1 files changed, 53 insertions, 0 deletions
diff --git a/vespajlib/src/main/java/com/yahoo/io/LazyInputStream.java b/vespajlib/src/main/java/com/yahoo/io/LazyInputStream.java
new file mode 100644
index 00000000000..3ff7ada6b59
--- /dev/null
+++ b/vespajlib/src/main/java/com/yahoo/io/LazyInputStream.java
@@ -0,0 +1,53 @@
+package com.yahoo.io;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.function.Supplier;
+
+/**
+ * Input stream wrapping an input stream supplier, which doesn't have content yet at declaration time.
+ *
+ * @author jonmv
+ */
+public class LazyInputStream extends InputStream {
+
+    private Supplier<InputStream> source;
+    private InputStream delegate;
+
+    public LazyInputStream(Supplier<InputStream> source) {
+        this.source = source;
+    }
+
+    private InputStream in() {
+        if (delegate == null) {
+            delegate = source.get();
+            source = null;
+        }
+        return delegate;
+    }
+
+    @Override
+    public int read() throws IOException { return in().read(); }
+
+    @Override
+    public int read(byte[] b, int off, int len) throws IOException { return in().read(b, off, len); }
+
+    @Override
+    public long skip(long n) throws IOException { return in().skip(n); }
+
+    @Override
+    public int available() throws IOException { return in().available(); }
+
+    @Override
+    public void close() throws IOException { in().close(); }
+
+    @Override
+    public synchronized void mark(int readlimit) { in().mark(readlimit); }
+
+    @Override
+    public synchronized void reset() throws IOException { in().reset(); }
+
+    @Override
+    public boolean markSupported() { return in().markSupported(); }
+
+}