ndn-js
Version:
A JavaScript client library for Named Data Networking
226 lines (203 loc) • 7.99 kB
JavaScript
/**
* Copyright (C) 2014-2019 Regents of the University of California.
* @author: Jeff Thompson <jefft0@remap.ucla.edu>
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
* A copy of the GNU Lesser General Public License is in the file COPYING.
*/
/** @ignore */
var TlvDecoder = require('./tlv-decoder.js').TlvDecoder;
/**
* A TlvStructureDecoder finds the end of an NDN-TLV element, even if the
* element is supplied in parts.
* Create and initialize a TlvStructureDecoder.
* @constructor
*/
var TlvStructureDecoder = function TlvStructureDecoder()
{
this.gotElementEnd_ = false;
this.offset_ = 0;
this.state_ = TlvStructureDecoder.READ_TYPE;
this.headerLength_ = 0;
this.useHeaderBuffer_ = false;
// 8 bytes is enough to hold the extended bytes in the length encoding
// where it is an 8-byte number.
this.headerBuffer_ = new Buffer(8);
this.nBytesToRead_ = 0;
};
exports.TlvStructureDecoder = TlvStructureDecoder;
TlvStructureDecoder.READ_TYPE = 0;
TlvStructureDecoder.READ_TYPE_BYTES = 1;
TlvStructureDecoder.READ_LENGTH = 2;
TlvStructureDecoder.READ_LENGTH_BYTES = 3;
TlvStructureDecoder.READ_VALUE_BYTES = 4;
/**
* Continue scanning input starting from this.offset_ to find the element end.
* If the end of the element which started at offset 0 is found, this returns
* true and getOffset() is the length of the element. Otherwise, this returns
* false which means you should read more into input and call again.
* @param {Buffer} input The input buffer. You have to pass in input each time
* because the buffer could be reallocated.
* @return {boolean} true if found the element end, false if not.
*/
TlvStructureDecoder.prototype.findElementEnd = function(input)
{
if (this.gotElementEnd_)
// Someone is calling when we already got the end.
return true;
var decoder = new TlvDecoder(input);
while (true) {
if (this.offset_ >= input.length)
// All the cases assume we have some input. Return and wait for more.
return false;
if (this.state_ == TlvStructureDecoder.READ_TYPE) {
var firstOctet = input[this.offset_];
this.offset_ += 1;
if (firstOctet < 253)
// The value is simple, so we can skip straight to reading the length.
this.state_ = TlvStructureDecoder.READ_LENGTH;
else {
// Set up to skip the type bytes.
if (firstOctet == 253)
this.nBytesToRead_ = 2;
else if (firstOctet == 254)
this.nBytesToRead_ = 4;
else
// value == 255.
this.nBytesToRead_ = 8;
this.state_ = TlvStructureDecoder.READ_TYPE_BYTES;
}
}
else if (this.state_ == TlvStructureDecoder.READ_TYPE_BYTES) {
var nRemainingBytes = input.length - this.offset_;
if (nRemainingBytes < this.nBytesToRead_) {
// Need more.
this.offset_ += nRemainingBytes;
this.nBytesToRead_ -= nRemainingBytes;
return false;
}
// Got the type bytes. Move on to read the length.
this.offset_ += this.nBytesToRead_;
this.state_ = TlvStructureDecoder.READ_LENGTH;
}
else if (this.state_ == TlvStructureDecoder.READ_LENGTH) {
var firstOctet = input[this.offset_];
this.offset_ += 1;
if (firstOctet < 253) {
// The value is simple, so we can skip straight to reading
// the value bytes.
this.nBytesToRead_ = firstOctet;
if (this.nBytesToRead_ == 0) {
// No value bytes to read. We're finished.
this.gotElementEnd_ = true;
return true;
}
this.state_ = TlvStructureDecoder.READ_VALUE_BYTES;
}
else {
// We need to read the bytes in the extended encoding of
// the length.
if (firstOctet == 253)
this.nBytesToRead_ = 2;
else if (firstOctet == 254)
this.nBytesToRead_ = 4;
else
// value == 255.
this.nBytesToRead_ = 8;
// We need to use firstOctet in the next state.
this.firstOctet_ = firstOctet;
this.state_ = TlvStructureDecoder.READ_LENGTH_BYTES;
}
}
else if (this.state_ == TlvStructureDecoder.READ_LENGTH_BYTES) {
var nRemainingBytes = input.length - this.offset_;
if (!this.useHeaderBuffer_ && nRemainingBytes >= this.nBytesToRead_) {
// We don't have to use the headerBuffer. Set nBytesToRead.
decoder.seek(this.offset_);
this.nBytesToRead_ = decoder.readExtendedVarNumber(this.firstOctet_);
// Update this.offset_ to the decoder's offset after reading.
this.offset_ = decoder.getOffset();
}
else {
this.useHeaderBuffer_ = true;
var nNeededBytes = this.nBytesToRead_ - this.headerLength_;
if (nNeededBytes > nRemainingBytes) {
// We can't get all of the header bytes from this input.
// Save in headerBuffer.
if (this.headerLength_ + nRemainingBytes > this.headerBuffer_.length)
// We don't expect this to happen.
throw new Error
("Cannot store more header bytes than the size of headerBuffer");
input.slice(this.offset_, this.offset_ + nRemainingBytes).copy
(this.headerBuffer_, this.headerLength_);
this.offset_ += nRemainingBytes;
this.headerLength_ += nRemainingBytes;
return false;
}
// Copy the remaining bytes into headerBuffer, read the
// length and set nBytesToRead.
if (this.headerLength_ + nNeededBytes > this.headerBuffer_.length)
// We don't expect this to happen.
throw new Error
("Cannot store more header bytes than the size of headerBuffer");
input.slice(this.offset_, this.offset_ + nNeededBytes).copy
(this.headerBuffer_, this.headerLength_);
this.offset_ += nNeededBytes;
// Use a local decoder just for the headerBuffer.
var bufferDecoder = new TlvDecoder(this.headerBuffer_);
// Replace nBytesToRead with the length of the value.
this.nBytesToRead_ = bufferDecoder.readExtendedVarNumber(this.firstOctet_);
}
if (this.nBytesToRead_ == 0) {
// No value bytes to read. We're finished.
this.gotElementEnd_ = true;
return true;
}
// Get ready to read the value bytes.
this.state_ = TlvStructureDecoder.READ_VALUE_BYTES;
}
else if (this.state_ == TlvStructureDecoder.READ_VALUE_BYTES) {
var nRemainingBytes = input.length - this.offset_;
if (nRemainingBytes < this.nBytesToRead_) {
// Need more.
this.offset_ += nRemainingBytes;
this.nBytesToRead_ -= nRemainingBytes;
return false;
}
// Got the bytes. We're finished.
this.offset_ += this.nBytesToRead_;
this.gotElementEnd_ = true;
return true;
}
else
// We don't expect this to happen.
throw new Error("findElementEnd: unrecognized state");
}
};
/**
* Get the current offset into the input buffer.
* @return {number} The offset.
*/
TlvStructureDecoder.prototype.getOffset = function()
{
return this.offset_;
};
/**
* Set the offset into the input, used for the next read.
* @param {number} offset The new offset.
*/
TlvStructureDecoder.prototype.seek = function(offset)
{
this.offset_ = offset;
};