Overall code structure

This directory imports the "printf" logic as-is from the Go standard library and instruments it for redaction of sensitive data.

Overall, the original Go code is structured as follows:

• the top-level API functions (Printf Fprintf etc) instantiate a "printer" struct called pp, then call the doPrint*() methods on it.

• the pp contains a byte slice (pp.buf, type buffer) that accumulates the result of formatting regardless of the final output of the API - i.e. a buffer is used even when using Fprint to an io.Writer. Only after the doPrint() method finishes, is the buffer copied to the final io.Writer in the Fprint* variants.

• each of the doPrint methods does some analysis on the argument list - quite simple for e.g. doPrintln, more intricate for doPrintf. As part of the analysis it emits "spacing" or no-op bytes directly on the pp.buf. For example doPrint emits spaces between arguments directly, doPrintf emits the non-formatting characters from the format string, as well as certain constant error strings (e.g. %(BADPREC)).

Refreshing the sources

The files in this directory have been imported from

$GOROOT/src/fmt/{format,print}.go

and

$GOROOT/src/internal/fmtsort

And patched using the included .diff files.

To upgrade to a newer Go implementation, import the files anew and re-apply the patches.

See the script refresh.sh for details.