BIO_should_retry(3) OpenSSL BIO_should_retry(3) NNAAMMEE BIO_should_retry, BIO_should_read, BIO_should_write, BIO_should_io_spe- cial, BIO_retry_type, BIO_should_retry, BIO_get_retry_BIO, BIO_get_retry_reason - BIO retry functions SSYYNNOOPPSSIISS #include #define BIO_should_read(a) ((a)->flags & BIO_FLAGS_READ) #define BIO_should_write(a) ((a)->flags & BIO_FLAGS_WRITE) #define BIO_should_io_special(a) ((a)->flags & BIO_FLAGS_IO_SPECIAL) #define BIO_retry_type(a) ((a)->flags & BIO_FLAGS_RWS) #define BIO_should_retry(a) ((a)->flags & BIO_FLAGS_SHOULD_RETRY) #define BIO_FLAGS_READ 0x01 #define BIO_FLAGS_WRITE 0x02 #define BIO_FLAGS_IO_SPECIAL 0x04 #define BIO_FLAGS_RWS (BIO_FLAGS_READ|BIO_FLAGS_WRITE|BIO_FLAGS_IO_SPECIAL) #define BIO_FLAGS_SHOULD_RETRY 0x08 BIO * BIO_get_retry_BIO(BIO *bio, int *reason); int BIO_get_retry_reason(BIO *bio); DDEESSCCRRIIPPTTIIOONN These functions determine why a BIO is not able to read or write data. They will typically be called after a failed _B_I_O___r_e_a_d_(_) or _B_I_O___w_r_i_t_e_(_) call. _B_I_O___s_h_o_u_l_d___r_e_t_r_y_(_) is true if the call that produced this condition should then be retried at a later time. If _B_I_O___s_h_o_u_l_d___r_e_t_r_y_(_) is false then the cause is an error condition. _B_I_O___s_h_o_u_l_d___r_e_a_d_(_) is true if the cause of the condition is that a BIO needs to read data. _B_I_O___s_h_o_u_l_d___w_r_i_t_e_(_) is true if the cause of the condition is that a BIO needs to read data. _B_I_O___s_h_o_u_l_d___i_o___s_p_e_c_i_a_l_(_) is true if some "special" condition, that is a reason other than reading or writing is the cause of the condition. _B_I_O___r_e_t_r_y___t_y_p_e_(_) returns a mask of the cause of a retry condition con- sisting of the values BBIIOO__FFLLAAGGSS__RREEAADD, BBIIOO__FFLLAAGGSS__WWRRIITTEE, BBIIOO__FFLLAAGGSS__IIOO__SSPPEECCIIAALL though current BIO types will only set one of these. _B_I_O___g_e_t___r_e_t_r_y___B_I_O_(_) determines the precise reason for the special con- dition, it returns the BIO that caused this condition and if rreeaassoonn is not NULL it contains the reason code. The meaning of the reason code and the action that should be taken depends on the type of BIO that resulted in this condition. _B_I_O___g_e_t___r_e_t_r_y___r_e_a_s_o_n_(_) returns the reason for a special condition if passed the relevant BIO, for example as returned by _B_I_O___g_e_t___r_e_t_r_y___B_I_O_(_). NNOOTTEESS If _B_I_O___s_h_o_u_l_d___r_e_t_r_y_(_) returns false then the precise "error condition" depends on the BIO type that caused it and the return code of the BIO operation. For example if a call to _B_I_O___r_e_a_d_(_) on a socket BIO returns 0 and _B_I_O___s_h_o_u_l_d___r_e_t_r_y_(_) is false then the cause will be that the con- nection closed. A similar condition on a file BIO will mean that it has reached EOF. Some BIO types may place additional information on the error queue. For more details see the individual BIO type manual pages. If the underlying I/O structure is in a blocking mode almost all cur- rent BIO types will not request a retry, because the underlying I/O calls will not. If the application knows that the BIO type will never signal a retry then it need not call _B_I_O___s_h_o_u_l_d___r_e_t_r_y_(_) after a failed BIO I/O call. This is typically done with file BIOs. SSL BIOs are the only current exception to this rule: they can request a retry even if the underlying I/O structure is blocking, if a hand- shake occurs during a call to _B_I_O___r_e_a_d_(_). An application can retry the failed call immediately or avoid this situation by setting SSL_MODE_AUTO_RETRY on the underlying SSL structure. While an application may retry a failed non blocking call immediately this is likely to be very inefficient because the call will fail repeatedly until data can be processed or is available. An application will normally wait until the necessary condition is satisfied. How this is done depends on the underlying I/O structure. For example if the cause is ultimately a socket and _B_I_O___s_h_o_u_l_d___r_e_a_d_(_) is true then a call to _s_e_l_e_c_t_(_) may be made to wait until data is available and then retry the BIO operation. By combining the retry con- ditions of several non blocking BIOs in a single _s_e_l_e_c_t_(_) call it is possible to service several BIOs in a single thread, though the perfor- mance may be poor if SSL BIOs are present because long delays can occur during the initial handshake process. It is possible for a BIO to block indefinitely if the underlying I/O structure cannot process or return any data. This depends on the behav- iour of the platforms I/O functions. This is often not desirable: one solution is to use non blocking I/O and use a timeout on the _s_e_l_e_c_t_(_) (or equivalent) call. BBUUGGSS The OpenSSL ASN1 functions cannot gracefully deal with non blocking I/O: that is they cannot retry after a partial read or write. This is usually worked around by only passing the relevant data to ASN1 func- tions when the entire structure can be read or written. SSEEEE AALLSSOO TBA 1.0.2u 2019-12-20 BIO_should_retry(3)