facil.io
0.7.x

#SSL/TLS Functions

SSL/TLS provides Transport Layer Security (TLS) for more secure communication.

facil.io attempts to make TLS connections easy by providing a simplified API that abstracts away the underlying TLS library.

Support for OpenSSL >= 1.1.0 is included starting with facil.io version 0.7.0.beta6.

Future support for BearSSL is planned and an example/template is provided under fio_tls_missing.c, making it easy to use your own SSL/TLS library.

The implementation leverages the Read/Write Hooks to allow TLS connections and unencrypted connections to share the same code-base and API (fio_write, fio_read, etc').

To use the facil.io TLS API, include the file fio_tls.h

#TLS Certificates and Settings

#fio_tls_new

c
fio_tls_s *fio_tls_new(const char *server_name,
                       const char *public_certificate_file,
                       const char *private_key_file,
                       const char *private_key_password);

Creates a new SSL/TLS context / settings object with a default certificate (if any).

c
fio_tls_s * tls = fio_tls_new("www.example.com",
                              "./ssl/public_key.pem",
                              "./ssl/private_key.pem",
                              NULL);

If a server name is provided, than NULL values can be used to create an anonymous (unverified) context / settings object.

c
fio_tls_s * tls = fio_tls_new("www.example.com", NULL, NULL, NULL);

If all values are NULL, a TLS object will be created without a certificate. This could be used for clients together with fio_tls_trust

c
fio_tls_s * tls = fio_tls_new(NULL, NULL, NULL, NULL);
fio_tls_trust(tls, "google-ca.pem" );

fio_tls_s * is an opaque type used as a handle for the SSL/TLS functions. It shouldn't be directly accessed.

Remember to call fio_tls_destroy once the fio_tls_s object is no longer in use.

#fio_tls_dup

c
void fio_tls_dup(fio_tls_s *tls);

Increase the reference count for the TLS object.

Decrease / free with fio_tls_destroy.

#fio_tls_destroy

c
void fio_tls_destroy(fio_tls_s *tls);

Destroys the SSL/TLS context / settings object and frees any related resources / memory.

#fio_tls_cert_add

c
void fio_tls_cert_add(fio_tls_s *, const char *server_name,
                      const char *public_cert_file,
                      const char *private_key_file,
                      const char *private_key_password);

Adds a certificate a new SSL/TLS context / settings object (SNI support).

The private_key_password can be NULL if the private key PEM file isn't password protected.

c
fio_tls_cert_add(tls, "www.example.com",
                      "./ssl/public_key.pem",
                      "./ssl/private_key.pem",
                      NULL);

#fio_tls_trust

c
void fio_tls_trust(fio_tls_s *, const char *public_cert_file);

Adds a certificate to the "trust" list, which automatically adds a peer verification requirement.

Note, when the fio_tls_s object is used for server connections, this will limit connections to clients that connect using a trusted certificate.

c
fio_tls_trust(tls, "google-ca.pem" );

#fio_tls_alpn_add

c
void fio_tls_alpn_add(fio_tls_s *tls,
                       const char *protocol_name,
                       void (*on_selected)(intptr_t uuid,
                                        void *udata_connection,
                                        void *udata_tls),
                       void *udata_tls,
                       void (*on_cleanup)(void *udata_tls));

Adds an ALPN protocol callback to the SSL/TLS context.

The first protocol added will act as the default protocol to be selected.

The on_selected callback should accept the connection's uuid, the user data pointer passed to either fio_tls_accept or fio_tls_connect (here: udata_connetcion) and the user data pointer passed to the fio_tls_alpn_add function (udata_tls).

The on_cleanup callback will be called when the TLS object is destroyed (or fio_tls_alpn_add is called again with the same protocol name). The udata_tls argument will be passed along, as is, to the callback (if set).

Except for the tls and protocol_name arguments, all arguments can be NULL.

#fio_tls_alpn_count

c
uintptr_t fio_tls_alpn_count(fio_tls_s *tls);

Returns the number of registered ALPN protocol names.

This could be used when deciding if protocol selection should be delegated to the ALPN mechanism, or whether a protocol should be immediately assigned.

If no ALPN protocols are registered, zero (0) is returned.

#TLS Connection Establishment

#fio_tls_accept

c
void fio_tls_accept(intptr_t uuid, fio_tls_s *tls, void *udata);

Establishes an SSL/TLS connection as an SSL/TLS Server, using the specified context / settings object.

The uuid should be a socket UUID that is already connected to a peer (i.e., the result of fio_accept).

The udata is an opaque user data pointer that is passed along to the protocol selected (if any protocols were added using fio_tls_alpn_add).

#fio_tls_connect

c
void fio_tls_connect(intptr_t uuid, fio_tls_s *tls, void *udata);

Establishes an SSL/TLS connection as an SSL/TLS Client, using the specified context / settings object.

The uuid should be a socket UUID that is already connected to a peer (i.e., one received by a fio_connect specified callback on_connect).

The udata is an opaque user data pointer that is passed along to the protocol selected (if any protocols were added using fio_tls_alpn_add).

#TLS Compile-Time Options

#FIO_TLS_PRINT_SECRET

c
#ifndef FIO_TLS_PRINT_SECRET
/* if true, the master key secret should be printed using FIO_LOG_DEBUG */
#define FIO_TLS_PRINT_SECRET 0
#endif

By setting FIO_TLS_PRINT_SECRET to a true value (1), facil.io will compile in a way that prints out the master key / secret to the debugging log, for use with WireShark or similar network debugging tools.