From 651d400a4f7cca02fe07d06b2d6b6bcc1de09bd9 Mon Sep 17 00:00:00 2001
From: Peter Wu <peter@lekensteyn.nl>
Date: Sat, 3 May 2014 00:07:47 +0200
Subject: More compression fixes

 * Fix magic check (bytes are read as signed numbers...).
 * Assume that a file can be compressed if the file is too small.
 * Try to convert a file only if the gzip detection is correctly closed.
---
 src/io/CompressableDataWriter.java | 21 ++++++++++++---------
 1 file changed, 12 insertions(+), 9 deletions(-)

diff --git a/src/io/CompressableDataWriter.java b/src/io/CompressableDataWriter.java
index 7460c96..a3b069f 100644
--- a/src/io/CompressableDataWriter.java
+++ b/src/io/CompressableDataWriter.java
@@ -56,20 +56,20 @@ public class CompressableDataWriter extends DataWriter {
                 bis = new BufferedInputStream(new FileInputStream(getFileName()));
                 // file found containing magic? OK, gzip writable!
                 compressable = isCompressed(bis);
-                if (!compressable) {
-                    if (CompressableDataWriter.this.convertUncompressed) {
-                        tryConvertToGzip();
-                    } else {
-                        getLogger().info(getFileName() + ": not compressed and "
-                                + "won't be compressed either.");
-                    }
-                }
             } catch (FileNotFoundException ex) {
                 // file not found? Then we are free to write.
                 compressable = true;
             } finally {
                 IOUtils.closeQuietly(bis);
             }
+            if (!compressable) {
+                if (CompressableDataWriter.this.convertUncompressed) {
+                    tryConvertToGzip();
+                } else {
+                    getLogger().info(getFileName() + ": not compressed and "
+                            + "won't be compressed either.");
+                }
+            }
             // now prepare a compressed output stream if possible...
             os = new FileOutputStream(getFileName(), true);
             if (compressable) {
@@ -83,9 +83,12 @@ public class CompressableDataWriter extends DataWriter {
                 // is compressed or not
                 byte[] header = new byte[2];
                 if (bis.read(header, 0, header.length) == 2) {
-                    int magic = (header[1] << 8) | header[0];
+                    int magic = ((header[1] & 0xFF) << 8) | (header[0] & 0xFF);
                     return magic == GZIPInputStream.GZIP_MAGIC;
                 }
+                // file is too small, it is likely empty or contains a single
+                // newline or other junk.
+                return true;
             } catch (IOException ex) {
                 // file is too small, do not overwrite.
             }
-- 
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