Use xz internal for RCompression.lzmaUncompressFromFile

com.oracle.truffle.r.runtime/src/com/oracle/truffle/r/runtime/RCompression.java

@@ -28,12 +28,15 @@ import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
 import java.lang.ProcessBuilder.Redirect;
+import java.nio.file.Files;
+import java.nio.file.Paths;
 import java.util.zip.GZIPInputStream;
 
 import com.oracle.truffle.r.runtime.conn.GZIPConnections.GZIPRConnection;
 import com.oracle.truffle.r.runtime.ffi.RFFIFactory;
 
 import org.tukaani.xz.LZMA2InputStream;
+import org.tukaani.xz.XZInputStream;
 
 /**
  * Abstracts the implementation of the various forms of compression used in R.
@@ -180,7 +183,28 @@ public class RCompression {
      * This is used by {@link GZIPRConnection}.
      */
     public static byte[] lzmaUncompressFromFile(String path) {
-        return genericUncompressFromFile(new String[]{"xz", "--decompress", "--lzma2", "--stdout", path});
+        try {
+            byte[] data = Files.readAllBytes(Paths.get(path));
+            byte[] buffer = new byte[data.length * 4];
+            try (XZInputStream lzmaStream = new XZInputStream(new ByteArrayInputStream(data))) {
+                int totalRead = 0;
+                int n;
+                while ((n = lzmaStream.read(buffer, totalRead, buffer.length - totalRead)) > 0) {
+                    totalRead += n;
+                    if (totalRead == buffer.length) {
+                        byte[] newbuffer = new byte[buffer.length * 2];
+                        System.arraycopy(buffer, 0, newbuffer, 0, buffer.length);
+                        buffer = newbuffer;
+                    }
+                }
+                byte[] result = new byte[totalRead];
+                System.arraycopy(buffer, 0, result, 0, totalRead);
+                return result;
+            }
+
+        } catch (IOException ex) {
+            throw RInternalError.shouldNotReachHere(ex);
+        }
     }
 
     public static byte[] bzipUncompressFromFile(String path) {