# Certificate Transparency: Go Code
[](https://travis-ci.org/google/certificate-transparency-go)
[](https://goreportcard.com/report/github.com/google/certificate-transparency-go)
[](https://godoc.org/github.com/google/certificate-transparency-go)
This repository holds Go code related to
[Certificate Transparency](https://www.certificate-transparency.org/) (CT). The
repository requires Go version 1.17.
- [Repository Structure](#repository-structure)
- [Trillian CT Personality](#trillian-ct-personality)
- [Working on the Code](#working-on-the-code)
- [Running Codebase Checks](#running-codebase-checks)
- [Rebuilding Generated Code](#rebuilding-generated-code)
- [Updating Vendor Code](#updating-vendor-code)
## Repository Structure
The main parts of the repository are:
- Encoding libraries:
- `asn1/` and `x509/` are forks of the upstream Go `encoding/asn1` and
`crypto/x509` libraries. We maintain separate forks of these packages
because CT is intended to act as an observatory of certificates across the
ecosystem; as such, we need to be able to process somewhat-malformed
certificates that the stricter upstream code would (correctly) reject.
Our `x509` fork also includes code for working with the
[pre-certificates defined in RFC 6962](https://tools.ietf.org/html/rfc6962#section-3.1).
- `tls` holds a library for processing TLS-encoded data as described in
[RFC 5246](https://tools.ietf.org/html/rfc5246).
- `x509util/` provides additional utilities for dealing with
`x509.Certificate`s.
- CT client libraries:
- The top-level `ct` package (in `.`) holds types and utilities for working
with CT data structures defined in
[RFC 6962](https://tools.ietf.org/html/rfc6962).
- `client/` and `jsonclient/` hold libraries that allow access to CT Logs
via HTTP entrypoints described in
[section 4 of RFC 6962](https://tools.ietf.org/html/rfc6962#section-4).
- `dnsclient/` has a library that allows access to CT Logs over
[DNS](https://github.com/google/certificate-transparency-rfcs/blob/master/dns/draft-ct-over-dns.md).
- `scanner/` holds a library for scanning the entire contents of an existing
CT Log.
- CT Personality for [Trillian](https://github.com/google/trillian):
- `trillian/` holds code that allows a Certificate Transparency Log to be
run using a Trillian Log as its back-end -- see
[below](#trillian-ct-personality).
- Command line tools:
- `./client/ctclient` allows interaction with a CT Log.
- `./ctutil/sctcheck` allows SCTs (signed certificate timestamps) from a CT
Log to be verified.
- `./scanner/scanlog` allows an existing CT Log to be scanned for certificates
of interest; please be polite when running this tool against a Log.
- `./x509util/certcheck` allows display and verification of certificates
- `./x509util/crlcheck` allows display and verification of certificate
revocation lists (CRLs).
- Other libraries related to CT:
- `ctutil/` holds utility functions for validating and verifying CT data
structures.
- `loglist3/` has a library for reading
[v3 JSON lists of CT Logs](https://groups.google.com/a/chromium.org/g/ct-policy/c/IdbrdAcDQto/m/i5KPyzYwBAAJ).
## Trillian CT Personality
The `trillian/` subdirectory holds code and scripts for running a CT Log based
on the [Trillian](https://github.com/google/trillian) general transparency Log,
and is [documented separately](trillian/README.md).
## Working on the Code
Developers who want to make changes to the codebase need some additional
dependencies and tools, described in the following sections. The
[Travis configuration](.travis.yml) for the codebase is also useful reference
for the required tools and scripts, as it may be more up-to-date than this
document.
### Running Codebase Checks
The [`scripts/presubmit.sh`](scripts/presubmit.sh) script runs various tools
and tests over the codebase; please ensure this script passes before sending
pull requests for review.
```bash
# Install golangci-lint
go install github.com/golangci/golangci-lint/cmd/golangci-lint@v1.46.1
# Run code generation, build, test and linters
./scripts/presubmit.sh
# Run build, test and linters but skip code generation
./scripts/presubmit.sh --no-generate
# Or just run the linters alone:
golangci-lint run
```
### Rebuilding Generated Code
Some of the CT Go code is autogenerated from other files:
- [Protocol buffer](https://developers.google.com/protocol-buffers/) message
definitions are converted to `.pb.go` implementations.
- A mock implementation of the Trillian gRPC API (in `trillian/mockclient`) is
created with [GoMock](https://github.com/golang/mock).
Re-generating mock or protobuffer files is only needed if you're changing
the original files; if you do, you'll need to install the prerequisites:
- tools written in `go` can be installed with a single run of `go install`
(courtesy of [`tools.go`](./tools/tools.go) and `go.mod`).
- `protoc` tool: you'll need [version 3.12.4](https://github.com/protocolbuffers/protobuf/releases/tag/v3.12.4) installed, and `PATH` updated to include its `bin/` directory.
With tools installed, run the following:
```bash
go generate -x ./... # hunts for //go:generate comments and runs them
```