Add Snapshot Create API

[wedneyyuri]

This PR adds support for Elasticsearch's snapshot create API.

Example program:

package main

import (
	"context"
	"log"
	"os"
	"time"

	elastic "gopkg.in/olivere/elastic.v5"
)

func main() {
	client, err := elastic.NewClient()
	if err != nil {
		panic(err)
	}

	// create snapshot repo
	repo := elastic.
		NewSnapshotCreateRepositoryService(client).
		Repository("repo1").
		BodyJson(map[string]interface{}{
			"type": "fs",
			"settings": map[string]interface{}{
				"location": "/tmp/elasticsearch",
			},
		})

	repoResponse, err := repo.Do(context.TODO())
	if err != nil {
		panic(err)
	}

	if !repoResponse.Acknowledged {
		panic("could not ack repository create")
	}

	// create snapshot
	service := elastic.
		NewSnapshotCreateService(client).
		Repository("repo1").
		Snapshot(time.Now().Format("2006-01-02-15-04-05")).
		WaitForCompletion(true).
		BodyJson(map[string]interface{}{
			"indices":              "website",
			"ignore_unavailable":   false,
			"include_global_state": true,
		})

	response, err := service.Do(context.TODO())
	if err != nil {
		panic(err)
	}

	if response.Snapshot.State != "SUCCESS" {
		panic("elasticsearch snapshot state != SUCCESS: " + response.Snapshot.State)
	}
}

[olivere]

This must be "gopkg.in/olivere/elastic.v5/uritemplates". The generator need some polish, I'm sorry.

[wedneyyuri]

No problem, the generator is pretty good 👍

[olivere]

The *struct, although valid, doesn't look that good. Does ES always send back the snapshot? We have to look it up in the Java source. If it does, we should make it a normal struct, not a pointer to a struct.

[wedneyyuri]

No, ES does not send the snapshot field when waitForCompletion is false.

https://github.com/elastic/elasticsearch/blob/45d4938fcc8f1a4cf988e119d7dd23bb2920b9e2/core/src/main/java/org/elasticsearch/action/admin/cluster/snapshots/create/CreateSnapshotResponse.java#L87

[olivere]

Did you compare these fields with what ES really sends, or did you make an educated guess? I typically consult the Java source to see what fields (and their types) ES really sends and, more often than not, I find fields that are undocumented but sent anyway.

[wedneyyuri]

On my previous commit I compared these field with what ES really sends (turning logging on), but today I made a new commit consulting the java source code.

[olivere]

This e.g. should be int64 if StartTimeInMillis is int64 as well.

[wedneyyuri]

👍

[olivere]

There is a shardsInfo in errors.go that you can use here.

[wedneyyuri]

👍

[olivere]

The PR is looking good. Can you please take a look at those comments, so I can merge in the next run. I'm off for vacation next week so it'll take a few more days, I'm afraid.

[wedneyyuri]

Thanks @olivere, I looked at your comments and pushed some changes.

[olivere]

It'll roll with 5.0.39. Thanks.

[wedneyyuri]

Thanks @olivere, can I backport it to v3?

[olivere]

@wedneyyuri Sure. That seems to be really easy. All you need to do is change some import paths.