Fix zlib compression (#901)

* add failing integrationtest for https://github.com/hierynomus/sshj/issues/893

* Fix zlib compression

---------

Co-authored-by: Malte Otten <malte.otten@emsysvpp.de>

src/itest/java/com/hierynomus/sshj/sftp/PutFileCompressedTest.java

@@ -0,0 +1,81 @@
+/*
+ * Copyright (C)2009 - SSHJ Contributors
+ *
+ * Licensed 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.
+ */
+package com.hierynomus.sshj.sftp;
+
+import com.hierynomus.sshj.SshdContainer;
+import net.schmizz.sshj.SSHClient;
+import net.schmizz.sshj.sftp.SFTPClient;
+import net.schmizz.sshj.xfer.InMemorySourceFile;
+import org.junit.jupiter.api.Test;
+import org.testcontainers.junit.jupiter.Container;
+import org.testcontainers.junit.jupiter.Testcontainers;
+
+import java.io.ByteArrayInputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.Random;
+
+@Testcontainers
+public class PutFileCompressedTest {
+
+    private static class TestInMemorySourceFile extends InMemorySourceFile {
+
+        private final String name;
+        private final byte[] data;
+
+        public TestInMemorySourceFile(String name, byte[] data) {
+            this.name = name;
+            this.data = data;
+        }
+
+        @Override
+        public String getName() {
+            return name;
+        }
+
+        @Override
+        public long getLength() {
+            return data.length;
+        }
+
+        @Override
+        public InputStream getInputStream() throws IOException {
+            return new ByteArrayInputStream(data);
+        }
+
+    }
+
+    @Container
+    private static SshdContainer sshd = new SshdContainer();
+
+    @Test
+    public void shouldPutCompressedFile_GH893() throws Throwable {
+        try (SSHClient client = sshd.getConnectedClient()) {
+            client.authPublickey("sshj", "src/test/resources/id_rsa");
+            client.useCompression();
+            try (SFTPClient sftp = client.newSFTPClient()) {
+                String filename = "test.txt";
+                // needs to be a larger file for bug taking effect
+                byte[] content = new byte[5000];
+                Random r = new Random(1);
+                r.nextBytes(content);
+
+                sftp.put(new TestInMemorySourceFile(filename,content), "/home/sshj/");
+            }
+
+        }
+    }
+}

src/main/java/net/schmizz/sshj/transport/compression/ZlibCompression.java

@@ -22,7 +22,6 @@ import java.util.zip.Inflater;
 import net.schmizz.sshj.common.Buffer;
 import net.schmizz.sshj.common.DisconnectReason;
 import net.schmizz.sshj.transport.TransportException;
-import net.schmizz.sshj.transport.compression.Compression;
 
 public class ZlibCompression implements Compression {
 
@@ -71,10 +70,14 @@ public class ZlibCompression implements Compression {
     public void compress(Buffer buffer) {
         deflater.setInput(buffer.array(), buffer.rpos(), buffer.available());
         buffer.wpos(buffer.rpos());
-        do {
+        while (true) {
             final int len = deflater.deflate(tempBuf, 0, BUF_SIZE, Deflater.SYNC_FLUSH);
+            if(len > 0) {
                 buffer.putRawBytes(tempBuf, 0, len);
-        } while (!deflater.needsInput());
+            } else {
+                return;
+            }
+        }
     }
 
     @Override