260 lines
9.7 KiB
Plaintext
260 lines
9.7 KiB
Plaintext
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.\" ========================================================================
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.\"
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.IX Title "BIO_READ 3ossl"
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.TH BIO_READ 3ossl "2024-01-30" "3.2.1" "OpenSSL"
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.\" For nroff, turn off justification. Always turn off hyphenation; it makes
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.\" way too many mistakes in technical documents.
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.if n .ad l
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.nh
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.SH "NAME"
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BIO_read_ex, BIO_write_ex, BIO_read, BIO_write,
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BIO_gets, BIO_get_line, BIO_puts
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\&\- BIO I/O functions
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.SH "SYNOPSIS"
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.IX Header "SYNOPSIS"
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.Vb 1
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\& #include <openssl/bio.h>
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\&
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\& int BIO_read_ex(BIO *b, void *data, size_t dlen, size_t *readbytes);
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\& int BIO_write_ex(BIO *b, const void *data, size_t dlen, size_t *written);
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\&
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\& int BIO_read(BIO *b, void *data, int dlen);
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\& int BIO_gets(BIO *b, char *buf, int size);
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\& int BIO_get_line(BIO *b, char *buf, int size);
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\& int BIO_write(BIO *b, const void *data, int dlen);
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\& int BIO_puts(BIO *b, const char *buf);
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.Ve
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.SH "DESCRIPTION"
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.IX Header "DESCRIPTION"
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\&\fIBIO_read_ex()\fR attempts to read \fIdlen\fR bytes from \s-1BIO \s0\fIb\fR and places the data
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in \fIdata\fR. If any bytes were successfully read then the number of bytes read is
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stored in \fI*readbytes\fR.
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.PP
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\&\fIBIO_write_ex()\fR attempts to write \fIdlen\fR bytes from \fIdata\fR to \s-1BIO \s0\fIb\fR.
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If successful then the number of bytes written is stored in \fI*written\fR
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unless \fIwritten\fR is \s-1NULL.\s0
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.PP
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\&\fIBIO_read()\fR attempts to read \fIlen\fR bytes from \s-1BIO \s0\fIb\fR and places
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the data in \fIbuf\fR.
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.PP
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\&\fIBIO_gets()\fR performs the BIOs \*(L"gets\*(R" operation and places the data
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in \fIbuf\fR. Usually this operation will attempt to read a line of data
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from the \s-1BIO\s0 of maximum length \fIsize\-1\fR. There are exceptions to this,
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however; for example, \fIBIO_gets()\fR on a digest \s-1BIO\s0 will calculate and
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return the digest and other BIOs may not support \fIBIO_gets()\fR at all.
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The returned string is always NUL-terminated and the '\en' is preserved
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if present in the input data.
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On binary input there may be \s-1NUL\s0 characters within the string;
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in this case the return value (if nonnegative) may give an incorrect length.
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.PP
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\&\fIBIO_get_line()\fR attempts to read from \s-1BIO \s0\fIb\fR a line of data up to the next '\en'
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or the maximum length \fIsize\-1\fR is reached and places the data in \fIbuf\fR.
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The returned string is always NUL-terminated and the '\en' is preserved
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if present in the input data.
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On binary input there may be \s-1NUL\s0 characters within the string;
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in this case the return value (if nonnegative) gives the actual length read.
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For implementing this, unfortunately the data needs to be read byte-by-byte.
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.PP
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\&\fIBIO_write()\fR attempts to write \fIlen\fR bytes from \fIbuf\fR to \s-1BIO \s0\fIb\fR.
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.PP
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\&\fIBIO_puts()\fR attempts to write a NUL-terminated string \fIbuf\fR to \s-1BIO \s0\fIb\fR.
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.SH "RETURN VALUES"
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.IX Header "RETURN VALUES"
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\&\fIBIO_read_ex()\fR returns 1 if data was successfully read, and 0 otherwise.
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.PP
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\&\fIBIO_write_ex()\fR returns 1 if no error was encountered writing data, 0 otherwise.
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Requesting to write 0 bytes is not considered an error.
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.PP
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\&\fIBIO_write()\fR returns \-2 if the \*(L"write\*(R" operation is not implemented by the \s-1BIO\s0
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or \-1 on other errors.
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Otherwise it returns the number of bytes written.
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This may be 0 if the \s-1BIO \s0\fIb\fR is \s-1NULL\s0 or \fIdlen <= 0\fR.
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.PP
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\&\fIBIO_gets()\fR returns \-2 if the \*(L"gets\*(R" operation is not implemented by the \s-1BIO\s0
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or \-1 on other errors.
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Otherwise it typically returns the amount of data read,
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but depending on the implementation it may return only the length up to
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the first \s-1NUL\s0 character contained in the data read.
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In any case the trailing \s-1NUL\s0 that is added after the data read
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is not included in the length returned.
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.PP
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All other functions return either the amount of data successfully read or
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written (if the return value is positive) or that no data was successfully
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read or written if the result is 0 or \-1. If the return value is \-2 then
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the operation is not implemented in the specific \s-1BIO\s0 type.
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.SH "NOTES"
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.IX Header "NOTES"
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A 0 or \-1 return is not necessarily an indication of an error. In
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particular when the source/sink is nonblocking or of a certain type
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it may merely be an indication that no data is currently available and that
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the application should retry the operation later.
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.PP
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One technique sometimes used with blocking sockets is to use a system call
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(such as \fIselect()\fR, \fIpoll()\fR or equivalent) to determine when data is available
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and then call \fIread()\fR to read the data. The equivalent with BIOs (that is call
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\&\fIselect()\fR on the underlying I/O structure and then call \fIBIO_read()\fR to
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read the data) should \fBnot\fR be used because a single call to \fIBIO_read()\fR
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can cause several reads (and writes in the case of \s-1SSL\s0 BIOs) on the underlying
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I/O structure and may block as a result. Instead \fIselect()\fR (or equivalent)
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should be combined with non blocking I/O so successive reads will request
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a retry instead of blocking.
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.PP
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See \fIBIO_should_retry\fR\|(3) for details of how to
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determine the cause of a retry and other I/O issues.
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.PP
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If the \*(L"gets\*(R" method is not supported by a \s-1BIO\s0 then \fIBIO_get_line()\fR can be used.
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It is also possible to make \fIBIO_gets()\fR usable even if the \*(L"gets\*(R" method is not
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supported by adding a buffering \s-1BIO \s0\fIBIO_f_buffer\fR\|(3) to the chain.
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.SH "SEE ALSO"
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.IX Header "SEE ALSO"
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\&\fIBIO_should_retry\fR\|(3)
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.SH "HISTORY"
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.IX Header "HISTORY"
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\&\fIBIO_gets()\fR on 1.1.0 and older when called on \fIBIO_fd()\fR based \s-1BIO\s0 did not
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keep the '\en' at the end of the line in the buffer.
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.PP
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\&\fIBIO_get_line()\fR was added in OpenSSL 3.0.
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.PP
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\&\fIBIO_write_ex()\fR returns 1 if the size of the data to write is 0 and the
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\&\fIwritten\fR parameter of the function can be \s-1NULL\s0 since OpenSSL 3.0.
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.SH "COPYRIGHT"
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.IX Header "COPYRIGHT"
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Copyright 2000\-2023 The OpenSSL Project Authors. All Rights Reserved.
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.PP
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Licensed under the Apache License 2.0 (the \*(L"License\*(R"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file \s-1LICENSE\s0 in the source distribution or at
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<https://www.openssl.org/source/license.html>.
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