http: add support to read and store the referrer header

- add CURLINFO_REFERER libcurl option
- add --write-out '%{referer}' command-line option
- extend --xattr command-line option to fill user.xdg.referrer.url extended
  attribute with the referrer (if there was any)

Closes #6591

src/tool_writeout.c

@@ -83,6 +83,7 @@ static const struct writeoutvar variables[] = {
   {"proxy_ssl_verify_result", VAR_PROXY_SSL_VERIFY_RESULT,
    CURLINFO_PROXY_SSL_VERIFYRESULT, writeLong},
   {"redirect_url", VAR_REDIRECT_URL, CURLINFO_REDIRECT_URL, writeString},
+  {"referer", VAR_REFERER, CURLINFO_REFERER, writeString},
   {"remote_ip", VAR_PRIMARY_IP, CURLINFO_PRIMARY_IP, writeString},
   {"remote_port", VAR_PRIMARY_PORT, CURLINFO_PRIMARY_PORT, writeLong},
   {"response_code", VAR_HTTP_CODE, CURLINFO_RESPONSE_CODE, writeLong},

src/tool_writeout.h

@@ -7,7 +7,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             \___|\___/|_| \_\_____|
  *
- * Copyright (C) 1998 - 2020, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 1998 - 2021, 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
@@ -54,6 +54,7 @@ typedef enum {
   VAR_REDIRECT_COUNT,
   VAR_REDIRECT_TIME,
   VAR_REDIRECT_URL,
+  VAR_REFERER,
   VAR_REQUEST_SIZE,
   VAR_SCHEME,
   VAR_SIZE_DOWNLOAD,

src/tool_xattr.c

@@ -5,7 +5,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             \___|\___/|_| \_\_____|
  *
- * Copyright (C) 1998 - 2020, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 1998 - 2021, 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
@@ -44,9 +44,10 @@ static const struct xattr_mapping {
   /* mappings proposed by
    * https://freedesktop.org/wiki/CommonExtendedAttributes/
    */
-  { "user.xdg.origin.url", CURLINFO_EFFECTIVE_URL },
-  { "user.mime_type",      CURLINFO_CONTENT_TYPE },
-  { NULL,                  CURLINFO_NONE } /* last element, abort loop here */
+  { "user.xdg.referrer.url", CURLINFO_REFERER },
+  { "user.xdg.origin.url",   CURLINFO_EFFECTIVE_URL },
+  { "user.mime_type",        CURLINFO_CONTENT_TYPE },
+  { NULL,                    CURLINFO_NONE } /* last element, abort here */
 };
 
 /* returns TRUE if a new URL is returned, that then needs to be freed */