HPCC-32649 Avoid writing any data to an empty compressed file

Signed-off-by: Gavin Halliday <[email protected]>
hpcc-systems · Sep 23, 2024 · 16dcf3b · 16dcf3b
1 parent 7513f82
commit 16dcf3b
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Showing 3 changed files with 53 additions and 13 deletions.
diff --git a/system/jlib/jlzw.cpp b/system/jlib/jlzw.cpp
@@ -2042,7 +2042,7 @@ class CCompressedFile : implements ICompressedFileIO, public CInterface
     Owned<IExpander> expander;
     MemoryAttr compressedInputBlock;
     unsigned compMethod;
-    offset_t lastFlushPos = (offset_t)-1;
+    offset_t lastFlushPos = 0;
     offset_t nextExpansionPos = (offset_t)-1;
     offset_t startBlockPos = (offset_t)-1;
     size32_t fullBlockSize = 0;
@@ -2456,19 +2456,23 @@ class CCompressedFile : implements ICompressedFileIO, public CInterface
                 throw MakeStringException(-1,"Partial row written at end of file %d of %d",ol,trailer.recordSize);
             }
             flush();
-            trailer.datacrc = trailer.crc;
-            if (setcrc) {
-                indexbuf.append(sizeof(trailer)-sizeof(trailer.crc),&trailer);
-                trailer.crc = crc32((const char *)indexbuf.toByteArray(),
-                                indexbuf.length(),trailer.crc);
-                indexbuf.append(trailer.crc);
-            }
-            else {
-                trailer.datacrc = 0;
-                trailer.crc = ~0U;
-                indexbuf.append(sizeof(trailer),&trailer);
+            //Avoid writing out a header/footer if the file is empty
+            if (indexbuf.length() != 0)
+            {
+                trailer.datacrc = trailer.crc;
+                if (setcrc) {
+                    indexbuf.append(sizeof(trailer)-sizeof(trailer.crc),&trailer);
+                    trailer.crc = crc32((const char *)indexbuf.toByteArray(),
+                                    indexbuf.length(),trailer.crc);
+                    indexbuf.append(trailer.crc);
+                }
+                else {
+                    trailer.datacrc = 0;
+                    trailer.crc = ~0U;
+                    indexbuf.append(sizeof(trailer),&trailer);
+                }
+                checkedwrite(trailer.indexPos,indexbuf.length(),indexbuf.toByteArray());
             }
-            checkedwrite(trailer.indexPos,indexbuf.length(),indexbuf.toByteArray());
             indexbuf.clear();
             if (fileio)
                 fileio->close();

diff --git a/testing/regress/ecl/emptycompressed.ecl b/testing/regress/ecl/emptycompressed.ecl
@@ -0,0 +1,32 @@
+/*##############################################################################
+
+    HPCC SYSTEMS software Copyright (C) 2012 HPCC Systems®.
+
+    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.
+############################################################################## */
+
+import Std.System.Thorlib;
+import Std.File AS FileServices;
+import Std.Str;
+import $.setup;
+
+prefix := setup.Files(false, false).QueryFilePrefix;
+
+filename := prefix+'empty';
+r := { string x};
+
+ds := DATASET(0, transform(r, SELF := []));
+output(ds,,filename, overwrite,compressed);
+
+iclData0 := DATASET(filename, r, flat);
+output(iclData0);
diff --git a/testing/regress/ecl/key/emptycompressed.xml b/testing/regress/ecl/key/emptycompressed.xml
@@ -0,0 +1,4 @@
+<Dataset name='Result 1'>
+</Dataset>
+<Dataset name='Result 2'>
+</Dataset>