---
c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
SPDX-License-Identifier: curl
Title: curl_global_trace
Section: 3
Source: libcurl
See-also:
  - curl_global_init (3)
  - libcurl (3)
Protocol:
  - All
---

# NAME

curl_global_trace - Global libcurl logging configuration

# SYNOPSIS

~~~c
#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 program. It
does not have to be. It can be called several times even, possibly 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_version_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 initialize
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silently ignored, outdated log configurations does not cause errors when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 logging
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 an 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.

## `doh`

Tracing of DNS-over-HTTP operations to resolve hostnames.

# EXAMPLE

~~~c
int main(void)
{
  /* 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 configuration
may not have any effects or may only been applied partially.
