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.
50 On success the ownership of the BIO is transferred to the channel,
51 so the caller must not free it directly.
53 OSSL_trace_set_prefix() and OSSL_trace_set_suffix() can be used to add
54 an extra line for each channel, to be output before and after group of
56 What constitutes an output group is decided by the code that produces
58 The lines given here are considered immutable; for more dynamic
59 tracing prefixes, consider setting a callback with
60 OSSL_trace_set_callback() instead.
62 OSSL_trace_set_callback() is used to enable the given trace
63 I<category> by giving it the tracer callback I<cb> with the associated
64 data I<data>, which will simply be passed through to I<cb> whenever
65 it's called. The callback function is internally wrapped by a
66 dedicated BIO object, the so-called I<callback trace channel>.
67 This should be used when it's desirable to do form the trace output to
68 something suitable for application needs where a prefix and suffix
71 OSSL_trace_set_channel() and OSSL_trace_set_callback() are mutually
72 exclusive, calling one of them will clear whatever was set by the
75 Calling OSSL_trace_set_channel() with NULL for I<channel> or
76 OSSL_trace_set_callback() with NULL for I<cb> disables tracing for
77 the given I<category>.
81 The tracer callback must return a B<size_t>, which must be zero on
82 error and otherwise return the number of bytes that were output.
83 It receives a text buffer I<buf> with I<cnt> bytes of text, as well as
84 the I<category>, a control number I<cmd>, and the I<data> that was
85 passed to OSSL_trace_set_callback().
87 The possible control numbers are:
91 =item B<OSSL_TRACE_CTRL_BEGIN>
93 The callback is called from OSSL_trace_begin(), which gives the
94 callback the possibility to output a dynamic starting line, or set a
95 prefix that should be output at the beginning of each line, or
98 =item B<OSSL_TRACE_CTRL_WRITE>
100 This callback is called whenever data is written to the BIO by some
101 regular BIO output routine.
102 An arbitrary number of B<OSSL_TRACE_CTRL_WRITE> callbacks can occur
103 inside a group marked by a pair of B<OSSL_TRACE_CTRL_BEGIN> and
104 B<OSSL_TRACE_CTRL_END> calls, but never outside such a group.
106 =item B<OSSL_TRACE_CTRL_END>
108 The callback is called from OSSL_trace_end(), which gives the callback
109 the possibility to output a dynamic ending line, or reset the line
110 prefix that was set with B<OSSL_TRACE_CTRL_BEGIN>, or something other.
114 =head2 Trace categories
116 The trace categories are simple numbers available through macros.
120 =item B<OSSL_TRACE_CATEGORY_TRACE>
122 Traces the OpenSSL trace API itself.
124 More precisely, this will generate trace output any time a new
127 =item B<OSSL_TRACE_CATEGORY_INIT>
129 Traces OpenSSL library initialization and cleanup.
131 This needs special care, as OpenSSL will do automatic cleanup after
132 exit from C<main()>, and any tracing output done during this cleanup
133 will be lost if the tracing channel or callback were cleaned away
135 A suggestion is to make such cleanup part of a function that's
136 registered very early with L<atexit(3)>.
138 =item B<OSSL_TRACE_CATEGORY_TLS>
140 Traces the TLS/SSL protocol.
142 =item B<OSSL_TRACE_CATEGORY_TLS_CIPHER>
144 Traces the ciphers used by the TLS/SSL protocol.
146 =item B<OSSL_TRACE_CATEGORY_CONF>
148 Traces details about the provider and engine configuration.
150 =item B<OSSL_TRACE_CATEGORY_ENGINE_TABLE>
152 Traces the ENGINE algorithm table selection.
154 More precisely, functions like ENGINE_get_pkey_asn1_meth_engine(),
155 ENGINE_get_pkey_meth_engine(), ENGINE_get_cipher_engine(),
156 ENGINE_get_digest_engine(), will generate trace summaries of the
157 handling of internal tables.
159 =item B<OSSL_TRACE_CATEGORY_ENGINE_REF_COUNT>
161 Traces the ENGINE reference counting.
163 More precisely, both reference counts in the ENGINE structure will be
164 monitored with a line of trace output generated for each change.
166 =item B<OSSL_TRACE_CATEGORY_PKCS5V2>
168 Traces PKCS#5 v2 key generation.
170 =item B<OSSL_TRACE_CATEGORY_PKCS12_KEYGEN>
172 Traces PKCS#12 key generation.
174 =item B<OSSL_TRACE_CATEGORY_PKCS12_DECRYPT>
176 Traces PKCS#12 decryption.
178 =item B<OSSL_TRACE_CATEGORY_X509V3_POLICY>
180 Traces X509v3 policy processing.
182 More precisely, this generates the complete policy tree at various
183 point during evaluation.
185 =item B<OSSL_TRACE_CATEGORY_BN_CTX>
187 Traces BIGNUM context operations.
189 =item B<OSSL_TRACE_CATEGORY_CMP>
191 Traces CMP client and server activity.
193 =item B<OSSL_TRACE_CATEGORY_STORE>
195 Traces STORE operations.
197 =item B<OSSL_TRACE_CATEGORY_DECODER>
199 Traces decoder operations.
201 =item B<OSSL_TRACE_CATEGORY_ENCODER>
203 Traces encoder operations.
205 =item B<OSSL_TRACE_CATEGORY_REF_COUNT>
207 Traces decrementing certain ASN.1 structure references.
209 =item B<OSSL_TRACE_CATEGORY_HTTP>
211 Traces the HTTP client, such as message headers being sent and received.
215 There is also B<OSSL_TRACE_CATEGORY_ALL>, which works as a fallback
216 and can be used to get I<all> trace output.
218 Note, however, that in this case all trace output will effectively be
219 associated with the 'ALL' category, which is undesirable if the
220 application intends to include the category name in the trace output.
221 In this case it is better to register separate channels for each
222 trace category instead.
226 OSSL_trace_set_channel(), OSSL_trace_set_prefix(),
227 OSSL_trace_set_suffix(), and OSSL_trace_set_callback() return 1 on
228 success, or 0 on failure.
232 In all examples below, the trace producing code is assumed to be
236 const char bar[] = { 0, 1, 2, 3, 4, 5, 6, 7,
237 8, 9, 10, 11, 12, 13, 14, 15 };
239 OSSL_TRACE_BEGIN(TLS) {
240 BIO_puts(trc_out, "foo: ");
241 BIO_printf(trc_out, "%d\n", foo);
242 BIO_dump(trc_out, bar, sizeof(bar));
243 } OSSL_TRACE_END(TLS);
245 =head2 Simple example
247 An example with just a channel and constant prefix / suffix.
249 int main(int argc, char *argv[])
251 BIO *err = BIO_new_fp(stderr, BIO_NOCLOSE | BIO_FP_TEXT);
252 OSSL_trace_set_channel(OSSL_TRACE_CATEGORY_SSL, err);
253 OSSL_trace_set_prefix(OSSL_TRACE_CATEGORY_SSL, "BEGIN TRACE[TLS]");
254 OSSL_trace_set_suffix(OSSL_TRACE_CATEGORY_SSL, "END TRACE[TLS]");
259 When the trace producing code above is performed, this will be output
264 0000 - 00 01 02 03 04 05 06 07-08 09 0a 0b 0c 0d 0e 0f ................
267 =head2 Advanced example
269 This example uses the callback, and depends on pthreads functionality.
271 static size_t cb(const char *buf, size_t cnt,
272 int category, int cmd, void *vdata)
275 const char *label = NULL;
278 case OSSL_TRACE_CTRL_BEGIN:
281 case OSSL_TRACE_CTRL_END:
292 tid.tid = pthread_self();
293 BIO_printf(bio, "%s TRACE[%s]:%lx\n",
294 label, OSSL_trace_get_category_name(category), tid.ltid);
296 return (size_t)BIO_puts(bio, buf);
299 int main(int argc, char *argv[])
301 BIO *err = BIO_new_fp(stderr, BIO_NOCLOSE | BIO_FP_TEXT);
302 OSSL_trace_set_callback(OSSL_TRACE_CATEGORY_SSL, cb, err);
307 The output is almost the same as for the simple example above.
309 BEGIN TRACE[TLS]:7f9eb0193b80
311 0000 - 00 01 02 03 04 05 06 07-08 09 0a 0b 0c 0d 0e 0f ................
312 END TRACE[TLS]:7f9eb0193b80
316 =head2 Configure Tracing
318 By default, the OpenSSL library is built with tracing disabled. To
319 use the tracing functionality documented here, it is therefore
320 necessary to configure and build OpenSSL with the 'enable-trace' option.
322 When the library is built with tracing disabled, the macro
323 B<OPENSSL_NO_TRACE> is defined in F<< <openssl/opensslconf.h> >> and all
324 functions described here are inoperational, i.e. will do nothing.
328 L<OSSL_TRACE_ENABLED(3)>, L<OSSL_TRACE_BEGIN(3)>, L<OSSL_TRACE1(3)>,
333 OSSL_trace_set_channel(), OSSL_trace_set_prefix(),
334 OSSL_trace_set_suffix(), and OSSL_trace_set_callback() were all added
339 Copyright 2019-2023 The OpenSSL Project Authors. All Rights Reserved.
341 Licensed under the Apache License 2.0 (the "License"). You may not use
342 this file except in compliance with the License. You can obtain a copy
343 in the file LICENSE in the source distribution or at
344 L<https://www.openssl.org/source/license.html>.