OSSL_trace_set_channel(3) | OpenSSL | OSSL_trace_set_channel(3) |
#include <openssl/trace.h> typedef size_t (*OSSL_trace_cb)(const char *buf, size_t cnt, int category, int cmd, void *data); void OSSL_trace_set_channel(int category, BIO *bio); void OSSL_trace_set_prefix(int category, const char *prefix); void OSSL_trace_set_suffix(int category, const char *suffix); void OSSL_trace_set_callback(int category, OSSL_trace_cb cb, void *data);
The trace output is divided into categories which can be enabled individually. Every category can be enabled individually by attaching a so called trace channel to it, which in the simplest case is just a BIO object to which the application can write the tracing output for this category. Alternatively, the application can provide a tracer callback in order to get more finegrained trace information. This callback will be wrapped internally by a dedicated BIO object.
For the tracing code, both trace channel types are indistinguishable. These are called a simple trace channel and a callback trace channel, respectively.
OSSL_trace_set_prefix() and OSSL_trace_set_suffix() can be used to add an extra line for each channel, to be output before and after group of tracing output. What constitutes an output group is decided by the code that produces the output. The lines given here are considered immutable; for more dynamic tracing prefixes, consider setting a callback with OSSL_trace_set_callback() instead.
OSSL_trace_set_callback() is used to enable the given trace category by giving it the tracer callback cb with the associated data data, which will simply be passed through to cb whenever it's called. The callback function is internally wrapped by a dedicated BIO object, the so called callback trace channel. This should be used when it's desirable to do form the trace output to something suitable for application needs where a prefix and suffix line aren't enough.
OSSL_trace_set_channel() and OSSL_trace_set_callback() are mutually exclusive, calling one of them will clear whatever was set by the previous call.
Calling OSSL_trace_set_channel() with NULL for channel or OSSL_trace_set_callback() with NULL for cb disables tracing for the given category.
The possible control numbers are:
More precisely, this will generate trace output any time a new trace hook is set.
This needs special care, as OpenSSL will do automatic cleanup after exit from "main()", and any tracing output done during this cleanup will be lost if the tracing channel or callback were cleaned away prematurely. A suggestion is to make such cleanup part of a function that's registered very early with atexit(3).
More precisely, functions like ENGINE_get_pkey_asn1_meth_engine(), ENGINE_get_pkey_meth_engine(), ENGINE_get_cipher_engine(), ENGINE_get_digest_engine(), will generate trace summaries of the handling of internal tables.
More precisely, both reference counts in the ENGINE structure will be monitored with a line of trace output generated for each change.
More precisely, this generates the complete policy tree at various point during evaluation.
There is also OSSL_TRACE_CATEGORY_ALL, which works as a fallback and can be used to get all trace output.
Note, however, that in this case all trace output will effectively be associated with the 'ALL' category, which is undesirable if the application intends to include the category name in the trace output. In this case it is better to register separate channels for each trace category instead.
int foo = 42; const char bar[] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 }; OSSL_TRACE_BEGIN(TLS) { BIO_puts(trc_out, "foo: "); BIO_printf(trc_out, "%d\n", foo); BIO_dump(trc_out, bar, sizeof(bar)); } OSSL_TRACE_END(TLS);
int main(int argc, char *argv[]) { BIO *err = BIO_new_fp(stderr, BIO_NOCLOSE | BIO_FP_TEXT); OSSL_trace_set_channel(OSSL_TRACE_CATEGORY_SSL, err); OSSL_trace_set_prefix(OSSL_TRACE_CATEGORY_SSL, "BEGIN TRACE[TLS]"); OSSL_trace_set_suffix(OSSL_TRACE_CATEGORY_SSL, "END TRACE[TLS]"); /* ... work ... */ }
When the trace producing code above is performed, this will be output on standard error:
BEGIN TRACE[TLS] foo: 42 0000 - 00 01 02 03 04 05 06 07-08 09 0a 0b 0c 0d 0e 0f ................ END TRACE[TLS]
static size_t cb(const char *buf, size_t cnt, int category, int cmd, void *vdata) { BIO *bio = vdata; const char *label = NULL; switch (cmd) { case OSSL_TRACE_CTRL_BEGIN: label = "BEGIN"; break; case OSSL_TRACE_CTRL_END: label = "END"; break; } if (label != NULL) { union { pthread_t tid; unsigned long ltid; } tid; tid.tid = pthread_self(); BIO_printf(bio, "%s TRACE[%s]:%lx\n", label, OSSL_trace_get_category_name(category), tid.ltid); } return (size_t)BIO_puts(bio, buf); } int main(int argc, char *argv[]) { BIO *err = BIO_new_fp(stderr, BIO_NOCLOSE | BIO_FP_TEXT); OSSL_trace_set_callback(OSSL_TRACE_CATEGORY_SSL, cb, err); /* ... work ... */ }
The output is almost the same as for the simple example above.
BEGIN TRACE[TLS]:7f9eb0193b80 foo: 42 0000 - 00 01 02 03 04 05 06 07-08 09 0a 0b 0c 0d 0e 0f ................ END TRACE[TLS]:7f9eb0193b80
When the library is built with tracing disabled, the macro OPENSSL_NO_TRACE is defined in <openssl/opensslconf.h> and all functions described here are inoperational, i.e. will do nothing.
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 <https://www.openssl.org/source/license.html>.
2023-10-25 | 3.0.12 |