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Use SO_EXCLUSIVEADDRUSE instead of SO_REUSEADDR on Windows #2584

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Use SO_EXCLUSIVEADDRUSE instead of SO_REUSEADDR on Windows #2584

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11 changes: 11 additions & 0 deletions httplib.h
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Original file line number Diff line number Diff line change
Expand Up @@ -10902,13 +10902,24 @@ inline bool setup_client_tls_session(
*/

inline void default_socket_options(socket_t sock) {
#ifdef _WIN32
// On Windows, SO_REUSEADDR has a different, dangerous meaning: it allows a
// socket to bind to a port that another socket is already bound to (i.e.
// the bind silently steals the port) instead of returning WSAEADDRINUSE.
// Use SO_EXCLUSIVEADDRUSE to get the POSIX-like exclusive binding; a bind
// to an occupied port then fails with WSAEADDRINUSE. (SO_EXCLUSIVEADDRUSE
// only affects bind, so this is harmless for client sockets which connect
// without binding.)
set_socket_opt(sock, SOL_SOCKET, SO_EXCLUSIVEADDRUSE, 1);
#else
set_socket_opt(sock, SOL_SOCKET,
#ifdef SO_REUSEPORT
SO_REUSEPORT,
#else
SO_REUSEADDR,
#endif
1);
#endif
}

inline bool set_socket_opt(socket_t sock, int level, int optname, int optval) {
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