libcurl-env-dbg(3) Introduction to Library Functions libcurl-env-dbg(3)

NAME

libcurl-env-dbg - environment variables libcurl DEBUGBUILD
understands

DESCRIPTION

This is a set of variables only recognized and used if libcurl was
built "debug enabled", which should never be true for a library used
in production. These variables are intended for internal use only,
subject to change and have many effects on the behavior of libcurl.
Refer to the source code to determine how exactly they are being
used.

CURL_ALTSVC_HTTP
Bypass the AltSvc HTTPS protocol restriction if this variable
exists.

CURL_DBG_SOCK_RBLOCK
The percentage of recv() calls that should be answered with a
EAGAIN at random. For TCP/UNIX sockets.

CURL_DBG_SOCK_RMAX
The maximum data that shall be received from the network in
one recv() call. For TCP/UNIX sockets. This is applied to
every recv.

Example: CURL_DBG_SOCK_RMAX=400 means recv buffer size is
limited to a maximum of 400 bytes.

CURL_DBG_SOCK_WBLOCK
The percentage of send() calls that should be answered with a
EAGAIN at random. For TCP/UNIX sockets.

CURL_DBG_SOCK_WPARTIAL
The percentage of data that shall be written to the network.
For TCP/UNIX sockets. This is applied to every send.

Example: CURL_DBG_SOCK_WPARTIAL=80 means a send with 1000
bytes would only send 800.

CURL_DBG_QUIC_WBLOCK
The percentage of send() calls that should be answered with
EAGAIN at random. QUIC only.

CURL_DEBUG
Trace logging behavior as an alternative to calling
curl_global_trace(3).

Example: CURL_DEBUG=http/2 means trace details about HTTP/2
handling.

In the curl command line tool, built with --enable-debug, this
environment variable adds to arguments like --verbose, -vvv.
At least a single -v is needed to make the run emit trace
output, but when it does, the contents of CURL_DEBUG are added
and can override existing options.

Example: CURL_DEBUG=tcp,-http/2 curl -vv url means trace
protocol details, triggered by -vv, add tracing of TCP in
addition and remove tracing of HTTP/2.

CURL_DEBUG_SIZE
Fake the size returned by CURLINFO_HEADER_SIZE and
CURLINFO_REQUEST_SIZE.

CURL_GETHOSTNAME
Fake the local machine's unqualified hostname for NTLM and
SMTP.

CURL_HSTS_HTTP
Bypass the HSTS HTTPS protocol restriction if this variable
exists.

CURL_FORCETIME
A time of 0 is used for AWS signatures and NTLM if this
variable exists.

CURL_ENTROPY
A fixed faked value to use instead of a proper random number
so that functions in libcurl that are otherwise getting random
outputs can be tested for what they generate.

CURL_SMALLREQSEND
An alternative size of HTTP data to be sent at a time only if
smaller than the current.

CURL_SMALLSENDS
An alternative size of socket data to be sent at a time only
if smaller than the current.

CURL_TIME
Fake Unix timestamp to use for AltSvc, HSTS and CURLINFO
variables that are time related.

This variable can also be used to fake the data returned by
some CURLINFO variables that are not time-related (such as
CURLINFO_LOCAL_PORT), and in that case the value is not a
timestamp.

CURL_TRACE
LDAP tracing is enabled if this variable exists and its value
is 1 or greater.

OpenLDAP tracing is separate. Refer to CURL_OPENLDAP_TRACE.

CURL_OPENLDAP_TRACE
OpenLDAP tracing is enabled if this variable exists and its
value is 1 or greater. There is a number of debug levels,
refer to openldap.c comments.

CURL_WS_CHUNK_SIZE
Used to influence the buffer chunk size used for WebSocket
encoding and decoding.

CURL_WS_CHUNK_EAGAIN
Used to simulate blocking sends after this chunk size for
WebSocket connections.

CURL_FORBID_REUSE
Used to set the CURLOPT_FORBID_REUSE flag on each transfer
initiated by the curl command line tool. The value of the
environment variable does not matter.

CURL_GRACEFUL_SHUTDOWN
Make a blocking, graceful shutdown of all remaining
connections when a multi handle is destroyed. This implicitly
triggers for easy handles that are run via easy_perform. The
value of the environment variable gives the shutdown timeout
in milliseconds.

SEE ALSO

libcurl-env(3)

libcurl 2025-02-25 libcurl-env-dbg(3)