This library and CLI tool is an experiment that, given a set of rules, will qualify bare images names to include a domain (e.g., registry.io) component.

An unqualified image is something like library/emacs or emacs, or emacs:v26. A qualified image has a domain component (e.g., prep.ai.mit.edu/library/emacs).

Pattern Matching Rules

• Rules are new-line separated
• There are two fields per line, separated by one or more whitespace characters
• First field is the pattern
• Second field is the domain
• Blank/Empty lines are skipped
• Comment lines are skipped and begin with #.

Rule Ordering (aka Partial Ordering)

(TBD) Should rules be automagically ordered when parsed?

• Currently no reordering of the rules is attempted
• Rules are attempted in the order presented
• the first match wins

Pattern Syntax

Note: semantics stolen from path.Match().

	pattern:
		{ term }
	term:
		'*'         matches any sequence of non-/ characters
		'?'         matches any single non-/ character
		'[' [ '^' ] { character-range } ']'
					character class (must be non-empty)
		c           matches character c (c != '*', '?', '\\', '[')
		'\\' c      matches character c

	character-range:
		c           matches character c (c != '\\', '-', ']')
		'\\' c      matches character c
		lo '-' hi   matches character c for lo <= c <= hi

Matching requires pattern to match all of name, not just a substring.

Examples

The simplest pattern to pull images that do not contain a repository component from internal.io is:

* internal.io

This pattern will transform any bare image to internal.io/<image>. Note: it will not transform myrepo/nginx to internal.io/myrepo/nginx because the pattern needs to match all segments of the [pattern] path.

To match any image and force it to pull from internal.io the following rules are required:

*/*   internal.io
*     internal.io

Making all latest tags come from a dev registry:

*/*:latest dev.io
*/*        internal.io
*          internal.io

Forcing nginx v1.2.3 to come from docker.io.

*/nginx:v1.2.3   docker.io

you/*            you.io
me/*             me.io

*/*              internal.io
*                internal.io

Sample Rules

$ cat $GOPATH/src/github.com/frobware/imagequalifier/testdata/sample-rules

busybox                    busybox.com
*/emacs                    emacs.com
myrepo/*                   myrepo.com
nginx:v[1-9].[0-9]*        nginx.com
*/*                        internal.com
*                          external.com

Sample Matches

Image	Qualified Image
emacs	external.com/emacs
busybox	busybox.com/busybox
myrepo/emacs	emacs.com/myrepo/emacs
nginx	external.com/nginx
nginx:v1.0	nginx.com/nginx

Test by example

$ go install github.com/frobware/imagequalifier/...

$ imagequalifier $GOPATH/src/github.com/frobware/imagequalifier/testdata/sample-rules emacs
internal.io/emacs

$ imagequalifier $GOPATH/src/github.com/frobware/imagequalifier/testdata/sample-rules library/emacs
emacs.com/library/emacs