This implements a new debug/trace infrastructure based on a slightly
hacked up logger. Instead of the traditional "if debug { ... }" I've
rewritten the logger to have no-op Debugln and Debugf, unless debugging
has been enabled for a given "facility". The "facility" is just a
string, typically a package name.
This will be slightly slower than before; but not that much as it's
mostly a function call that returns immediately. For the cases where it
matters (the Debugln takes a hex.Dump() of something for example, and
it's not in a very occasional "if err != nil" branch) there is an
l.ShouldDebug(facility) that is fast enough to be used like the old "if
debug".
The point of all this is that we can now toggle debugging for the
various packages on and off at runtime. There's a new method
/rest/system/debug that can be POSTed a set of facilities to enable and
disable debug for, or GET from to get a list of facilities with
descriptions and their current debug status.
Similarly a /rest/system/log?since=... can grab the latest log entries,
up to 250 of them (hardcoded constant in main.go) plus the initial few.
Not implemented in this commit (but planned) is a simple debug GUI
available on /debug that shows the current log in an easily pasteable
format and has checkboxes to enable the various debug facilities.
The debug instructions to a user then becomes "visit this URL, check
these boxes, reproduce your problem, copy and paste the log". The actual
log viewer on the hypothetical /debug URL can poll regularly for new log
entries and this bypass the 250 line limit.
The existing STTRACE=foo variable is still obeyed and just sets the
start state of the system.
Integers are for numbers, enabling arithmetic like subtractions and for
loops without getting shot in the foot. Unsigneds are for bitfields.
- "int" for numbers that will always be laughably smaller than four
billion, and where we don't care about the serialization format.
- "int32" for numbers that will always be laughably smaller than four
billion, and will be serialized to four bytes.
- "int64" for numbers that may approach four billion or will be
serialized to eight bytes.
- "uint32" and "uint64" for bitfields, depending on required number of
bits and serialization format. Likewise "uint8" and "uint16", although
rare in this project since they don't exist in XDR.
- "int8", "int16" and plain "uint" are almost never useful.
This change makes sure that things work smoothly when "we" are a newer
version than our peer and have more fields in our messages than they do.
Missing fields will be left at zero/nil.
(The other side will ignore our extra fields, for the same effect.)
