ConnectionConfigCallback Is Unnecessary

[001mertiya]

There is an important corner case to be aware of when using ConnectionConfigCallback. If a user tries to configure connection properties through ConnectionConfigCallback while also setting a custom connectionManager in HttpClientConfigCallback, the connection properties set via ConnectionConfigCallback will not work as expected.

This happens because when a custom connectionManager is provided in HttpClientConfigCallback, it effectively overrides the connection settings configured in ConnectionConfigCallback. As a result, any connection properties passed through ConnectionConfigCallback are ignored or replaced by the custom connection manager’s settings.

Therefore, users should be cautious when using both ConnectionConfigCallback and a custom connectionManager together. To avoid unexpected behavior, we can either remove ConnectionConfigCallback for now or document it.

[001mertiya]

@reta , Could you please take a look at this when you have time? It’s regarding your suggestion to add ConnectionConfigCallback.
CC: @Xtansia

[reta]

Thanks @001mertiya , there is nothing particular about RequestConfigCallback or ConnectionConfigCallback. As I clarified here on the matter #1633 (comment) , we provide a means to minimize the amount of the code or/and customizations that users have to write. If RequestConfigCallback or /and ConnectionConfigCallback is enough is sufficient - fine, if not - HttpClientConfigCallback

[001mertiya]

Correct, it makes sense for RequestConfigCallback because we can set RequestConfig in HttpClientBuilder, but ConnectionConfig is not set directly in HttpClientBuilder, which may confuse users.

Eg.
Users should not assume that passing ConnectionConfig in ConnectionConfigCallback and also passing a connectionManager to set maxConnTotal or maxConnPerRoute will work as expected, since these settings are not part of ConnectionConfig.

ApacheHttpClient5TransportBuilder httpClientTransportBuilder = ApacheHttpClient5TransportBuilder.builder(hosts)
                .setHttpClientConfigCallback(httpClientBuilder -> {
                   

               BasicCredentialsProvider credentialsProvider = new BasicCredentialsProvider();

               PoolingAsyncClientConnectionManager connectionManager = PoolingAsyncClientConnectionManagerBuilder
                            .create()
                            .setMaxConnPerRoute(openSearchClientConfigurations.getMaxConnectionPerRoute())
                            .setMaxConnTotal(openSearchClientConfigurations.getMaxConnectionTotal())
                            .build();  

                    return httpClientBuilder.setDefaultCredentialsProvider(credentialsProvider).setConnectionManager(connectionManager);
                })
                .setConnectionConfigCallback(httpClientBuilder -> {
                    return ConnectionConfig.custom()
                            .setConnectTimeout(Timeout.of(openSearchClientConfigurations.getConnectTimeout()))
                            .setSocketTimeout(Timeout.of(openSearchClientConfigurations.getConnectTimeout()));
                } )
               

Updated doc for the same

[001mertiya]

Updated the doc for ConnectionConfigCallback