diff --git a/src/main/java/org/cobbzilla/util/io/FixedByteArrayInputStream.java b/src/main/java/org/cobbzilla/util/io/FixedByteArrayInputStream.java
new file mode 100644
index 0000000..633468f
--- /dev/null
+++ b/src/main/java/org/cobbzilla/util/io/FixedByteArrayInputStream.java
@@ -0,0 +1,20 @@
+package org.cobbzilla.util.io;
+
+import lombok.Getter;
+
+import java.io.ByteArrayInputStream;
+
+public class FixedByteArrayInputStream extends ByteArrayInputStream implements FixedSizeInputStream {
+
+    @Getter private final int size;
+
+    public FixedByteArrayInputStream(byte[] buf) {
+        super(buf);
+        size = buf.length;
+    }
+
+    public FixedByteArrayInputStream(byte[] buf, int offset, int length) {
+        super(buf, offset, length);
+        size = length;
+    }
+}
diff --git a/src/main/java/org/cobbzilla/util/io/FixedSizeInputStream.java b/src/main/java/org/cobbzilla/util/io/FixedSizeInputStream.java
new file mode 100644
index 0000000..b0d65bf
--- /dev/null
+++ b/src/main/java/org/cobbzilla/util/io/FixedSizeInputStream.java
@@ -0,0 +1,7 @@
+package org.cobbzilla.util.io;
+
+public interface FixedSizeInputStream {
+
+    long getSize ();
+
+}
diff --git a/src/main/java/org/cobbzilla/util/io/NullInputStream.java b/src/main/java/org/cobbzilla/util/io/NullInputStream.java
index bfe5a6f..1557ac1 100644
--- a/src/main/java/org/cobbzilla/util/io/NullInputStream.java
+++ b/src/main/java/org/cobbzilla/util/io/NullInputStream.java
@@ -2,7 +2,7 @@ package org.cobbzilla.util.io;
 
 import java.io.InputStream;
 
-public class NullInputStream extends InputStream {
+public class NullInputStream extends InputStream implements FixedSizeInputStream {
 
     public static final NullInputStream instance = new NullInputStream();
 
@@ -10,4 +10,6 @@ public class NullInputStream extends InputStream {
     @Override public int read(byte[] b) { return -1; }
     @Override public int read(byte[] b, int off, int len) { return -1; }
 
+    @Override public long getSize() { return 0; }
+
 }