// Copyright 2012 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
export class ByteReader {
private readonly view_: DataView;
private pos_ = 0;
private readonly seekStack_: number[] = [];
private littleEndian_ = false;
/**
* @param arrayBuffer An array of buffers to be read from.
* @param offset Offset to read bytes at.
* @param length Number of bytes to read.
*/
constructor(arrayBuffer: ArrayBuffer, offset = 0, length?: number) {
length = length || (arrayBuffer.byteLength - offset);
this.view_ = new DataView(arrayBuffer, offset, length);
}
/**
* Throw an error if (0 > pos >= end) or if (pos + size > end).
*
* Static utility function.
*
* @param pos Position in the file.
* @param size Number of bytes to read.
* @param end Maximum position to read from.
*/
static validateRead(pos: number, size: number, end: number) {
if (pos < 0 || pos >= end) {
throw new Error('Invalid read position');
}
if (pos + size > end) {
throw new Error('Read past end of buffer');
}
}
/**
* Read as a sequence of characters, returning them as a single string.
*
* This is a static utility function. There is a member function with the
* same name which side-effects the current read position.
*
* @param dataView Data view instance.
* @param pos Position in bytes to read from.
* @param size Number of bytes to read.
* @param end Maximum position to read from.
* @return Read string.
*/
static readString(
dataView: DataView, pos: number, size: number, end?: number): string {
ByteReader.validateRead(pos, size, end || dataView.byteLength);
const codes = [];
for (let i = 0; i < size; ++i) {
codes.push(dataView.getUint8(pos + i));
}
return String.fromCharCode.apply(null, codes);
}
/**
* Read as a sequence of characters, returning them as a single string.
*
* This is a static utility function. There is a member function with the
* same name which side-effects the current read position.
*
* @param dataView Data view instance.
* @param pos Position in bytes to read from.
* @param size Number of bytes to read.
* @param end Maximum position to read from.
* @return Read string.
*/
static readNullTerminatedString(
dataView: DataView, pos: number, size: number, end?: number): string {
ByteReader.validateRead(pos, size, end || dataView.byteLength);
const codes = [];
for (let i = 0; i < size; ++i) {
const code = dataView.getUint8(pos + i);
if (code === 0) {
break;
}
codes.push(code);
}
return String.fromCharCode.apply(null, codes);
}
/**
* Read as a sequence of UTF16 characters, returning them as a single string.
*
* This is a static utility function. There is a member function with the
* same name which side-effects the current read position.
*
* @param dataView Data view instance.
* @param pos Position in bytes to read from.
* @param bom True if BOM should be parsed.
* @param size Number of bytes to read.
* @param end Maximum position to read from.
* @return Read string.
*/
static readNullTerminatedStringUtf16(
dataView: DataView, pos: number, bom: boolean, size: number,
end?: number): string {
ByteReader.validateRead(pos, size, end || dataView.byteLength);
let littleEndian = false;
let start = 0;
if (bom) {
littleEndian = (dataView.getUint8(pos) === 0xFF);
start = 2;
}
const codes = [];
for (let i = start; i < size; i += 2) {
const code = dataView.getUint16(pos + i, littleEndian);
if (code === 0) {
break;
}
codes.push(code);
}
return String.fromCharCode.apply(null, codes);
}
/**
* Read as a sequence of bytes, returning them as a single base64 encoded
* string.
*
* This is a static utility function. There is a member function with the
* same name which side-effects the current read position.
*
* @param dataView Data view instance.
* @param pos Position in bytes to read from.
* @param size Number of bytes to read.
* @param end Maximum position to read from.
* @return Base 64 encoded value.
*/
static readBase64(
dataView: DataView, pos: number, size: number, end?: number): string {
ByteReader.validateRead(pos, size, end || dataView.byteLength);
const rv: string[] = [];
const chars: string[] = [];
let padding = 0;
for (let i = 0; i < size; /* incremented inside */) {
let bits = dataView.getUint8(pos + (i++)) << 16;
if (i < size) {
bits |= dataView.getUint8(pos + (i++)) << 8;
if (i < size) {
bits |= dataView.getUint8(pos + (i++));
} else {
padding = 1;
}
} else {
padding = 2;
}
chars[3] = BASE64_ALPHABET[bits & 63]!;
chars[2] = BASE64_ALPHABET[(bits >> 6) & 63]!;
chars[1] = BASE64_ALPHABET[(bits >> 12) & 63]!;
chars[0] = BASE64_ALPHABET[(bits >> 18) & 63]!;
rv.push.apply(rv, chars);
}
if (padding > 0) {
rv[rv.length - 1] = '=';
}
if (padding > 1) {
rv[rv.length - 2] = '=';
}
return rv.join('');
}
/**
* Read as an image encoded in a data url.
*
* This is a static utility function. There is a member function with the
* same name which side-effects the current read position.
*
* @param dataView Data view instance.
* @param pos Position in bytes to read from.
* @param size Number of bytes to read.
* @param end Maximum position to read from.
* @return Image as a data url.
*/
static readImage(dataView: DataView, pos: number, size: number, end?: number):
string {
end = end || dataView.byteLength;
ByteReader.validateRead(pos, size, end);
// Two bytes is enough to identify the mime type.
const prefixToMime: Record<string, string> = {
'\x89P': 'png',
'\xFF\xD8': 'jpeg',
'BM': 'bmp',
'GI': 'gif',
};
const prefix = ByteReader.readString(dataView, pos, 2, end);
const mime = prefixToMime[prefix] ||
dataView.getUint16(pos, false).toString(16); // For debugging.
const b64 = ByteReader.readBase64(dataView, pos, size, end);
return 'data:image/' + mime + ';base64,' + b64;
}
/**
* Return true if the requested number of bytes can be read from the buffer.
*
* @param size Number of bytes to read.
* @return True if allowed, false otherwise.
*/
canRead(size: number): boolean {
return this.pos_ + size <= this.view_.byteLength;
}
/**
* Return true if the current position is past the end of the buffer.
* @return True if EOF, otherwise false.
*/
eof(): boolean {
return this.pos_ >= this.view_.byteLength;
}
/**
* Return true if the current position is before the beginning of the buffer.
* @return True if BOF, otherwise false.
*/
bof(): boolean {
return this.pos_ < 0;
}
/**
* Return true if the current position is outside the buffer.
* @return True if outside, false if inside.
*/
beof(): boolean {
return this.pos_ >= this.view_.byteLength || this.pos_ < 0;
}
/**
* Set the expected byte ordering for future reads.
* @param order Byte order. Either LITTLE_ENDIAN or BIG_ENDIAN.
*/
setByteOrder(order: ByteOrder) {
this.littleEndian_ = order === ByteOrder.LITTLE_ENDIAN;
}
/**
* Throw an error if the reader is at an invalid position, or if a read a read
* of |size| would put it in one.
*
* You may optionally pass |end| to override what is considered to be the
* end of the buffer.
*
* @param size Number of bytes to read.
* @param end Maximum position to read from.
*/
validateRead(size: number, end?: number) {
if (typeof end === 'undefined') {
end = this.view_.byteLength;
}
ByteReader.validateRead(this.pos_, size, end);
}
/**
* @param width Number of bytes to read.
* @param signed True if signed, false otherwise.
* @param end Maximum position to read from.
* @return Scalar value.
*/
readScalar(
width: keyof typeof WIDTH_TO_DATA_VIEW_METHOD, signed?: boolean,
end?: number): number {
this.validateRead(width, end);
const method = WIDTH_TO_DATA_VIEW_METHOD[width][signed ? 1 : 0];
let rv;
if (method === 'getInt8' || method === 'getUint8') {
rv = this.view_[method](this.pos_);
} else {
rv = this.view_[method](this.pos_, this.littleEndian_);
}
this.pos_ += width;
return rv;
}
/**
* Read as a sequence of characters, returning them as a single string.
*
* Adjusts the current position on success. Throws an exception if the
* read would go past the end of the buffer.
*
* @param size Number of bytes to read.
* @param end Maximum position to read from.
* @return String value.
*/
readString(size: number, end?: number): string {
const rv = ByteReader.readString(this.view_, this.pos_, size, end);
this.pos_ += size;
return rv;
}
/**
* Read as a sequence of characters, returning them as a single string.
*
* Adjusts the current position on success. Throws an exception if the
* read would go past the end of the buffer.
*
* @param size Number of bytes to read.
* @param end Maximum position to read from.
* @return Null-terminated string value.
*/
readNullTerminatedString(size: number, end?: number): string {
const rv =
ByteReader.readNullTerminatedString(this.view_, this.pos_, size, end);
this.pos_ += rv.length;
if (rv.length < size) {
// If we've stopped reading because we found '0' but didn't hit size limit
// then we should skip additional '0' character
this.pos_++;
}
return rv;
}
/**
* Read as a sequence of UTF16 characters, returning them as a single string.
*
* Adjusts the current position on success. Throws an exception if the
* read would go past the end of the buffer.
*
* @param bom True if BOM should be parsed.
* @param size Number of bytes to read.
* @param end Maximum position to read from.
* @return Read string.
*/
readNullTerminatedStringUtf16(bom: boolean, size: number, end?: number):
string {
const rv = ByteReader.readNullTerminatedStringUtf16(
this.view_, this.pos_, bom, size, end);
if (bom) {
// If the BOM word was present advance the position.
this.pos_ += 2;
}
this.pos_ += rv.length;
if (rv.length < size) {
// If we've stopped reading because we found '0' but didn't hit size limit
// then we should skip additional '0' character
this.pos_ += 2;
}
return rv;
}
/**
* Read as a sequence of bytes, returning them as a single base64 encoded
* string.
*
* Adjusts the current position on success. Throws an exception if the
* read would go past the end of the buffer.
*
* @param size Number of bytes to read.
* @param end Maximum position to read from.
* @return Base 64 encoded value.
*/
readBase64(size: number, end: number|undefined): string {
const rv = ByteReader.readBase64(this.view_, this.pos_, size, end);
this.pos_ += size;
return rv;
}
/**
* Read an image returning it as a data url.
*
* Adjusts the current position on success. Throws an exception if the
* read would go past the end of the buffer.
*
* @param size Number of bytes to read.
* @param end Maximum position to read from.
* @return Image as a data url.
*/
readImage(size: number, end?: number): string {
const rv = ByteReader.readImage(this.view_, this.pos_, size, end);
this.pos_ += size;
return rv;
}
/**
* Seek to a give position relative to seekStart.
*
* @param pos Position in bytes to seek to.
* @param seekStart Relative position in bytes.
* @param end Maximum position to seek to.
*/
seek(pos: number, seekStart = SeekOrigin.SEEK_BEG, end?: number) {
end = end || this.view_.byteLength;
let newPos;
if (seekStart === SeekOrigin.SEEK_CUR) {
newPos = this.pos_ + pos;
} else if (seekStart === SeekOrigin.SEEK_END) {
newPos = end + pos;
} else {
newPos = pos;
}
if (newPos < 0 || newPos > this.view_.byteLength) {
throw new Error('Seek outside of buffer: ' + (newPos - end));
}
this.pos_ = newPos;
}
/**
* Seek to a given position relative to seekStart, saving the current
* position.
*
* Recover the current position with a call to seekPop.
*
* @param pos Position in bytes to seek to.
* @param seekStart Relative position in bytes.
*/
pushSeek(pos: number, seekStart?: number) {
const oldPos = this.pos_;
this.seek(pos, seekStart);
// Alter the seekStack_ after the call to seek(), in case it throws.
this.seekStack_.push(oldPos);
}
/**
* Undo a previous seekPush.
*/
popSeek() {
const lastSeek = this.seekStack_.pop();
if (lastSeek !== undefined) {
this.seek(lastSeek);
}
}
/**
* Return the current read position.
* @return Current position in bytes.
*/
tell(): number {
return this.pos_;
}
}
export enum ByteOrder {
// Intel, 0x1234 is [0x34, 0x12]
LITTLE_ENDIAN = 0,
// Motorola, 0x1234 is [0x12, 0x34]
BIG_ENDIAN = 1,
}
export enum SeekOrigin {
// Seek relative to the beginning of the buffer.
SEEK_BEG = 0,
// Seek relative to the current position.
SEEK_CUR = 1,
// Seek relative to the end of the buffer.
SEEK_END = 2,
}
const BASE64_ALPHABET =
('ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/')
.split('');
const WIDTH_TO_DATA_VIEW_METHOD = {
1: ['getUint8', 'getInt8'],
2: ['getUint16', 'getInt16'],
4: ['getUint32', 'getInt32'],
} as const;
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