BIO_S_FD(3)

🌈 BIO_S_FD(3) — file descriptor BIO, bestie edition 💅

okay so bestie, welcome to BIO_S_FD(3), straight out of the Library Functions Manual — and yes, we're making file descriptor BIOs make sense. no cap. ✨

🎀 NAME 🎀

The whole squad is BIO_s_fd, BIO_set_fd, BIO_get_fd, BIO_new_fd, BIO_fd_non_fatal_error, and BIO_fd_should_retry — together they're the file descriptor BIO. 💖

✨ SYNOPSIS ✨

#include <openssl/bio.h>

const BIO_METHOD *
BIO_s_fd(void);

long
BIO_set_fd(BIO *b, int fd, long close_flag);

long
BIO_get_fd(BIO *b, int *c);

BIO *
BIO_new_fd(int fd, int close_flag);

int
BIO_fd_non_fatal_error(int errnum);

int
BIO_fd_should_retry(int retval);

🦋 DESCRIPTION 🦋

BIO_s_fd() hands you the file descriptor BIO method. It's basically a wrapper around the platform's file descriptor routines, like read(2) and write(2). slay.

BIO_read(3) and BIO_write(3) do the actual reading and writing on the underlying descriptor. BIO_puts(3) is supported, but BIO_gets(3) is not — so don't come for her with gets. 🙈

If the close flag is set, close(2) gets called on the underlying file descriptor when the BIO is freed.

BIO_reset(3) attempts to set the file pointer to the start of the file using lseek(fd, 0, 0).

BIO_seek(3) sets the file pointer to position ofs from the start of the file using lseek(fd, ofs, 0).

BIO_tell(3) returns the current file position by calling lseek(fd, 0, 1).

BIO_set_fd() sets the file descriptor of BIO b to fd and the close flag to close_flag.

BIO_get_fd() places the file descriptor in c if it is not NULL, and also returns the file descriptor.

BIO_new_fd() returns a file descriptor BIO using fd and close_flag.

BIO_fd_non_fatal_error() figures out whether the error status code errnum represents a recoverable error. BIO_fd_should_retry() figures out whether a recoverable error occurred by inspecting both errno(2) and retval — and retval is supposed to usually be the return value of a previously called function like BIO_read(3) or BIO_write(3). These two functions are mostly used internally; in application code, it's usually easier and more robust to use BIO_should_retry(3), which works for any BIO type. iykyk. 💅

The behaviour of BIO_read(3) and BIO_write(3) depends on the behavior of the platform's read(2) and write(2) calls on the descriptor. If the underlying file descriptor is in a non-blocking mode, then the BIO will behave in the manner described in the BIO_read(3) and BIO_should_retry(3) manual pages.

⚠️ file descriptor BIOs should not be used for socket I/O. Use socket BIOs instead, bestie. periodt.

BIO_ctrl(3) cmd arguments correspond to macros like this:

• BIO_C_FILE_SEEK — corresponds to BIO_seek(3)
• BIO_C_FILE_TELL — corresponds to BIO_tell(3)
• BIO_C_GET_FD — corresponds to BIO_get_fd()
• BIO_C_SET_FD — corresponds to BIO_set_fd()
• BIO_CTRL_GET_CLOSE — corresponds to BIO_get_close(3)
• BIO_CTRL_RESET — corresponds to BIO_reset(3)
• BIO_CTRL_SET_CLOSE — corresponds to BIO_set_close(3)

💖 RETURN VALUES 💖

BIO_s_fd() returns the file descriptor BIO method.

When called on a file descriptor BIO object, BIO_method_type(3) returns the constant BIO_TYPE_FD, and BIO_method_name(3) returns a pointer to the static string "file descriptor".

BIO_set_fd() always returns 1. iconic.

BIO_get_fd() returns the file descriptor, or -1 if the BIO has not been initialized.

BIO_new_fd() returns the newly allocated BIO, or NULL if an error occurred.

BIO_fd_non_fatal_error() returns 1 if errnum is EAGAIN, EALREADY, EINPROGRESS, EINTR, or ENOTCONN, and 0 otherwise — even if errnum is 0. yes really. 💀

BIO_fd_should_retry() returns 1 if BIO_fd_non_fatal_error(errno) is 1 and retval is either 0 or -1, or 0 otherwise.

🌸 EXAMPLES 🌸

This is a file descriptor BIO version of “Hello World”:

BIO *out;
out = BIO_new_fd(fileno(stdout), BIO_NOCLOSE);
BIO_printf(out, "Hello World\n");
BIO_free(out);

🔥 SEE ALSO 🔥

Go check out BIO_new(3), BIO_read(3), BIO_s_socket(3), BIO_seek(3), and BIO_should_retry(3). 🫶

🕰️ HISTORY 🕰️

BIO_s_fd(), BIO_set_fd(), and BIO_get_fd() first appeared in SSLeay 0.6.0, BIO_fd_should_retry() in SSLeay 0.6.5, and BIO_new_fd() and BIO_fd_non_fatal_error() in SSLeay 0.8.0. All these functions have been available since OpenBSD 2.4. main character energy. ✨

kisses and sparkles from Debian 💖 — this one's dated November 16, 2023, signing off from BIO_S_FD(3). 🎀