1 files changed, 97 insertions, 0 deletions
diff --git a/vespajlib/src/main/java/com/yahoo/io/TeeInputStream.java b/vespajlib/src/main/java/com/yahoo/io/TeeInputStream.java
new file mode 100644
index 00000000000..f9e803df08f
--- /dev/null
+++ b/vespajlib/src/main/java/com/yahoo/io/TeeInputStream.java
@@ -0,0 +1,97 @@
+package com.yahoo.io;
+
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.io.IOException;
+
+/**
+ * Forwards input from a source InputStream while making a copy of it into an outputstream.
+ * Note that it also does read-ahead and copies up to 64K of data more than was used.
+ */
+class TeeInputStream extends InputStream {
+    final InputStream src;
+    final OutputStream dst;
+
+    static final int CAPACITY = 65536;
+
+    byte[] buf = new byte[CAPACITY];
+    int readPos = 0;
+    int writePos = 0;
+
+    private int inBuf() { return writePos - readPos; }
+
+    private void fillBuf() throws IOException {
+        if (readPos == writePos) {
+            readPos = 0;
+            writePos = 0;
+        }
+        if (readPos * 3 > CAPACITY) {
+            int had = inBuf();
+            System.arraycopy(buf, readPos, buf, 0, had);
+            readPos = 0;
+            writePos = had;
+        }
+        int wantToRead = CAPACITY - writePos;
+        if (inBuf() > 0) {
+            // if we have data already, do not block, read only what is available
+            wantToRead = Math.min(wantToRead, src.available());
+        }
+        if (wantToRead > 0) {
+            int got = src.read(buf, writePos, wantToRead);
+            if (got > 0) {
+                dst.write(buf, writePos, got);
+                writePos += got;
+            }
+        }
+    }
+
+    /** Construct a Tee */
+    public TeeInputStream(InputStream from, OutputStream to) {
+        super();
+        this.src = from;
+        this.dst = to;
+    }
+
+    @Override
+    public int available() throws IOException {
+        return inBuf() + src.available();
+    }
+
+    @Override
+    public void close() throws IOException {
+        src.close();
+        dst.close();
+    }
+
+    @Override
+    public int read() throws IOException {
+        fillBuf();
+        if (inBuf() > 0) {
+            int r = buf[readPos++];
+            return r & 0xff;
+        }
+        return -1;
+    }
+
+    @Override
+    public int read(byte[] b) throws IOException {
+        return read(b, 0, b.length);
+    }
+
+    @Override
+    public int read(byte[] b, int off, int len) throws IOException {
+        if (len <= 0) {
+            return 0;
+        }
+        fillBuf();
+        int had = inBuf();
+        if (had > 0) {
+            len = Math.min(len, had);
+            System.arraycopy(buf, readPos, b, off, len);
+            readPos += len;
+            return len;
+        }
+        return -1;
+    }
+
+}