fix(elasticsearch sink): Elasticsearch sink with api_version set to auto does not recognize the API version of ES6 as V6 (vectordotdev#17226)

Author: syedriko

src/sinks/elasticsearch/common.rs

@@ -145,7 +145,10 @@ impl ElasticsearchCommon {
                     )
                     .await
                     {
-                        Ok(version) => version,
+                        Ok(version) => {
+			    debug!(message = "Auto-detected Elasticsearch API version.", %version);
+                            version
+			}
                         // This error should be fatal, but for now we only emit it as a warning
                         // to make the transition smoother.
                         Err(error) => {
@@ -277,28 +280,34 @@ async fn get_version(
     proxy_config: &ProxyConfig,
 ) -> crate::Result<usize> {
     #[derive(Deserialize)]
-    struct ClusterState {
-        version: Option<usize>,
+    struct Version {
+        number: Option<String>,
+    }
+    #[derive(Deserialize)]
+    struct ResponsePayload {
+        version: Option<Version>,
     }
 
     let client = HttpClient::new(tls_settings.clone(), proxy_config)?;
-    let response = get(
-        base_url,
-        http_auth,
-        aws_auth,
-        region,
-        request,
-        client,
-        "/_cluster/state/version",
-    )
-    .await
-    .map_err(|error| format!("Failed to get Elasticsearch API version: {}", error))?;
+    let response = get(base_url, http_auth, aws_auth, region, request, client, "/")
+	.await
+	.map_err(|error| format!("Failed to get Elasticsearch API version: {}", error))?;
 
     let (_, body) = response.into_parts();
     let mut body = body::aggregate(body).await?;
     let body = body.copy_to_bytes(body.remaining());
-    let ClusterState { version } = serde_json::from_slice(&body)?;
-    version.ok_or_else(||"Unexpected response from Elasticsearch endpoint `/_cluster/state/version`. Missing `version`. Consider setting `api_version` option.".into())
+    let ResponsePayload { version } = serde_json::from_slice(&body)?;
+    if let Some(version) = version {
+        if let Some(number) = version.number {
+            let v: Vec<&str> = number.split('.').collect();
+            if !v.is_empty() {
+                if let Ok(major_version) = v[0].parse::<usize>() {
+                    return Ok(major_version);
+                }
+            }
+        }
+    }
+    Err("Unexpected response from Elasticsearch endpoint `/`. Missing `version`. Consider setting `api_version` option.".into())
 }
 
 async fn get(