jinterface: fix writing small compressed values

This is a regression of 4390e43558 in the OtpOutputStream class.

We can not call java.util.zip.DeflaterOutputStream.close() in the finally
block of the OtpOutputStream.write_compressed(OtpErlangObject, int) method.
This leads to a NullPointerException when encoding "{}" which is caused by
the DeflaterOutputStream trying to write bytes to the deflater which was
"destroyed" by calling java.util.zip.Deflater.end().
Further possibilities to call close() in the finally block are not suitable
either (see the comment in the source). This leaves no choice but to revert
the change from 4390e43558 in this class (and add an appropriate test case).

2 files changed, 18 insertions, 7 deletions

diff --git a/lib/jinterface/java_src/com/ericsson/otp/erlang/OtpOutputStream.java b/lib/jinterface/java_src/com/ericsson/otp/erlang/OtpOutputStream.java
index 2830a7842e..4faae2a157 100644
--- a/lib/jinterface/java_src/com/ericsson/otp/erlang/OtpOutputStream.java
+++ b/lib/jinterface/java_src/com/ericsson/otp/erlang/OtpOutputStream.java
@@ -922,8 +922,22 @@ public class OtpOutputStream extends ByteArrayOutputStream {
                 oos.writeTo(dos);
                 dos.close(); // note: closes this, too!
             } catch (final IllegalArgumentException e) {
-                // discard further un-compressed data
-                // -> if not called, there may be memory leaks!
+                /*
+                 * Discard further un-compressed data (if not called, there may
+                 * be memory leaks).
+                 *
+                 * After calling java.util.zip.Deflater.end(), the deflater
+                 * should not be used anymore, not even the close() method of
+                 * dos. Calling dos.close() before def.end() is prevented since
+                 * an unfinished DeflaterOutputStream will try to deflate its
+                 * unprocessed data to the (fixed) byte array which is prevented
+                 * by ensureCapacity() and would also unnecessarily process
+                 * further data that is discarded anyway.
+                 *
+                 * Since we are re-using the byte array of this object below, we
+                 * must not call close() in e.g. a finally block either (with or
+                 * without a call to def.end()).
+                 */
                 def.end();
                 // could not make the value smaller than originally
                 // -> reset to starting count, write uncompressed
@@ -942,11 +956,6 @@ public class OtpOutputStream extends ByteArrayOutputStream {
                         "Intermediate stream failed for Erlang object " + o);
             } finally {
                 fixedSize = Integer.MAX_VALUE;
-                try {
-                    dos.close();
-                } catch (final IOException e) {
-                    // ignore
-                }
             }
         }
     }
diff --git a/lib/jinterface/test/nc_SUITE.erl b/lib/jinterface/test/nc_SUITE.erl
index 9679b90a0d..c5f3198c21 100644
--- a/lib/jinterface/test/nc_SUITE.erl
+++ b/lib/jinterface/test/nc_SUITE.erl
@@ -215,6 +215,7 @@ decompress_roundtrip(Config) when is_list(Config) ->
 	 0.0,
 	 math:sqrt(2),
 	 <<1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,31:5>>,
+	 "{}",
 	 RandomBin1k,
 	 RandomBin1M,
 	 RandomBin10M,
@@ -244,6 +245,7 @@ compress_roundtrip(Config) when is_list(Config) ->
 	 0.0,
 	 math:sqrt(2),
 	 <<1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,31:5>>,
+	 "{}",
 	 RandomBin1k,
 	 RandomBin1M,
 	 RandomBin10M,