Inconsistent handling of invalid rendered JSON in search template APIs

[Mikep86]

Elasticsearch Version

8.10.4

Installed Plugins

No response

Java Version

bundled

OS Version

Cloud

Problem Description

The search template API and render search template API handle invalid rendered JSON differently.

The search template API (correctly) returns a 400 response, while the render search template API returns a500 response. This is due to the fact that the render search template API implementation returns early from the convert method, skipping the code that would throw XContentParseException.

Steps to Reproduce

1. Create a search template that will render invalid JSON:

PUT _scripts/test-search-template
{
  "script": {
    "lang": "mustache",
    "source": """
    {
      "query": {
        "multi_match": {
          "query": "{{query_string}}",
          "fields": [{{#text_fields}}"{{name}}^{{boost}}"{{/text_fields}}]
        }
      },
      "from": "{{from}}",
      "size": "{{size}}"
    }
    """,
    "params": {
      "query_string": "My query string"
    }
  }
}

2. Use the search template API to run a query:

GET my-index/_search/template
{
  "id": "test-search-template",
  "params": {
    "text_fields": [
      {"name": "title", "boost": 10},
      {"name": "description", "boost": 5}
    ],
    "from": 0,
    "size": 10
  }
}

Observe the 400 response:

{
  "error": {
    "root_cause": [
      {
        "type": "x_content_parse_exception",
        "reason": """[6:33] Unexpected character ('"' (code 34)): was expecting comma to separate Array entries
 at [Source: (String)"
    {
      "query": {
        "multi_match": {
          "query": "",
          "fields": ["title^10""description^5"]
        }
      },
      "from": "0",
      "size": "10"
    }
    "; line: 6, column: 33]"""
      }
    ],
    "type": "x_content_parse_exception",
    "reason": """[6:33] Unexpected character ('"' (code 34)): was expecting comma to separate Array entries
 at [Source: (String)"
    {
      "query": {
        "multi_match": {
          "query": "",
          "fields": ["title^10""description^5"]
        }
      },
      "from": "0",
      "size": "10"
    }
    "; line: 6, column: 33]""",
    "caused_by": {
      "type": "json_parse_exception",
      "reason": """Unexpected character ('"' (code 34)): was expecting comma to separate Array entries
 at [Source: (String)"
    {
      "query": {
        "multi_match": {
          "query": "",
          "fields": ["title^10""description^5"]
        }
      },
      "from": "0",
      "size": "10"
    }
    "; line: 6, column: 33]"""
    }
  },
  "status": 400
}

3. Use the render search template API to render the search template:

POST _render/template
{
  "id": "test-search-template",
  "params": {
    "text_fields": [
      {"name": "title", "boost": 10},
      {"name": "description", "boost": 5}
    ],
    "from": 0,
    "size": 10
  }
}

Observe the 500 response:

{
  "error": {
    "root_cause": [
      {
        "type": "json_parse_exception",
        "reason": """Unexpected character ('"' (code 34)): was expecting comma to separate Array entries
 at [Source: (org.elasticsearch.common.io.stream.ByteBufferStreamInput); line: 6, column: 33]"""
      }
    ],
    "type": "json_parse_exception",
    "reason": """Unexpected character ('"' (code 34)): was expecting comma to separate Array entries
 at [Source: (org.elasticsearch.common.io.stream.ByteBufferStreamInput); line: 6, column: 33]""",
    "suppressed": [
      {
        "type": "illegal_state_exception",
        "reason": "Failed to close the XContentBuilder",
        "caused_by": {
          "type": "i_o_exception",
          "reason": "Unclosed object or array found"
        }
      }
    ]
  },
  "status": 500
}

Logs (if relevant)

No response

[elasticsearchmachine]

Pinging @elastic/es-search (Team:Search)

[elasticsearchmachine]

Pinging @elastic/ent-search-eng (Team:Enterprise Search)