Merge pull request #3985 from ntherning/fix-Mono.Posix-on-windows

[mono.git] / support / stdio.c

diff --git a/support/stdio.c b/support/stdio.c
index c05913fbe248dc180443701fefae557f9409f50c..b7cc689deb51087588140936b4f99f1cd10d5bf8 100644 (file)
--- a/support/stdio.c
+++ b/support/stdio.c
@@ -49,7 +49,21 @@ Mono_Posix_Stdlib_fwrite (unsigned char *ptr, mph_size_t size, mph_size_t nmemb,
        mph_return_if_size_t_overflow (size);
        mph_return_if_size_t_overflow (nmemb);
 
-       return fwrite (ptr, (size_t) size, (size_t) nmemb, (FILE*) stream);
+       size_t ret = fwrite (ptr, (size_t) size, (size_t) nmemb, (FILE*) stream);
+#ifdef HOST_WIN32
+       // Workaround for a particular weirdness on Windows triggered by the
+       // StdioFileStreamTest.Write() test method. The test writes 15 bytes to a
+       // file, then rewinds the file pointer and reads the same bytes. It then
+       // writes 15 additional bytes to the file. This second write fails on
+       // Windows with 0 returned from fwrite(). Calling fseek() followed by a retry
+       // of fwrite() like we do here fixes the issue.
+       if (ret != nmemb)
+       {
+               fseek (stream, 0, SEEK_CUR);
+               ret = fwrite (ptr + (ret * nmemb), (size_t) size, (size_t) nmemb - ret, (FILE*) stream);
+       }
+#endif
+       return ret;
 }
 
 #ifdef HAVE_VSNPRINTF