+/* pay attention to levels of indirection */
+typedef struct socket_function_table **Socket;
+typedef struct plug_function_table **Plug;
+
+struct socket_function_table {
+ Plug(*plug) (Socket s, Plug p);
+ /* use a different plug (return the old one) */
+ /* if p is NULL, it doesn't change the plug */
+ /* but it does return the one it's using */
+ void (*close) (Socket s);
+ int (*write) (Socket s, const char *data, int len);
+ int (*write_oob) (Socket s, const char *data, int len);
+ void (*write_eof) (Socket s);
+ void (*flush) (Socket s);
+ void (*set_frozen) (Socket s, int is_frozen);
+ /* ignored by tcp, but vital for ssl */
+ const char *(*socket_error) (Socket s);
+ char *(*peer_info) (Socket s);
+};
+
+typedef union { void *p; int i; } accept_ctx_t;
+typedef Socket (*accept_fn_t)(accept_ctx_t ctx, Plug plug);
+
+struct plug_function_table {
+ void (*log)(Plug p, int type, SockAddr addr, int port,
+ const char *error_msg, int error_code);
+ /*
+ * Passes the client progress reports on the process of setting
+ * up the connection.
+ *
+ * - type==0 means we are about to try to connect to address
+ * `addr' (error_msg and error_code are ignored)
+ * - type==1 means we have failed to connect to address `addr'
+ * (error_msg and error_code are supplied). This is not a
+ * fatal error - we may well have other candidate addresses
+ * to fall back to. When it _is_ fatal, the closing()
+ * function will be called.
+ */
+ int (*closing)
+ (Plug p, const char *error_msg, int error_code, int calling_back);
+ /* error_msg is NULL iff it is not an error (ie it closed normally) */
+ /* calling_back != 0 iff there is a Plug function */
+ /* currently running (would cure the fixme in try_send()) */
+ int (*receive) (Plug p, int urgent, char *data, int len);
+ /*
+ * - urgent==0. `data' points to `len' bytes of perfectly
+ * ordinary data.
+ *
+ * - urgent==1. `data' points to `len' bytes of data,
+ * which were read from before an Urgent pointer.
+ *
+ * - urgent==2. `data' points to `len' bytes of data,
+ * the first of which was the one at the Urgent mark.
+ */
+ void (*sent) (Plug p, int bufsize);
+ /*
+ * The `sent' function is called when the pending send backlog
+ * on a socket is cleared or partially cleared. The new backlog
+ * size is passed in the `bufsize' parameter.
+ */
+ int (*accepting)(Plug p, accept_fn_t constructor, accept_ctx_t ctx);
+ /*
+ * `accepting' is called only on listener-type sockets, and is
+ * passed a constructor function+context that will create a fresh
+ * Socket describing the connection. It returns nonzero if it
+ * doesn't want the connection for some reason, or 0 on success.
+ */
+};
+
+/* proxy indirection layer */
+/* NB, control of 'addr' is passed via new_connection, which takes
+ * responsibility for freeing it */
+Socket new_connection(SockAddr addr, const char *hostname,
+ int port, int privport,
+ int oobinline, int nodelay, int keepalive,
+ Plug plug, Conf *conf);
+Socket new_listener(const char *srcaddr, int port, Plug plug,
+ int local_host_only, Conf *conf, int addressfamily);
+SockAddr name_lookup(const char *host, int port, char **canonicalname,
+ Conf *conf, int addressfamily);
+int proxy_for_destination (SockAddr addr, const char *hostname, int port,
+ Conf *conf);
+
+/* platform-dependent callback from new_connection() */
+/* (same caveat about addr as new_connection()) */
+Socket platform_new_connection(SockAddr addr, const char *hostname,
+ int port, int privport,
+ int oobinline, int nodelay, int keepalive,
+ Plug plug, Conf *conf);
+
+/* socket functions */
+
+void sk_init(void); /* called once at program startup */
+void sk_cleanup(void); /* called just before program exit */
+
+SockAddr sk_namelookup(const char *host, char **canonicalname, int address_family);
+SockAddr sk_nonamelookup(const char *host);
+void sk_getaddr(SockAddr addr, char *buf, int buflen);
+int sk_addr_needs_port(SockAddr addr);
+int sk_hostname_is_local(const char *name);
+int sk_address_is_local(SockAddr addr);
+int sk_address_is_special_local(SockAddr addr);
+int sk_addrtype(SockAddr addr);
+void sk_addrcopy(SockAddr addr, char *buf);
+void sk_addr_free(SockAddr addr);
+/* sk_addr_dup generates another SockAddr which contains the same data
+ * as the original one and can be freed independently. May not actually
+ * physically _duplicate_ it: incrementing a reference count so that
+ * one more free is required before it disappears is an acceptable
+ * implementation. */
+SockAddr sk_addr_dup(SockAddr addr);
+
+/* NB, control of 'addr' is passed via sk_new, which takes responsibility
+ * for freeing it, as for new_connection() */
+Socket sk_new(SockAddr addr, int port, int privport, int oobinline,
+ int nodelay, int keepalive, Plug p);
+
+Socket sk_newlistener(const char *srcaddr, int port, Plug plug,
+ int local_host_only, int address_family);
+
+#define sk_plug(s,p) (((*s)->plug) (s, p))
+#define sk_close(s) (((*s)->close) (s))
+#define sk_write(s,buf,len) (((*s)->write) (s, buf, len))
+#define sk_write_oob(s,buf,len) (((*s)->write_oob) (s, buf, len))
+#define sk_write_eof(s) (((*s)->write_eof) (s))
+#define sk_flush(s) (((*s)->flush) (s))
+
+#ifdef DEFINE_PLUG_METHOD_MACROS
+#define plug_log(p,type,addr,port,msg,code) (((*p)->log) (p, type, addr, port, msg, code))
+#define plug_closing(p,msg,code,callback) (((*p)->closing) (p, msg, code, callback))
+#define plug_receive(p,urgent,buf,len) (((*p)->receive) (p, urgent, buf, len))
+#define plug_sent(p,bufsize) (((*p)->sent) (p, bufsize))
+#define plug_accepting(p, constructor, ctx) (((*p)->accepting)(p, constructor, ctx))
+#endif