AutoCloseInputStream(InputStream) uses ClosedInputStream.INSTANCE when

its input is null

Author: garydgregory

src/changes/changes.xml

@@ -60,6 +60,7 @@ The <action> type attribute can be add,update,fix,remove.
       <action dev="ggregory" type="fix"                due-to="Gary Gregory">Fix PMD UnnecessaryFullyQualifiedName.</action>
       <action dev="ggregory" type="fix"                due-to="sullis">Add test for CircularByteBuffer clear() #620.</action>
       <action dev="ggregory" type="fix"                due-to="Gary Gregory">PathUtils.isPosix(Path, LinkOption...) should return false on null input.</action>
+      <action dev="ggregory" type="fix"                due-to="Gary Gregory">AutoCloseInputStream(InputStream) uses ClosedInputStream.INSTANCE when its input is null.</action>
       <!-- UPDATE -->
       <action dev="ggregory" type="update"             due-to="Dependabot">Bump tests commons.bytebuddy.version from 1.14.13 to 1.14.17 #615, #621, #631, #635.</action>
       <action dev="ggregory" type="update"             due-to="Dependabot">Bump tests commons-codec:commons-codec from 1.16.1 to 1.17.0.</action>

src/main/java/org/apache/commons/io/input/AutoCloseInputStream.java

@@ -106,9 +106,10 @@ public static Builder builder() {
      * @param in underlying input stream
      * @deprecated Use {@link #builder()}, {@link Builder}, and {@link Builder#get()}
      */
+    @SuppressWarnings("resource") // ClosedInputStream.nonNull() doesn't allocate
     @Deprecated
     public AutoCloseInputStream(final InputStream in) {
-        super(in);
+        super(ClosedInputStream.ifNull(in));
     }
 
     /**

src/main/java/org/apache/commons/io/input/ClosedInputStream.java

@@ -24,7 +24,7 @@
 import org.apache.commons.io.IOUtils;
 
 /**
- * Always returns {@link IOUtils#EOF} to all attempts to read something from the stream.
+ * Always returns {@link IOUtils#EOF} to all attempts to read something from an input stream.
  * <p>
  * Typically uses of this class include testing for corner cases in methods that accept input streams and acting as a
  * sentinel value instead of a {@code null} input stream.
@@ -49,6 +49,16 @@ public class ClosedInputStream extends InputStream {
     @Deprecated
     public static final ClosedInputStream CLOSED_INPUT_STREAM = INSTANCE;
 
+    /**
+     * Returns {@link #INSTANCE} if the given InputStream is null, otherwise returns the given input stream.
+     * 
+     * @param in the InputStream to test.
+     * @return {@link #INSTANCE} if the given InputStream is null, otherwise returns the given input stream.
+     */
+    static InputStream ifNull(final InputStream in) {
+        return in != null ? in : INSTANCE;
+    }
+
     /**
      * Returns -1 to indicate that the stream is closed.
      *

src/test/java/org/apache/commons/io/input/AutoCloseInputStreamTest.java

@@ -23,7 +23,9 @@
 
 import java.io.ByteArrayInputStream;
 import java.io.IOException;
+import java.io.InputStream;
 
+import org.apache.commons.io.IOUtils;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
@@ -50,6 +52,23 @@ public void close() {
         closed = false;
     }
 
+    @Test
+    public void testAvailableAll() throws IOException {
+        try (InputStream inputStream = new AutoCloseInputStream(new ByteArrayInputStream(data))) {
+            assertEquals(3, inputStream.available());
+            IOUtils.toByteArray(inputStream);
+            assertEquals(0, inputStream.available());
+        }
+    }
+
+    @Test
+    public void testAvailableNull() throws IOException {
+        try (InputStream inputStream = new AutoCloseInputStream(null)) {
+            assertEquals(0, inputStream.available());
+            assertEquals(0, inputStream.available());
+        }
+    }
+
     @Test
     public void testBuilderGet() {
         // java.lang.IllegalStateException: origin == null

src/test/java/org/apache/commons/io/input/ClosedInputStreamTest.java

@@ -18,6 +18,7 @@
 
 import static org.apache.commons.io.IOUtils.EOF;
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertSame;
 
 import org.junit.jupiter.api.Test;
 
@@ -30,6 +31,14 @@ private void assertEof(final ClosedInputStream cis) {
         assertEquals(EOF, cis.read(), "read()");
     }
 
+    @SuppressWarnings("resource")
+    @Test
+    public void testNonNull() throws Exception {
+        assertSame(ClosedInputStream.INSTANCE, ClosedInputStream.ifNull(null));
+        assertSame(ClosedInputStream.INSTANCE, ClosedInputStream.ifNull(ClosedInputStream.INSTANCE));
+        assertSame(System.in, ClosedInputStream.ifNull(System.in));
+    }
+
     @Test
     public void testRead() throws Exception {
         try (ClosedInputStream cis = new ClosedInputStream()) {