If HTTP_USER_AGENT is defined but empty, don't send User-Agent at all.

PR:		184507
Submitted by:	jbeich@tormail.org (with modifications)
MFC after:	1 week

2 files changed, 10 insertions, 4 deletions

diff --git a/lib/libfetch/fetch.3 b/lib/libfetch/fetch.3
index 6b2e4c0..0a83a35 100644
--- a/lib/libfetch/fetch.3
+++ b/lib/libfetch/fetch.3
@@ -627,6 +627,7 @@ the document URL will be used as referrer URL.
 Specifies the User-Agent string to use for HTTP requests.
 This can be useful when working with HTTP origin or proxy servers that
 differentiate between user agents.
+If defined but empty, no User-Agent header is sent.
 .It Ev NETRC
 Specifies a file to use instead of
 .Pa ~/.netrc
diff --git a/lib/libfetch/http.c b/lib/libfetch/http.c
index cbbb8a8..983936c 100644
--- a/lib/libfetch/http.c
+++ b/lib/libfetch/http.c
@@ -1683,10 +1683,15 @@ http_request(struct url *URL, const char *op, struct url_stat *us,
 			else
 				http_cmd(conn, "Referer: %s", p);
 		}
-		if ((p = getenv("HTTP_USER_AGENT")) != NULL && *p != '\0')
-			http_cmd(conn, "User-Agent: %s", p);
-		else
-			http_cmd(conn, "User-Agent: %s " _LIBFETCH_VER, getprogname());
+		if ((p = getenv("HTTP_USER_AGENT")) != NULL) {
+			/* no User-Agent if defined but empty */
+			if  (*p != '\0')
+				http_cmd(conn, "User-Agent: %s", p);
+		} else {
+			/* default User-Agent */
+			http_cmd(conn, "User-Agent: %s " _LIBFETCH_VER,
+			    getprogname());
+		}
 		if (url->offset > 0)
 			http_cmd(conn, "Range: bytes=%lld-", (long long)url->offset);
 		http_cmd(conn, "Connection: close");