libcurl 8.16.0 and setopt_long/setopt_bool

From: Jicea via curl-library <curl-library_at_lists.haxx.se>
Date: Sun, 14 Sep 2025 12:11:16 +0000

Hello all,

I'm maintaining a Rust cli that uses libcurl for HTTP exchanges. I'm trying to understand why I see a libcurl log in my Rust sample

`* boolean setopt(81) got unsupported argument 2, treated as 1`

(81 => CURLOPT_SSL_VERIFYHOST) in some basic samples appearing with libcurl 8.16.0 (I'm testing it on Archlinux)

I'm reaching this channel, because, in my investigation, I've found that there are some relatively recent changes in curl regarding `setopt_long`/ `setopt_bool` (see <https://github.com/curl/curl/pull/17887>). The cullprit is certainly in Rust wrapping code around C libcurl but I want to get some advices from libcurl expert.

The Rust code that trigges this warning is:

```
fn fetch_url(url: &str) {
    unsafe {
        curl_sys::curl_global_init(curl_sys::CURL_GLOBAL_ALL);

        let handle = curl_sys::curl_easy_init();

        let url = CString::new(url).unwrap();

        let ret = curl_sys::curl_easy_setopt(handle, curl_sys::CURLOPT_URL, url.as_ptr());
        ok_or_exit(ret);

        let ret = curl_sys::curl_easy_setopt(handle, curl_sys::CURLOPT_VERBOSE, 1);
        ok_or_exit(ret);

        let ret = curl_sys::curl_easy_setopt(handle, curl_sys::CURLOPT_SSL_VERIFYHOST, 2);
        ok_or_exit(ret);

        let ret = curl_sys::curl_easy_perform(handle);
        ok_or_exit(ret);
    }
}
```

The Rust function `curl_sys::curl_easy_setopt` is defined as (still Rust code sorry!):

```
extern "C" {
        ...
        pub fn curl_easy_setopt(curl: *mut CURL, option: CURLoption, ...) -> CURLcode;
```


This seems to me (certainly wrongly) a direct call to the C libcurl function `CURL_EXTERN CURLcode curl_easy_setopt(CURL *curl, CURLoption option, ...)`

So, when the Rust call is

```
let ret = curl_sys::curl_easy_setopt(handle, curl_sys::CURLOPT_SSL_VERIFYHOST, 2);
```

It should call the corresponding libcurl function `CURLcode curl_easy_setopt`, then `Curl_vsetopt` and finally `setopt_long`.

All this code seems OK to me, I don't see any "weird" logic in Rust warpping around libcurl and yet, at runtime, with libcurl 8.16.0 I see this log:

`* boolean setopt(81) got unsupported argument 2, treated as 1` in some basic sample with libcurl 8.16.0.`

As if the path code call triggers a `setopt_bool`.

I'm sorry to ask for advices for this problem (for a Rust cli and certainlty not a libcurl issue) but I'm a litle stuck in trying to understand this issue.

Thanks for any thought!

Jicea






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Received on 2025-09-14