Add Render Template API (#7219) (#7571)

_api-reference/render-template.md

@@ -0,0 +1,114 @@
+---
+layout: default
+title: Render Template
+nav_order: 82
+---
+
+# Render Template 
+
+The Render Template API renders a [search template]({{site.url}}{{site.baseurl}}/search-plugins/search-template/) as a search query.
+
+## Paths and HTTP methods
+
+```
+GET /_render/template
+POST /_render/template
+GET /_render/template/<id>
+POST /_render/template/<id>
+```
+
+## Path parameters
+
+The Render Template API supports the following optional path parameter. 
+
+| Parameter | Type | Description |
+| :--- | :--- | :--- |
+| `id` | String | The ID of the search template to render. |
+
+## Request options
+
+The following options are supported in the request body of the Render Template API.
+
+| Parameter | Required | Type | Description | 
+| :--- | :--- | :--- | :--- |
+| `id` | Conditional | String | The ID of the search template to render. Is not required if the ID is provided in the path or if an inline template is specified by the `source`. | 
+| `params` | No | Object | A list of key-value pairs that replace Mustache variables found in the search template. The key-value pairs must exist in the documents being searched. |
+| `source` | Conditional | Object | An inline search template to render if a search template is not specified. Supports the same parameters as a [Search]({{site.url}}{{site.baseurl}}/api-reference/search/) API request and [Mustache](https://mustache.github.io/mustache.5.html) variables. | 
+
+## Example request
+
+Both of the following request examples use the search template with the template ID `play_search_template`:
+
+```json
+{
+  "source": {
+    "query": {
+      "match": {
+        "play_name": "{{play_name}}"
+      }
+    }
+  },
+  "params": {
+    "play_name": "Henry IV"
+  }
+}
+```
+
+### Render template using template ID
+
+The following example request validates a search template with the ID `play_search_template`:
+
+```json
+POST _render/template
+{
+  "id": "play_search_template",
+  "params": {
+    "play_name": "Henry IV"
+  }
+}
+```
+{% include copy.html %}
+
+### Render template using `_source`
+
+If you don't want to use a saved template, or want to test a template before saving, you can test a template with the `_source` parameter using [Mustache](https://mustache.github.io/mustache.5.html) variables, as shown in the following example:
+
+```
+{
+  "source": {
+    "from": "{{from}}{{^from}}10{{/from}}",
+    "size": "{{size}}{{^size}}10{{/size}}",
+    "query": {
+      "match": {
+        "play_name": "{{play_name}}"
+      }
+    }
+  },
+  "params": {
+    "play_name": "Henry IV"
+  }
+}
+```
+{% include copy.html %}
+
+## Example response
+
+OpenSearch responds with information about the template's output:
+
+```json
+{
+  "template_output": {
+    "from": "0",
+    "size": "10",
+    "query": {
+      "match": {
+        "play_name": "Henry IV"
+      }
+    }
+  }
+}
+```
+
+
+
+