Implement GZIPCompressingInputStream, re #54

Author: safris

src/main/java/org/libj/util/zip/GZIPCompressingInputStream.java

@@ -0,0 +1,105 @@
+/* Copyright (c) 2024 LibJ
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * You should have received a copy of The MIT License (MIT) along with this
+ * program. If not, see <http://opensource.org/licenses/MIT/>.
+ */
+
+package org.libj.util.zip;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.util.zip.DeflaterOutputStream;
+
+/**
+ * Compresses an {@link InputStream} in a memory-optimal, on-demand way only compressing enough to fill a buffer.
+ */
+public class GZIPCompressingInputStream extends InputStream {
+  private final InputStream in;
+  private final DeflaterOutputStream out;
+  private final byte[] readBuf = new byte[8192];
+
+  private byte[] buf = new byte[8192];
+  private int read = 0;
+  private int write = 0;
+
+  public GZIPCompressingInputStream(final InputStream in) {
+    this.in = in;
+    this.out = new UnsynchronizedGZIPOutputStream(new OutputStream() {
+      private void ensureCapacity(final int len) {
+        final int length = buf.length;
+        if (write + len >= length) {
+          final byte[] newbuf = new byte[(length + len) * 2];
+          System.arraycopy(buf, 0, newbuf, 0, length);
+          buf = newbuf;
+        }
+      }
+
+      @Override
+      public void write(final byte[] b, final int off, final int len) throws IOException {
+        ensureCapacity(len);
+        System.arraycopy(b, off, buf, write, len);
+        write += len;
+      }
+
+      @Override
+      public void write(final int b) throws IOException {
+        ensureCapacity(1);
+        buf[write++] = (byte)b;
+      }
+    });
+  }
+
+  private void compressStream() throws IOException {
+    // If the reader has caught up with the writer, then zero the positions out.
+    if (read == write) {
+      read = 0;
+      write = 0;
+    }
+
+    while (write == 0) {
+      // Feed the gzip stream data until it spits out a block.
+      final int val = in.read(readBuf);
+      if (val > 0) {
+        out.write(readBuf, 0, val);
+      }
+      else if (val == -1) {
+        // Nothing left to do, we've hit the end of the stream, so close and break out.
+        out.close();
+        break;
+      }
+    }
+  }
+
+  @Override
+  public int read(final byte[] b, final int off, final int len) throws IOException {
+    compressStream();
+    final int noBytes = Math.min(len, write - read);
+    if (noBytes > 0) {
+      System.arraycopy(buf, read, b, off, noBytes);
+      read += noBytes;
+    }
+    else if (len > 0) {
+      // If bytes were requested, but we have none, then we're at the end of the stream.
+      return -1;
+    }
+
+    return noBytes;
+  }
+
+  @Override
+  public int read() throws IOException {
+    compressStream();
+    return write == 0 ? -1 : buf[read++] & 0xFF;
+  }
+}

src/test/java/org/libj/util/zip/GZIPCompressingInputStreamTest.java

@@ -0,0 +1,41 @@
+package org.libj.util.zip;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.PipedInputStream;
+import java.io.PipedOutputStream;
+import java.util.Random;
+import java.util.zip.GZIPInputStream;
+
+import org.junit.Test;
+import org.libj.lang.Strings;
+
+public class GZIPCompressingInputStreamTest {
+  private static void test(final String str) throws IOException {
+    final byte[] bytes = str.getBytes();
+    final InputStream in = new GZIPCompressingInputStream(new ByteArrayInputStream(bytes));
+    final PipedInputStream pin = new PipedInputStream(8192);
+    try (final PipedOutputStream pout = new PipedOutputStream(pin)) {
+      for (int c; (c = in.read()) != -1;) // [ST]
+        pout.write(c);
+    }
+
+    final GZIPInputStream zin = new GZIPInputStream(pin);
+    final ByteArrayOutputStream out = new ByteArrayOutputStream();
+    for (int c; (c = zin.read()) != -1;) // [ST]
+      out.write(c);
+
+    assertArrayEquals(bytes, out.toByteArray());
+  }
+
+  @Test
+  public void test() throws IOException {
+    final Random random = new Random();
+    for (int i = 0; i < 100; ++i)
+      test(Strings.getRandomAlphaNumeric(random, i * i + 1));
+  }
+}