---
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
Added-in: 8.3
---

# NAME

curl_global_trace - log configuration

# SYNOPSIS

~~~c
#include <curl/curl.h>

CURLcode curl_global_trace(const char *config);
~~~

# DESCRIPTION

This function configures the logging behavior 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silently ignored, outdated log configurations does not cause errors when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, sends, receives.

## `ssl`

Tracing of SSL/TLS operations, whichever SSL backend is used in your build.

## `ftp`

Tracing of FTP operations when this protocol is enabled 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.

## `dns`

Tracing of DNS operations to resolve hostnames and HTTPS records.

## `lib-ids`

Adds transfer and connection identifiers as prefix to every call to
CURLOPT_DEBUGFUNCTION(3). The format is `[n-m]` where `n` is the identifier
of the transfer and `m` is the identifier of the connection. A literal `x`
is used for internal transfers or when no connection is assigned.

For example, `[5-x]` is the prefix for transfer 5 that has no
connection. The command line tool `curl`uses the same format for its
`--trace-ids` option.

`lib-ids` is intended for libcurl applications that handle multiple
transfers but have no own way to identify in trace output which transfer
a trace event is connected to.

## `doh`

Former name for DNS-over-HTTP operations. Now an alias for `dns`.

## `multi`

Traces multi operations managing transfers' state changes and sockets poll
states.

## `read`

Traces reading of upload data from the application in order to send it to the
server.

## `ssls`

Tracing of SSL Session handling, e.g. caching/import/export.

## `smtp`

Tracing of SMTP operations when this protocol is enabled in your build.

## `write`

Traces writing of download data, received from the server, to the application.

## `ws`

Tracing of WebSocket operations when this protocol is enabled in your build.

# TRACE GROUPS

Besides the specific component names there are the following group names
defined:

## `all`

## `network`

All components involved in bare network I/O, including the SSL layer.

All components that your libcurl is built with.

## `protocol`

All components involved in transfer protocols, such as 'ftp' and 'http/2'.

## `proxy`

All components involved in use of proxies.

# %PROTOCOLS%

# 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%

# 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.
