Fix failure to honor -Z compression level option in pg_dump -Fd.

cfopen() and cfopen_write() failed to pass the compression level through
to zlib, so that you always got the default compression level if you got
any at all.

In passing, also fix these and related functions so that the correct errno
is reliably returned on failure; the original coding supposes that free()
cannot change errno, which is untrue on at least some platforms.

Per bug #12779 from Christoph Berg.  Back-patch to 9.1 where the faulty
code was introduced.

Michael Paquier

src/bin/pg_dump/compress_io.c

@@ -453,6 +453,16 @@ struct cfp
 static int	hasSuffix(const char *filename, const char *suffix);
 #endif
 
+/* free() without changing errno; useful in several places below */
+static void
+free_keep_errno(void *p)
+{
+	int			save_errno = errno;
+
+	free(p);
+	errno = save_errno;
+}
+
 /*
  * Open a file for reading. 'path' is the file to open, and 'mode' should
  * be either "r" or "rb".
@@ -460,6 +470,8 @@ static int	hasSuffix(const char *filename, const char *suffix);
  * If the file at 'path' does not exist, we append the ".gz" suffix (if 'path'
  * doesn't already have it) and try again. So if you pass "foo" as 'path',
  * this will open either "foo" or "foo.gz".
+ *
+ * On failure, return NULL with an error code in errno.
  */
 cfp *
 cfopen_read(const char *path, const char *mode)
@@ -480,7 +492,7 @@ cfopen_read(const char *path, const char *mode)
 
 			fname = psprintf("%s.gz", path);
 			fp = cfopen(fname, mode, 1);
-			free(fname);
+			free_keep_errno(fname);
 		}
 #endif
 	}
@@ -493,8 +505,10 @@ cfopen_read(const char *path, const char *mode)
  * ("w", "wb", "a", or "ab").
  *
  * If 'compression' is non-zero, a gzip compressed stream is opened, and
- * and 'compression' indicates the compression level used. The ".gz" suffix
+ * 'compression' indicates the compression level used. The ".gz" suffix
  * is automatically added to 'path' in that case.
+ *
+ * On failure, return NULL with an error code in errno.
  */
 cfp *
 cfopen_write(const char *path, const char *mode, int compression)
@@ -509,8 +523,8 @@ cfopen_write(const char *path, const char *mode, int compression)
 		char	   *fname;
 
 		fname = psprintf("%s.gz", path);
-		fp = cfopen(fname, mode, 1);
-		free(fname);
+		fp = cfopen(fname, mode, compression);
+		free_keep_errno(fname);
 #else
 		exit_horribly(modulename, "not built with zlib support\n");
 		fp = NULL;				/* keep compiler quiet */
@@ -521,7 +535,9 @@ cfopen_write(const char *path, const char *mode, int compression)
 
 /*
  * Opens file 'path' in 'mode'. If 'compression' is non-zero, the file
- * is opened with libz gzopen(), otherwise with plain fopen()
+ * is opened with libz gzopen(), otherwise with plain fopen().
+ *
+ * On failure, return NULL with an error code in errno.
  */
 cfp *
 cfopen(const char *path, const char *mode, int compression)
@@ -531,11 +547,15 @@ cfopen(const char *path, const char *mode, int compression)
 	if (compression != 0)
 	{
 #ifdef HAVE_LIBZ
-		fp->compressedfp = gzopen(path, mode);
+		char		mode_compression[32];
+
+		snprintf(mode_compression, sizeof(mode_compression), "%s%d",
+				 mode, compression);
+		fp->compressedfp = gzopen(path, mode_compression);
 		fp->uncompressedfp = NULL;
 		if (fp->compressedfp == NULL)
 		{
-			free(fp);
+			free_keep_errno(fp);
 			fp = NULL;
 		}
 #else
@@ -550,7 +570,7 @@ cfopen(const char *path, const char *mode, int compression)
 		fp->uncompressedfp = fopen(path, mode);
 		if (fp->uncompressedfp == NULL)
 		{
-			free(fp);
+			free_keep_errno(fp);
 			fp = NULL;
 		}
 	}
@@ -659,7 +679,7 @@ cfclose(cfp *fp)
 		result = fclose(fp->uncompressedfp);
 		fp->uncompressedfp = NULL;
 	}
-	free(fp);
+	free_keep_errno(fp);
 
 	return result;
 }