Debugging Hooks

How can I debug a Hook?

The Hook API provides a set of functions in the namespace trace which write output to the xrpld log file when xrpld is configured with the trace log-level. These functions, generally speaking, allow you to see the value of variables, buffers and otherwise trace the execution and state of a Hook at runtime.

Trace APIs

The following trace functions are available in the Hooks API

Hook API	What it does
trace	Print a utf-8 message, followed by a user-specified buffer (this last optionally as hex.)
trace_num	Print a utf-8 message, followed by an integer.
trace_float	Print a utf-8 message, followed by an XFL Floating point number.

Example

The following code will print a single trace line then accept the Originating Transaction.

#include "../hookapi.h"
int64_t hook(int64_t reserved)
{
  trace_num(SBUF("A number"), 10);
  accept(0,0,0);
  return 0;
}

An example of the log-line produced by xahaud when a payment is sent out of or into the Hook Account:

2021-Apr-13 13:59:11.083700726 UTC View:TRC
    HookTrace[rHb9CJAWyB4rj91VRWn96DkukG4bwdtyTh-rE3SfnjwfzZFL3JK9cLVfJuy8Ar1XnCqPw]:
        A number 10

The above appears in the log as all-one-line, but split here for visibility.

Log format

A breakdown of the log format appears in the table below

Part	Description	#
2021-Apr-13 13:59:11.083700726 UTC View:TRC	`xahaud`’s prefix to the log line	1
HookTrace	This is a trace initiated by the Hook itself not some other information about the Hook. Other information is available on tags `HookError`, `HookEmit` and `HookInfo`.	2
[rHb9CJAWyB4rj91VRWn96DkukG4bwdtyTh	The first account in the square brackets is the Hook Account.	3
-rE3SfnjwfzZFL3JK9cLVfJuy8Ar1XnCqPw]:	The second account in the square brackets is the Originating Account.	4
A number	This is the message the Hook was told to deliver before the trace payload	5
10	This is the trace payload	6