JSON lines protocol

Unless --no-jsonl is given, the reconstruction programs report progress as JSON lines: one JSON object per line, written to stderr by default (see Progress output). forgeview and FORGE Studio both read this stream.

Every object has a type field.

Message types

type	Fields	Sent
start	app, version	Once, first
log	ts (ISO 8601 time), level (trace, debug, info, warn, error or critical), file, line, msg	For each log message at or above --log-level
progress	action, id, and more fields by action (below)	As stages start, advance and finish
metrics	bar_id, iter, error_norm, penalty, and in CUDA builds dev_free_mb, dev_total_mb	Once per conjugate gradient iteration
image_preview	bar_id, iter, planes	Once per iteration, from forgeSense, forgePcSense and forgePcSenseTimeSeg
exit	code	Once, last. code is the exit code.

progress

action	Extra fields
add	label, max: a new progress bar with this many steps
tick	current, postfix: the bar has reached step current. postfix is a short status such as iter 4/20 err=3.5e-02.
done	optional error: the bar is finished, with an error message if it failed

id identifies the bar. metrics and image_preview messages carry the id of the solver's bar in bar_id.

image_preview

planes is an array of objects with label (Image, Axial, Coronal or Sagittal), nx, ny and data. data is the base64 encoding of nx × ny 32-bit floats in the machine's byte order (little-endian on every supported platform), row-major, scaled to [0, 1]. 3D reconstructions send three orthogonal planes.

Example

{"type":"start","app":"forgeSense","version":"0.14.0"}
{"type":"progress","action":"add","id":0,"label":"PCG","max":20}
{"type":"progress","action":"tick","id":0,"current":1,"postfix":"iter 1/20 err=9.3618e-05"}
{"type":"metrics","bar_id":0,"iter":1,"error_norm":9.361785e-05,"penalty":0.000000e+00}
{"type":"progress","action":"done","id":0}
{"type":"exit","code":0}

Reading the stream

Lines that are not valid JSON can appear on the same stream, for example from a library that prints directly to stderr. forgeview shows them as plain log text, and other readers should skip them rather than stop.