http: fix conflicts EVHTTP_CON_AUTOFREE and EVHTTP_CON_REUSE_CONNECTE…

…D_ADDR

And we can't make them continuous, since the latest is a public API, and
otherwise we will break binary compatibility.
Also extra check for EVHTTP_CON_PUBLIC_FLAGS_END, in case somebody forgot about
this (implementer I mean).

Refs: libevent#182

http-internal.h

@@ -71,10 +71,11 @@ struct evhttp_connection {
 	ev_uint64_t max_body_size;
 
 	int flags;
-#define EVHTTP_CON_INCOMING	0x0001	/* only one request on it ever */
-#define EVHTTP_CON_OUTGOING	0x0002  /* multiple requests possible */
-#define EVHTTP_CON_CLOSEDETECT  0x0004  /* detecting if persistent close */
-#define EVHTTP_CON_AUTOFREE 0x0008  /* set when we want to auto free the connection */
+#define EVHTTP_CON_INCOMING	0x0001       /* only one request on it ever */
+#define EVHTTP_CON_OUTGOING	0x0002       /* multiple requests possible */
+#define EVHTTP_CON_CLOSEDETECT	0x0004   /* detecting if persistent close */
+/* set when we want to auto free the connection */
+#define EVHTTP_CON_AUTOFREE	EVHTTP_CON_PUBLIC_FLAGS_END
 
 	struct timeval timeout;		/* timeout for events */
 	int retry_cnt;			/* retry count */

http.c

@@ -2342,13 +2342,14 @@ void evhttp_connection_set_family(struct evhttp_connection *evcon,
 int evhttp_connection_set_flags(struct evhttp_connection *evcon,
 	int flags)
 {
-	if (flags & ~(EVHTTP_CON_REUSE_CONNECTED_ADDR)) {
-		return 1;
-	}
+	int avail_flags = 0;
+	avail_flags |= EVHTTP_CON_REUSE_CONNECTED_ADDR;
 
-	evcon->flags &= ~(EVHTTP_CON_REUSE_CONNECTED_ADDR);
+	if (flags & ~avail_flags || flags > EVHTTP_CON_PUBLIC_FLAGS_END)
+		return 1;
+	evcon->flags &= ~avail_flags;
 
-	evcon->flags |= EVHTTP_CON_REUSE_CONNECTED_ADDR;
+	evcon->flags |= flags;
 
 	return 0;
 }

include/event2/http.h

@@ -637,7 +637,10 @@ EVENT2_EXPORT_SYMBOL
 void evhttp_connection_set_family(struct evhttp_connection *evcon,
 	int family);
 
-#define EVHTTP_CON_REUSE_CONNECTED_ADDR  0x0008  /* reuse connection address on retry */
+/* reuse connection address on retry */
+#define EVHTTP_CON_REUSE_CONNECTED_ADDR	0x0008
+/* Padding for public flags, @see EVHTTP_CON_* in http-internal.h */
+#define EVHTTP_CON_PUBLIC_FLAGS_END	0x100000
 /**
  * Set connection flags.
  *