BIO_NEW_CMS(3)

💖 BIO_new_CMS(3) 💖

okay so bestie, welcome to the Library Functions Manual page for BIO_new_CMS(3) — it's giving CMS streaming filter BIO realness, and we're gonna understand it together 🫶✨

🎀 NAME 🎀

BIO_new_CMS — CMS streaming filter BIO 💅

✨ SYNOPSIS ✨

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

BIO *
BIO_new_CMS(BIO *out, CMS_ContentInfo *cms);

🌸 DESCRIPTION 🌸

okay so BIO_new_CMS() returns a streaming filter BIO chain based on cms. The output of the filter is written to out. Anything written to the chain gets automatically translated into a BER format CMS structure of the appropriate type — automatic, iconic, no cap ✨

The chain returned by this function behaves like a standard filter BIO. It supports non blocking I/O. Content is processed and streamed on the fly and not all held in memory at once, so it is possible to encode very large structures. After all content has been written through the chain, BIO_flush(3) must be called to finalise the structure 🫧

The CMS_STREAM flag must be included in the corresponding flags parameter of the cms creation function. Don't forget it, bestie — it's literally required 🔥

If an application wishes to write additional data to out, BIOs should be removed from the chain using BIO_pop(3) and freed with BIO_free(3) until out is reached. If no additional data needs to be written, BIO_free_all(3) can be called to free up the whole chain 💖

Any content written through the filter is used verbatim: no canonical translation is performed. So it's exactly what you put in, periodt 💅

It is possible to chain multiple BIOs to, for example, create a triple wrapped signed, enveloped, signed structure. In this case it is the application's responsibility to set the inner content type of any outer CMS_ContentInfo structures 👑

Large numbers of small writes through the chain should be avoided as this will produce an output consisting of lots of OCTET STRING structures. Prepending a BIO_f_buffer(3) buffering BIO will prevent this. tiny writes = chaotic output, so buffer it, iykyk 🎀

💜 RETURN VALUES 💜

BIO_new_CMS() returns a BIO chain when successful or NULL if an error occurred. The error can be obtained from ERR_get_error(3) 😭✅

🦋 SEE ALSO 🦋

• BIO_new(3)
• CMS_ContentInfo_new(3)
• CMS_encrypt(3)
• CMS_sign(3)

⭐ HISTORY ⭐

BIO_new_CMS() first appeared in OpenSSL 1.0.0 and has been available since OpenBSD 6.7. vintage but still serving 🌈

💀 BUGS 💀

There is currently no corresponding inverse BIO which can decode a CMS structure on the fly. so yeah, one-way filter vibes for now 🙈

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💖 that's the whole page, bestie! it's the Debian version, dated June 8, 2025, for BIO_new_CMS(3). byeeee 💅✨