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libcurl-env-dbg(3) Library Functions Manual 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.

Bypass the AltSvc HTTPS protocol restriction if this variable exists.
The percentage of recv() calls that should be answered with a EAGAIN at random. For TCP/UNIX sockets.
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.

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

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

Fake the size returned by CURLINFO_HEADER_SIZE and CURLINFO_REQUEST_SIZE.
Fake the local machine's unqualified hostname for NTLM and SMTP.
Bypass the HSTS HTTPS protocol restriction if this variable exists.
A time of 0 is used for AWS signatures and NTLM if this variable exists.
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.
An alternative size of HTTP data to be sent at a time only if smaller than the current.
An alternative size of socket data to be sent at a time only if smaller than the current.
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.

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

OpenLDAP tracing is separate. Refer to 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.
Used to influence the buffer chunk size used for WebSocket encoding and decoding.
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.
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)

2024-12-11 libcurl