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curl_global_trace(3) libcurl curl_global_trace(3)
NAME
curl_global_trace - Global libcurl logging configuration
SYNOPSIS
#include <curl/curl.h>
CURLcode curl_global_trace(const char *config);
DESCRIPTION
This function configures the logging behavior, allowing to make some
parts of curl more verbose or silent than others.
This function may be called during the initialization phase of a pro-
gram. It does not have to be. It can be called several times even, pos-
sibly overwriting settings of previous calls.
Calling this function after transfers have been started is undefined.
On some platforms/architectures it might take effect, on others not.
This function is thread-safe since libcurl 8.3.0 if curl_ver-
sion_info(3) has the CURL_VERSION_THREADSAFE feature bit set (most
platforms).
If this is not thread-safe, you must not call this function when any
other thread in the program (i.e. a thread sharing the same memory) is
running. This does not just mean no other thread that is using
libcurl. Because curl_global_init(3) may call functions of other
libraries that are similarly thread unsafe, it could conflict with any
other thread that uses these other libraries.
If you are initializing libcurl from a Windows DLL you should not ini-
tialize it from DllMain or a static initializer because Windows holds
the loader lock during that time and it could cause a deadlock.
The config string is a list of comma-separated component names. Names
are case-insensitive and unknown names are ignored. The special name
"all" applies to all components. Names may be prefixed with '+' or '-'
to enable or disable detailed logging for a component.
The list of component names is not part of curl's public API. Names may
be added or disappear in future versions of libcurl. Since unknown
names are silently ignored, outdated log configurations does not cause
errors when upgrading libcurl. Given that, some names can be expected
to be fairly stable and are listed below for easy reference.
Note that log configuration applies only to transfers where debug log-
ging is enabled. See CURLOPT_VERBOSE(3) or CURLOPT_DEBUGFUNCTION(3) on
how to control that.
TRACE COMPONENTS
tcp Tracing of TCP socket handling: connect, reads, writes.
ssl Tracing of SSL/TLS operations, whichever SSL backend is used in
your build.
http/2 Details about HTTP/2 handling: frames, events, I/O, etc.
http/3 Details about HTTP/3 handling: connect, frames, events, I/O etc.
http-proxy
Involved when transfers are tunneled through a HTTP proxy.
"h1-proxy" or "h2-proxy" are also involved, depending on the
HTTP version negotiated with the proxy.
In order to find out all components involved in a transfer, run
it with "all" configured. You can then see all names involved in
your libcurl version in the trace.
EXAMPLE
/* log details of HTTP/2 and SSL handling */
curl_global_trace("http/2,ssl");
/* log all details, except SSL handling */
curl_global_trace("all,-ssl");
Below is a trace sample where "http/2" was configured. The trace output
of an enabled component appears at the beginning in brackets.
* [HTTP/2] [h2sid=1] cf_send(len=96) submit https://example.com/
* [HTTP/2] [h2sid=1] FRAME[HEADERS]
* [HTTP/2] [h2sid=1] 249 header bytes
AVAILABILITY
Added in 8.3
RETURN VALUE
If this function returns non-zero, something went wrong and the config-
uration may not have any effects or may only been applied partially.
SEE ALSO
curl_global_init(3), libcurl(3)
libcurl 8.4.0 September 26, 2023 curl_global_trace(3)
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