# tagcmp

Comparison operations for image tags. Because registries aren't doing this for
us 🙄 This library is helpful if you're aiming to use only "stable" and
"semver-like" tags want to be able to do things like compare them, find which
tags are more recent, sort them and other types of comparisons.

A best-effort implementation which follows the wisdom of [Renovate].

> Docker doesn't really have versioning, instead it supports "tags" and these
> are usually used by Docker image authors as a form of versioning ... It's
> pretty "wild west" for tagging and not always compliant with SemVer.

The [Renovate implementation], which allows image tags to be automatically
upgraded, is the only show in town, apparently. This library follows that
implementation quite closely.

[renovate]: https://github.com/renovatebot/renovate/blob/main/lib/versioning/docker/readme.md
[renovate implementation]: https://github.com/renovatebot/renovate/tree/main/lib/datasource/docker

## Public API

> TODO

## Types of versions supported

```golang
// semver
"5",
"2.6",
"4.3.5",

// semver with 'v'
"v1",
"v2.3",
"v1.0.2",

// semver with suffix
"6-alpine",
"6.2-alpine",
"6.2.1-alpine",

// semver with sufixx and 'v'
"v6-alpine",
"v6.2-alpine",
"v6.2.1-alpine",
"v6.2.1-alpine",

// semver with multiple suffix values
"v6.2.1-alpine-foo",
```

## Types of versions not supported

> Please note, we could support some of these versions if people really need
> them to be supported. Some tags are using a unique format which we could
> support by implementing a very specific parser for (e.g. `ParseMinioTag`,
> `ParseZncTag`). For now, this library tries to provide a `Parse` function
> which handles more general cases. Please open an issue, change sets are
> welcome.

```golang
// empty
"",

// patametrized
"${MAILU_VERSION:-master}",
"${PHP_VERSION}-fpm-alpine3.13",

// commit hash like
"0a1b2c3d4e5f6a7b8c9d0a1b2c3d4e5f6a7b8c9d",

// numeric
"20191109",
"e02267d",

// not semver
"3.0.6.0",
"r1295",
"version-r1070",

// prerelease
"3.7.0b1",
"3.8.0b1-alpine",

// multiple versions
"5.36-backdrop-php7.4",
"v1.0.5_3.4.0",
"v1.0.5_3.4.0_openid-sso",

// tz based
"RELEASE.2021-04-22T15-44-28Z",

// only text
"alpine",
"latest",
"master",

// multiple - delimters
"apache-debian-1.8-prod",
"version-znc-1.8.2",
```