoding_ defines a mapping from a byte sequence to a Unicode code point
+ * sequence and, in most cases, vice versa. Each encoding has a name, an output
+ * encoding, and one or more labels.
+ *
+ * _Labels_ are ASCII-case-insensitive strings that are used to identify an
+ * encoding in formats and protocols. The _name_ of the encoding is the
+ * preferred label in the case appropriate for returning from the
+ * `characterSet` property of the `Document` DOM interface, except for
+ * the replacement encoding whose name is not one of its labels.
+ *
+ * The _output encoding_ is the encoding used for form submission and URL
+ * parsing on Web pages in the encoding. This is UTF-8 for the replacement,
+ * UTF-16LE and UTF-16BE encodings and the encoding itself for other
+ * encodings.
+ *
+ * # Streaming vs. Non-Streaming
+ *
+ * When you have the entire input in a single buffer, you can use the
+ * methods `Decode()`, `DecodeWithBOMRemoval()`,
+ * `DecodeWithoutBOMHandling()`,
+ * `DecodeWithoutBOMHandlingAndWithoutReplacement()` and
+ * `Encode()`. Unlike the rest of the API (apart from the `NewDecoder()` and
+ * NewEncoder()` methods), these methods perform heap allocations. You should
+ * the `Decoder` and `Encoder` objects when your input is split into multiple
+ * buffers or when you want to control the allocation of the output buffers.
+ *
+ * # Instances
+ *
+ * All instances of `Encoding` are statically allocated and have the process's
+ * lifetime. There is precisely one unique `Encoding` instance for each
+ * encoding defined in the Encoding Standard.
+ *
+ * To obtain a reference to a particular encoding whose identity you know at
+ * compile time, use a `static` that refers to encoding. There is a `static`
+ * for each encoding. The `static`s are named in all caps with hyphens
+ * replaced with underscores and with `_ENCODING` appended to the
+ * name. For example, if you know at compile time that you will want to
+ * decode using the UTF-8 encoding, use the `UTF_8_ENCODING` `static`.
+ *
+ * If you don't know what encoding you need at compile time and need to
+ * dynamically get an encoding by label, use `Encoding::for_label()`.
+ *
+ * Pointers to `Encoding` can be compared with `==` to check for the sameness
+ * of two encodings.
+ *
+ * A pointer to a `mozilla::Encoding` in C++ is the same thing as a pointer
+ * to an `encoding_rs::Encoding` in Rust. When writing FFI code, use
+ * `const mozilla::Encoding*` in the C signature and
+ * `*const encoding_rs::Encoding` is the corresponding Rust signature.
+ */
+class Encoding final {
+ public:
+  /**
+   * Implements the _get an encoding_ algorithm
+   * (https://encoding.spec.whatwg.org/#concept-encoding-get).
+   *
+   * If, after ASCII-lowercasing and removing leading and trailing
+   * whitespace, the argument matches a label defined in the Encoding
+   * Standard, `const Encoding*` representing the corresponding
+   * encoding is returned. If there is no match, `nullptr` is returned.
+   *
+   * This is the right method to use if the action upon the method returning
+   * `nullptr` is to use a fallback encoding (e.g. `WINDOWS_1252_ENCODING`)
+   * instead. When the action upon the method returning `nullptr` is not to
+   * proceed with a fallback but to refuse processing,
+   * `ForLabelNoReplacement()` is more appropriate.
+   */
+  static inline const Encoding* ForLabel(Span<const char> aLabel) {
+    return encoding_for_label(
+        reinterpret_cast<const uint8_t*>(aLabel.Elements()), aLabel.Length());
+  }
+
+  /**
+   * `nsAString` argument version. See above for docs.
+   */
+  static inline const Encoding* ForLabel(const nsAString& aLabel) {
+    return Encoding::ForLabel(NS_ConvertUTF16toUTF8(aLabel));
+  }
+
+  /**
+   * This method behaves the same as `ForLabel()`, except when `ForLabel()`
+   * would return `REPLACEMENT_ENCODING`, this method returns `nullptr` instead.
+   *
+   * This method is useful in scenarios where a fatal error is required
+   * upon invalid label, because in those cases the caller typically wishes
+   * to treat the labels that map to the replacement encoding as fatal
+   * errors, too.
+   *
+   * It is not OK to use this method when the action upon the method returning
+   * `nullptr` is to use a fallback encoding (e.g. `WINDOWS_1252_ENCODING`). In
+   * such a case, the `ForLabel()` method should be used instead in order to
+   * avoid unsafe fallback for labels that `ForLabel()` maps to
+   * `REPLACEMENT_ENCODING`.
+   */
+  static inline const Encoding* ForLabelNoReplacement(Span<const char> aLabel) {
+    return encoding_for_label_no_replacement(
+        reinterpret_cast<const uint8_t*>(aLabel.Elements()), aLabel.Length());
+  }
+
+  /**
+   * `nsAString` argument version. See above for docs.
+   */
+  static inline const Encoding* ForLabelNoReplacement(const nsAString& aLabel) {
+    return Encoding::ForLabelNoReplacement(NS_ConvertUTF16toUTF8(aLabel));
+  }
+
+  /**
+   * Performs non-incremental BOM sniffing.
+   *
+   * The argument must either be a buffer representing the entire input
+   * stream (non-streaming case) or a buffer representing at least the first
+   * three bytes of the input stream (streaming case).
+   *
+   * Returns `{UTF_8_ENCODING, 3}`,
+   * `{UTF_16LE_ENCODING, 2}` or
+   * `{UTF_16BE_ENCODING, 3}` if the argument starts with the
+   * UTF-8, UTF-16LE or UTF-16BE BOM or `{nullptr, 0}` otherwise.
+   */
+  static inline std::tuple<const Encoding*, size_t> ForBOM(
+      Span<const uint8_t> aBuffer) {
+    size_t len = aBuffer.Length();
+    const Encoding* encoding = encoding_for_bom(aBuffer.Elements(), &len);
+    return {encoding, len};
+  }
+
+  /**
+   * Writes the name of this encoding into `aName`.
+   *
+   * This name is appropriate to return as-is from the DOM
+   * `document.characterSet` property.
+   */
+  inline void Name(nsACString& aName) const {
+    aName.SetLength(ENCODING_NAME_MAX_LENGTH);
+    size_t length =
+        encoding_name(this, reinterpret_cast<uint8_t*>(aName.BeginWriting()));
+    aName.SetLength(length);  // truncation is the 64-bit case is OK
+  }
+
+  /**
+   * Checks whether the _output encoding_ of this encoding can encode every
+   * Unicode code point. (Only true if the output encoding is UTF-8.)
+   */
+  inline bool CanEncodeEverything() const {
+    return encoding_can_encode_everything(this);
+  }
+
+  /**
+   * Checks whether this encoding maps one byte to one Basic Multilingual
+   * Plane code point (i.e. byte length equals decoded UTF-16 length) and
+   * vice versa (for mappable characters).
+   *
+   * `true` iff this encoding is on the list of Legacy single-byte
+   * encodings (https://encoding.spec.whatwg.org/#legacy-single-byte-encodings)
+   * in the spec or x-user-defined.
+   */
+  inline bool IsSingleByte() const { return encoding_is_single_byte(this); }
+
+  /**
+   * Checks whether the bytes 0x00...0x7F map exclusively to the characters
+   * U+0000...U+007F and vice versa.
+   */
+  inline bool IsAsciiCompatible() const {
+    return encoding_is_ascii_compatible(this);
+  }
+
+  /**
+   * Checks whether this is a Japanese legacy encoding.
+   */
+  inline bool IsJapaneseLegacy() const {
+    return this == SHIFT_JIS_ENCODING || this == EUC_JP_ENCODING ||
+           this == ISO_2022_JP_ENCODING;
+  }
+
+  /**
+   * Returns the _output encoding_ of this encoding. This is UTF-8 for
+   * UTF-16BE, UTF-16LE and replacement and the encoding itself otherwise.
+   */
+  inline NotNull<const mozilla::Encoding*> OutputEncoding() const {
+    return WrapNotNull(encoding_output_encoding(this));
+  }
+
+  /**
+   * Decode complete input to `nsACString` _with BOM sniffing_ and with
+   * malformed sequences replaced with the REPLACEMENT CHARACTER when the
+   * entire input is available as a single buffer (i.e. the end of the
+   * buffer marks the end of the stream).
+   *
+   * This method implements the (non-streaming version of) the
+   * _decode_ (https://encoding.spec.whatwg.org/#decode) spec concept.
+   *
+   * The second item in the returned tuple is the encoding that was actually
+   * used (which may differ from this encoding thanks to BOM sniffing).
+   *
+   * Returns `NS_ERROR_OUT_OF_MEMORY` upon OOM, `NS_OK_HAD_REPLACEMENTS`
+   * if there were malformed sequences (that were replaced with the
+   * REPLACEMENT CHARACTER) and `NS_OK` otherwise as the first item of the
+   * tuple.
+   *
+   * The backing buffer of the string isn't copied if the input buffer
+   * is heap-allocated and decoding from UTF-8 and the input is valid
+   * BOMless UTF-8, decoding from an ASCII-compatible encoding and
+   * the input is valid ASCII or decoding from ISO-2022-JP and the
+   * input stays in the ASCII state of ISO-2022-JP. It is OK to pass
+   * the same string as both arguments.
+   *
+   * _Note:_ It is wrong to use this when the input buffer represents only
+   * a segment of the input instead of the whole input. Use `NewDecoder()`
+   * when decoding segmented input.
+   */
+  inline std::tuple<nsresult, NotNull<const mozilla::Encoding*>> Decode(
+      const nsACString& aBytes, nsACString& aOut) const {
+    const Encoding* encoding = this;
+    const nsACString* bytes = &aBytes;
+    nsACString* out = &aOut;
+    nsresult rv;
+    if (bytes == out) {
+      nsAutoCString temp(aBytes);
+      rv = mozilla_encoding_decode_to_nscstring(&encoding, &temp, out);
+    } else {
+      rv = mozilla_encoding_decode_to_nscstring(&encoding, bytes, out);
+    }
+    return {rv, WrapNotNull(encoding)};
+  }
+
+  /**
+   * Decode complete input to `nsAString` _with BOM sniffing_ and with
+   * malformed sequences replaced with the REPLACEMENT CHARACTER when the
+   * entire input is available as a single buffer (i.e. the end of the
+   * buffer marks the end of the stream).
+   *
+   * This method implements the (non-streaming version of) the
+   * _decode_ (https://encoding.spec.whatwg.org/#decode) spec concept.
+   *
+   * The second item in the returned tuple is the encoding that was actually
+   * used (which may differ from this encoding thanks to BOM sniffing).
+   *
+   * Returns `NS_ERROR_OUT_OF_MEMORY` upon OOM, `NS_OK_HAD_REPLACEMENTS`
+   * if there were malformed sequences (that were replaced with the
+   * REPLACEMENT CHARACTER) and `NS_OK` otherwise as the first item of the
+   * tuple.
+   *
+   * _Note:_ It is wrong to use this when the input buffer represents only
+   * a segment of the input instead of the whole input. Use `NewDecoder()`
+   * when decoding segmented input.
+   */
+  inline std::tuple<nsresult, NotNull<const mozilla::Encoding*>> Decode(
+      Span<const uint8_t> aBytes, nsAString& aOut) const {
+    const Encoding* encoding = this;
+    nsresult rv = mozilla_encoding_decode_to_nsstring(
+        &encoding, aBytes.Elements(), aBytes.Length(), &aOut);
+    return {rv, WrapNotNull(encoding)};
+  }
+
+  /**
+   * Decode complete input to `nsACString` _with BOM removal_ and with
+   * malformed sequences replaced with the REPLACEMENT CHARACTER when the
+   * entire input is available as a single buffer (i.e. the end of the
+   * buffer marks the end of the stream).
+   *
+   * When invoked on `UTF_8`, this method implements the (non-streaming
+   * version of) the _UTF-8 decode_
+   * (https://encoding.spec.whatwg.org/#utf-8-decode) spec concept.
+   *
+   * Returns `NS_ERROR_OUT_OF_MEMORY` upon OOM, `NS_OK_HAD_REPLACEMENTS`
+   * if there were malformed sequences (that were replaced with the
+   * REPLACEMENT CHARACTER) and `NS_OK` otherwise.
+   *
+   * The backing buffer of the string isn't copied if the input buffer
+   * is heap-allocated and decoding from UTF-8 and the input is valid
+   * BOMless UTF-8, decoding from an ASCII-compatible encoding and
+   * the input is valid ASCII or decoding from ISO-2022-JP and the
+   * input stays in the ASCII state of ISO-2022-JP. It is OK to pass
+   * the same string as both arguments.
+   *
+   * _Note:_ It is wrong to use this when the input buffer represents only
+   * a segment of the input instead of the whole input. Use
+   * `NewDecoderWithBOMRemoval()` when decoding segmented input.
+   */
+  inline nsresult DecodeWithBOMRemoval(const nsACString& aBytes,
+                                       nsACString& aOut) const {
+    const nsACString* bytes = &aBytes;
+    nsACString* out = &aOut;
+    if (bytes == out) {
+      nsAutoCString temp(aBytes);
+      return mozilla_encoding_decode_to_nscstring_with_bom_removal(this, &temp,
+                                                                   out);
+    }
+    return mozilla_encoding_decode_to_nscstring_with_bom_removal(this, bytes,
+                                                                 out);
+  }
+
+  /**
+   * Decode complete input to `nsAString` _with BOM removal_ and with
+   * malformed sequences replaced with the REPLACEMENT CHARACTER when the
+   * entire input is available as a single buffer (i.e. the end of the
+   * buffer marks the end of the stream).
+   *
+   * When invoked on `UTF_8`, this method implements the (non-streaming
+   * version of) the _UTF-8 decode_
+   * (https://encoding.spec.whatwg.org/#utf-8-decode) spec concept.
+   *
+   * Returns `NS_ERROR_OUT_OF_MEMORY` upon OOM, `NS_OK_HAD_REPLACEMENTS`
+   * if there were malformed sequences (that were replaced with the
+   * REPLACEMENT CHARACTER) and `NS_OK` otherwise.
+   *
+   * _Note:_ It is wrong to use this when the input buffer represents only
+   * a segment of the input instead of the whole input. Use
+   * `NewDecoderWithBOMRemoval()` when decoding segmented input.
+   */
+  inline nsresult DecodeWithBOMRemoval(Span<const uint8_t> aBytes,
+                                       nsAString& aOut) const {
+    return mozilla_encoding_decode_to_nsstring_with_bom_removal(
+        this, aBytes.Elements(), aBytes.Length(), &aOut);
+  }
+
+  /**
+   * Decode complete input to `nsACString` _without BOM handling_ and
+   * with malformed sequences replaced with the REPLACEMENT CHARACTER when
+   * the entire input is available as a single buffer (i.e. the end of the
+   * buffer marks the end of the stream).
+   *
+   * When invoked on `UTF_8`, this method implements the (non-streaming
+   * version of) the _UTF-8 decode without BOM_
+   * (https://encoding.spec.whatwg.org/#utf-8-decode-without-bom) spec concept.
+   *
+   * Returns `NS_ERROR_OUT_OF_MEMORY` upon OOM, `NS_OK_HAD_REPLACEMENTS`
+   * if there were malformed sequences (that were replaced with the
+   * REPLACEMENT CHARACTER) and `NS_OK` otherwise.
+   *
+   * The backing buffer of the string isn't copied if the input buffer
+   * is heap-allocated and decoding from UTF-8 and the input is valid
+   * UTF-8, decoding from an ASCII-compatible encoding and the input
+   * is valid ASCII or decoding from ISO-2022-JP and the input stays
+   * in the ASCII state of ISO-2022-JP. It is OK to pass the same string
+   * as both arguments.
+   *
+   * _Note:_ It is wrong to use this when the input buffer represents only
+   * a segment of the input instead of the whole input. Use
+   * `NewDecoderWithoutBOMHandling()` when decoding segmented input.
+   */
+  inline nsresult DecodeWithoutBOMHandling(const nsACString& aBytes,
+                                           nsACString& aOut) const {
+    const nsACString* bytes = &aBytes;
+    nsACString* out = &aOut;
+    if (bytes == out) {
+      nsAutoCString temp(aBytes);
+      return mozilla_encoding_decode_to_nscstring_without_bom_handling(
+          this, &temp, out);
+    }
+    return mozilla_encoding_decode_to_nscstring_without_bom_handling(
+        this, bytes, out);
+  }
+
+  /**
+   * Decode complete input to `nsAString` _without BOM handling_ and
+   * with malformed sequences replaced with the REPLACEMENT CHARACTER when
+   * the entire input is available as a single buffer (i.e. the end of the
+   * buffer marks the end of the stream).
+   *
+   * When invoked on `UTF_8`, this method implements the (non-streaming
+   * version of) the _UTF-8 decode without BOM_
+   * (https://encoding.spec.whatwg.org/#utf-8-decode-without-bom) spec concept.
+   *
+   * Returns `NS_ERROR_OUT_OF_MEMORY` upon OOM, `NS_OK_HAD_REPLACEMENTS`
+   * if there were malformed sequences (that were replaced with the
+   * REPLACEMENT CHARACTER) and `NS_OK` otherwise.
+   *
+   * _Note:_ It is wrong to use this when the input buffer represents only
+   * a segment of the input instead of the whole input. Use
+   * `NewDecoderWithoutBOMHandling()` when decoding segmented input.
+   */
+  inline nsresult DecodeWithoutBOMHandling(Span<const uint8_t> aBytes,
+                                           nsAString& aOut) const {
+    return mozilla_encoding_decode_to_nsstring_without_bom_handling(
+        this, aBytes.Elements(), aBytes.Length(), &aOut);
+  }
+
+  /**
+   * Decode complete input to `nsACString` _without BOM handling_ and
+   * _with malformed sequences treated as fatal_ when the entire input is
+   * available as a single buffer (i.e. the end of the buffer marks the end
+   * of the stream).
+   *
+   * When invoked on `UTF_8`, this method implements the (non-streaming
+   * version of) the _UTF-8 decode without BOM or fail_
+   * (https://encoding.spec.whatwg.org/#utf-8-decode-without-bom-or-fail)
+   * spec concept.
+   *
+   * Returns `NS_ERROR_OUT_OF_MEMORY` upon OOM, `NS_ERROR_UDEC_ILLEGALINPUT`
+   * if a malformed sequence was encountered and `NS_OK` otherwise.
+   *
+   * The backing buffer of the string isn't copied if the input buffer
+   * is heap-allocated and decoding from UTF-8 and the input is valid
+   * UTF-8, decoding from an ASCII-compatible encoding and the input
+   * is valid ASCII or decoding from ISO-2022-JP and the input stays
+   * in the ASCII state of ISO-2022-JP. It is OK to pass the same string
+   * as both arguments.
+   *
+   * _Note:_ It is wrong to use this when the input buffer represents only
+   * a segment of the input instead of the whole input. Use
+   * `NewDecoderWithoutBOMHandling()` when decoding segmented input.
+   */
+  inline nsresult DecodeWithoutBOMHandlingAndWithoutReplacement(
+      const nsACString& aBytes, nsACString& aOut) const {
+    const nsACString* bytes = &aBytes;
+    nsACString* out = &aOut;
+    if (bytes == out) {
+      nsAutoCString temp(aBytes);
+      return mozilla_encoding_decode_to_nscstring_without_bom_handling_and_without_replacement(
+          this, &temp, out);
+    }
+    return mozilla_encoding_decode_to_nscstring_without_bom_handling_and_without_replacement(
+        this, bytes, out);
+  }
+
+  /**
+   * Decode complete input to `nsACString` _without BOM handling_ and
+   * with malformed sequences replaced with the REPLACEMENT CHARACTER when
+   * the entire input is available as a single buffer (i.e. the end of the
+   * buffer marks the end of the stream) _asserting that a number of bytes
+   * from the start are already known to be valid UTF-8_.
+   *
+   * The use case for this method is avoiding copying when dealing with
+   * input that has a UTF-8 BOM. _When in doubt, do not use this method._
+   *
+   * When invoked on `UTF_8`, this method implements the (non-streaming
+   * version of) the _UTF-8 decode without BOM_
+   * (https://encoding.spec.whatwg.org/#utf-8-decode-without-bom) spec concept.
+   *
+   * Returns `NS_ERROR_OUT_OF_MEMORY` upon OOM, `NS_OK_HAD_REPLACEMENTS`
+   * if there were malformed sequences (that were replaced with the
+   * REPLACEMENT CHARACTER) and `NS_OK` otherwise.
+   *
+   * _Note:_ It is wrong to use this when the input buffer represents only
+   * a segment of the input instead of the whole input. Use
+   * `NewDecoderWithoutBOMHandling()` when decoding segmented input.
+   *
+   * # Safety
+   *
+   * The first `aAlreadyValidated` bytes of `aBytes` _must_ be valid UTF-8.
+   * `aBytes` _must not_ alias the buffer (if any) of `aOut`.
+   */
+  inline nsresult DecodeWithoutBOMHandling(Span<const uint8_t> aBytes,
+                                           nsACString& aOut,
+                                           size_t aAlreadyValidated) const {
+    return mozilla_encoding_decode_from_slice_to_nscstring_without_bom_handling(
+        this, aBytes.Elements(), aBytes.Length(), &aOut, aAlreadyValidated);
+  }
+
+  /**
+   * Decode complete input to `nsAString` _without BOM handling_ and
+   * _with malformed sequences treated as fatal_ when the entire input is
+   * available as a single buffer (i.e. the end of the buffer marks the end
+   * of the stream).
+   *
+   * When invoked on `UTF_8`, this method implements the (non-streaming
+   * version of) the _UTF-8 decode without BOM or fail_
+   * (https://encoding.spec.whatwg.org/#utf-8-decode-without-bom-or-fail)
+   * spec concept.
+   *
+   * Returns `NS_ERROR_OUT_OF_MEMORY` upon OOM, `NS_ERROR_UDEC_ILLEGALINPUT`
+   * if a malformed sequence was encountered and `NS_OK` otherwise.
+   *
+   * _Note:_ It is wrong to use this when the input buffer represents only
+   * a segment of the input instead of the whole input. Use
+   * `NewDecoderWithoutBOMHandling()` when decoding segmented input.
+   */
+  inline nsresult DecodeWithoutBOMHandlingAndWithoutReplacement(
+      Span<const uint8_t> aBytes, nsAString& aOut) const {
+    return mozilla_encoding_decode_to_nsstring_without_bom_handling_and_without_replacement(
+        this, aBytes.Elements(), aBytes.Length(), &aOut);
+  }
+
+  /**
+   * Encode complete input to `nsACString` with unmappable characters
+   * replaced with decimal numeric character references when the entire input
+   * is available as a single buffer (i.e. the end of the buffer marks the
+   * end of the stream).
+   *
+   * This method implements the (non-streaming version of) the
+   * _encode_ (https://encoding.spec.whatwg.org/#encode) spec concept.
+   *
+   * The second item in the returned tuple is the encoding that was actually
+   * used (which may differ from this encoding thanks to some encodings
+   * having UTF-8 as their output encoding).
+   *
+   * The first item of the returned tuple is `NS_ERROR_UDEC_ILLEGALINPUT` if
+   * the input is not valid UTF-8, `NS_ERROR_OUT_OF_MEMORY` upon OOM,
+   * `NS_OK_HAD_REPLACEMENTS` if there were unmappable code points (that were
+   * replaced with numeric character references) and `NS_OK` otherwise.
+   *
+   * The backing buffer of the string isn't copied if the input buffer
+   * is heap-allocated and encoding to UTF-8 and the input is valid
+   * UTF-8, encoding to an ASCII-compatible encoding and the input
+   * is valid ASCII or encoding from ISO-2022-JP and the input stays
+   * in the ASCII state of ISO-2022-JP. It is OK to pass the same string
+   * as both arguments.
+   *
+   * _Note:_ It is wrong to use this when the input buffer represents only
+   * a segment of the input instead of the whole input. Use `NewEncoder()`
+   * when encoding segmented output.
+   */
+  inline std::tuple<nsresult, NotNull<const mozilla::Encoding*>> Encode(
+      const nsACString& aString, nsACString& aOut) const {
+    const Encoding* encoding = this;
+    const nsACString* string = &aString;
+    nsACString* out = &aOut;
+    nsresult rv;
+    if (string == out) {
+      nsAutoCString temp(aString);
+      rv = mozilla_encoding_encode_from_nscstring(&encoding, &temp, out);
+    } else {
+      rv = mozilla_encoding_encode_from_nscstring(&encoding, string, out);
+    }
+    return {rv, WrapNotNull(encoding)};
+  }
+
+  /**
+   * Encode complete input to `nsACString` with unmappable characters
+   * replaced with decimal numeric character references when the entire input
+   * is available as a single buffer (i.e. the end of the buffer marks the
+   * end of the stream).
+   *
+   * This method implements the (non-streaming version of) the
+   * _encode_ (https://encoding.spec.whatwg.org/#encode) spec concept.
+   *
+   * The second item in the returned tuple is the encoding that was actually
+   * used (which may differ from this encoding thanks to some encodings
+   * having UTF-8 as their output encoding).
+   *
+   * The first item of the returned tuple is `NS_ERROR_OUT_OF_MEMORY` upon
+   * OOM, `NS_OK_HAD_REPLACEMENTS` if there were unmappable code points (that
+   * were replaced with numeric character references) and `NS_OK` otherwise.
+
+   * _Note:_ It is wrong to use this when the input buffer represents only
+   * a segment of the input instead of the whole input. Use `NewEncoder()`
+   * when encoding segmented output.
+   */
+  inline std::tuple<nsresult, NotNull<const mozilla::Encoding*>> Encode(
+      Span<const char16_t> aString, nsACString& aOut) const {
+    const Encoding* encoding = this;
+    nsresult rv = mozilla_encoding_encode_from_utf16(
+        &encoding, aString.Elements(), aString.Length(), &aOut);
+    return {rv, WrapNotNull(encoding)};
+  }
+
+  /**
+   * Instantiates a new decoder for this encoding with BOM sniffing enabled.
+   *
+   * BOM sniffing may cause the returned decoder to morph into a decoder
+   * for UTF-8, UTF-16LE or UTF-16BE instead of this encoding.
+   */
+  inline UniquePtr<Decoder> NewDecoder() const {
+    UniquePtr<Decoder> decoder(encoding_new_decoder(this));
+    return decoder;
+  }
+
+  /**
+   * Instantiates a new decoder for this encoding with BOM sniffing enabled
+   * into memory occupied by a previously-instantiated decoder.
+   *
+   * BOM sniffing may cause the returned decoder to morph into a decoder
+   * for UTF-8, UTF-16LE or UTF-16BE instead of this encoding.
+   */
+  inline void NewDecoderInto(Decoder& aDecoder) const {
+    encoding_new_decoder_into(this, &aDecoder);
+  }
+
+  /**
+   * Instantiates a new decoder for this encoding with BOM removal.
+   *
+   * If the input starts with bytes that are the BOM for this encoding,
+   * those bytes are removed. However, the decoder never morphs into a
+   * decoder for another encoding: A BOM for another encoding is treated as
+   * (potentially malformed) input to the decoding algorithm for this
+   * encoding.
+   */
+  inline UniquePtr<Decoder> NewDecoderWithBOMRemoval() const {
+    UniquePtr<Decoder> decoder(encoding_new_decoder_with_bom_removal(this));
+    return decoder;
+  }
+
+  /**
+   * Instantiates a new decoder for this encoding with BOM removal
+   * into memory occupied by a previously-instantiated decoder.
+   *
+   * If the input starts with bytes that are the BOM for this encoding,
+   * those bytes are removed. However, the decoder never morphs into a
+   * decoder for another encoding: A BOM for another encoding is treated as
+   * (potentially malformed) input to the decoding algorithm for this
+   * encoding.
+   */
+  inline void NewDecoderWithBOMRemovalInto(Decoder& aDecoder) const {
+    encoding_new_decoder_with_bom_removal_into(this, &aDecoder);
+  }
+
+  /**
+   * Instantiates a new decoder for this encoding with BOM handling disabled.
+   *
+   * If the input starts with bytes that look like a BOM, those bytes are
+   * not treated as a BOM. (Hence, the decoder never morphs into a decoder
+   * for another encoding.)
+   *
+   * _Note:_ If the caller has performed BOM sniffing on its own but has not
+   * removed the BOM, the caller should use `NewDecoderWithBOMRemoval()`
+   * instead of this method to cause the BOM to be removed.
+   */
+  inline UniquePtr<Decoder> NewDecoderWithoutBOMHandling() const {
+    UniquePtr<Decoder> decoder(encoding_new_decoder_without_bom_handling(this));
+    return decoder;
+  }
+
+  /**
+   * Instantiates a new decoder for this encoding with BOM handling disabled
+   * into memory occupied by a previously-instantiated decoder.
+   *
+   * If the input starts with bytes that look like a BOM, those bytes are
+   * not treated as a BOM. (Hence, the decoder never morphs into a decoder
+   * for another encoding.)
+   *
+   * _Note:_ If the caller has performed BOM sniffing on its own but has not
+   * removed the BOM, the caller should use `NewDecoderWithBOMRemovalInto()`
+   * instead of this method to cause the BOM to be removed.
+   */
+  inline void NewDecoderWithoutBOMHandlingInto(Decoder& aDecoder) const {
+    encoding_new_decoder_without_bom_handling_into(this, &aDecoder);
+  }
+
+  /**
+   * Instantiates a new encoder for the output encoding of this encoding.
+   */
+  inline UniquePtr<Encoder> NewEncoder() const {
+    UniquePtr<Encoder> encoder(encoding_new_encoder(this));
+    return encoder;
+  }
+
+  /**
+   * Instantiates a new encoder for the output encoding of this encoding
+   * into memory occupied by a previously-instantiated encoder.
+   */
+  inline void NewEncoderInto(Encoder& aEncoder) const {
+    encoding_new_encoder_into(this, &aEncoder);
+  }
+
+  /**
+   * Validates UTF-8.
+   *
+   * Returns the index of the first byte that makes the input malformed as
+   * UTF-8 or the length of the input if the input is entirely valid.
+   */
+  static inline size_t UTF8ValidUpTo(Span<const uint8_t> aBuffer) {
+    return encoding_utf8_valid_up_to(aBuffer.Elements(), aBuffer.Length());
+  }
+
+  /**
+   * Validates ASCII.
+   *
+   * Returns the index of the first byte that makes the input malformed as
+   * ASCII or the length of the input if the input is entirely valid.
+   */
+  static inline size_t ASCIIValidUpTo(Span<const uint8_t> aBuffer) {
+    return encoding_ascii_valid_up_to(aBuffer.Elements(), aBuffer.Length());
+  }
+
+  /**
+   * Validates ISO-2022-JP ASCII-state data.
+   *
+   * Returns the index of the first byte that makes the input not
+   * representable in the ASCII state of ISO-2022-JP or the length of the
+   * input if the input is entirely representable in the ASCII state of
+   * ISO-2022-JP.
+   */
+  static inline size_t ISO2022JPASCIIValidUpTo(Span<const uint8_t> aBuffer) {
+    return encoding_iso_2022_jp_ascii_valid_up_to(aBuffer.Elements(),
+                                                  aBuffer.Length());
+  }
+
+ private:
+  Encoding() = delete;
+  Encoding(const Encoding&) = delete;
+  Encoding& operator=(const Encoding&) = delete;
+  ~Encoding() = delete;
+};
+
+/**
+ * A converter that decodes a byte stream into Unicode according to a
+ * character encoding in a streaming (incremental) manner.
+ *
+ * The various `Decode*` methods take an input buffer (`aSrc`) and an output
+ * buffer `aDst` both of which are caller-allocated. There are variants for
+ * both UTF-8 and UTF-16 output buffers.
+ *
+ * A `Decode*` method decodes bytes from `aSrc` into Unicode characters stored
+ * into `aDst` until one of the following three things happens:
+ *
+ * 1. A malformed byte sequence is encountered (`*WithoutReplacement`
+ *    variants only).
+ *
+ * 2. The output buffer has been filled so near capacity that the decoder
+ *    cannot be sure that processing an additional byte of input wouldn't
+ *    cause so much output that the output buffer would overflow.
+ *
+ * 3. All the input bytes have been processed.
+ *
+ * The `Decode*` method then returns tuple of a status indicating which one
+ * of the three reasons to return happened, how many input bytes were read,
+ * how many output code units (`uint8_t` when decoding into UTF-8 and `char16_t`
+ * when decoding to UTF-16) were written, and in the case of the
+ * variants performing replacement, a boolean indicating whether an error was
+ * replaced with the REPLACEMENT CHARACTER during the call.
+ *
+ * The number of bytes "written" is what's logically written. Garbage may be
+ * written in the output buffer beyond the point logically written to.
+ *
+ * In the case of the `*WithoutReplacement` variants, the status is a
+ * `uint32_t` whose possible values are packed info about a malformed byte
+ * sequence, `kOutputFull` and `kInputEmpty` corresponding to the three cases
+ * listed above).
+ *
+ * Packed info about malformed sequences has the following format:
+ * The lowest 8 bits, which can have the decimal value 0, 1, 2 or 3,
+ * indicate the number of bytes that were consumed after the malformed
+ * sequence and whose next-lowest 8 bits, when shifted right by 8 indicate
+ * the length of the malformed byte sequence (possible decimal values 1, 2,
+ * 3 or 4). The maximum possible sum of the two is 6.
+ *
+ * In the case of methods whose name does not end with
+ * `*WithoutReplacement`, malformed sequences are automatically replaced
+ * with the REPLACEMENT CHARACTER and errors do not cause the methods to
+ * return early.
+ *
+ * When decoding to UTF-8, the output buffer must have at least 4 bytes of
+ * space. When decoding to UTF-16, the output buffer must have at least two
+ * UTF-16 code units (`char16_t`) of space.
+ *
+ * When decoding to UTF-8 without replacement, the methods are guaranteed
+ * not to return indicating that more output space is needed if the length
+ * of the output buffer is at least the length returned by
+ * `MaxUTF8BufferLengthWithoutReplacement()`. When decoding to UTF-8
+ * with replacement, the length of the output buffer that guarantees the
+ * methods not to return indicating that more output space is needed is given
+ * by `MaxUTF8BufferLength()`. When decoding to UTF-16 with
+ * or without replacement, the length of the output buffer that guarantees
+ * the methods not to return indicating that more output space is needed is
+ * given by `MaxUTF16BufferLength()`.
+ *
+ * The output written into `aDst` is guaranteed to be valid UTF-8 or UTF-16,
+ * and the output after each `Decode*` call is guaranteed to consist of
+ * complete characters. (I.e. the code unit sequence for the last character is
+ * guaranteed not to be split across output buffers.)
+ *
+ * The boolean argument `aLast` indicates that the end of the stream is reached
+ * when all the bytes in `aSrc` have been consumed.
+ *
+ * A `Decoder` object can be used to incrementally decode a byte stream.
+ *
+ * During the processing of a single stream, the caller must call `Decode*`
+ * zero or more times with `aLast` set to `false` and then call `Decode*` at
+ * least once with `aLast` set to `true`. If `Decode*` returns `kInputEmpty`,
+ * the processing of the stream has ended. Otherwise, the caller must call
+ * `Decode*` again with `aLast` set to `true` (or treat a malformed result,
+ * i.e. neither `kInputEmpty` nor `kOutputFull`, as a fatal error).
+ *
+ * Once the stream has ended, the `Decoder` object must not be used anymore.
+ * That is, you need to create another one to process another stream.
+ *
+ * When the decoder returns `kOutputFull` or the decoder returns a malformed
+ * result and the caller does not wish to treat it as a fatal error, the input
+ * buffer `aSrc` may not have been completely consumed. In that case, the caller
+ * must pass the unconsumed contents of `aSrc` to `Decode*` again upon the next
+ * call.
+ *
+ * # Infinite loops
+ *
+ * When converting with a fixed-size output buffer whose size is too small to
+ * accommodate one character of output, an infinite loop ensues. When
+ * converting with a fixed-size output buffer, it generally makes sense to
+ * make the buffer fairly large (e.g. couple of kilobytes).
+ */
+class Decoder final {
+ public:
+  ~Decoder() = default;
+  static void operator delete(void* aDecoder) {
+    decoder_free(reinterpret_cast<Decoder*>(aDecoder));
+  }
+
+  /**
+   * The `Encoding` this `Decoder` is for.
+   *
+   * BOM sniffing can change the return value of this method during the life
+   * of the decoder.
+   */
+  inline NotNull<const mozilla::Encoding*> Encoding() const {
+    return WrapNotNull(decoder_encoding(this));
+  }
+
+  /**
+   * Query the worst-case UTF-8 output size _with replacement_.
+   *
+   * Returns the size of the output buffer in UTF-8 code units (`uint8_t`)
+   * that will not overflow given the current state of the decoder and
+   * `aByteLength` number of additional input bytes when decoding with
+   * errors handled by outputting a REPLACEMENT CHARACTER for each malformed
+   * sequence.
+   */
+  inline CheckedInt<size_t> MaxUTF8BufferLength(size_t aByteLength) const {
+    CheckedInt<size_t> max(decoder_max_utf8_buffer_length(this, aByteLength));
+    if (max.value() == std::numeric_limits<size_t>::max()) {
+      // Mark invalid by overflowing
+      max++;
+      MOZ_ASSERT(!max.isValid());
+    }
+    return max;
+  }
+
+  /**
+   * Query the worst-case UTF-8 output size _without replacement_.
+   *
+   * Returns the size of the output buffer in UTF-8 code units (`uint8_t`)
+   * that will not overflow given the current state of the decoder and
+   * `aByteLength` number of additional input bytes when decoding without
+   * replacement error handling.
+   *
+   * Note that this value may be too small for the `WithReplacement` case.
+   * Use `MaxUTF8BufferLength()` for that case.
+   */
+  inline CheckedInt<size_t> MaxUTF8BufferLengthWithoutReplacement(
+      size_t aByteLength) const {
+    CheckedInt<size_t> max(
+        decoder_max_utf8_buffer_length_without_replacement(this, aByteLength));
+    if (max.value() == std::numeric_limits<size_t>::max()) {
+      // Mark invalid by overflowing
+      max++;
+      MOZ_ASSERT(!max.isValid());
+    }
+    return max;
+  }
+
+  /**
+   * Incrementally decode a byte stream into UTF-8 with malformed sequences
+   * replaced with the REPLACEMENT CHARACTER.
+   *
+   * See the documentation of the class for documentation for `Decode*`
+   * methods collectively.
+   */
+  inline std::tuple<uint32_t, size_t, size_t, bool> DecodeToUTF8(
+      Span<const uint8_t> aSrc, Span<uint8_t> aDst, bool aLast) {
+    size_t srcRead = aSrc.Length();
+    size_t dstWritten = aDst.Length();
+    bool hadReplacements;
+    uint32_t result =
+        decoder_decode_to_utf8(this, aSrc.Elements(), &srcRead, aDst.Elements(),
+                               &dstWritten, aLast, &hadReplacements);
+    return {result, srcRead, dstWritten, hadReplacements};
+  }
+
+  /**
+   * Incrementally decode a byte stream into UTF-8 _without replacement_.
+   *
+   * See the documentation of the class for documentation for `Decode*`
+   * methods collectively.
+   */
+  inline std::tuple<uint32_t, size_t, size_t> DecodeToUTF8WithoutReplacement(
+      Span<const uint8_t> aSrc, Span<uint8_t> aDst, bool aLast) {
+    size_t srcRead = aSrc.Length();
+    size_t dstWritten = aDst.Length();
+    uint32_t result = decoder_decode_to_utf8_without_replacement(
+        this, aSrc.Elements(), &srcRead, aDst.Elements(), &dstWritten, aLast);
+    return {result, srcRead, dstWritten};
+  }
+
+  /**
+   * Query the worst-case UTF-16 output size (with or without replacement).
+   *
+   * Returns the size of the output buffer in UTF-16 code units (`char16_t`)
+   * that will not overflow given the current state of the decoder and
+   * `aByteLength` number of additional input bytes.
+   *
+   * Since the REPLACEMENT CHARACTER fits into one UTF-16 code unit, the
+   * return value of this method applies also in the
+   * `_without_replacement` case.
+   */
+  inline CheckedInt<size_t> MaxUTF16BufferLength(size_t aU16Length) const {
+    CheckedInt<size_t> max(decoder_max_utf16_buffer_length(this, aU16Length));
+    if (max.value() == std::numeric_limits<size_t>::max()) {
+      // Mark invalid by overflowing
+      max++;
+      MOZ_ASSERT(!max.isValid());
+    }
+    return max;
+  }
+
+  /**
+   * Incrementally decode a byte stream into UTF-16 with malformed sequences
+   * replaced with the REPLACEMENT CHARACTER.
+   *
+   * See the documentation of the class for documentation for `Decode*`
+   * methods collectively.
+   */
+  inline std::tuple<uint32_t, size_t, size_t, bool> DecodeToUTF16(
+      Span<const uint8_t> aSrc, Span<char16_t> aDst, bool aLast) {
+    size_t srcRead = aSrc.Length();
+    size_t dstWritten = aDst.Length();
+    bool hadReplacements;
+    uint32_t result = decoder_decode_to_utf16(this, aSrc.Elements(), &srcRead,
+                                              aDst.Elements(), &dstWritten,
+                                              aLast, &hadReplacements);
+    return {result, srcRead, dstWritten, hadReplacements};
+  }
+
+  /**
+   * Incrementally decode a byte stream into UTF-16 _without replacement_.
+   *
+   * See the documentation of the class for documentation for `Decode*`
+   * methods collectively.
+   */
+  inline std::tuple<uint32_t, size_t, size_t> DecodeToUTF16WithoutReplacement(
+      Span<const uint8_t> aSrc, Span<char16_t> aDst, bool aLast) {
+    size_t srcRead = aSrc.Length();
+    size_t dstWritten = aDst.Length();
+    uint32_t result = decoder_decode_to_utf16_without_replacement(
+        this, aSrc.Elements(), &srcRead, aDst.Elements(), &dstWritten, aLast);
+    return {result, srcRead, dstWritten};
+  }
+
+  /**
+   * Checks for compatibility with storing Unicode scalar values as unsigned
+   * bytes taking into account the state of the decoder.
+   *
+   * Returns `mozilla::Nothing()` if the decoder is not in a neutral state,
+   * including waiting for the BOM, or if the encoding is never
+   * Latin1-byte-compatible.
+   *
+   * Otherwise returns the index of the first byte whose unsigned value doesn't
+   * directly correspond to the decoded Unicode scalar value, or the length
+   * of the input if all bytes in the input decode directly to scalar values
+   * corresponding to the unsigned byte values.
+   *
+   * Does not change the state of the decoder.
+   *
+   * Do not use this unless you are supporting SpiderMonkey-style string
+   * storage optimizations.
+   */
+  inline mozilla::Maybe<size_t> Latin1ByteCompatibleUpTo(
+      Span<const uint8_t> aBuffer) const {
+    size_t upTo = decoder_latin1_byte_compatible_up_to(this, aBuffer.Elements(),
+                                                       aBuffer.Length());
+    if (upTo == std::numeric_limits<size_t>::max()) {
+      return mozilla::Nothing();
+    }
+    return mozilla::Some(upTo);
+  }
+
+ private:
+  Decoder() = delete;
+  Decoder(const Decoder&) = delete;
+  Decoder& operator=(const Decoder&) = delete;
+};
+
+/**
+ * A converter that encodes a Unicode stream into bytes according to a
+ * character encoding in a streaming (incremental) manner.
+ *
+ * The various `Encode*` methods take an input buffer (`aSrc`) and an output
+ * buffer `aDst` both of which are caller-allocated. There are variants for
+ * both UTF-8 and UTF-16 input buffers.
+ *
+ * An `Encode*` method encode characters from `aSrc` into bytes characters
+ * stored into `aDst` until one of the following three things happens:
+ *
+ * 1. An unmappable character is encountered (`*WithoutReplacement` variants
+ *    only).
+ *
+ * 2. The output buffer has been filled so near capacity that the decoder
+ *    cannot be sure that processing an additional character of input wouldn't
+ *    cause so much output that the output buffer would overflow.
+ *
+ * 3. All the input characters have been processed.
+ *
+ * The `Encode*` method then returns tuple of a status indicating which one
+ * of the three reasons to return happened, how many input code units (`uint8_t`
+ * when encoding from UTF-8 and `char16_t` when encoding from UTF-16) were read,
+ * how many output bytes were written, and in the case of the variants that
+ * perform replacement, a boolean indicating whether an unmappable
+ * character was replaced with a numeric character reference during the call.
+ *
+ * The number of bytes "written" is what's logically written. Garbage may be
+ * written in the output buffer beyond the point logically written to.
+ *
+ * In the case of the methods whose name ends with
+ * `*WithoutReplacement`, the status is a `uint32_t` whose possible values
+ * are an unmappable code point, `kOutputFull` and `kInputEmpty` corresponding
+ * to the three cases listed above).
+ *
+ * In the case of methods whose name does not end with
+ * `*WithoutReplacement`, unmappable characters are automatically replaced
+ * with the corresponding numeric character references and unmappable
+ * characters do not cause the methods to return early.
+ *
+ * When encoding from UTF-8 without replacement, the methods are guaranteed
+ * not to return indicating that more output space is needed if the length
+ * of the output buffer is at least the length returned by
+ * `MaxBufferLengthFromUTF8WithoutReplacement()`. When encoding from
+ * UTF-8 with replacement, the length of the output buffer that guarantees the
+ * methods not to return indicating that more output space is needed in the
+ * absence of unmappable characters is given by
+ * `MaxBufferLengthFromUTF8IfNoUnmappables()`. When encoding from
+ * UTF-16 without replacement, the methods are guaranteed not to return
+ * indicating that more output space is needed if the length of the output
+ * buffer is at least the length returned by
+ * `MaxBufferLengthFromUTF16WithoutReplacement()`. When encoding
+ * from UTF-16 with replacement, the the length of the output buffer that
+ * guarantees the methods not to return indicating that more output space is
+ * needed in the absence of unmappable characters is given by
+ * `MaxBufferLengthFromUTF16IfNoUnmappables()`.
+ * When encoding with replacement, applications are not expected to size the
+ * buffer for the worst case ahead of time but to resize the buffer if there
+ * are unmappable characters. This is why max length queries are only available
+ * for the case where there are no unmappable characters.
+ *
+ * When encoding from UTF-8, each `aSrc` buffer _must_ be valid UTF-8. When
+ * encoding from UTF-16, unpaired surrogates in the input are treated as U+FFFD
+ * REPLACEMENT CHARACTERS. Therefore, in order for astral characters not to
+ * turn into a pair of REPLACEMENT CHARACTERS, the caller must ensure that
+ * surrogate pairs are not split across input buffer boundaries.
+ *
+ * After an `Encode*` call returns, the output produced so far, taken as a
+ * whole from the start of the stream, is guaranteed to consist of a valid
+ * byte sequence in the target encoding. (I.e. the code unit sequence for a
+ * character is guaranteed not to be split across output buffers. However, due
+ * to the stateful nature of ISO-2022-JP, the stream needs to be considered
+ * from the start for it to be valid. For other encodings, the validity holds
+ * on a per-output buffer basis.)
+ *
+ * The boolean argument `aLast` indicates that the end of the stream is reached
+ * when all the characters in `aSrc` have been consumed. This argument is needed
+ * for ISO-2022-JP and is ignored for other encodings.
+ *
+ * An `Encoder` object can be used to incrementally encode a byte stream.
+ *
+ * During the processing of a single stream, the caller must call `Encode*`
+ * zero or more times with `aLast` set to `false` and then call `Encode*` at
+ * least once with `aLast` set to `true`. If `Encode*` returns `kInputEmpty`,
+ * the processing of the stream has ended. Otherwise, the caller must call
+ * `Encode*` again with `aLast` set to `true` (or treat an unmappable result,
+ * i.e. neither `kInputEmpty` nor `kOutputFull`, as a fatal error).
+ *
+ * Once the stream has ended, the `Encoder` object must not be used anymore.
+ * That is, you need to create another one to process another stream.
+ *
+ * When the encoder returns `kOutputFull` or the encoder returns an unmappable
+ * result and the caller does not wish to treat it as a fatal error, the input
+ * buffer `aSrc` may not have been completely consumed. In that case, the caller
+ * must pass the unconsumed contents of `aSrc` to `Encode*` again upon the next
+ * call.
+ *
+ * # Infinite loops
+ *
+ * When converting with a fixed-size output buffer whose size is too small to
+ * accommodate one character of output, an infinite loop ensues. When
+ * converting with a fixed-size output buffer, it generally makes sense to
+ * make the buffer fairly large (e.g. couple of kilobytes).
+ */
+class Encoder final {
+ public:
+  ~Encoder() = default;
+
+  static void operator delete(void* aEncoder) {
+    encoder_free(reinterpret_cast<Encoder*>(aEncoder));
+  }
+
+  /**
+   * The `Encoding` this `Encoder` is for.
+   */
+  inline NotNull<const mozilla::Encoding*> Encoding() const {
+    return WrapNotNull(encoder_encoding(this));
+  }
+
+  /**
+   * Returns `true` if this is an ISO-2022-JP encoder that's not in the
+   * ASCII state and `false` otherwise.
+   */
+  inline bool HasPendingState() const {
+    return encoder_has_pending_state(this);
+  }
+
+  /**
+   * Query the worst-case output size when encoding from UTF-8 with
+   * replacement.
+   *
+   * Returns the size of the output buffer in bytes that will not overflow
+   * given the current state of the encoder and `aByteLength` number of
+   * additional input code units if there are no unmappable characters in
+   * the input.
+   */
+  inline CheckedInt<size_t> MaxBufferLengthFromUTF8IfNoUnmappables(
+      size_t aByteLength) const {
+    CheckedInt<size_t> max(
+        encoder_max_buffer_length_from_utf8_if_no_unmappables(this,
+                                                              aByteLength));
+    if (max.value() == std::numeric_limits<size_t>::max()) {
+      // Mark invalid by overflowing
+      max++;
+      MOZ_ASSERT(!max.isValid());
+    }
+    return max;
+  }
+
+  /**
+   * Query the worst-case output size when encoding from UTF-8 without
+   * replacement.
+   *
+   * Returns the size of the output buffer in bytes that will not overflow
+   * given the current state of the encoder and `aByteLength` number of
+   * additional input code units.
+   */
+  inline CheckedInt<size_t> MaxBufferLengthFromUTF8WithoutReplacement(
+      size_t aByteLength) const {
+    CheckedInt<size_t> max(
+        encoder_max_buffer_length_from_utf8_without_replacement(this,
+                                                                aByteLength));
+    if (max.value() == std::numeric_limits<size_t>::max()) {
+      // Mark invalid by overflowing
+      max++;
+      MOZ_ASSERT(!max.isValid());
+    }
+    return max;
+  }
+
+  /**
+   * Incrementally encode into byte stream from UTF-8 with unmappable
+   * characters replaced with HTML (decimal) numeric character references.
+   *
+   * See the documentation of the class for documentation for `Encode*`
+   * methods collectively.
+   *
+   * WARNING WARNING WARNING WARNING WARNING WARNING WARNING WARNING:
+   * The input ***MUST*** be valid UTF-8 or bad things happen! Unless
+   * absolutely sure, use `Encoding::UTF8ValidUpTo()` to check.
+   */
+  inline std::tuple<uint32_t, size_t, size_t, bool> EncodeFromUTF8(
+      Span<const uint8_t> aSrc, Span<uint8_t> aDst, bool aLast) {
+    size_t srcRead = aSrc.Length();
+    size_t dstWritten = aDst.Length();
+    bool hadReplacements;
+    uint32_t result = encoder_encode_from_utf8(this, aSrc.Elements(), &srcRead,
+                                               aDst.Elements(), &dstWritten,
+                                               aLast, &hadReplacements);
+    return {result, srcRead, dstWritten, hadReplacements};
+  }
+
+  /**
+   * Incrementally encode into byte stream from UTF-8 _without replacement_.
+   *
+   * See the documentation of the class for documentation for `Encode*`
+   * methods collectively.
+   *
+   * WARNING WARNING WARNING WARNING WARNING WARNING WARNING WARNING:
+   * The input ***MUST*** be valid UTF-8 or bad things happen! Unless
+   * absolutely sure, use `Encoding::UTF8ValidUpTo()` to check.
+   */
+  inline std::tuple<uint32_t, size_t, size_t> EncodeFromUTF8WithoutReplacement(
+      Span<const uint8_t> aSrc, Span<uint8_t> aDst, bool aLast) {
+    size_t srcRead = aSrc.Length();
+    size_t dstWritten = aDst.Length();
+    uint32_t result = encoder_encode_from_utf8_without_replacement(
+        this, aSrc.Elements(), &srcRead, aDst.Elements(), &dstWritten, aLast);
+    return {result, srcRead, dstWritten};
+  }
+
+  /**
+   * Query the worst-case output size when encoding from UTF-16 with
+   * replacement.
+   *
+   * Returns the size of the output buffer in bytes that will not overflow
+   * given the current state of the encoder and `aU16Length` number of
+   * additional input code units if there are no unmappable characters in
+   * the input.
+   */
+  inline CheckedInt<size_t> MaxBufferLengthFromUTF16IfNoUnmappables(
+      size_t aU16Length) const {
+    CheckedInt<size_t> max(
+        encoder_max_buffer_length_from_utf16_if_no_unmappables(this,
+                                                               aU16Length));
+    if (max.value() == std::numeric_limits<size_t>::max()) {
+      // Mark invalid by overflowing
+      max++;
+      MOZ_ASSERT(!max.isValid());
+    }
+    return max;
+  }
+
+  /**
+   * Query the worst-case output size when encoding from UTF-16 without
+   * replacement.
+   *
+   * Returns the size of the output buffer in bytes that will not overflow
+   * given the current state of the encoder and `aU16Length` number of
+   * additional input code units.
+   */
+  inline CheckedInt<size_t> MaxBufferLengthFromUTF16WithoutReplacement(
+      size_t aU16Length) const {
+    CheckedInt<size_t> max(
+        encoder_max_buffer_length_from_utf16_without_replacement(this,
+                                                                 aU16Length));
+    if (max.value() == std::numeric_limits<size_t>::max()) {
+      // Mark invalid by overflowing
+      max++;
+      MOZ_ASSERT(!max.isValid());
+    }
+    return max;
+  }
+
+  /**
+   * Incrementally encode into byte stream from UTF-16 with unmappable
+   * characters replaced with HTML (decimal) numeric character references.
+   *
+   * See the documentation of the class for documentation for `Encode*`
+   * methods collectively.
+   */
+  inline std::tuple<uint32_t, size_t, size_t, bool> EncodeFromUTF16(
+      Span<const char16_t> aSrc, Span<uint8_t> aDst, bool aLast) {
+    size_t srcRead = aSrc.Length();
+    size_t dstWritten = aDst.Length();
+    bool hadReplacements;
+    uint32_t result = encoder_encode_from_utf16(this, aSrc.Elements(), &srcRead,
+                                                aDst.Elements(), &dstWritten,
+                                                aLast, &hadReplacements);
+    return {result, srcRead, dstWritten, hadReplacements};
+  }
+
+  /**
+   * Incrementally encode into byte stream from UTF-16 _without replacement_.
+   *
+   * See the documentation of the class for documentation for `Encode*`
+   * methods collectively.
+   */
+  inline std::tuple<uint32_t, size_t, size_t> EncodeFromUTF16WithoutReplacement(
+      Span<const char16_t> aSrc, Span<uint8_t> aDst, bool aLast) {
+    size_t srcRead = aSrc.Length();
+    size_t dstWritten = aDst.Length();
+    uint32_t result = encoder_encode_from_utf16_without_replacement(
+        this, aSrc.Elements(), &srcRead, aDst.Elements(), &dstWritten, aLast);
+    return {result, srcRead, dstWritten};
+  }
+
+ private:
+  Encoder() = delete;
+  Encoder(const Encoder&) = delete;
+  Encoder& operator=(const Encoder&) = delete;
+};
+
+};  // namespace mozilla
+
+#endif  // mozilla_Encoding_h