add byMeta function

[bofm]

byMeta

Takes a list of services returned by the service or
services and returns a map that groups services by ServiceMeta values.
Multiple service meta keys can be passed as a comma separated string. |int can be added to
a meta key to convert numbers from service meta values to padded numbers in printf "%05d" % value format (useful for sorting as Go Template sorts maps by keys).

Example:

If we have the following services registered in Consul:

{
  "Services": [
     {
       "ID": "redis-dev-1",
       "Name": "redis",
       "ServiceMeta": {
         "environment": "dev",
         "shard_number": "1"
       },
       ...
     },
     {
       "ID": "redis-prod-1",
       "Name": "redis",
       "ServiceMeta": {
         "environment": "prod",
         "shard_number": "1"
       },
       ...
     },
     {
       "ID": "redis-prod-2",
       "Name": "redis",
       "ServiceMeta": {
         "environment": "prod",
         "shard_number": "2",
       },
       ...
     }
   ]
}

{{ service "redis|any" | byMeta "environment,shard_number|int" | toJson }}

The code above will produce a map of services grouped by meta:

{
  "dev_00001": [
    {
      "ID": "redis-dev-1",
      ...
    }
  ],
  "prod_00001": [
    {
      "ID": "redis-prod-1",
      ...
    }
  ],
  "prod_00002": [
    {
      "ID": "redis-prod-2",
      ...
    }
  ]
}

[eikenb]

Thanks for the PR @bofm.

I'll happily accept it with one caveat... Would you mind adding a simple set of tests for this? An executable version of your example would be enough. Just something to exercise the code a bit and demonstrate its API in use.

I know as is the functions don't really have tests, but I'd really like to start addressing that. There is one example in place that you can use for some guidance.

Thanks.

[bofm]

Added test. Rebased onto master.

[eikenb]

Great. Thanks.