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Title "BIO_read 3" For nroff, turn off justification. Always turn off hyphenation; it makes
way too many mistakes in technical documents.
BIO_read, BIO_write, BIO_gets, BIO_puts - BIO I/O functions Header "SYNOPSIS" .Vb 1 #include <openssl/bio.h> \& int BIO_read(BIO *b, void *buf, int len); int BIO_gets(BIO *b,char *buf, int size); int BIO_write(BIO *b, const void *buf, int len); int BIO_puts(BIO *b,const char *buf); .Ve Header "DESCRIPTION" \fIBIO_read() attempts to read len bytes from \s-1BIO \s0b and places the data in buf.

\fIBIO_gets() performs the BIOs \*(L"gets\*(R" operation and places the data in buf. Usually this operation will attempt to read a line of data from the \s-1BIO\s0 of maximum length len. There are exceptions to this however, for example BIO_gets() on a digest \s-1BIO\s0 will calculate and return the digest and other BIOs may not support BIO_gets() at all.

\fIBIO_write() attempts to write len bytes from buf to \s-1BIO \s0b.

\fIBIO_puts() attempts to write a null terminated string buf to \s-1BIO \s0b

Header "RETURN VALUES" All these functions return either the amount of data successfully read or written (if the return value is positive) or that no data was successfully read or written if the result is 0 or -1. If the return value is -2 then the operation is not implemented in the specific \s-1BIO\s0 type. Header "NOTES" A 0 or -1 return is not necessarily an indication of an error. In particular when the source/sink is non-blocking or of a certain type it may merely be an indication that no data is currently available and that the application should retry the operation later.

One technique sometimes used with blocking sockets is to use a system call (such as select(), poll() or equivalent) to determine when data is available and then call read() to read the data. The equivalent with BIOs (that is call \fIselect() on the underlying I/O structure and then call BIO_read() to read the data) should not be used because a single call to BIO_read() can cause several reads (and writes in the case of \s-1SSL\s0 BIOs) on the underlying I/O structure and may block as a result. Instead select() (or equivalent) should be combined with non blocking I/O so successive reads will request a retry instead of blocking.

See BIO_should_retry\|(3) for details of how to determine the cause of a retry and other I/O issues.

If the BIO_gets() function is not supported by a \s-1BIO\s0 then it possible to work around this by adding a buffering \s-1BIO \s0BIO_f_buffer\|(3) to the chain.

Header "SEE ALSO" \fIBIO_should_retry\|(3)

\s-1TBA\s0