BIO_F_BUFFER(3)

💅 BIO_F_BUFFER(3) — buffering BIO 💅

okay bestie, this page is coming at you from the Library Functions Manual, and it’s lowkey one of those glow-up pages for buffering BIOs. no cap, it’s giving “let me hold your data for a sec.” 💖

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🌸 NAME 🌸

• BIO_f_buffer
• BIO_get_buffer_num_lines
• BIO_set_read_buffer_size
• BIO_set_write_buffer_size
• BIO_set_buffer_size
• BIO_set_buffer_read_data

…and together they’re all about the buffering BIO. periodt. 💅

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🌈 SYNOPSIS 🌈

library “libcrypto” #include <openssl/bio.h>

const BIO_METHOD *
BIO_f_buffer(void);

long
BIO_get_buffer_num_lines(BIO *b);

long
BIO_set_read_buffer_size(BIO *b, long size);

long
BIO_set_write_buffer_size(BIO *b, long size);

long
BIO_set_buffer_size(BIO *b, long size);

long
BIO_set_buffer_read_data(BIO *b, void *buf, long num);

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✨ DESCRIPTION ✨

BIO_f_buffer() returns the buffering BIO method. that’s the whole vibe. 🫶

Data written to a buffering BIO is buffered, then periodically written to the next BIO in the chain. Data read from a buffering BIO comes from an internal buffer, and that buffer gets filled from the next BIO in the chain. Both BIO_gets(3) and BIO_puts(3) are supported, so yes, bestie, it really does eat. 🔥

Calling BIO_reset(3) on a buffering BIO clears any buffered data. poof. gone. 💨

BIO_get_buffer_num_lines() returns the number of lines currently buffered. simple, iconic. 💖

BIO_set_read_buffer_size(), BIO_set_write_buffer_size(), and BIO_set_buffer_size() set the read, write, or both read and write buffer sizes to size. The initial buffer size is DEFAULT_BUFFER_SIZE, currently 4096. Any attempt to reduce the buffer size below DEFAULT_BUFFER_SIZE is ignored. Any buffered data is cleared when the buffer is resized. so, like, resize responsibly. 🎀

BIO_set_buffer_read_data() clears the read buffer and fills it with num bytes of buf. If num is larger than the current buffer size, the buffer is expanded. slay expansion. 🌱

Buffering BIOs implement BIO_gets(3) by using BIO_read(3) operations on the next BIO in the chain. By prepending a buffering BIO to a chain, it is therefore possible to provide the functionality of BIO_gets(3) if the following BIOs do not support it — for example, SSL BIOs. iykyk. 🦋

Data is only written to the next BIO in the chain when the write buffer fills or when BIO_flush(3) is called. It is therefore important to call BIO_flush(3) whenever any pending data should be written, such as when removing a buffering BIO using BIO_pop(3). BIO_flush(3) may need to be retried if the ultimate source/sink BIO is non-blocking. this is the part where you don’t forget to flush. 😭

When a chain containing a buffering BIO is copied with BIO_dup_chain(3), BIO_set_read_buffer_size() and BIO_set_write_buffer_size() are called internally to automatically copy both buffer sizes from the original BIO object to the new one. cute little copy-paste moment, honestly. 💜

BIO_ctrl(3) cmd arguments correspond to macros as follows:

• BIO_C_GET_BUFF_NUM_LINES → BIO_get_buffer_num_lines()
• BIO_C_SET_BUFF_READ_DATA → BIO_set_buffer_read_data()
• BIO_C_SET_BUFF_SIZE → BIO_set_buffer_size()
• BIO_CTRL_FLUSH → BIO_flush(3)
• BIO_CTRL_PENDING → BIO_pending(3)
• BIO_CTRL_RESET → BIO_reset(3)
• BIO_CTRL_WPENDING → BIO_wpending(3)

The cmd constant BIO_C_SET_BUFF_SIZE is special. It is also used for BIO_int_ctrl(3) with the following iarg arguments:

• BIO_C_SET_BUFF_SIZE with iarg 0 → BIO_set_read_buffer_size()
• BIO_C_SET_BUFF_SIZE with iarg 1 → BIO_set_write_buffer_size()

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🎀 RETURN VALUES 🎀

BIO_f_buffer() returns the buffering BIO method. again. because she said what she said. 💅

When called on a buffering BIO object, BIO_method_type(3) returns the constant BIO_TYPE_BUFFER and BIO_method_name(3) returns a pointer to the static string "buffer". name dropping done right. ✨

BIO_get_buffer_num_lines() returns the number of lines buffered (may be 0). zero is valid, bestie. 🙈

BIO_set_read_buffer_size(), BIO_set_write_buffer_size(), and BIO_set_buffer_size() return 1 if the buffer was successfully resized or 0 for failure.

BIO_set_buffer_read_data() returns 1 if the data was set correctly or 0 if there was an error.

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🦋 SEE ALSO 🦋

• BIO_ctrl(3)
• BIO_flush(3)
• BIO_new(3)
• BIO_pop(3)
• BIO_reset(3)

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👑 HISTORY 👑

BIO_f_buffer() first appeared in SSLeay 0.6.0.

BIO_get_buffer_num_lines() and BIO_set_buffer_size() first appeared in SSLeay 0.6.5.

BIO_set_read_buffer_size() and BIO_set_write_buffer_size() first appeared in SSLeay 0.8.0.

BIO_set_buffer_read_data() first appeared in SSLeay 0.9.0.

All these functions have been available since OpenBSD 2.4. legacy icons, honestly. 🌈⭐

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🫶 signed, sealed, delivered: Debian, June 8, 2025 — BIO_F_BUFFER(3) 💖 mwah.