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Kiwi is a utility library. We really like Google's Guava, and also use Apache Commons. But if they don't have something we need, and we think it is useful, this is where we put it.

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package org.kiwiproject.retry;

import static java.util.Objects.nonNull;
import static org.apache.commons.lang3.exception.ExceptionUtils.getRootCause;
import static org.apache.commons.lang3.exception.ExceptionUtils.indexOfType;

import lombok.experimental.UtilityClass;

import javax.net.ssl.SSLHandshakeException;
import javax.ws.rs.core.Response;
import java.net.ConnectException;
import java.net.NoRouteToHostException;
import java.net.SocketTimeoutException;
import java.net.UnknownHostException;
import java.util.function.Predicate;

/**
 * Some potentially useful predicates that can be used out of the box with {@link KiwiRetryer} or directly with
 * {@link org.kiwiproject.retry.RetryerBuilder}, or anything else that accepts a {@link Predicate}.
 * 
 * Note that the Jakarta RS-API needs to be available at runtime to use the {@link Response} predicates.
 */
@UtilityClass
public class KiwiRetryerPredicates {

    /**
     * Check if a given {@link Exception} is or has a root cause of {@link UnknownHostException}.
     *
     * @implNote UnknownHostException does not have a cause, which is why we check only the instance and root cause
     */
    public static final Predicate UNKNOWN_HOST = ex ->
            ex instanceof UnknownHostException || getRootCause(ex) instanceof UnknownHostException;


    /**
     * Check if a given {@link Exception} is or has a root cause of {@link ConnectException}.
     *
     * @implNote ConnectException does not have a cause, which is why we check only the instance and root cause
     */
    public static final Predicate CONNECTION_ERROR = ex ->
            ex instanceof ConnectException || getRootCause(ex) instanceof ConnectException;


    /**
     * Check if a given {@link Exception} is or has a root cause of {@link SocketTimeoutException}.
     *
     * @implNote SocketTimeoutException does not have a cause, which is why we check only the instance and root cause
     */
    public static final Predicate SOCKET_TIMEOUT = ex ->
            ex instanceof SocketTimeoutException || getRootCause(ex) instanceof SocketTimeoutException;


    /**
     * Check if a given {@link Exception} is or contains a {@link javax.net.ssl.SSLHandshakeException} somewhere in
     * the causal chain.
     */
    public static final Predicate SSL_HANDSHAKE_ERROR = ex ->
            ex instanceof SSLHandshakeException || indexOfType(ex, SSLHandshakeException.class) > -1;


    /**
     * Check if a given {@link Exception} is or has a root cause of {@link NoRouteToHostException}.
     *
     * @implNote NoRouteToHostException does not have a cause, which is why we check only the instance and root cause
     */
    public static final Predicate NO_ROUTE_TO_HOST = ex ->
            ex instanceof NoRouteToHostException || getRootCause(ex) instanceof NoRouteToHostException;

    /**
     * Check if a given JAX-RS {@link Response} is a client error (4xx).
     */
    public static final Predicate IS_HTTP_400s = response ->
            nonNull(response) && Response.Status.Family.CLIENT_ERROR == response.getStatusInfo().getFamily();

    /**
     * Check if a given JAX-RS {@link Response} is a server error (5xx).
     */
    public static final Predicate IS_HTTP_500s = response ->
            nonNull(response) && Response.Status.Family.SERVER_ERROR == response.getStatusInfo().getFamily();

}