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This module provides a very fast (as in gigabytes per second), compiled implementation of yEnc and CRC32 (IEEE) hash calculation for node.js. The implementations are optimised for speed, and uses x86/ARM SIMD optimised routines if such CPU features are available.

This module should be 1-2 orders of magnitude faster than pure Javascript versions.


  • fast raw yEnc encoding with the ability to specify line length. A single thread can achieve >450MB/s on a Raspberry Pi 3, or >5GB/s on a Core-i series CPU.
  • fast yEnc decoding, with and without NNTP layer dot unstuffing. A single thread can achieve >300MB/s on a Raspberry Pi 3, or >4.5GB/s on a Core-i series CPU.
  • SIMD optimised encoding and decoding routines, which can use ARMv7 NEON, ARMv8 ASIMD or the following x86 CPU features when available (with dynamic dispatch): SSE2, SSSE3, AVX, AVX2, AVX512-BW (128/256-bit), AVX512-VBMI2
  • full yEnc encoding for single and multi-part posts, according to the version 1.3 specifications
  • full yEnc decoding of posts
  • fast compiled CRC32 implementation via crcutil or PCLMULQDQ instruction (if available) or ARMv8’s CRC instructions, with incremental support (>1GB/s on a low power Atom/ARM CPU, >15GB/s on a modern Intel CPU)
  • ability to combine two CRC32 hashes into one (useful for amalgamating pcrc32s into a crc32 for yEnc), as well as quickly compute the CRC32 of a sequence of null bytes
  • eventually may support incremental processing (algorithms internally support it, they’re just not exposed to the Javascript interface)
  • context awareness (NodeJS 10.7.0 or later), enabling use within worker threads
  • supports NodeJS 0.10.x to 12.x.x and beyond


npm install yencode

Or you can download the package and run

npm install -g node-gyp # if you don't have it already
node-gyp rebuild

Note, Windows builds are always compiled with SSE2 support. If you can’t have this, delete all instances of "msvs_settings": {"VCCLCompilerTool": {"EnableEnhancedInstructionSet": "2"}}, in binding.gyp before compiling.

Redistributable Builds

By default, non-Windows builds are built with -march=native flag, which means that the compiler will optimise the build for the CPU of the build machine. If you’re looking to run built binaries elsewhere, this may be undesirable. To make builds redistributable, replace "enable_native_tuning%": 1, from binding.gyp with "enable_native_tuning%": 0, and (re)compile.

Windows builds are redistributable by default as MSVC doesn’t support native CPU targeting.

Older Compilers

Unfortunately node-gyp doesn’t provide much in the way of compiler version detection. As such, the build script assumes the compiler isn’t too old and supports AVX. If you are trying to build using an older compiler (such as Visual Studio 2008), you may need to edit binding.gyp to remove AVX related options, such as -mavx, -mpopcnt and "EnableEnhancedInstructionSet": "3"

GCC 9 on ARMv7

I’ve noticed that GCC 9.2.1 (which may include GCC 9.x.x), with ARMv7 targets, seems to generate code which crashes. I‘m not yet sure on the reason, but have not seen the issue with GCC 8.3.0 or Clang, or GCC 9 with ARMv8 targets.


Note, on node v0.10, functions returning a Buffer actually return a SlowBuffer object, similar to how node’s crypto functions work.

Buffer encode(Buffer data, int line_size=128, int column_offset=0)

Performs raw yEnc encoding on data returning the result.
line_size controls how often to insert newlines (note, as per yEnc specifications, it's possible to have lines longer than this length)
column_offset is the column of the first character

int encodeTo(Buffer data, Buffer output, int line_size=128, int column_offset=0)

Same as above, but instead of returning a Buffer, writes it to the supplied output Buffer. Returns the length of the encoded data.
Note that the output Buffer must be at least large enough to hold the largest possible output size (use the maxSize function to determine this), otherwise an error will be thrown. Whilst this amount of space is usually not required, for performance reasons this is not checked during encoding, so the space is needed to prevent possible overflow conditions.

int maxSize(int length, int line_size=128, float escape_ratio=1)

Returns the maximum possible size for a raw yEnc encoded message of length bytes. Note that this does include some provision for dealing with alignment issues specific to yencode‘s implementation; in other words, the returned value is actually an over-estimate for the maximum size.

You can manually specify expected yEnc character escaping ratio with the escape_ratio parameter if you wish to calculate an “expected size” rather than the maximum. The ratio must be between 0 (no characters ever escaped) and 1 (all characters escaped, i.e. calculates maximum possible size, the default behavior). For random data, and a line size of 128, the expected escape ratio for yEnc is roughly 0.0158. For 1KB of random data, the probability that the escape ratio exceeds 5% would be about 2.188*10^-12^ (or 1 in 4.571*10^11^). For 128KB of random data, exceeding a 1.85% ratio has a likelihood of 1.174*10^-14^ (or 1 in 8.517*10^13^).

For usage with encodeTo, the escape_ratio must be 1.

int minSize(int length, int line_size=128)

Returns the minimum possible size for a raw yEnc encoded message of length bytes. Unlike maxSize, this does not include alignment provisions for yencode‘s implementation of yEnc.

This is equivalent to maxSize(length, line_size, 0) - 2 (maxSize adds a 2 to provision for an early end-of-line due to a line offset being used).

Buffer decode(Buffer data, bool stripDots=false)

Performs raw yEnc decoding on data returning the result. If stripDots is true, will perform NNTP's "dot unstuffing" during decode. If data was sourced from an NNTP abstraction layer which already performs unstuffing, stripDots should be false, otherwise, if you're processing data from the socket yourself and haven't othewise performed unstuffing, stripDots should be set to true.

int decodeTo(Buffer data, Buffer output, bool stripDots=false)

Same as above, but instead of returning a Buffer, writes it to the supplied output Buffer. Returns the length of the decoded data.
Note that the output Buffer must be at least large enough to hold the largest possible output size (i.e. length of the input), otherwise an error is thrown.

Object decodeChunk(Buffer data [, string state=null][, Buffer output])

Perform raw yEnc decoding on a chunk of data sourced from NNTP. This function is designed to incrementally process a stream from the network, and will perform NNTP "dot unstuffing" as well as stop when the end of the data is reached.

data is the data to be decoded
state is the current state of the incremental decode. Set to null if this is starting the decode of a new article, otherwise this should be set to the value of state given from the previous invocation of decodeChunk
If output is supplied, the output will be written here (see decodeTo for notes on required size), otherwise a new buffer will be created where the output will be written to.

Returns an object with the following keys:

  • int read: number of bytes read from the data. Will be equal to the length of the input unless the end was reached (ended set to true).
  • int written: number of bytes written to the output
  • Buffer output: the output data. If the output parameter was supplied to this function, this will just be a reference to it.
  • bool ended: whether the end of the yEnc data was reached. The state value will indicate the type of end which was reached
  • string state: the state after decoding. This indicates the last few (up to 4) characters encountered, if they affect the decoding of subsequent characters. For example, a state of "=" suggests that the first byte of the next call to decodeChunk needs to be unescaped. Feed this into the next invocation of decodeChunk Note that this value is after NNTP “dot unstuffing”, where applicable (\r\n.= sequences are replaced with \r\n=) If the end was reached (ended set to true), this will indicate the type of end which was reached, which can be either \r\n=y (yEnc control line encountered) or \r\n.\r\n (end of article marker encountered)

Buffer(4) crc32(Buffer data, Buffer(4) initial=false)

Calculate CRC32 hash of data, returning the hash as a 4 byte Buffer.
You can perform incremental CRC32 calculation by specifying a 4 byte Buffer in the second argument.


y.crc32(new Buffer('the fox jumped'))
// <Buffer f8 7b 6f 30>
y.crc32(new Buffer(' into the fence'), new Buffer([0xf8, 0x7b, 0x6f, 0x30]))
// <Buffer 70 4f 00 7e>

Buffer(4) crc32_combine(Buffer(4) crc1, Buffer(4) crc2, int len2)

Combines two CRC32s, returning the resulting CRC32 as a 4 byte Buffer. To put it another way, it calculates crc32(a+b) given crc32(a), crc32(b) and b.length.
crc1 is the first CRC, crc2 is the CRC to append onto the end, where len2 represents then length of the data being appended.


  y.crc32(new Buffer('the fox jumped')),
  y.crc32(new Buffer(' into the fence')),
  ' into the fence'.length
// <Buffer 70 4f 00 7e>

Buffer(4) crc32_zeroes(int len, Buffer(4) initial=false)

Calculates the CRC32 of a sequence of len null bytes, returning the resulting CRC32 as a 4 byte Buffer. You can supply a starting CRC32 value by passing it in the second parameter.


// <Buffer 41 d9 12 ff>
y.crc32(new Buffer([0, 0]))
// <Buffer 41 d9 12 ff>
y.crc32_zeroes(2, y.crc32(new Buffer([1, 2])))
// <Buffer 9a 7c 6c 17>
y.crc32(new Buffer([1, 2, 0, 0]))
// <Buffer 9a 7c 6c 17>

Buffer post(string filename, data, int line_size=128)

Returns a single yEnc encoded post, suitable for posting to newsgroups.
Note that data can be a Buffer or string or anything that Buffer.from or new Buffer accepts (this differs from the above functions).

Example'bytes.bin', [0, 1, 2, 3, 4]).toString()
// '=ybegin line=128 size=5 name=bytes.bin\r\n*+,-.\r\n=yend size=5 crc32=515ad3cc'

YEncoder multi_post(string filename, int size, int parts, int line_size=128)

Returns a YEncoder instance for generating multi-part yEnc posts. This implementation will only generate multi-part posts sequentially.
You need to supply the size of the file, and the number of parts that it will be broken into (typically this will be Math.ceil(file_size/article_size))

The YEncoder instance has the following method and read-only properties:

  • Buffer encode(data) : Encode the next part (data) and returns the result.

  • int size : The file's size

  • int parts : Number of parts to post

  • int line_size : Size of each line

  • int part : Current part

  • int pos : Current position in file

  • int crc : CRC32 of data already fed through encode()


enc = y.multi_post('bytes.bin', 5, 1)
enc.encode([0, 1, 2, 3, 4]).toString()
// '=ybegin line=128 size=5 name=bytes.bin\r\n*+,-.\r\n=yend size=5 crc32=515ad3cc'
<Buffer 51 5a d3 cc>

Example 2

enc = y.multi_post('bytes.bin', 5, 2)
enc.encode([0, 1, 2, 3]).toString()
// '=ybegin part=1 total=2 line=128 size=5 name=bytes.bin\r\n=ypart begin=1 end=4\r\n*+,-\r\n=yend size=4 part=1 pcrc32=8bb98613'
// '=ybegin part=2 total=2 line=128 size=5 name=bytes.bin\r\n=ypart begin=5 end=5\r\n=n\r\n=yend size=1 part=2 pcrc32=d56f2b94 crc32=515ad3cc'

{Object|DecoderError} from_post(Buffer data, bool stripDots=false)

Decode post specified in data. Set stripDots to true if NNTP “dot unstuffing” has not yet been performed.

Returns an object detailing the info parsed from the post, where the keys are:

  • int yencStart: location of the =ybegin sequence (is usually 0 for most posts)
  • int dataStart: location of where the yEnc raw data begins
  • int dataEnd: location of where the yEnc raw data ends
  • int yencEnd: location of the end of the =yend line (after the trailing newline)
  • Buffer data: decoded data
  • Buffer(4) crc32: 4 byte CRC32 of decoded data
  • Object<Object<string>> props: two-level structure listing the properties given in the yEnc metadata. First level represents the line type (e.g. =ybegin line is keyed as begin), and the second level maps keys to values within that line. For example, the line =ybegin line=128 name=my-file.dat would be decoded as {begin: {line: "128", name: "my-file.dat"}}
  • Array<DecoderWarning> warnings: a list of non-fatal issues encountered when decoding the post. Each DecoderWarning is an object with two properties:
    • string code: type of issue
    • string message: description of issue

If the post failed to decode, a DecoderError is returned, which is an Error object where the code property indicates the type of error. There are 3 possible error codes which could be returned:

  • no_start_found: the =ybegin sequence could not be found
  • no_end_found: the =yend sequence could not be found
  • missing_required_properties: required properties could not be found

string encoding='utf8'

The default character set used for encoding filenames.


var y = require('yencode');
var data = new Buffer(768000);
var post = Buffer.concat([
    // yEnc header
    new Buffer('=ybegin line=128 size=768000 name=rubbish.bin\r\n'),
    // encode the data
    // yEnc footer
    new Buffer('\r\n=yend size=768000 crc32=' + y.crc32(data).toString('hex'))


A brief description of how the SIMD yEnc encoding algorithm works can be found here. I may eventually write up something more detailed, regarding optimizations and such used.


This module is Public Domain or CC0 (or equivalent) if PD isn’t recognised.

crcutil, used for CRC32 calculation, is licensed under the Apache License 2.0

zlib-ng, from where the CRC32 calculation using folding approach was stolen, is under a zlib license


SIMD accelerated yEnc encoder/decoder and CRC32 calculator for node.js




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