doc/man3/OSSL_trace_set_channel.pod - third_party/openssl - Git at Google

 =pod

 =for openssl foreign manual atexit(3)

 =head1 NAME

 OSSL_trace_set_channel, OSSL_trace_set_prefix, OSSL_trace_set_suffix,
 OSSL_trace_set_callback, OSSL_trace_cb - Enabling trace output

 =head1 SYNOPSIS

  #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);

 =head1 DESCRIPTION

 If available (see L</NOTES> below), the application can request
 internal trace output.
 This output comes in form of free text for humans to read.

 The trace output is divided into categories which can be
 enabled individually.
 Every category can be enabled individually by attaching a so called
 I<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 I<simple trace channel> and a I<callback trace channel>,
 respectively.

 =head2 Functions

 OSSL_trace_set_channel() is used to enable the given trace C<category>
 by attaching the B<BIO> I<bio> object as (simple) trace channel.

 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
 I<category> by giving it the tracer callback I<cb> with the associated
 data I<data>, which will simply be passed through to I<cb> whenever
 it's called. The callback function is internally wrapped by a
 dedicated BIO object, the so called I<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 I<channel> or
 OSSL_trace_set_callback() with NULL for I<cb> disables tracing for
 the given I<category>.

 =head2 Trace callback

 The tracer callback must return a B<size_t>, which must be zero on
 error and otherwise return the number of bytes that were output.
 It receives a text buffer I<buf> with I<cnt> bytes of text, as well as
 the I<category>, a control number I<cmd>, and the I<data> that was
 passed to OSSL_trace_set_callback().

 The possible control numbers are:

 =over 4

 =item B<OSSL_TRACE_CTRL_BEGIN>

 The callback is called from OSSL_trace_begin(), which gives the
 callback the possibility to output a dynamic starting line, or set a
 prefix that should be output at the beginning of each line, or
 something other.

 =item B<OSSL_TRACE_CTRL_WRITE>

 This callback is called whenever data is written to the BIO by some
 regular BIO output routine.
 An arbitrary number of B<OSSL_TRACE_CTRL_WRITE> callbacks can occur
 inside a group marked by a pair of B<OSSL_TRACE_CTRL_BEGIN> and
 B<OSSL_TRACE_CTRL_END> calls, but never outside such a group.

 =item B<OSSL_TRACE_CTRL_END>

 The callback is called from OSSL_trace_end(), which gives the callback
 the possibility to output a dynamic ending line, or reset the line
 prefix that was set with B<OSSL_TRACE_CTRL_BEGIN>, or something other.

 =back

 =head2 Trace categories

 The trace categories are simple numbers available through macros.

 =over 4

 =item B<OSSL_TRACE_CATEGORY_TRACE>

 Traces the OpenSSL trace API itself.

 More precisely, this will generate trace output any time a new
 trace hook is set.

 =item B<OSSL_TRACE_CATEGORY_INIT>

 Traces OpenSSL library initialization and cleanup.

 This needs special care, as OpenSSL will do automatic cleanup after
 exit from C<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 L<atexit(3)>.

 =item B<OSSL_TRACE_CATEGORY_TLS>

 Traces the TLS/SSL protocol.

 =item B<OSSL_TRACE_CATEGORY_TLS_CIPHER>

 Traces the ciphers used by the TLS/SSL protocol.

 =item B<OSSL_TRACE_CATEGORY_ENGINE_TABLE>

 Traces the ENGINE algorithm table selection.

 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.

 =item B<OSSL_TRACE_CATEGORY_ENGINE_REF_COUNT>

 Traces the ENGINE reference counting.

 More precisely, both reference counts in the ENGINE structure will be
 monitored with a line of trace output generated for each change.

 =item B<OSSL_TRACE_CATEGORY_PKCS5V2>

 Traces PKCS#5 v2 key generation.

 =item B<OSSL_TRACE_CATEGORY_PKCS12_KEYGEN>

 Traces PKCS#12 key generation.

 =item B<OSSL_TRACE_CATEGORY_PKCS12_DECRYPT>

 Traces PKCS#12 decryption.

 =item B<OSSL_TRACE_CATEGORY_X509V3_POLICY>

 Traces X509v3 policy processing.

 More precisely, this generates the complete policy tree at various
 point during evaluation.

 =item B<OSSL_TRACE_CATEGORY_BN_CTX>

 Traces BIGNUM context operations.

 =item B<OSSL_TRACE_CATEGORY_CONF>

 Traces details about the provider and engine configuration.

 =back

 There is also B<OSSL_TRACE_CATEGORY_ALL>, which works as a fallback
 and can be used to get I<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.

 =head1 RETURN VALUES

 OSSL_trace_set_channel(), OSSL_trace_set_prefix(),
 OSSL_trace_set_suffix(), and OSSL_trace_set_callback() return 1 on
 success, or 0 on failure.

 =head1 EXAMPLES

 In all examples below, the trace producing code is assumed to be
 the following:

  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);

 =head2 Simple example

 An example with just a channel and constant prefix / suffix.

  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]

 =head2 Advanced example

 This example uses the callback, and depends on pthreads functionality.

  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

 =head1 NOTES

 =head2 Configure Tracing

 By default, the OpenSSL library is built with tracing disabled. To
 use the tracing functionality documented here, it is therefore
 necessary to configure and build OpenSSL with the 'enable-trace' option.

 When the library is built with tracing disabled, the macro
 B<OPENSSL_NO_TRACE> is defined in F<< <openssl/opensslconf.h> >> and all
 functions described here are inoperational, i.e. will do nothing.

 =head1 HISTORY

 OSSL_trace_set_channel(), OSSL_trace_set_prefix(),
 OSSL_trace_set_suffix(), and OSSL_trace_set_callback() were all added
 in OpenSSL 3.0.

 =head1 COPYRIGHT

 Copyright 2019-2022 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<https://www.openssl.org/source/license.html>.

 =cut
	=pod

	=for openssl foreign manual atexit(3)

	=head1 NAME

	OSSL_trace_set_channel, OSSL_trace_set_prefix, OSSL_trace_set_suffix,
	OSSL_trace_set_callback, OSSL_trace_cb - Enabling trace output

	=head1 SYNOPSIS

	#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);

	=head1 DESCRIPTION

	If available (see L</NOTES> below), the application can request
	internal trace output.
	This output comes in form of free text for humans to read.

	The trace output is divided into categories which can be
	enabled individually.
	Every category can be enabled individually by attaching a so called
	I<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 I<simple trace channel> and a I<callback trace channel>,
	respectively.

	=head2 Functions

	OSSL_trace_set_channel() is used to enable the given trace C<category>
	by attaching the B<BIO> I<bio> object as (simple) trace channel.

	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
	I<category> by giving it the tracer callback I<cb> with the associated
	data I<data>, which will simply be passed through to I<cb> whenever
	it's called. The callback function is internally wrapped by a
	dedicated BIO object, the so called I<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 I<channel> or
	OSSL_trace_set_callback() with NULL for I<cb> disables tracing for
	the given I<category>.

	=head2 Trace callback

	The tracer callback must return a B<size_t>, which must be zero on
	error and otherwise return the number of bytes that were output.
	It receives a text buffer I<buf> with I<cnt> bytes of text, as well as
	the I<category>, a control number I<cmd>, and the I<data> that was
	passed to OSSL_trace_set_callback().

	The possible control numbers are:

	=over 4

	=item B<OSSL_TRACE_CTRL_BEGIN>

	The callback is called from OSSL_trace_begin(), which gives the
	callback the possibility to output a dynamic starting line, or set a
	prefix that should be output at the beginning of each line, or
	something other.

	=item B<OSSL_TRACE_CTRL_WRITE>

	This callback is called whenever data is written to the BIO by some
	regular BIO output routine.
	An arbitrary number of B<OSSL_TRACE_CTRL_WRITE> callbacks can occur
	inside a group marked by a pair of B<OSSL_TRACE_CTRL_BEGIN> and
	B<OSSL_TRACE_CTRL_END> calls, but never outside such a group.

	=item B<OSSL_TRACE_CTRL_END>

	The callback is called from OSSL_trace_end(), which gives the callback
	the possibility to output a dynamic ending line, or reset the line
	prefix that was set with B<OSSL_TRACE_CTRL_BEGIN>, or something other.

	=back

	=head2 Trace categories

	The trace categories are simple numbers available through macros.

	=over 4

	=item B<OSSL_TRACE_CATEGORY_TRACE>

	Traces the OpenSSL trace API itself.

	More precisely, this will generate trace output any time a new
	trace hook is set.

	=item B<OSSL_TRACE_CATEGORY_INIT>

	Traces OpenSSL library initialization and cleanup.

	This needs special care, as OpenSSL will do automatic cleanup after
	exit from C<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 L<atexit(3)>.

	=item B<OSSL_TRACE_CATEGORY_TLS>

	Traces the TLS/SSL protocol.

	=item B<OSSL_TRACE_CATEGORY_TLS_CIPHER>

	Traces the ciphers used by the TLS/SSL protocol.

	=item B<OSSL_TRACE_CATEGORY_ENGINE_TABLE>

	Traces the ENGINE algorithm table selection.

	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.

	=item B<OSSL_TRACE_CATEGORY_ENGINE_REF_COUNT>

	Traces the ENGINE reference counting.

	More precisely, both reference counts in the ENGINE structure will be
	monitored with a line of trace output generated for each change.

	=item B<OSSL_TRACE_CATEGORY_PKCS5V2>

	Traces PKCS#5 v2 key generation.

	=item B<OSSL_TRACE_CATEGORY_PKCS12_KEYGEN>

	Traces PKCS#12 key generation.

	=item B<OSSL_TRACE_CATEGORY_PKCS12_DECRYPT>

	Traces PKCS#12 decryption.

	=item B<OSSL_TRACE_CATEGORY_X509V3_POLICY>

	Traces X509v3 policy processing.

	More precisely, this generates the complete policy tree at various
	point during evaluation.

	=item B<OSSL_TRACE_CATEGORY_BN_CTX>

	Traces BIGNUM context operations.

	=item B<OSSL_TRACE_CATEGORY_CONF>

	Traces details about the provider and engine configuration.

	=back

	There is also B<OSSL_TRACE_CATEGORY_ALL>, which works as a fallback
	and can be used to get I<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.

	=head1 RETURN VALUES

	OSSL_trace_set_channel(), OSSL_trace_set_prefix(),
	OSSL_trace_set_suffix(), and OSSL_trace_set_callback() return 1 on
	success, or 0 on failure.

	=head1 EXAMPLES

	In all examples below, the trace producing code is assumed to be
	the following:

	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);

	=head2 Simple example

	An example with just a channel and constant prefix / suffix.

	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]

	=head2 Advanced example

	This example uses the callback, and depends on pthreads functionality.

	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

	=head1 NOTES

	=head2 Configure Tracing

	By default, the OpenSSL library is built with tracing disabled. To
	use the tracing functionality documented here, it is therefore
	necessary to configure and build OpenSSL with the 'enable-trace' option.

	When the library is built with tracing disabled, the macro
	B<OPENSSL_NO_TRACE> is defined in F<< <openssl/opensslconf.h> >> and all
	functions described here are inoperational, i.e. will do nothing.

	=head1 HISTORY

	OSSL_trace_set_channel(), OSSL_trace_set_prefix(),
	OSSL_trace_set_suffix(), and OSSL_trace_set_callback() were all added
	in OpenSSL 3.0.

	=head1 COPYRIGHT

	Copyright 2019-2022 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<https://www.openssl.org/source/license.html>.

	=cut