+#ifdef HAVE_ZSTD
+ /* from the zstd docs (https://facebook.github.io/zstd/zstd_manual.html):
+ * compression runs faster if `dstCapacity` >= `ZSTD_compressBound(srcSize)`.
+ */
+ size_t out_size = ZSTD_compressBound(in_data_size);
+ void * out = malloc(out_size);
+
+ size_t ret = ZSTD_compress(out, out_size, in_data, in_data_size,
+ ZSTD_COMPRESSION_LEVEL);
+ if (ZSTD_isError(ret)) {
+ free(out);
+ return 0;
+ }
+ ssize_t written = write_all(dest, out, ret);
+ if (written == -1) {
+ free(out);
+ return 0;
+ }
+ free(out);
+ return ret;
+#else