BIO_READ(3)

✨ BIO_READ(3) ✨

okay so bestie, welcome to the BIO_READ(3) page — this is the Library Functions Manual and it's literally all about the BIO I/O functions and honestly? it's giving essential. no cap. 💅

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🎀 NAME 🎀

BIO_read, BIO_number_read, BIO_gets, BIO_write, BIO_puts, BIO_indent, BIO_number_written — the BIO I/O functions, aka the whole squad. 💖

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🦋 SYNOPSIS 🦋

#include <openssl/bio.h>

int
BIO_read(BIO *b, void *buf, int len);

unsigned long
BIO_number_read(BIO *b);

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 *string);

int
BIO_indent(BIO *b, int indent, int max);

unsigned long
BIO_number_written(BIO *b);

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🌸 DESCRIPTION 🌸

okay so let's break it down, function by function, because there's a lot going on here and you deserve to know all of it. 🫶

• BIO_read() — attempts to read len bytes from b and places that data into buf. that's the whole vibe. ✨
• BIO_number_read() — returns the grand total of bytes read from b using BIO_read() so far. lowkey important: bytes read with BIO_gets() do not count. nope, not even a little. BIO_new(3) and BIO_set(3) initialize the counter to 0. and bestie, when you're reading very large amounts of data, the counter will eventually wrap around from ULONG_MAX to 0. so like... keep that in mind. 💀
• BIO_gets() — performs the BIOs "gets" operation and places the data in buf. usually this operation will attempt to read a line of data from the BIO of maximum length size - 1. there are exceptions though — for example, BIO_gets() on a digest BIO will calculate and return the digest, and other BIOs may not support BIO_gets() at all. the returned string is always NUL-terminated. always. periodt. 💅
• BIO_write() — attempts to write len bytes from buf to b. simple as that. 🦋
• BIO_puts() — attempts to write the NUL-terminated string to b. yup. 🌈
• BIO_indent() — attempts to write indent space characters to b, but not more than max characters. so it's like, indenting but with boundaries. iconic. 🎀
• BIO_number_written() — returns the grand total of bytes written to b using BIO_write(), BIO_puts(), and BIO_indent() so far. BIO_new(3) and BIO_set(3) initialize the counter to 0. and same thing as before: when writing very large amounts of data, the counter will eventually wrap around from ULONG_MAX to 0. wrap around queen. 👑

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okay so now the important PSA, bestie. one technique sometimes used with blocking sockets is to use a system call (such as select(2), poll(2) or equivalent) to determine when data is available and then call read(2) to read the data. the equivalent with BIOs — that is, calling select(2) on the underlying I/O structure and then calling BIO_read() to read the data — should not be used. why? because a single call to BIO_read() can cause several reads (and writes in the case of SSL BIOs) on the underlying I/O structure and may block as a result. so like, don't do that. 🙈 instead select(2) (or equivalent) should be combined with non-blocking I/O so successive reads will request a retry instead of blocking. noted. 📝

see BIO_should_retry(3) for details of how to determine the cause of a retry and other I/O issues. it's literally the glow-up you need for retry debugging. ✨

and if the BIO_gets() function is not supported by a BIO then it is possible to work around this by adding a buffering BIO BIO_f_buffer(3) to the chain. workaround slay. 💖

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💜 RETURN VALUES 💜

• BIO_indent() returns 1 if successful — even if nothing was written — or 0 if writing fails. so 1 means "we good" even if it wrote zero spaces. iykyk. 🎀
• BIO_number_read() and BIO_number_written() return a number of bytes or 0 if b is a NULL pointer. null? zero. bye. 👋
• the other 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 BIO type. -2 is giving "not my department" energy. 💀 the trailing NUL is not included in the length returned by BIO_gets(). important detail, don't forget it. 📌

⚠️ bestie listen — 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. so don't panic. retry and slay. 💅

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🌟 SEE ALSO 🌟

BIO_meth_new(3), BIO_new(3), BIO_should_retry(3) — go read these too, they're part of the lore. 📚✨

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🌈 HISTORY 🌈

BIO_read(), BIO_gets(), BIO_write(), and BIO_puts() first appeared in SSLeay 0.6.0. BIO_number_read() and BIO_number_written() first appeared in SSLeay 0.6.5. these functions have been available since OpenBSD 2.4. OG status. 👑

BIO_indent() first appeared in OpenSSL 0.9.7 and has been available since OpenBSD 3.4. late bloomer but still iconic. 🌸

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okay that's the whole page bestie! this was brought to you by Debian, dated December 18, 2022, and honestly? it's giving vintage but make it useful. go forth and BIO responsibly. 🫶💖✨