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Re: Wrapper function for curl_easy_setopt()
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From: Vladimir Levijev via curl-library <curl-library_at_lists.haxx.se>
Date: Tue, 24 Oct 2023 15:06:46 +0300
> On 24 Oct 2023, at 14:30, Timothe Litt via curl-library <curl-library_at_lists.haxx.se> wrote:
>
> On 24-Oct-23 06:24, Vladimir Levijev via curl-library wrote:
>> Hi,
>>
>> We use curl library and a lot of curl_easy_setopt() calls in our application. When our application is run with curl library compiled without some features we can get the following error message from failed curl_easy_setopt() call:
>>
>> "An unknown option was passed in to libcurl”
>>
>> I understand that this is all that cURL can tell because the option that was passed to it was part of the functionality that wasn’t chosen at a compile time.
>>
>> For example, target library was compiled without support for SMTP protocol. Our application tries to send email using cURL, tries to set CURLOPT_MAIL_FROM and gets an error that this option is unknown. All clear at this point.
>>
>> Now what we would like is to have the identifier “CURLOPT_MAIL_FROM”, that caused the failure, in the error message that we print to the user. I don’t want to specify the option 2 times in every call (pseudo code):
>>
>> if (!curl_easy_setopt(... CURLOPT_MAIL_FROM…) ) {
>> snprintf(error, “setting CURLOPT_MAIL_FROM failed: …”);
>> goto out;
>> }
>>
>> So I tried it with #define but then you deal with static name of the error buffer and the GOTO label (in some parts we use it, but not everythere). So it seems I need a kind of wrapper function that returns an error message together with an option that was attempted to be set. For example:
>>
>> "cannot set CURLOPT_MAIL_FROM: An unknown option was passed in to libcurl"
>>
>> This way we would understand from the error message what exactly is missing from the target library.
>>
>> I see in the source code of the library there is a function Curl_vsetopt(), I thought this is what I could use, but it’s internal. Any idea how I could achieve this?
>>
>> Or maybe there are plans to improve the error message by saying which option (name) it failed to set?
>>
>> TIA!
>>
>> Cheers,
>>
>> VL
> It certainly would be helpful if the error messages were improved to include the failed parameter name (or even number).
>
> However, you might want to look at calling curl_version_info() https://curl.se/libcurl/c/curl_version_info.html
>
> Your application can make a high level decision on what's supported by checking the list returned in the protocols and/or feature_names elements, rather than checking each curl_easy_setopt. (For curl < CURLVERSION_ELEVENTH, check the deprecated features bit mask.)
>
> In the case you mentioned, look for /smtps?/ in protocols.
>
> This is likely to simplify your application.
>
Yeah, was considering it and was looking in “features” field. Thanks for pointing me to the right field. This is one nice and clean solution.
Thanks again!
VL
Date: Tue, 24 Oct 2023 15:06:46 +0300
> On 24 Oct 2023, at 14:30, Timothe Litt via curl-library <curl-library_at_lists.haxx.se> wrote:
>
> On 24-Oct-23 06:24, Vladimir Levijev via curl-library wrote:
>> Hi,
>>
>> We use curl library and a lot of curl_easy_setopt() calls in our application. When our application is run with curl library compiled without some features we can get the following error message from failed curl_easy_setopt() call:
>>
>> "An unknown option was passed in to libcurl”
>>
>> I understand that this is all that cURL can tell because the option that was passed to it was part of the functionality that wasn’t chosen at a compile time.
>>
>> For example, target library was compiled without support for SMTP protocol. Our application tries to send email using cURL, tries to set CURLOPT_MAIL_FROM and gets an error that this option is unknown. All clear at this point.
>>
>> Now what we would like is to have the identifier “CURLOPT_MAIL_FROM”, that caused the failure, in the error message that we print to the user. I don’t want to specify the option 2 times in every call (pseudo code):
>>
>> if (!curl_easy_setopt(... CURLOPT_MAIL_FROM…) ) {
>> snprintf(error, “setting CURLOPT_MAIL_FROM failed: …”);
>> goto out;
>> }
>>
>> So I tried it with #define but then you deal with static name of the error buffer and the GOTO label (in some parts we use it, but not everythere). So it seems I need a kind of wrapper function that returns an error message together with an option that was attempted to be set. For example:
>>
>> "cannot set CURLOPT_MAIL_FROM: An unknown option was passed in to libcurl"
>>
>> This way we would understand from the error message what exactly is missing from the target library.
>>
>> I see in the source code of the library there is a function Curl_vsetopt(), I thought this is what I could use, but it’s internal. Any idea how I could achieve this?
>>
>> Or maybe there are plans to improve the error message by saying which option (name) it failed to set?
>>
>> TIA!
>>
>> Cheers,
>>
>> VL
> It certainly would be helpful if the error messages were improved to include the failed parameter name (or even number).
>
> However, you might want to look at calling curl_version_info() https://curl.se/libcurl/c/curl_version_info.html
>
> Your application can make a high level decision on what's supported by checking the list returned in the protocols and/or feature_names elements, rather than checking each curl_easy_setopt. (For curl < CURLVERSION_ELEVENTH, check the deprecated features bit mask.)
>
> In the case you mentioned, look for /smtps?/ in protocols.
>
> This is likely to simplify your application.
>
Yeah, was considering it and was looking in “features” field. Thanks for pointing me to the right field. This is one nice and clean solution.
Thanks again!
VL
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