Transparent async content (de)compression with gzip

httpclient5/src/main/java/org/apache/hc/client5/http/async/methods/DeflatingGzipEntityProducer.java

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+/*
+ * ====================================================================
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ * ====================================================================
+ *
+ * This software consists of voluntary contributions made by many
+ * individuals on behalf of the Apache Software Foundation.  For more
+ * information on the Apache Software Foundation, please see
+ * <http://www.apache.org/>.
+ *
+ */
+package org.apache.hc.client5.http.async.methods;
+
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.util.Collections;
+import java.util.List;
+import java.util.Set;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.zip.CRC32;
+import java.util.zip.Deflater;
+
+import org.apache.hc.core5.http.Header;
+import org.apache.hc.core5.http.nio.AsyncEntityProducer;
+import org.apache.hc.core5.http.nio.DataStreamChannel;
+import org.apache.hc.core5.util.Args;
+
+/**
+ * Streams an {@link AsyncEntityProducer} through raw DEFLATE
+ * and wraps the result in a valid GZIP container.
+ * <p>
+ * Memory usage is bounded (8 KiB buffers) and back-pressure
+ * from the I/O reactor is honoured.
+ *
+ * @since 5.6
+ */
+public final class DeflatingGzipEntityProducer implements AsyncEntityProducer {
+
+    /* ---------------- constants & buffers --------------------------- */
+
+    private static final int IN_BUF = 8 * 1024;
+    private static final int OUT_BUF = 8 * 1024;
+
+    private final AsyncEntityProducer delegate;
+    private final CRC32 crc = new CRC32();
+    private final Deflater deflater = new Deflater(Deflater.DEFAULT_COMPRESSION, true);
+    private final byte[] in = new byte[IN_BUF];
+    private final ByteBuffer outBuf = ByteBuffer.allocate(OUT_BUF);
+
+    private boolean headerSent = false;
+    private boolean finished = false;
+    private long uncompressed = 0;
+
+    private final AtomicBoolean released = new AtomicBoolean(false);
+
+    public DeflatingGzipEntityProducer(final AsyncEntityProducer delegate) {
+        this.delegate = Args.notNull(delegate, "delegate");
+        outBuf.flip(); // start in “read mode” with no data
+    }
+
+    /* ------------------- metadata ------------------- */
+
+    @Override
+    public boolean isRepeatable() {
+        return delegate.isRepeatable();
+    }
+
+    @Override
+    public long getContentLength() {
+        return -1;
+    } // unknown
+
+    @Override
+    public String getContentType() {
+        return delegate.getContentType();
+    }
+
+    @Override
+    public String getContentEncoding() {
+        return "gzip";
+    }
+
+    @Override
+    public boolean isChunked() {
+        return true;
+    }
+
+    @Override
+    public Set<String> getTrailerNames() {
+        return Collections.emptySet();
+    }
+
+    @Override
+    public int available() {
+        return outBuf.hasRemaining() ? outBuf.remaining() : delegate.available();
+    }
+
+    /* ------------------- core ----------------------- */
+
+    @Override
+    public void produce(final DataStreamChannel chan) throws IOException {
+
+        flushOut(chan);                    // 1) flush any pending data
+
+        if (finished) {
+            return;                        // already done
+        }
+
+        delegate.produce(new InnerChannel(chan)); // 2) pull more input
+
+        /* 3) when delegate is done → finish deflater, drain, trailer */
+        if (delegate.available() == 0 && !finished) {
+
+            deflater.finish();             // signal EOF to compressor
+            while (!deflater.finished()) { // drain *everything*
+                deflateToOut();
+                flushOut(chan);
+            }
+
+            /* ---------------- little-endian trailer ---------------- */
+            final int crcVal = (int) crc.getValue();
+            final int size = (int) uncompressed;
+
+            final byte[] trailer = {
+                    (byte) crcVal, (byte) (crcVal >>> 8),
+                    (byte) (crcVal >>> 16), (byte) (crcVal >>> 24),
+                    (byte) size, (byte) (size >>> 8),
+                    (byte) (size >>> 16), (byte) (size >>> 24)
+            };
+            chan.write(ByteBuffer.wrap(trailer));
+
+            finished = true;
+            chan.endStream();
+        }
+    }
+
+    /* copy all currently available bytes from deflater into outBuf */
+    private void deflateToOut() {
+        outBuf.compact();                  // switch to “write mode”
+        byte[] arr = outBuf.array();
+        int pos = outBuf.position();
+        int lim = outBuf.limit();
+        int n;
+        while ((n = deflater.deflate(arr, pos, lim - pos, Deflater.NO_FLUSH)) > 0) {
+            pos += n;
+            if (pos == lim) {              // buffer full → grow 2×
+                final ByteBuffer bigger = ByteBuffer.allocate(arr.length * 2);
+                outBuf.flip();
+                bigger.put(outBuf);
+                outBuf.clear();
+                outBuf.put(bigger);
+                arr = outBuf.array();
+                lim = outBuf.limit();
+                pos = outBuf.position();
+            }
+        }
+        outBuf.position(pos);
+        outBuf.flip();                     // back to “read mode”
+    }
+
+    /* send as much of outBuf as the channel will accept */
+    private void flushOut(final DataStreamChannel chan) throws IOException {
+        while (outBuf.hasRemaining()) {
+            final int written = chan.write(outBuf);
+            if (written == 0) {
+                break; // back-pressure
+            }
+        }
+    }
+
+    /* --------------- inner channel feeding deflater ---------------- */
+
+    private final class InnerChannel implements DataStreamChannel {
+        private final DataStreamChannel chan;
+
+        InnerChannel(final DataStreamChannel chan) {
+            this.chan = chan;
+        }
+
+        @Override
+        public void requestOutput() {
+            chan.requestOutput();
+        }
+
+        @Override
+        public int write(final ByteBuffer src) throws IOException {
+
+            if (!headerSent) {             // write 10-byte GZIP header
+                chan.write(ByteBuffer.wrap(new byte[]{
+                        0x1f, (byte) 0x8b, 8, 0, 0, 0, 0, 0, 0, 0
+                }));
+                headerSent = true;
+            }
+
+            int consumed = 0;
+            while (src.hasRemaining()) {
+                final int chunk = Math.min(src.remaining(), in.length);
+                src.get(in, 0, chunk);
+
+                crc.update(in, 0, chunk);
+                uncompressed += chunk;
+
+                deflater.setInput(in, 0, chunk);
+                consumed += chunk;
+
+                deflateToOut();
+                flushOut(chan);
+            }
+            return consumed;
+        }
+
+        @Override
+        public void endStream() { /* delegate.available()==0 is our signal */ }
+
+        @Override
+        public void endStream(final List<? extends Header> t) {
+            endStream();
+        }
+    }
+
+    /* ---------------- failure / cleanup ---------------------------- */
+
+    @Override
+    public void failed(final Exception cause) {
+        delegate.failed(cause);
+    }
+
+    @Override
+    public void releaseResources() {
+        if (released.compareAndSet(false, true)) {
+            deflater.end();
+            delegate.releaseResources();
+        }
+    }
+}