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Pechkin

Gem

Who the heck is Pechkin?

Pechkin is a postman from soviet animated film series.

What is pechkin (gem) ?

Pechkin is webhook to IM (currently Telegram, Slack) proxy. It allows you to transform any request into pretty message in your working channels. Long story short:

  • You describe set of templates and channel configurations to instruct pechkin how to render received json data into messages and where to send them
  • When pechkin started process any POST request and acts according to your instrcutions

Table of Contents

Configuration basics

Bots

First. You need to create bot to allow pechkin interact with IM APIs. All bots stored in bots/ directory, one yaml file per bot.

bots/marvin.yml
bots/bender.yml

Each bot/*.yml is bot description. It has following fields:

  • token - API token to authorize bot requests. See IM documentation for details.
  • connector - connector type. Currenlty: slack or telegram.

Bot name is taken from yml file name. So bot/bender.yml is bender and bot/marvin.yml is marvin

Next. You need to create views/ directory and create your first template. Template is *.erb file. Each template is rendered with ruby internal ERB class with trim_mode: '-'. Let's create very simple erb template views/hello.erb:

Hello, <% name %>!

Channels

Now we need destination where to send our message. This destinations are grouped in channels and each channel has list of messages it can receive. Channel descriptions are stored under channels/ directory. It has following structure:

channels/
  | - %channel-name%
       | - _channel.yml
       | - %message-name%.yml

Common channel setting are stored in _channel.yml file. You can configure following parameters:

  • chat_ids - list of chats or channels to send your message to
  • bot - name of bot to use for sending messages

Messages

Then we create hello.yml to send hello in channels chats. Messages are configured with following parameters:

  • template - template file path relative to views/ directory (i.e. 'hello.erb')
  • One can also use { 'template': '..path..' } object, to denote that we need template expansion for such value. For example:
template: gitlab-commit.erb
slack_attachements:
  - text:
      template: gitlab-commit-attachment.erb
  • variables - is a mapping (key - value) for configurable values in shared templates. For example one may want to share commit.erb among multiple channels but with sligthly different parameters. It may be repository_base_url wich you want to override for each channel separately. variables content will be merged with received data. So data can override variable parameters too.

Message values substitution

As well as you can inject variable parametedatars into template data through variables field in message configuration you also can substitute some values in message config. This is honestly very dirty way to set slack_attachments (see below) values, without any external scripting.

Any top-level value can be substitued with ${...} syntax in any field inside message description. For example:

slack_attachments:
  - title: Author
    value: "${author}"

No value processing is supported.

Allow / Forbid

Pechkin provides filter mechanism to allow users to select which messages are need processing and which are not. This can be expressed in allow / forbid rules in message configuration. For example:

# { "branch": "master", ... } => process
# { "branch": "testing", ... } => skip
allow:
  - branch: 'master'

will match all requests which data object contains 'master' on key branch.

Same is aplicable to forbid. Following means do not process objects with 'testing' value set to branch field.

# { "branch": "testing", ... } => skip
# { "branch": "master", ... } => process
forbid:
  - branch: 'testing'

Both forbid and allow parameters should contain list of rules. When data arrives, Pechkin will find first matching rule and will make desicion based on whether it 'allow' rule or 'forbid' rule.

Connector specific parameters

Telegram:

  • telegram_parse_mode - markdown or html mode for Telegram messages

Slack:

  • slack_attachments - description of attachments to use with Slack message. Slack allows to send messages with empty text and only attachments set. Content of this field is direct mapping for attachments field in Slack API. See documentation for more details.

Authorization

Pechkin can make simple request authorization. If configuration directory contains pechkin.htpasswd file or path to *.htpasswd file provided via CLI options pechkin will use it to check Authorization header against it. Pechkin checks only Basic Auth at the moment.

To create .htpasswd file one can use --add-auth flag to create or update htpasswd file with provided credentials. For example

# Create or update pechkin.htpasswd file in examples/ directory with user
# root and password root123
pechkin -c examples --add-user root:root123

# Create or update pechkin-global.htpasswd file at /etc/config
pechkin --add-user root:root123 --auth-file /etc/config/pechkin-global.htpasswd

# Launch pechkin with explicitly provided htpasswd file
pechkin -c examples --auth-file /etc/config/pechkin-global.htpasswd

Wrapping up

Create bot file bots/marvin.yml

token: xob-1234567890987654321
connector: slack

Create view views/hello.erb

Hello, <% name %>!

Create channel channels/my-org-random/_channel.yml

chat_ids: '#random'
bot: marvin

Create message channels/my-org-random/hello.yml

template: hello.erb

Check configuration

pechkin -c . -k -l

Preview message

pechkin -c -s /my-org-random/hello --data '{"name": "all"}' --preview

Try to send message manualy

pechkin -c -s /my-org-random/hello --data '{"name": "all"}'

Start pechkin:

pechkin -c . --port 8080

Send message:

curl -X POST -H 'Content-Type: application/json' --data '{"name": "all"}' \
     localhost:8080/my-org-random/hello

Check metrics:

curl localhost:8080/metrics

CLI options

Usage: pechkin [options]
Run options
    -c, --config-dir FILE            Path to configuration file
        --port PORT
        --address ADDRESS            The host address to bind to
    -p, --pid-file [FILE]            Path to output PID file
        --log-dir [DIR]              Path to log directory. Output will be writen topechkin.log file. If not specified will write to STDOUT
        --auth-file FILE             Path to .htpasswd file. By default `pechkin.htpasswd` file will be looked up in configuration directory and if found then authorization will be enabled implicitly. Providing this option enables htpasswd based authorization explicitly. When making requests use Basic auth to authorize.

Utils for configuration maintenance
    -l, --[no-]list                  List all endpoints
    -k, --[no-]check                 Load configuration and exit
    -s, --send ENDPOINT              Send data to specified ENDPOINT and exit. Requires --data to be set.
        --preview                    Print rendering result to STDOUT and exit. Use with --send
        --data DATA                  Data to send with --send flag. Json string or @filename.

Auth utils
        --add-auth USER:PASSWORD     Add auth entry to .htpasswd file. By default pechkin.htpasswd from configuration directory will be used. Use --auth-file to specify other file to update. If file does not exist it will be created.

Debug options
        --[no-]debug                 Print debug information and stack trace on errors

Common options:
    -h, --help                       Show this message
        --version                    Show version

Metrics

Pechkin uses prometheus ruby client to expose basic rack server metrics. And own metrics as well:

  • pechkin_start_time_seconds - startup timestamp