Debug Tags¶
Use the API macro
Dbg(ctl, const char *format_str, ...)
to add
traces in your plugin. In this macro:
ctl
is the Traffic Server parameter that enables Traffic Server to print outformat_str
. It is an instance of the classDbgCtl
....
are variables forformat_str
in the standardprintf
style.
The DbgCtl
control is enabled when debug output is
enabled globally by configuration, and tag
matches a configured
regular expression.
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):
records:
diags:
debug:
enabled: 1
tags: debug-tag-name
In this case, debug output goes to traffic.out
.
The statement "Starting my-plugin at <time>"
appears whenever you
run Traffic Server with the my-plugin
tag:
traffic_server -T"my-plugin"
Example:
namespace
{
DbgCtl my_dbg_ctl{"my-plugin"}; // Non-local variable.
}
...
Dbg(my_dbg_ctl, "Starting my-plugin at %d", the_time);
...
Dbg(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 eventsdns
- DNS operationshostdb
- Host name lookupiocore_net
- Socket and low level IO (very voluminous)socket
- socket operationsssl
- SSL related eventscache
- Cache operations (many subtags, examine the output to narrow the tag set)cache_update
- Cache updates including writescache_read
- Cache read events.dir_probe
- Cache searches.sdk
- gives some warning concerning API usage.