Debug Tags

Use the API macro TSDbg(ctlptr, const char *format_str, ...) to add traces in your plugin. In this macro:

  • ctlptr is the Traffic Server parameter that enables Traffic Server to print out format_str. It is returned by TSDbgCtlCreate().

  • ... are variables for format_str in the standard printf style.

TSDbgCtlCreate (const char *tag) returns a (const) pointer to TSDbgCtl. The TSDbgCtl control is enabled when debug output is enabled globally by configuration, and tag matches a configured regular expression.

TSDbgCtlDestroy (TSDbgCtl const *dbg_ctl) destroys a debug control created by TSDbgCtlCreast().

The deprecated API void TSDebug (const char *tag, const char *format_str, ...) also outputs traces. In this API:

  • tag is the Traffic Server parameter that enables Traffic Server to print out format_str

  • ... are variables for format_str in the standard printf style.

Use of TSDebug() causes trace output to have a more negative impact on proxy throughput.

Run Traffic Server with the -Ttag option. For example, if the tag is my-plugin, then the debug output goes to traffic.out.See below:

traffic_server -T"my-plugin"

Sets the following variables in records.yaml (in the Traffic Server config directory):

CONFIG proxy.config.diags.debug.enabled INT 1
CONFIG proxy.config.diags.debug.tags STRING debug-tag-name

(Performance will be better if enabled is set to 3 rather than 1, but, using 3, output from TSDebug() will not be enabled, only from TSDbg().) In this case, debug output goes to traffic.out.

Example:

static TSDbgCtl const *my_dbg_ctl; // Non-local variable.
...
my_dbg_ctl = TSDbgCtlCreate("my-plugin"); // In TSPluginInit() or TSRemapInit().
...
TSDbg(my_dbg_ctl, "Starting my-plugin at %d", the_time);
...
TSDbg(my_dbg_ctl, "Later on in my-plugin");
...
TSDbgCtlDestroy(my_dbg_ctl);

The statement "Starting my-plugin at <time>" appears whenever you run Traffic Server with the my-plugin tag:

traffic_server -T"my-plugin"

If your plugin is a C++ plugin, the above example can be written as:

#include <tscpp/api/Cleanup.h>
...
static TSDbgCtlUniqPtr my_dbg_ctl_guard{TSDbgCtlCreate("my-plugin")}; // Non-local variable.
TSDbgCtl const * const my_dbg_ctl{my_dbg_ctl_guard.get()}; // Non-local variable.
...
TSDbg(my_dbg_ctl, "Starting my-plugin at %d", the_time);
...
TSDbg(my_dbg_ctl, "Later on in my-plugin");

Other Useful Internal Debug Tags

Embedded in the base Traffic Server code are many debug tags for internal debugging purposes. These can also be used to follow Traffic Server behavior for testing and analysis.

The debug tag setting (-T and proxy.config.diags.debug.tags) is a anchored regular expression (PCRE) against which the tag for a specific debug message is matched. This means the value “http” matches debug messages with the tag “http” but also “http_seq” and “http_trans”. If you want multiple tags then use a pipe symbol to separate the tags. For example “http_tproxy|dns|hostdb” will match any of the message tags “http_tproxy”, “dns”, “hostdb”, or “dns_srv” (but not “http_trans” nor “splitdns”).

Some of the useful HTTP debug tags are:

  • http_hdrs - traces all incoming and outgoing HTTP headers.

  • http_trans - traces actions in an HTTP transaction.

  • http_seq - traces the sequence of the HTTP state machine.

  • http_tproxy - transparency related HTTP events

  • dns - DNS operations

  • hostdb - Host name lookup

  • iocore_net - Socket and low level IO (very voluminous)

  • socket - socket operations

  • ssl - SSL related events

  • cache - Cache operations (many subtags, examine the output to narrow the tag set)

  • cache_update - Cache updates including writes

  • cache_read - Cache read events.

  • dir_probe - Cache searches.

  • sdk - gives some warning concerning API usage.