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, 10 insertions, 0 deletions

diff --git a/lib/version.c b/lib/version.c
index 8170106ee..c7fe42a07 100644
--- a/lib/version.c
+++ b/lib/version.c
@@ -127,6 +127,16 @@ char *curl_version(void)
   int i = 0;
   int j;
 
+#ifdef DEBUGBUILD
+  /* Override version string when environment variable CURL_VERSION is set */
+  const char *debugversion = getenv("CURL_VERSION");
+  if(debugversion) {
+    strncpy(out, debugversion, sizeof(out)-1);
+    out[sizeof(out)-1] = '\0';
+    return out;
+  }
+#endif
+
   src[i++] = LIBCURL_NAME "/" LIBCURL_VERSION;
 #ifdef USE_SSL
   Curl_ssl_version(ssl_version, sizeof(ssl_version));