Rewrite README to be more up-to-date/accurate

README.md

@@ -1,29 +1,113 @@
-This is the beginnings of a certificate transparency log
-client written in Go, along with a log scanner tool.
+# Certificate Transparency: Go Code
 
-You'll need go v1.8 or higher to compile.
+[![Build Status](https://travis-ci.org/google/certificate-transparency-go.svg?branch=master)](https://travis-ci.org/google/certificate-transparency-go)
+[![Go Report Card](https://goreportcard.com/badge/github.com/google/certificate-transparency-go)](https://goreportcard.com/report/github.com/google/certificate-transparency-go)
+[![GoDoc](https://godoc.org/github.com/google/certificate-transparency-go?status.svg)](https://godoc.org/github.com/google/certificate-transparency-go)
 
-# Installation
+This repository holds Go code related to
+[Certificate Transparency](https://www.certificate-transparency.org/) (CT).  The
+repository requires Go version 1.9.
 
-This go code must be imported into your go workspace before you can
-use it, which can be done with:
+ - [Repository Structure](#repository-structure)
+ - [Working on the Code](#working-on-the-code)
+     - [Rebuilding Generated Code](#rebuilding-generated-code)
+     - [Updating Vendor Code](#updating-vendor-code)
+     - [Running Codebase Checks](#running-codebase-checks)
+
+## 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 entrypoints described in
+     [section 4 of RFC 6962](https://tools.ietf.org/html/rfc6962#section-4).
+   - `scanner/` holds a library for scanning the entire contents of an existing
+     CT Log.
+ - Command line tools:
+   - `./client/ctclient` allows interaction with a CT Log
+   - `./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).
+ - 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.
+
+
+## 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.
+
+### 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 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:
+
+  - `mockgen` tool from https://github.com/golang/mock
+  - `protoc`, [Go support for protoc](https://github.com/golang/protobuf) (see
+     documentation linked from the
+     [protobuf site](https://github.com/google/protobuf))
+
+and run the following:
 
 ```bash
-go get github.com/google/certificate-transparency-go/client
-go get github.com/google/certificate-transparency-go/scanner
-# etc.
+go generate -x ./...  # hunts for //go:generate comments and runs them
 ```
 
-# Building the binaries
+### Updating Vendor Code
+
+The codebase includes a couple of external projects under the `vendor/`
+subdirectory, to ensure that builds use a fixed version (typically because the
+upstream repository does not guarantee back-compatibility between the tip
+`master` branch and the current stable release).  See
+[instructions in the Trillian repo](https://github.com/google/trillian#updating-vendor-code)
+for how to update vendored subtrees.
+
 
-To compile the log scanner run:
+### Running Codebase Checks
+
+The [`scripts/presubmit.sh`](scripts/presubmit.sh) script runs various tools
+and tests over the codebase.
 
 ```bash
-go get github.com/google/certificate-transparency-go/scanner/scanlog
-```
+# Install gometalinter and all linters
+go get -u github.com/alecthomas/gometalinter
+gometalinter --install
 
-# Contributing
+# Run code generation, build, test and linters
+./scripts/presubmit.sh
 
-When sending pull requests, please ensure that everything's been run
-through ```gofmt``` beforehand so we can keep everything nice and
-tidy.
+# Run build, test and linters but skip code generation
+./scripts/presubmit.sh  --no-generate
+
+# Or just run the linters alone:
+gometalinter --config=gometalinter.json ./...
+```