BufferedFileChannelInputStream.available() returns 0 before any reads.

Author: garydgregory

src/changes/changes.xml

@@ -62,6 +62,7 @@ The <action> type attribute can be add,update,fix,remove.
       <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>
       <action dev="ggregory" type="add"                due-to="Gary Gregory">Avoid NullPointerException in ProxyInputStream.available() when the underlying input stream is null.</action>
+      <action dev="ggregory" type="add"                due-to="Gary Gregory">BufferedFileChannelInputStream.available() returns 0 before any reads.</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/BufferedFileChannelInputStream.java

@@ -169,6 +169,9 @@ public BufferedFileChannelInputStream(final Path path, final int bufferSize) thr
 
     @Override
     public synchronized int available() throws IOException {
+        if (!refill()) {
+            return EOF;
+        }
         return byteBuffer.remaining();
     }
 

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

@@ -16,12 +16,15 @@
  */
 package org.apache.commons.io.input;
 
+import static org.junit.jupiter.api.Assertions.assertNotEquals;
 import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import java.io.IOException;
 import java.io.InputStream;
 import java.nio.file.StandardOpenOption;
 
+import org.apache.commons.io.IOUtils;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
@@ -50,10 +53,26 @@ public void setUp() throws IOException {
         //@formatter:on
     }
 
+    @Test
+    public void testAvailableAfterRead() throws Exception {
+        for (final InputStream inputStream : inputStreams) {
+            assertNotEquals(IOUtils.EOF, inputStream.read());
+            assertTrue(inputStream.available() > 0);
+        }
+    }
+
+    @Test
+    public void testAvailableFirst() throws Exception {
+        for (final InputStream inputStream : inputStreams) {
+            assertTrue(inputStream.available() > 0);
+        }
+    }
+
     @Test
     public void testBuilderGet() {
         // java.lang.IllegalStateException: origin == null
         assertThrows(IllegalStateException.class, () -> BufferedFileChannelInputStream.builder().get());
     }
 
+
 }