3 =for openssl foreign manual atexit(3)
7 OSSL_trace_set_channel, OSSL_trace_set_prefix, OSSL_trace_set_suffix,
8 OSSL_trace_set_callback, OSSL_trace_cb - Enabling trace output
12 #include <openssl/trace.h>
14 typedef size_t (*OSSL_trace_cb)(const char *buf, size_t cnt,
15 int category, int cmd, void *data);
17 void OSSL_trace_set_channel(int category, BIO *bio);
18 void OSSL_trace_set_prefix(int category, const char *prefix);
19 void OSSL_trace_set_suffix(int category, const char *suffix);
20 void OSSL_trace_set_callback(int category, OSSL_trace_cb cb, void *data);
24 If available (see L</Configure Tracing> below), the application can request
25 internal trace output.
26 This output comes in form of free text for humans to read.
28 The trace output is divided into categories which can be
30 Every category can be enabled individually by attaching a so-called
31 I<trace channel> to it, which in the simplest case is just a BIO object
32 to which the application can write the tracing output for this category.
33 Alternatively, the application can provide a tracer callback in order to
34 get more finegrained trace information. This callback will be wrapped
35 internally by a dedicated BIO object.
37 For the tracing code, both trace channel types are indistinguishable.
38 These are called a I<simple trace channel> and a I<callback trace channel>,
41 L<OSSL_TRACE_ENABLED(3)> can be used to check whether tracing is currently
42 enabled for the given category.
43 Functions like L<OSSL_TRACE1(3)> and macros like L<OSSL_TRACE_BEGIN(3)>
44 can be used for producing free-text trace output.
48 OSSL_trace_set_channel() is used to enable the given trace C<category>
49 by attaching the B<BIO> I<bio> object as (simple) trace channel.
51 OSSL_trace_set_prefix() and OSSL_trace_set_suffix() can be used to add
52 an extra line for each channel, to be output before and after group of
54 What constitutes an output group is decided by the code that produces
56 The lines given here are considered immutable; for more dynamic
57 tracing prefixes, consider setting a callback with
58 OSSL_trace_set_callback() instead.
60 OSSL_trace_set_callback() is used to enable the given trace
61 I<category> by giving it the tracer callback I<cb> with the associated
62 data I<data>, which will simply be passed through to I<cb> whenever
63 it's called. The callback function is internally wrapped by a
64 dedicated BIO object, the so-called I<callback trace channel>.
65 This should be used when it's desirable to do form the trace output to
66 something suitable for application needs where a prefix and suffix
69 OSSL_trace_set_channel() and OSSL_trace_set_callback() are mutually
70 exclusive, calling one of them will clear whatever was set by the
73 Calling OSSL_trace_set_channel() with NULL for I<channel> or
74 OSSL_trace_set_callback() with NULL for I<cb> disables tracing for
75 the given I<category>.
79 The tracer callback must return a B<size_t>, which must be zero on
80 error and otherwise return the number of bytes that were output.
81 It receives a text buffer I<buf> with I<cnt> bytes of text, as well as
82 the I<category>, a control number I<cmd>, and the I<data> that was
83 passed to OSSL_trace_set_callback().
85 The possible control numbers are:
89 =item B<OSSL_TRACE_CTRL_BEGIN>
91 The callback is called from OSSL_trace_begin(), which gives the
92 callback the possibility to output a dynamic starting line, or set a
93 prefix that should be output at the beginning of each line, or
96 =item B<OSSL_TRACE_CTRL_WRITE>
98 This callback is called whenever data is written to the BIO by some
99 regular BIO output routine.
100 An arbitrary number of B<OSSL_TRACE_CTRL_WRITE> callbacks can occur
101 inside a group marked by a pair of B<OSSL_TRACE_CTRL_BEGIN> and
102 B<OSSL_TRACE_CTRL_END> calls, but never outside such a group.
104 =item B<OSSL_TRACE_CTRL_END>
106 The callback is called from OSSL_trace_end(), which gives the callback
107 the possibility to output a dynamic ending line, or reset the line
108 prefix that was set with B<OSSL_TRACE_CTRL_BEGIN>, or something other.
112 =head2 Trace categories
114 The trace categories are simple numbers available through macros.
118 =item B<OSSL_TRACE_CATEGORY_TRACE>
120 Traces the OpenSSL trace API itself.
122 More precisely, this will generate trace output any time a new
125 =item B<OSSL_TRACE_CATEGORY_INIT>
127 Traces OpenSSL library initialization and cleanup.
129 This needs special care, as OpenSSL will do automatic cleanup after
130 exit from C<main()>, and any tracing output done during this cleanup
131 will be lost if the tracing channel or callback were cleaned away
133 A suggestion is to make such cleanup part of a function that's
134 registered very early with L<atexit(3)>.
136 =item B<OSSL_TRACE_CATEGORY_TLS>
138 Traces the TLS/SSL protocol.
140 =item B<OSSL_TRACE_CATEGORY_TLS_CIPHER>
142 Traces the ciphers used by the TLS/SSL protocol.
144 =item B<OSSL_TRACE_CATEGORY_ENGINE_TABLE>
146 Traces the ENGINE algorithm table selection.
148 More precisely, functions like ENGINE_get_pkey_asn1_meth_engine(),
149 ENGINE_get_pkey_meth_engine(), ENGINE_get_cipher_engine(),
150 ENGINE_get_digest_engine(), will generate trace summaries of the
151 handling of internal tables.
153 =item B<OSSL_TRACE_CATEGORY_ENGINE_REF_COUNT>
155 Traces the ENGINE reference counting.
157 More precisely, both reference counts in the ENGINE structure will be
158 monitored with a line of trace output generated for each change.
160 =item B<OSSL_TRACE_CATEGORY_PKCS5V2>
162 Traces PKCS#5 v2 key generation.
164 =item B<OSSL_TRACE_CATEGORY_PKCS12_KEYGEN>
166 Traces PKCS#12 key generation.
168 =item B<OSSL_TRACE_CATEGORY_PKCS12_DECRYPT>
170 Traces PKCS#12 decryption.
172 =item B<OSSL_TRACE_CATEGORY_X509V3_POLICY>
174 Traces X509v3 policy processing.
176 More precisely, this generates the complete policy tree at various
177 point during evaluation.
179 =item B<OSSL_TRACE_CATEGORY_BN_CTX>
181 Traces BIGNUM context operations.
183 =item B<OSSL_TRACE_CATEGORY_CONF>
185 Traces details about the provider and engine configuration.
189 There is also B<OSSL_TRACE_CATEGORY_ALL>, which works as a fallback
190 and can be used to get I<all> trace output.
192 Note, however, that in this case all trace output will effectively be
193 associated with the 'ALL' category, which is undesirable if the
194 application intends to include the category name in the trace output.
195 In this case it is better to register separate channels for each
196 trace category instead.
200 OSSL_trace_set_channel(), OSSL_trace_set_prefix(),
201 OSSL_trace_set_suffix(), and OSSL_trace_set_callback() return 1 on
202 success, or 0 on failure.
206 In all examples below, the trace producing code is assumed to be
210 const char bar[] = { 0, 1, 2, 3, 4, 5, 6, 7,
211 8, 9, 10, 11, 12, 13, 14, 15 };
213 OSSL_TRACE_BEGIN(TLS) {
214 BIO_puts(trc_out, "foo: ");
215 BIO_printf(trc_out, "%d\n", foo);
216 BIO_dump(trc_out, bar, sizeof(bar));
217 } OSSL_TRACE_END(TLS);
219 =head2 Simple example
221 An example with just a channel and constant prefix / suffix.
223 int main(int argc, char *argv[])
225 BIO *err = BIO_new_fp(stderr, BIO_NOCLOSE | BIO_FP_TEXT);
226 OSSL_trace_set_channel(OSSL_TRACE_CATEGORY_SSL, err);
227 OSSL_trace_set_prefix(OSSL_TRACE_CATEGORY_SSL, "BEGIN TRACE[TLS]");
228 OSSL_trace_set_suffix(OSSL_TRACE_CATEGORY_SSL, "END TRACE[TLS]");
233 When the trace producing code above is performed, this will be output
238 0000 - 00 01 02 03 04 05 06 07-08 09 0a 0b 0c 0d 0e 0f ................
241 =head2 Advanced example
243 This example uses the callback, and depends on pthreads functionality.
245 static size_t cb(const char *buf, size_t cnt,
246 int category, int cmd, void *vdata)
249 const char *label = NULL;
252 case OSSL_TRACE_CTRL_BEGIN:
255 case OSSL_TRACE_CTRL_END:
266 tid.tid = pthread_self();
267 BIO_printf(bio, "%s TRACE[%s]:%lx\n",
268 label, OSSL_trace_get_category_name(category), tid.ltid);
270 return (size_t)BIO_puts(bio, buf);
273 int main(int argc, char *argv[])
275 BIO *err = BIO_new_fp(stderr, BIO_NOCLOSE | BIO_FP_TEXT);
276 OSSL_trace_set_callback(OSSL_TRACE_CATEGORY_SSL, cb, err);
281 The output is almost the same as for the simple example above.
283 BEGIN TRACE[TLS]:7f9eb0193b80
285 0000 - 00 01 02 03 04 05 06 07-08 09 0a 0b 0c 0d 0e 0f ................
286 END TRACE[TLS]:7f9eb0193b80
290 =head2 Configure Tracing
292 By default, the OpenSSL library is built with tracing disabled. To
293 use the tracing functionality documented here, it is therefore
294 necessary to configure and build OpenSSL with the 'enable-trace' option.
296 When the library is built with tracing disabled, the macro
297 B<OPENSSL_NO_TRACE> is defined in F<< <openssl/opensslconf.h> >> and all
298 functions described here are inoperational, i.e. will do nothing.
302 L<OSSL_TRACE_ENABLED(3)>, L<OSSL_TRACE_BEGIN(3)>, L<OSSL_TRACE1(3)>,
307 OSSL_trace_set_channel(), OSSL_trace_set_prefix(),
308 OSSL_trace_set_suffix(), and OSSL_trace_set_callback() were all added
313 Copyright 2019-2022 The OpenSSL Project Authors. All Rights Reserved.
315 Licensed under the Apache License 2.0 (the "License"). You may not use
316 this file except in compliance with the License. You can obtain a copy
317 in the file LICENSE in the source distribution or at
318 L<https://www.openssl.org/source/license.html>.