search template mustache loop quoting

[jpcarey]

Elasticsearch version: 2.3.4

JVM version: java version "1.8.0_65", Java(TM) SE Runtime Environment (build 1.8.0_65-b17), Java HotSpot(TM) 64-Bit Server VM (build 25.65-b01, mixed mode)

OS version: OS X 10.11.5 (15F34)

Description of the problem including expected versus actual behavior: mustache loop inserting extra quotes and commas.

Steps to reproduce:

1. Use example from https://www.elastic.co/guide/en/elasticsearch/reference/current/search-template.html#_validating_templates

   GET /_render/template
   {
     "inline": {
       "query": {
         "terms": {
           "status": [
             "{{#status}}",
             "{{.}}",
             "{{/status}}"
           ]
         }
       }
     },
     "params": {
       "status": [ "pending", "published" ]
     }
   }
   

2. Expected (from the documentation)

   {
     "template_output": {
       "query": {
         "terms": {
           "status": [ 
             "pending",
             "published"
           ]
         }
       }
     }
   }
   

3. Actual Result

   {
     "template_output": {
       "query": {
         "terms": {
           "status": [
             "",
             "pending",
             "",
             "published",
             ""
           ]
         }
       }
     }
   }
   

[tlrx]

This is unfortunately a known issue of Mustache. We added a helper function to better render arrays of values in #18856 using the notation {{#join}}my_iterable{{/join}}. It will be released in the next 2.4 / 5.0 versions.

[clintongormley]

Closed by 8afb8da and 69c25bf

[jpcarey]

@clintongormley @tlrx is there a workaround for the currently impacted versions? I think we should update or remove that particular example for those versions, as one would be more prone to hitting this issue by having a bad example in our docs. I spent about an hour pulling apart a configured watch before I realized what the actual issue was. This might be worth a separate bug, but hitting a _search template with the described issue from above provides a fairly useless response error:

{
   "error": {
      "root_cause": [
         {
            "type": "query_parsing_exception",
            "reason": "[_na] query malformed, no field after start_object",
            "index": "logstash-uptime-test",
            "line": 1,
            "col": 2
         }
      ],
      "type": "search_phase_execution_exception",
      "reason": "all shards failed",
      "phase": "query",
      "grouped": true,
      "failed_shards": [
         {
            "shard": 0,
            "index": "logstash-uptime-test",
            "node": "4sTl4inGTWC0sHRirlCrZg",
            "reason": {
               "type": "query_parsing_exception",
               "reason": "[_na] query malformed, no field after start_object",
               "index": "logstash-uptime-test",
               "line": 1,
               "col": 2
            }
         }
      ]
   },
   "status": 400
}

[clintongormley]

@jpcarey i updated the 2.x docs to reflect the real rendering (as mentioned by you above). The exception that you're getting means you're doing something different from the example, eg this works:

PUT t/t/1
{
  "status": "pending"
}

GET /_search/template
{
  "inline": {
    "query": {
      "terms": {
        "status": [
          "{{#status}}",
          "{{.}}",
          "{{/status}}"
        ]
      }
    }
  },
  "params": {
    "status": [ "pending", "published" ]
  }
}

Try using /_render/template with the code giving you this error and you will be able to see where it is going wrong.