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CURLOPT_SSL_CTX_FUNCTION.md: no promises of lifetime after return

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... and cleanup other language.

Closes #12999
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Daniel Stenberg 2024-02-26 22:27:07 +01:00
parent 5929822114
commit f73cb3ebd2
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69
docs/libcurl/opts/CURLOPT_SSL_CTX_FUNCTION.md
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@ -7,11 +7,12 @@ Source: libcurl
See-also:
- CURLOPT_SSL_CTX_DATA (3)
- CURLOPT_SSL_VERIFYPEER (3)
- CURLOPT_CAINFO (3)
---
# NAME
CURLOPT_SSL_CTX_FUNCTION - SSL context callback for OpenSSL, wolfSSL or mbedTLS
CURLOPT_SSL_CTX_FUNCTION - SSL context callback
# SYNOPSIS
@ -26,49 +27,49 @@ CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSL_CTX_FUNCTION,
# DESCRIPTION
This option only works for libcurl powered by OpenSSL, wolfSSL, mbedTLS or
BearSSL. If libcurl was built against another SSL library this functionality
is absent.
Pass a pointer to your callback function, which should match the prototype
shown above.
This callback function gets called by libcurl just before the initialization
of an SSL connection after having processed all other SSL related options to
give a last chance to an application to modify the behavior of the SSL
initialization. The *ssl_ctx* parameter is actually a pointer to the SSL
library's *SSL_CTX* for OpenSSL or wolfSSL, a pointer to
*mbedtls_ssl_config* for mbedTLS or a pointer to
*br_ssl_client_context* for BearSSL. If an error is returned from the
callback no attempt to establish a connection is made and the perform
operation returns the callback's error code. Set the *clientp* argument
with the CURLOPT_SSL_CTX_DATA(3) option.
initialization. The *ssl_ctx* parameter is a pointer to the SSL library's
*SSL_CTX* for OpenSSL or wolfSSL, a pointer to *mbedtls_ssl_config* for
mbedTLS or a pointer to *br_ssl_client_context* for BearSSL. If an error is
returned from the callback no attempt to establish a connection is made and
the perform operation returns the callback's error code. Set the *clientp*
argument passed in to this callback with the CURLOPT_SSL_CTX_DATA(3) option.
This function gets called on all new connections made to a server, during the
SSL negotiation. The *ssl_ctx* points to a newly initialized object each
time, but note the pointer may be the same as from a prior call.
This function gets called for all new connections made to a server, during the
SSL negotiation. While *ssl_ctx* points to a newly initialized object each
time, the pointer may still be the same as in a prior call.
To use this properly, a non-trivial amount of knowledge of your SSL library is
To use this callback, a non-trivial amount of knowledge of your SSL library is
necessary. For example, you can use this function to call library-specific
callbacks to add additional validation code for certificates, and even to
change the actual URI of an HTTPS request.
For OpenSSL, asynchronous certificate verification via
*SSL_set_retry_verify* is supported. (Added in 8.3.0)
For OpenSSL, asynchronous certificate verification via *SSL_set_retry_verify*
is supported. (Added in 8.3.0)
WARNING: The CURLOPT_SSL_CTX_FUNCTION(3) callback allows the application
to reach in and modify SSL details in the connection without libcurl itself
knowing anything about it, which then subsequently can lead to libcurl
unknowingly reusing SSL connections with different properties. To remedy this
you may set CURLOPT_FORBID_REUSE(3) from the callback function.
The CURLOPT_SSL_CTX_FUNCTION(3) callback allows the application to reach in
and modify SSL details in the connection without libcurl itself knowing
anything about it, which then subsequently can lead to libcurl unknowingly
reusing SSL connections with different properties. To remedy this you may set
CURLOPT_FORBID_REUSE(3) from the callback function.
WARNING: If you are using DNS-over-HTTPS (DoH) via CURLOPT_DOH_URL(3)
then this callback is also called for those transfers and the curl handle is
set to an internal handle. **This behavior is subject to change.** We
recommend before performing your transfer set CURLOPT_PRIVATE(3) on your
curl handle so you can identify it in the context callback. If you have a
reason to modify DoH SSL context please let us know on the curl-library
mailing list because we are considering removing this capability.
If you are using DNS-over-HTTPS (DoH) via CURLOPT_DOH_URL(3) then this
callback is also called for those transfers and the curl handle is set to an
internal handle. **This behavior is subject to change.** We recommend setting
CURLOPT_PRIVATE(3) on your curl handle so you can identify it correctly in the
context callback. If you have a reason to modify DoH SSL context please let us
know on the curl-library mailing list because we are considering removing this
capability.
libcurl does not guarantee the lifetime of the passed in object once this
callback function has returned. Your application must not assume that it can
keep using the SSL context or data derived from it once this function is
completed.
# DEFAULT
@ -155,13 +156,13 @@ int main(void)
# AVAILABILITY
Added in 7.11.0 for OpenSSL, in 7.42.0 for wolfSSL, in 7.54.0 for mbedTLS,
in 7.83.0 in BearSSL. Other SSL backends are not supported.
libcurl built with OpenSSL (added in 7.11.0), wolfSSL (added in 7.42.0), mbedTLS
(added in 7.54.0) or BearSSL (added in 7.83.0)
No other SSL backend is supported.
# RETURN VALUE
CURLE_OK if supported; or an error such as:
CURLE_NOT_BUILT_IN - Not supported by the SSL backend
CURLE_UNKNOWN_OPTION