=pod =head1 NAME OSSL_trace_enabled, OSSL_trace_begin, OSSL_trace_end - OpenSSL Tracing API =head1 SYNOPSIS #include int OSSL_trace_enabled(int category); BIO *OSSL_trace_begin(int category); void OSSL_trace_end(int category, BIO *channel); =head1 DESCRIPTION The functions described here are mainly interesting for those who provide OpenSSL functionality, either in OpenSSL itself or in engine modules or similar. If operational (see L below), these functions are used to generate free text tracing output. The tracing output is divided into types which are enabled individually by the application. The tracing types are described in detail in L. The fallback type C should I be used with the functions described here. =head2 Functions OSSL_trace_enabled() can be used to check if tracing for the given C is enabled. OSSL_trace_begin() is used to starts a tracing section, and get the channel for the given C in form of a BIO. This BIO can only be used for output. OSSL_trace_end() is used to end a tracing section. Using OSSL_trace_begin() and OSSL_trace_end() to wrap tracing sections is I. The result of trying to produce tracing output outside of such sections is undefined. =head2 Convenience Macros There are a number of convenience macros defined, to make tracing easy and consistent. C and C reserve the B C and are used as follows to wrap a trace section: OSSL_TRACE_BEGIN(TLS) { BIO_fprintf(trc_out, ... ); } OSSL_TRACE_END(TLS); This will normally expands to: do { BIO *trc_out = OSSL_trace_begin(OSSL_TRACE_CATEGORY_TLS); if (trc_out != NULL) { ... BIO_fprintf(trc_out, ...); } OSSL_trace_end(OSSL_TRACE_CATEGORY_TLS, trc_out); } while (0); C must be used before returning from or jumping out of a trace section: OSSL_TRACE_BEGIN(TLS) { if (condition) { OSSL_TRACE_CANCEL(TLS); goto err; } BIO_fprintf(trc_out, ... ); } OSSL_TRACE_END(TLS); This will normally expand to: do { BIO *trc_out = OSSL_trace_begin(OSSL_TRACE_CATEGORY_TLS); if (trc_out != NULL) { if (condition) { OSSL_trace_end(OSSL_TRACE_CATEGORY_TLS, trc_out); goto err; } BIO_fprintf(trc_out, ... ); } OSSL_trace_end(OSSL_TRACE_CATEGORY_TLS, trc_out); } while (0); =head1 NOTES It is advisable to always check that a trace type is enabled with OSSL_trace_enabled() before generating any output, for example: if (OSSL_trace_enabled(OSSL_TRACE_CATEGORY_TLS)) { BIO *trace = OSSL_trace_begin(OSSL_TRACE_CATEGORY_TLS); BIO_printf(trace, "FOO %d\n", somevalue); BIO_dump(trace, somememory, somememory_l); OSSL_trace_end(OSSL_TRACE_CATEGORY_TLS, trace); } =head2 Tracing disabled The OpenSSL library may be built with tracing disabled, which makes everything documented here inoperational. When the library is built with tracing disabled: =over 4 =item * The macro C is defined in C. =item * all functions are still present, bu OSSL_trace_enabled() will always report the categories as disabled, and all other functions will do nothing. =item * the convenience macros are defined to produce dead code. For example, take this example from L above: OSSL_TRACE_BEGIN(TLS) { if (condition) { OSSL_TRACE_CANCEL(TLS); goto err; } BIO_fprintf(trc_out, ... ); } OSSL_TRACE_END(TLS); When the tracing API isn't operational, that will expand to: do { BIO *trc_out = NULL; if (0) { if (condition) { ((void)0); goto err; } BIO_fprintf(trc_out, ... ); } } while (0); =back =head1 RETURN VALUES OSSL_trace_enabled() returns 1 if tracing for the given B is operational and enabled, otherwise 0. OSSL_trace_begin() returns a C if the given B is enabled, otherwise C. =head1 HISTORY The OpenSSL Tracing API was added ino OpenSSL 3.0.0. =head1 COPYRIGHT Copyright 2019 The OpenSSL Project Authors. All Rights Reserved. Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at L. =cut