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.tr \(*W- . ds -- \(*W- . ds PI pi . if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch . if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\" diablo 12 pitch . ds L" "" . ds R" "" . ds C` "" . ds C' "" 'br\} . ds -- \|\(em\| . ds PI \(*p . ds L" `` . ds R" '' . ds C` . ds C' 'br\}
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Title "BIO_s_accept 3"
way too many mistakes in technical documents.
Using accept BIOs, \s-1TCP/IP\s0 connections can be accepted and data transferred using only \s-1BIO\s0 routines. In this way any platform specific operations are hidden by the \s-1BIO\s0 abstraction.
Read and write operations on an accept \s-1BIO\s0 will perform I/O on the underlying connection. If no connection is established and the port (see below) is set up properly then the \s-1BIO\s0 waits for an incoming connection.
Accept BIOs support BIO_puts() but not BIO_gets().
If the close flag is set on an accept \s-1BIO\s0 then any active connection on that chain is shutdown and the socket closed when the \s-1BIO\s0 is freed.
Calling BIO_reset() on a accept \s-1BIO\s0 will close any active connection and reset the \s-1BIO\s0 into a state where it awaits another incoming connection.
\fIBIO_get_fd() and BIO_set_fd() can be called to retrieve or set the accept socket. See BIO_s_fd\|(3)
\fIBIO_set_accept_port() uses the string name to set the accept port. The port is represented as a string of the form \*(L"host:port\*(R", where \*(L"host\*(R" is the interface to use and \*(L"port\*(R" is the port. Either or both values can be \*(L"*\*(R" which is interpreted as meaning any interface or port respectively. \*(L"port\*(R" has the same syntax as the port specified in BIO_set_conn_port() for connect BIOs, that is it can be a numerical port string or a string to lookup using getservbyname() and a string table.
\fIBIO_new_accept() combines BIO_new() and BIO_set_accept_port() into a single call: that is it creates a new accept \s-1BIO\s0 with port \fBhost_port.
\fIBIO_set_nbio_accept() sets the accept socket to blocking mode (the default) if n is 0 or non blocking mode if n is 1.
\fIBIO_set_accept_bios() can be used to set a chain of BIOs which will be duplicated and prepended to the chain when an incoming connection is received. This is useful if, for example, a buffering or \s-1SSL BIO\s0 is required for each connection. The chain of BIOs must not be freed after this call, they will be automatically freed when the accept \s-1BIO\s0 is freed.
\fIBIO_set_bind_mode() and BIO_get_bind_mode() set and retrieve the current bind mode. If \s-1BIO_BIND_NORMAL \s0(the default) is set then another socket cannot be bound to the same port. If \s-1BIO_BIND_REUSEADDR\s0 is set then other sockets can bind to the same port. If \s-1BIO_BIND_REUSEADDR_IF_UNUSED\s0 is set then and attempt is first made to use \s-1BIO_BIN_NORMAL,\s0 if this fails and the port is not in use then a second attempt is made using \s-1BIO_BIND_REUSEADDR.\s0
\fIBIO_do_accept() serves two functions. When it is first called, after the accept \s-1BIO\s0 has been setup, it will attempt to create the accept socket and bind an address to it. Second and subsequent calls to BIO_do_accept() will await an incoming connection, or request a retry in non blocking mode.
When a connection is established a new socket \s-1BIO\s0 is created for the connection and appended to the chain. That is the chain is now accept->socket. This effectively means that attempting I/O on an initial accept socket will await an incoming connection then perform I/O on it.
If any additional BIOs have been set using BIO_set_accept_bios() then they are placed between the socket and the accept \s-1BIO,\s0 that is the chain will be accept->otherbios->socket.
If a server wishes to process multiple connections (as is normally the case) then the accept \s-1BIO\s0 must be made available for further incoming connections. This can be done by waiting for a connection and then calling:
.Vb 1 connection = BIO_pop(accept); .Ve
After this call connection will contain a \s-1BIO\s0 for the recently established connection and accept will now be a single \s-1BIO\s0 again which can be used to await further incoming connections. If no further connections will be accepted the accept can be freed using BIO_free().
If only a single connection will be processed it is possible to perform I/O using the accept \s-1BIO\s0 itself. This is often undesirable however because the accept \s-1BIO\s0 will still accept additional incoming connections. This can be resolved by using BIO_pop() (see above) and freeing up the accept \s-1BIO\s0 after the initial connection.
If the underlying accept socket is non-blocking and BIO_do_accept() is called to await an incoming connection it is possible for \fIBIO_should_io_special() with the reason \s-1BIO_RR_ACCEPT.\s0 If this happens then it is an indication that an accept attempt would block: the application should take appropriate action to wait until the underlying socket has accepted a connection and retry the call.
\fIBIO_set_accept_port(), BIO_get_accept_port(), BIO_set_nbio_accept(), \fIBIO_set_accept_bios(), BIO_set_bind_mode(), BIO_get_bind_mode() and \fIBIO_do_accept() are macros.
.Vb 3 BIO *abio, *cbio, *cbio2; ERR_load_crypto_strings(); abio = BIO_new_accept("4444"); \& /* First call to BIO_accept() sets up accept BIO */ if(BIO_do_accept(abio) <= 0) { fprintf(stderr, "Error setting up accept\en"); ERR_print_errors_fp(stderr); exit(0); } \& /* Wait for incoming connection */ if(BIO_do_accept(abio) <= 0) { fprintf(stderr, "Error accepting connection\en"); ERR_print_errors_fp(stderr); exit(0); } fprintf(stderr, "Connection 1 established\en"); /* Retrieve BIO for connection */ cbio = BIO_pop(abio); BIO_puts(cbio, "Connection 1: Sending out Data on initial connection\en"); fprintf(stderr, "Sent out data on connection 1\en"); /* Wait for another connection */ if(BIO_do_accept(abio) <= 0) { fprintf(stderr, "Error accepting connection\en"); ERR_print_errors_fp(stderr); exit(0); } fprintf(stderr, "Connection 2 established\en"); /* Close accept BIO to refuse further connections */ cbio2 = BIO_pop(abio); BIO_free(abio); BIO_puts(cbio2, "Connection 2: Sending out Data on second\en"); fprintf(stderr, "Sent out data on connection 2\en"); \& BIO_puts(cbio, "Connection 1: Second connection established\en"); /* Close the two established connections */ BIO_free(cbio); BIO_free(cbio2); .Ve