OpenSearch/docs/reference/api-conventions.asciidoc

[[api-conventions]]
= API Conventions

[partintro]
--
The *elasticsearch* REST APIs are exposed using <<modules-http,JSON over HTTP>>.

The conventions listed in this chapter can be applied throughout the REST
API, unless otherwise specified.

* <<multi-index>>
* <<common-options>>

--

[[multi-index]]
== Multiple Indices

Most APIs that refer to an `index` parameter support execution across multiple indices,
using simple `test1,test2,test3` notation (or `_all` for all indices). It also
support wildcards, for example: `test*`, and the ability to "add" (`+`)
and "remove" (`-`), for example: `+test*,-test3`.

All multi indices API support the following url query string parameters:

`ignore_unavailable`::

Controls whether to ignore if any specified indices are unavailable, this
includes indices that don't exist or closed indices. Either `true` or `false`
can be specified.

`allow_no_indices`::

Controls whether to fail if a wildcard indices expressions results into no
concrete indices. Either `true` or `false` can be specified. For example if
the wildcard expression `foo*` is specified and no indices are available that
start with `foo` then depending on this setting the request will fail. This
setting is also applicable when `_all`, `*` or no index has been specified. This
settings also applies for aliases, in case an alias points to a closed index.

`expand_wildcards`::

Controls to what kind of concrete indices wildcard indices expression expand
to. If `open` is specified then the wildcard expression is expanded to only
open indices and if `closed` is specified then the wildcard expression is
expanded only to closed indices. Also both values (`open,closed`) can be
specified to expand to all indices.

If `none` is specified then wildcard expansion will be disabled and if `all`
is specified, wildcard expressions will expand to all indices (this is equivalent
to specifying `open,closed`).

The defaults settings for the above parameters depend on the api being used.

NOTE: Single index APIs such as the <<docs>> and the
<<indices-aliases,single-index `alias` APIs>> do not support multiple indices.

[[common-options]]
== Common options

The following options can be applied to all of the REST APIs.

[float]
=== Pretty Results

When appending `?pretty=true` to any request made, the JSON returned
will be pretty formatted (use it for debugging only!). Another option is
to set `?format=yaml` which will cause the result to be returned in the
(sometimes) more readable yaml format.


[float]
=== Human readable output

Statistics are returned in a format suitable for humans
(eg `"exists_time": "1h"` or `"size": "1kb"`) and for computers
(eg `"exists_time_in_millis": 3600000` or `"size_in_bytes": 1024`).
The human readable values can be turned off by adding `?human=false`
to the query string. This makes sense when the stats results are
being consumed by a monitoring tool, rather than intended for human
consumption.  The default for the `human` flag is
`false`.

[float]
=== Response Filtering

All REST APIs accept a `filter_path` parameter that can be used to reduce
the response returned by elasticsearch. This parameter takes a comma
separated list of filters expressed with the dot notation:

[source,sh]
--------------------------------------------------
curl -XGET 'localhost:9200/_search?pretty&filter_path=took,hits.hits._id,hits.hits._score'
{
  "took" : 3,
  "hits" : {
    "hits" : [
      {
        "_id" : "3640",
        "_score" : 1.0
      },
      {
        "_id" : "3642",
        "_score" : 1.0
      }
    ]
  }
}
--------------------------------------------------

It also supports the `*` wildcard character to match any field or part
of a field's name:

[source,sh]
--------------------------------------------------
curl -XGET 'localhost:9200/_nodes/stats?filter_path=nodes.*.ho*'
{
  "nodes" : {
    "lvJHed8uQQu4brS-SXKsNA" : {
      "host" : "portable"
    }
  }
}
--------------------------------------------------

And the `**` wildcard can be used to include fields without knowing the
exact path of the field. For example, we can return the Lucene version
of every segment with this request:

[source,sh]
--------------------------------------------------
curl 'localhost:9200/_segments?pretty&filter_path=indices.**.version'
{
  "indices" : {
    "movies" : {
      "shards" : {
        "0" : [ {
          "segments" : {
            "_0" : {
              "version" : "5.2.0"
            }
          }
        } ],
        "2" : [ {
          "segments" : {
            "_0" : {
              "version" : "5.2.0"
            }
          }
        } ]
      }
    },
    "books" : {
      "shards" : {
        "0" : [ {
          "segments" : {
            "_0" : {
              "version" : "5.2.0"
            }
          }
        } ]
      }
    }
  }
}
--------------------------------------------------

Note that elasticsearch sometimes returns directly the raw value of a field,
like the `_source` field. If you want to filter _source fields, you should
consider combining the already existing `_source` parameter (see
<<get-source-filtering,Get API>> for more details) with the `filter_path`
 parameter like this:

[source,sh]
--------------------------------------------------
curl -XGET 'localhost:9200/_search?pretty&filter_path=hits.hits._source&_source=title'
{
  "hits" : {
    "hits" : [ {
      "_source":{"title":"Book #2"}
    }, {
      "_source":{"title":"Book #1"}
    }, {
      "_source":{"title":"Book #3"}
    } ]
  }
}
--------------------------------------------------


[float]
=== Flat Settings

The `flat_settings` flag affects rendering of the lists of settings. When
`flat_settings` flag is `true` settings are returned in a flat format:

[source,js]
--------------------------------------------------
{
  "persistent" : { },
  "transient" : {
    "discovery.zen.minimum_master_nodes" : "1"
  }
}
--------------------------------------------------

When the `flat_settings` flag is `false` settings are returned in a more
human readable structured format:

[source,js]
--------------------------------------------------
{
  "persistent" : { },
  "transient" : {
    "discovery" : {
      "zen" : {
        "minimum_master_nodes" : "1"
      }
    }
  }
}
--------------------------------------------------

By default the `flat_settings` is set to `false`.

[float]
=== Parameters

Rest parameters (when using HTTP, map to HTTP URL parameters) follow the
convention of using underscore casing.

[float]
=== Boolean Values

All REST APIs parameters (both request parameters and JSON body) support
providing boolean "false" as the values: `false`, `0`, `no` and `off`.
All other values are considered "true". Note, this is not related to
fields within a document indexed treated as boolean fields.

[float]
=== Number Values

All REST APIs support providing numbered parameters as `string` on top
of supporting the native JSON number types.

[[time-units]]
[float]
=== Time units

Whenever durations need to be specified, eg for a `timeout` parameter, the duration
can be specified as a whole number representing time in milliseconds, or as a time value like `2d` for 2 days.  The supported units are:

[horizontal]
`y`::   Year
`M`::   Month
`w`::   Week
`d`::   Day
`h`::   Hour
`m`::   Minute
`s`::   Second

[[distance-units]]
[float]
=== Distance Units

Wherever distances need to be specified, such as the `distance` parameter in
the <<query-dsl-geo-distance-query>>), the default unit if none is specified is
the meter. Distances can be specified in other units, such as `"1km"` or
`"2mi"` (2 miles).

The full list of units is listed below:

[horizontal]
Mile::          `mi` or `miles`
Yard::          `yd` or `yards`
Feet::          `ft` or `feet`
Inch::          `in` or `inch`
Kilometer::     `km` or `kilometers`
Meter::         `m` or `meters`
Centimeter::    `cm` or `centimeters`
Millimeter::    `mm` or `millimeters`
Nautical mile:: `NM`, `nmi` or `nauticalmiles`

The `precision` parameter in the <<query-dsl-geohash-cell-query>> accepts
distances with the above units, but if no unit is specified, then the
precision is interpreted as the length of the geohash.

[[fuzziness]]
[float]
=== Fuzziness

Some queries and APIs support parameters to allow inexact _fuzzy_ matching,
using the `fuzziness` parameter. The `fuzziness` parameter is context
sensitive which means that it depends on the type of the field being queried:

[float]
==== Numeric, date and IPv4 fields

When querying numeric, date and IPv4 fields, `fuzziness` is interpreted as a
`+/-` margin. It behaves like a <<query-dsl-range-query>> where:

    -fuzziness <= field value <= +fuzziness

The `fuzziness` parameter should be set to a numeric value, eg `2` or `2.0`. A
`date` field interprets a long as milliseconds, but also accepts a string
containing a time value -- `"1h"` -- as explained in <<time-units>>. An `ip`
field accepts a long or another IPv4 address (which will be converted into a
long).

[float]
==== String fields

When querying `string` fields, `fuzziness` is interpreted as a
http://en.wikipedia.org/wiki/Levenshtein_distance[Levenshtein Edit Distance]
-- the number of one character changes that need to be made to one string to
make it the same as another string.

The `fuzziness` parameter can be specified as:

`0`, `1`, `2`::

the maximum allowed Levenshtein Edit Distance (or number of edits)

`AUTO`::
+
--
generates an edit distance based on the length of the term. For lengths:

`0..2`:: must match exactly
`3..5`:: one edit allowed
`>5`:: two edits allowed

`AUTO` should generally be the preferred value for `fuzziness`.
--

[float]
=== Result Casing

All REST APIs accept the `case` parameter. When set to `camelCase`, all
field names in the result will be returned in camel casing, otherwise,
underscore casing will be used. Note, this does not apply to the source
document indexed.

[float]
=== Request body in query string

For libraries that don't accept a request body for non-POST requests,
you can pass the request body as the `source` query string parameter
instead.

[[url-access-control]]
== URL-based access control

Many users use a proxy with URL-based access control to secure access to
Elasticsearch indices. For <<search-multi-search,multi-search>>,
<<docs-multi-get,multi-get>> and <<docs-bulk,bulk>> requests, the user has
the choice of specifying an index in the URL and on each individual request
within the request body. This can make URL-based access control challenging.

To prevent the user from overriding the index which has been specified in the
URL, add this setting to the `config.yml` file:

    rest.action.multi.allow_explicit_index: false

The default value is `true`, but when set to `false`, Elasticsearch will
reject requests that have an explicit index specified in the request body.