json-mindiff

Minimize diff introduced to json files by tools that treat json dictionary as unordered hash map (kind of right thing to do but annoying anyway).

WORK IN PROGRESS

Usage

The primary goal is to restrict packer from reformatting templates even when there are no changes.

First make sure templates are sane formatted, lets use jq for this. This way we make sure to have a fixed base point to blame packer.

$ jq . template.json          > tmp && mv tmp template.json
$ jq . template.outdated.json > tmp && mv tmp template.outdated.json

Add current directory to PATH to make sure all examples work for you as well:

$ export PATH=${PATH}:$(pwd)

Here is the default packer behaviour (😠). There are no changes, packer simply reformats the template:

$ packer fix template.json | jq . > template.json.new
$ diff template.json template.json.new
2,8d1
<   "min_packer_version": "1.2.0",
<   "variables": {
<     "box_file": "",
<     "iso_url": "",
<     "iso_checksum_type": "",
<     "iso_checksum": ""
<   },
11,14d3
<       "type": "virtualbox-iso",
<       "iso_url": "{{user `iso_url`}}",
<       "iso_checksum_type": "{{user `iso_checksum_type`}}",
<       "iso_checksum": "{{user `iso_checksum`}}",
19d7
<       "shutdown_command": "echo '/sbin/halt -h -p' > /tmp/shutdown.sh; echo 'vagrant'|sudo -S sh '/tmp/shutdown.sh'",
21d8
<       "guest_os_type": "RedHat_64",
22a10
>       "guest_os_type": "RedHat_64",
25c13,16
<       "ssh_port": 22,
---
>       "iso_checksum": "{{user `iso_checksum`}}",
>       "iso_checksum_type": "{{user `iso_checksum_type`}}",
>       "iso_url": "{{user `iso_url`}}",
>       "shutdown_command": "echo '/sbin/halt -h -p' > /tmp/shutdown.sh; echo 'vagrant'|sudo -S sh '/tmp/shutdown.sh'",
26a18
>       "ssh_port": 22,
29c21
<       "virtualbox_version_file": ".vbox_version",
---
>       "type": "virtualbox-iso",
43c35,45
<       ]
---
>       ],
>       "virtualbox_version_file": ".vbox_version"
>     }
>   ],
>   "min_packer_version": "1.2.0",
>   "post-processors": [
>     {
>       "compression_level": 9,
>       "keep_input_artifact": false,
>       "output": "{{user `box_file`}}",
>       "type": "vagrant"
48d49
<       "type": "shell",
59c60,61
<       }
---
>       },
>       "type": "shell"
62,69c64,69
<   "post-processors": [
<     {
<       "type": "vagrant",
<       "keep_input_artifact": false,
<       "compression_level": 9,
<       "output": "{{user `box_file`}}"
<     }
<   ]
---
>   "variables": {
>     "box_file": "",
>     "iso_checksum": "",
>     "iso_checksum_type": "",
>     "iso_url": ""
>   }

Here is the default packer behaviour piped through json-mindiff (🙂). There are no changes and we keep it this way:

$ packer fix template.json | json-mindiff template.json | jq . > template.json.new
$ diff template.json template.json.new

Here is the fix packer behaviour (😠). Packer should fix iso_md5 usage. Note that it fixes and reformats, it is hard to see what is going on:

$ packer fix template.outdated.json | jq . > template.outdated.json.new
$ diff template.outdated.json template.outdated.json.new
2,7d1
<   "min_packer_version": "1.2.0",
<   "variables": {
<     "box_file": "",
<     "iso_url": "",
<     "iso_checksum": ""
<   },
10,12d3
<       "type": "virtualbox-iso",
<       "iso_url": "{{user `iso_url`}}",
<       "iso_md5": "{{user `iso_checksum`}}",
17d7
<       "shutdown_command": "echo '/sbin/halt -h -p' > /tmp/shutdown.sh; echo 'vagrant'|sudo -S sh '/tmp/shutdown.sh'",
19d8
<       "guest_os_type": "RedHat_64",
20a10
>       "guest_os_type": "RedHat_64",
23c13,16
<       "ssh_port": 22,
---
>       "iso_checksum": "{{user `iso_checksum`}}",
>       "iso_checksum_type": "md5",
>       "iso_url": "{{user `iso_url`}}",
>       "shutdown_command": "echo '/sbin/halt -h -p' > /tmp/shutdown.sh; echo 'vagrant'|sudo -S sh '/tmp/shutdown.sh'",
24a18
>       "ssh_port": 22,
27c21
<       "virtualbox_version_file": ".vbox_version",
---
>       "type": "virtualbox-iso",
41c35,45
<       ]
---
>       ],
>       "virtualbox_version_file": ".vbox_version"
>     }
>   ],
>   "min_packer_version": "1.2.0",
>   "post-processors": [
>     {
>       "compression_level": 9,
>       "keep_input_artifact": false,
>       "output": "{{user `box_file`}}",
>       "type": "vagrant"
46d49
<       "type": "shell",
57c60,61
<       }
---
>       },
>       "type": "shell"
60,67c64,68
<   "post-processors": [
<     {
<       "type": "vagrant",
<       "keep_input_artifact": false,
<       "compression_level": 9,
<       "output": "{{user `box_file`}}"
<     }
<   ]
---
>   "variables": {
>     "box_file": "",
>     "iso_checksum": "",
>     "iso_url": ""
>   }

Here is the fix packer behaviour piped through json-mindiff (🙂). Packer should fix iso_md5 usage. Note that diff is the absolute minimum.:

$ packer fix template.outdated.json | json-mindiff template.json | jq . > template.outdated.json.new
$ diff template.outdated.json template.outdated.json.new
12c12,13
<       "iso_md5": "{{user `iso_checksum`}}",
---
>       "iso_checksum_type": "md5",
>       "iso_checksum": "{{user `iso_checksum`}}",