BIO_S_SOCKET(3)

💅 BIO_S_SOCKET(3) — the socket BIO page, bestie edition

okay so this is BIO_S_SOCKET(3) from the Library Functions Manual, living over in libcrypto land. buckle up, we're talking sockets 🌸

---

✨ NAME ✨

BIO_s_socket, BIO_new_socket — the socket BIO, no cap 🫶

---

✨ SYNOPSIS ✨

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

const BIO_METHOD *
BIO_s_socket(void);

BIO *
BIO_new_socket(int sock, int close_flag);

---

✨ DESCRIPTION ✨

so BIO_s_socket() returns the socket BIO method 💫 literally it's a wrapper around the platform's socket routines. that's the whole vibe.

BIO_read(3) and BIO_write(3) read or write the underlying socket. BIO_puts(3) is supported but BIO_gets(3) is not. not me telling you BIO_gets is not invited to the party 😭

if the close flag is set, then the socket is shut down and closed when the BIO is freed. clean exit, iconic behavior 💅

BIO_new_socket() returns a socket BIO using sock and close_flag.

socket BIOs also support any relevant functionality of file descriptor BIOs. it's giving "we share a closet" 🎀

and now the part that's actually important, so listen up bestie 👑 — the reason for having separate file descriptor and socket BIOs is that on some platforms, sockets are not file descriptors and use distinct I/O routines. Windows is one such platform. any code mixing the two will not work on all platforms. so like... don't do that 🙈

lowkey a real warning: mix file descriptor BIOs and socket BIOs at your own risk, because on platforms where sockets aren't file descriptors it will absolutely fall apart. fr fr 💀

---

✨ RETURN VALUES ✨

• BIO_s_socket() returns the socket BIO method ✨
• BIO_new_socket() returns the newly allocated BIO or NULL if an error occurred 😭
• when called on a socket BIO object, BIO_method_type(3) returns the constant BIO_TYPE_SOCKET and BIO_method_name(3) returns a pointer to the static string "socket" 🎀

---

✨ SEE ALSO ✨

BIO_get_fd(3), BIO_new(3) — go read those next, bestie, iykyk 🦋

---

✨ HISTORY ✨

BIO_s_socket() first appeared in SSLeay 0.6.0. BIO_new_socket() first appeared in SSLeay 0.8.0. both functions have been available since OpenBSD 2.4. we love a long-running icon ⭐

---

and that's the whole page, bestie — Debian, dated June 8, 2025, BIO_S_SOCKET(3), slay 💖🧚‍♀️