NNG_HTTP_RES_ADD_HEADER(3http)

okay so bestie, this is the nng_http_res_add_header(3http) page from the NNG Reference Manual 💖

💅 NAME

nng_http_res_add_header — add HTTP response header

✨ SYNOPSIS

#include <nng/nng.h>
#include <nng/supplemental/http/http.h>

int nng_http_res_add_header(nng_http_res *res, const char *key,
    const char *val);

🎀 DESCRIPTION

So nng_http_res_add_header() adds an HTTP header to the response res, mapping the header name key to the value val. Both key and val get copied — yes, copied, not borrowed, no cap 🫶.

If a header with the value of key already exists, then a comma and whitespace separator are appended to it, followed by val ✨.

If no such header already exists, then one is created with the value val. Easy.

💡 Tip: the HTTP specification requires duplicate headers to be treated identically to a single header with multiple comma-delimited values.

💡 Tip: peep nng_http_res_set_header() if you want to replace an existing header instead of appending to it 👑

The value of key is case insensitive, and it should not include the final colon in an HTTP header. For example, Host and hOSt are equivalent, whereas Host: is not a legal header key. periodt 💅

🌸 RETURN VALUES

This function returns 0 on success, and non-zero otherwise. That's it, that's the vibe check ✨.

🦋 ERRORS

• NNG_ENOMEM — Insufficient memory to perform the operation 😭.
• NNG_ENOTSUP — No support for HTTP in the library.

🔥 SEE ALSO

• nng_http_res_alloc(3http)
• nng_http_res_del_header(3http)
• nng_http_res_get_header(3http)
• nng_http_res_set_header(3http)
• nng(7)

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xoxo, your Unix bestie 🧚 — that's the tea from NNG_HTTP_...ADD_HEADER(3http), dated 2026-01-13 💜