Update networking layer w/ CURL and emscripten impl
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---
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c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
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SPDX-License-Identifier: curl
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Title: CURLOPT_SSL_CTX_FUNCTION
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Section: 3
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Source: libcurl
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See-also:
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- CURLOPT_CA_CACHE_TIMEOUT (3)
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- CURLOPT_CAINFO (3)
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- CURLOPT_CAINFO_BLOB (3)
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- CURLOPT_SSL_CTX_DATA (3)
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- CURLOPT_SSL_VERIFYHOST (3)
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- CURLOPT_SSL_VERIFYPEER (3)
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Protocol:
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- TLS
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TLS-backend:
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- OpenSSL
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- wolfSSL
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- mbedTLS
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Added-in: 7.10.6
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---
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# NAME
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CURLOPT_SSL_CTX_FUNCTION - SSL context callback
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# SYNOPSIS
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~~~c
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#include <curl/curl.h>
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CURLcode ssl_ctx_callback(CURL *curl, void *ssl_ctx, void *clientp);
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CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSL_CTX_FUNCTION,
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ssl_ctx_callback);
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~~~
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# DESCRIPTION
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Pass a pointer to your callback function, which should match the prototype
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shown above.
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This callback function gets called by libcurl just before the initialization
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of an SSL connection after having processed all other SSL related options to
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give a last chance to an application to modify the behavior of the SSL
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initialization. The *ssl_ctx* parameter is a pointer to the SSL library's
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*SSL_CTX* for OpenSSL or wolfSSL, a pointer to *mbedtls_ssl_config* for
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mbedTLS. If an error is returned from the callback no attempt to establish a
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connection is made and the perform operation returns the callback's error
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code. Set the *clientp* argument passed in to this callback with the
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CURLOPT_SSL_CTX_DATA(3) option.
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This function gets called for all new connections made to a server, during the
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SSL negotiation. While *ssl_ctx* points to a newly initialized object each
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time, the pointer may still be the same as in a prior call.
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To use this callback, a non-trivial amount of knowledge of your SSL library is
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necessary. For example, you can use this function to call library-specific
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callbacks to add additional validation code for certificates, and even to
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change the actual URI of an HTTPS request.
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For OpenSSL, asynchronous certificate verification via *SSL_set_retry_verify*
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is supported. When *SSL_set_retry_verify* is set, the transfer is paused.
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When verification should continue, call curl_easy_pause(3) to unpause
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the transfer. (Added in 8.3.0, Pausing added in 8.16.0)
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The CURLOPT_SSL_CTX_FUNCTION(3) callback allows the application to reach in
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and modify SSL details in the connection without libcurl itself knowing
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anything about it, which then subsequently can lead to libcurl unknowingly
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reusing SSL connections with different properties. To remedy this you may set
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CURLOPT_FORBID_REUSE(3) from the callback function.
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If you are using DNS-over-HTTPS (DoH) via CURLOPT_DOH_URL(3) then this
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callback is also called for those transfers and the curl handle is set to an
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internal handle. **This behavior is subject to change.** We recommend setting
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CURLOPT_PRIVATE(3) on your curl handle so you can identify it correctly in the
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context callback. If you have a reason to modify DoH SSL context please let us
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know on the curl-library mailing list because we are considering removing this
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capability.
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libcurl does not guarantee the lifetime of the passed in object once this
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callback function has returned. Your application must not assume that it can
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keep using the SSL context or data derived from it once this function is
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completed.
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For libcurl builds using TLS backends that support CA caching and
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CURLOPT_CA_CACHE_TIMEOUT(3) is not set to zero, multiple calls to this
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callback may be done with the same CA store in memory.
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# DEFAULT
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NULL
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# %PROTOCOLS%
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# EXAMPLE
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~~~c
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/* OpenSSL specific */
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#include <openssl/ssl.h>
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#include <curl/curl.h>
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#include <stdio.h>
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static CURLcode sslctx_function(CURL *curl, void *sslctx, void *pointer)
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{
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X509_STORE *store;
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X509 *cert = NULL;
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BIO *bio;
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char *mypem = pointer;
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/* get a BIO */
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bio = BIO_new_mem_buf(mypem, -1);
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/* use it to read the PEM formatted certificate from memory into an
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* X509 structure that SSL can use
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*/
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PEM_read_bio_X509(bio, &cert, 0, NULL);
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if(!cert)
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printf("PEM_read_bio_X509 failed...\n");
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/* get a pointer to the X509 certificate store (which may be empty) */
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store = SSL_CTX_get_cert_store((SSL_CTX *)sslctx);
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/* add our certificate to this store */
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if(X509_STORE_add_cert(store, cert) == 0)
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printf("error adding certificate\n");
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/* decrease reference counts */
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X509_free(cert);
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BIO_free(bio);
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/* all set to go */
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return CURLE_OK;
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}
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int main(void)
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{
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CURL *ch;
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CURLcode rv;
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char *mypem = /* CA cert in PEM format, replace the XXXs */
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"-----BEGIN CERTIFICATE-----\n"
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"XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX\n"
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"XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX\n"
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"XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX\n"
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"XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX\n"
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"XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX\n"
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"XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX\n"
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"-----END CERTIFICATE-----\n";
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curl_global_init(CURL_GLOBAL_ALL);
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ch = curl_easy_init();
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curl_easy_setopt(ch, CURLOPT_SSLCERTTYPE, "PEM");
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curl_easy_setopt(ch, CURLOPT_SSL_VERIFYPEER, 1L);
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curl_easy_setopt(ch, CURLOPT_URL, "https://www.example.com/");
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curl_easy_setopt(ch, CURLOPT_SSL_CTX_FUNCTION, *sslctx_function);
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curl_easy_setopt(ch, CURLOPT_SSL_CTX_DATA, mypem);
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rv = curl_easy_perform(ch);
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if(!rv)
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printf("*** transfer succeeded ***\n");
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else
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printf("*** transfer failed ***\n");
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curl_easy_cleanup(ch);
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curl_global_cleanup();
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return rv;
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}
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~~~
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# %AVAILABILITY%
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# RETURN VALUE
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CURLE_OK if supported; or an error such as:
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CURLE_NOT_BUILT_IN - Not supported by the SSL backend
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