IOFunction functional interface
diff --git a/httpcore5/src/main/java/org/apache/hc/core5/function/IOFunction.java b/httpcore5/src/main/java/org/apache/hc/core5/function/IOFunction.java
new file mode 100644
index 0000000..43ba5da
--- /dev/null
+++ b/httpcore5/src/main/java/org/apache/hc/core5/function/IOFunction.java
@@ -0,0 +1,52 @@
+/*
+ * ====================================================================
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ * ====================================================================
+ *
+ * This software consists of voluntary contributions made by many
+ * individuals on behalf of the Apache Software Foundation. For more
+ * information on the Apache Software Foundation, please see
+ * <http://www.apache.org/>.
+ *
+ */
+
+package org.apache.hc.core5.function;
+
+import java.io.IOException;
+
+/**
+ * Minimal equivalent of {@link java.util.function.Function} whose
+ * {@link #apply(Object)} method is allowed to throw {@link IOException}.
+ *
+ * @param <T> input type
+ * @param <R> result type
+ * @since 5.4
+ */
+@FunctionalInterface
+public interface IOFunction<T, R> {
+
+ /**
+ * Applies the transformation.
+ *
+ * @param value source value (never {@code null})
+ * @return transformed value
+ * @throws IOException if the transformation cannot be performed
+ */
+ R apply(T value) throws IOException;
+
+}
\ No newline at end of file
