writeout: support to generate JSON output

This commit adds support to generate JSON via the writeout feature:

    -w "%{json}"

It leverages the existing infrastructure as much as possible. Thus,
generating the JSON on STDERR is possible by:

    -w "%{stderr}%{json}"

This implements a variant of
https://github.com/curl/curl/wiki/JSON#--write-out-json.

Closes #4870

1 files changed, 30 insertions, 0 deletions

diff --git a/src/tool_writeout_json.h b/src/tool_writeout_json.h
new file mode 100644
index 000000000..d3988d521
--- /dev/null
+++ b/src/tool_writeout_json.h
@@ -0,0 +1,30 @@
+#ifndef HEADER_CURL_TOOL_WRITEOUT_JSON_H
+#define HEADER_CURL_TOOL_WRITEOUT_JSON_H
+/***************************************************************************
+ *                                  _   _ ____  _
+ *  Project                     ___| | | |  _ \| |
+ *                             / __| | | | |_) | |
+ *                            | (__| |_| |  _ <| |___
+ *                             \___|\___/|_| \_\_____|
+ *
+ * Copyright (C) 1998 - 2020, Daniel Stenberg, <daniel@haxx.se>, et al.
+ *
+ * This software is licensed as described in the file COPYING, which
+ * you should have received as part of this distribution. The terms
+ * are also available at https://curl.haxx.se/docs/copyright.html.
+ *
+ * You may opt to use, copy, modify, merge, publish, distribute and/or sell
+ * copies of the Software, and permit persons to whom the Software is
+ * furnished to do so, under the terms of the COPYING file.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ ***************************************************************************/
+#include "tool_setup.h"
+#include "tool_writeout.h"
+
+void ourWriteOutJSON(const struct writeoutvar mappings[],
+        CURL *curl, struct OutStruct *outs, FILE *stream);
+
+#endif /* HEADER_CURL_TOOL_WRITEOUT_H */