lbcd/txscript/README.md
Dave Collins ac002d6422 txscript: Introduce zero-alloc script tokenizer.
This implements an efficient and zero-allocation script tokenizer that
is exported to both provide a new capability to tokenize scripts to
external consumers of the API as well as to serve as a base for
refactoring the existing highly inefficient internal code.

It is important to note that this tokenizer is intended to be used in
consensus critical code in the future, so it must exactly follow the
existing semantics.

The current script parsing mechanism used throughout the txscript module
is to fully tokenize the scripts into an array of internal parsed
opcodes which are then examined and passed around in order to implement
virtually everything related to scripts.

While that approach does simplify the analysis of certain scripts and
thus provide some nice properties in that regard, it is both extremely
inefficient in many cases, and makes it impossible for external
consumers of the API to implement any form of custom script analysis
without manually implementing a bunch of error prone tokenizing code or,
alternatively, the script engine exposing internal structures.

For example, as shown by profiling the total memory allocations of an
initial sync, the existing script parsing code allocates a total of
around 295.12GB, which equates to around 50% of all allocations
performed.  The zero-alloc tokenizer this introduces will allow that to
be reduced to virtually zero.

The following is a before and after comparison of tokenizing a large
script with a high opcode count using the existing code versus the
tokenizer this introduces for both speed and memory allocations:

benchmark                    old ns/op     new ns/op     delta
BenchmarkScriptParsing-8     63464         677           -98.93%

benchmark                    old allocs     new allocs     delta
BenchmarkScriptParsing-8     1              0              -100.00%

benchmark                    old bytes     new bytes     delta
BenchmarkScriptParsing-8     311299        0             -100.00%

The following is an overview of the changes:

- Introduce new error code ErrUnsupportedScriptVersion
- Implement zero-allocation script tokenizer
- Add a full suite of tests to ensure the tokenizer works as intended
  and follows the required consensus semantics
- Add an example of using the new tokenizer to count the number of
  opcodes in a script
- Update README.md to include the new example
- Update script parsing benchmark to use the new tokenizer
2022-05-23 21:46:20 -07:00

2.6 KiB

txscript

Build Status ISC License GoDoc

Package txscript implements the bitcoin transaction script language. There is a comprehensive test suite.

This package has intentionally been designed so it can be used as a standalone package for any projects needing to use or validate bitcoin transaction scripts.

Bitcoin Scripts

Bitcoin provides a stack-based, FORTH-like language for the scripts in the bitcoin transactions. This language is not turing complete although it is still fairly powerful. A description of the language can be found at https://en.bitcoin.it/wiki/Script

Installation and Updating

$ go get -u github.com/btcsuite/btcd/txscript

Examples

GPG Verification Key

All official release tags are signed by Conformal so users can ensure the code has not been tampered with and is coming from the btcsuite developers. To verify the signature perform the following:

  • Download the public key from the Conformal website at https://opensource.conformal.com/GIT-GPG-KEY-conformal.txt

  • Import the public key into your GPG keyring:

    gpg --import GIT-GPG-KEY-conformal.txt
    
  • Verify the release tag with the following command where TAG_NAME is a placeholder for the specific tag:

    git tag -v TAG_NAME
    

License

Package txscript is licensed under the copyfree ISC License.