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bc8857bf70
Document the libssl and command line application aspects of async. Reviewed-by: Rich Salz <rsalz@openssl.org>
107 lines
3.2 KiB
Plaintext
107 lines
3.2 KiB
Plaintext
=pod
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=head1 NAME
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SSL_CTX_set_mode, SSL_set_mode, SSL_CTX_get_mode, SSL_get_mode - manipulate SSL engine mode
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=head1 SYNOPSIS
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#include <openssl/ssl.h>
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long SSL_CTX_set_mode(SSL_CTX *ctx, long mode);
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long SSL_set_mode(SSL *ssl, long mode);
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long SSL_CTX_get_mode(SSL_CTX *ctx);
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long SSL_get_mode(SSL *ssl);
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=head1 DESCRIPTION
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SSL_CTX_set_mode() adds the mode set via bitmask in B<mode> to B<ctx>.
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Options already set before are not cleared.
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SSL_set_mode() adds the mode set via bitmask in B<mode> to B<ssl>.
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Options already set before are not cleared.
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SSL_CTX_get_mode() returns the mode set for B<ctx>.
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SSL_get_mode() returns the mode set for B<ssl>.
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=head1 NOTES
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The following mode changes are available:
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=over 4
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=item SSL_MODE_ENABLE_PARTIAL_WRITE
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Allow SSL_write(..., n) to return r with 0 < r < n (i.e. report success
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when just a single record has been written). When not set (the default),
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SSL_write() will only report success once the complete chunk was written.
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Once SSL_write() returns with r, r bytes have been successfully written
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and the next call to SSL_write() must only send the n-r bytes left,
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imitating the behaviour of write().
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=item SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER
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Make it possible to retry SSL_write() with changed buffer location
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(the buffer contents must stay the same). This is not the default to avoid
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the misconception that non-blocking SSL_write() behaves like
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non-blocking write().
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=item SSL_MODE_AUTO_RETRY
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Never bother the application with retries if the transport is blocking.
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If a renegotiation take place during normal operation, a
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L<SSL_read(3)> or L<SSL_write(3)> would return
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with -1 and indicate the need to retry with SSL_ERROR_WANT_READ.
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In a non-blocking environment applications must be prepared to handle
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incomplete read/write operations.
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In a blocking environment, applications are not always prepared to
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deal with read/write operations returning without success report. The
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flag SSL_MODE_AUTO_RETRY will cause read/write operations to only
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return after the handshake and successful completion.
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=item SSL_MODE_RELEASE_BUFFERS
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When we no longer need a read buffer or a write buffer for a given SSL,
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then release the memory we were using to hold it.
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Using this flag can
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save around 34k per idle SSL connection.
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This flag has no effect on SSL v2 connections, or on DTLS connections.
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=item SSL_MODE_SEND_FALLBACK_SCSV
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Send TLS_FALLBACK_SCSV in the ClientHello.
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To be set only by applications that reconnect with a downgraded protocol
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version; see draft-ietf-tls-downgrade-scsv-00 for details.
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DO NOT ENABLE THIS if your application attempts a normal handshake.
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Only use this in explicit fallback retries, following the guidance
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in draft-ietf-tls-downgrade-scsv-00.
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=item SSL_MODE_ASYNC
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Enable asynchronous processing. TLS I/O operations may indicate a retry with
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SSL_ERROR_WANT_ASYNC with this mode set if an asynchronous capable engine is
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used to perform cryptographic operations. See L<SSL_get_error(3)>.
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=back
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=head1 RETURN VALUES
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SSL_CTX_set_mode() and SSL_set_mode() return the new mode bitmask
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after adding B<mode>.
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SSL_CTX_get_mode() and SSL_get_mode() return the current bitmask.
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=head1 SEE ALSO
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L<ssl(3)>, L<SSL_read(3)>, L<SSL_write(3)>, L<SSL_get_error(3)>
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=======
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=head1 HISTORY
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SSL_MODE_ASYNC was first added to OpenSSL 1.1.0.
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=cut
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