Fix two issues with apr_file_trunc() for buffered files:

 - The Win32 implementation incorrectly flushes the buffered writes _after_
   truncating a file.  Such files will have unexpected data written after
   the position at which they should've been truncated. PR 51017.
   (Under Unix, this issue has been fixed in r1044440)

 - Both Win32 and Unix implementations incorrectly keep the data read into
   a buffer after the file is truncated.  Thus, reading from a file after
   apr_file_trunc() can return invalid data from the previous file offset.

* file_io/win32/seek.c
  (apr_file_trunc): Flush the write buffer or discard the read buffer
   before truncating.  Propely update the internal file offset (filePtr)
   and the eof_hit marker.

* file_io/unix/seek.c
  (apr_file_trunc): Discard the read buffer before truncating.

* test/testfile.c
  (test_file_trunc): Extend the checks.  Factor out part of this test...
  (test_file_trunc_buffered_write): ...into this new test.
  (test_file_trunc_buffered_write2, test_file_trunc_buffered_read): New tests.
  (testfile): Run the new tests.

Patch by: Evgeny Kotkov <evgeny.kotkov {at} visualsvn.com>


git-svn-id: http://svn.apache.org/repos/asf/apr/apr/trunk@1788929 13f79535-47bb-0310-9956-ffa450edef68

1 files changed, 30 insertions, 4 deletions

diff --git a/file_io/win32/seek.c b/file_io/win32/seek.c
index b412fd4cb..afe6edb00 100644
--- a/file_io/win32/seek.c
+++ b/file_io/win32/seek.c
@@ -161,17 +161,43 @@ APR_DECLARE(apr_status_t) apr_file_trunc(apr_file_t *thefile, apr_off_t offset)
     LONG  offhi = (LONG)(offset >> 32);
     DWORD rc;
 
+    if (thefile->buffered) {
+        if (thefile->direction == 1) {
+            /* Figure out what needs to be flushed.  Don't flush the part
+             * of the write buffer that will get truncated anyway.
+             */
+            if (offset < thefile->filePtr) {
+                thefile->bufpos = 0;
+            }
+            else if (offset < thefile->filePtr + (apr_off_t)thefile->bufpos) {
+                thefile->bufpos = offset - thefile->filePtr;
+            }
+
+            if (thefile->bufpos != 0) {
+                rv = apr_file_flush(thefile);
+                if (rv != APR_SUCCESS)
+                    return rv;
+            }
+        }
+        else if (thefile->direction == 0) {
+            /* Discard the read buffer, as we are about to reposition
+             * ourselves to the end of file.
+             */
+            thefile->bufpos = 0;
+            thefile->dataRead = 0;
+        }
+    }
+
     rc = SetFilePointer(thefile->filehand, offlo, &offhi, FILE_BEGIN);
     if (rc == 0xFFFFFFFF)
         if ((rv = apr_get_os_error()) != APR_SUCCESS)
             return rv;
+    thefile->filePtr = offset;
+    /* Don't report EOF until the next read. */
+    thefile->eof_hit = 0;
 
     if (!SetEndOfFile(thefile->filehand))
         return apr_get_os_error();
 
-    if (thefile->buffered) {
-        return setptr(thefile, offset);
-    }
-
     return APR_SUCCESS;
 }