debugger: add edit-free runtime expression probes to node inspect#62713
debugger: add edit-free runtime expression probes to node inspect#62713joyeecheung wants to merge 3 commits intonodejs:mainfrom
node inspect#62713Conversation
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Add a non-interactive probe mode to `node inspect` for inspecting
runtime values in a run-to-completion application. This allows
users to perform printf-style debugging without having to modify
the application code and clean up afterwards, it also supports
structured output to be consumed by tools.
Probe mode launches the application, sets one or more source
breakpoints, evaluates one expression at each hit, and prints a
single text or JSON report when execution ends.
Interface:
node inspect [--json] [--preview] [--timeout=<ms>] [--port=<port>]
--probe <file>:<line>[:<col>] --expr <expr> ...
[--] <script> [args...]
Example:
```js
// cli.js
let maxRSS = 0;
for (let i = 0; i < 2; i++) {
const { rss } = process.memoryUsage();
maxRSS = Math.max(maxRSS, rss);
}
```
```
$ node inspect --probe cli.js:5 --expr 'rss' cli.js
Hit 1 at cli.js:5
rss = 54935552
Hit 2 at cli.js:5
rss = 55083008
Completed
```
(Prettified JSON to fit in commit message restrictions).
```js
$ node inspect --json --probe cli.js:5 --expr 'rss' cli.js
{"v":1,"probes":[{"expr":"rss","target":["cli.js",5]}],
"results":[
{"probe":0,"event":"hit","hit":1,
"result":{"type":"number","value":55443456,
"description":"55443456"}},
{"probe":0,"event":"hit","hit":2,
"result":{"type":"number","value":55574528,
"description":"55574528"}},
{"event":"completed"}]}
```
Signed-off-by: Joyee Cheung <joyeec9h3@gmail.com>
Codecov Report❌ Patch coverage is
Additional details and impacted files@@ Coverage Diff @@
## main #62713 +/- ##
==========================================
- Coverage 89.81% 89.64% -0.17%
==========================================
Files 699 706 +7
Lines 216379 218921 +2542
Branches 41366 41916 +550
==========================================
+ Hits 194340 196257 +1917
- Misses 14139 14571 +432
- Partials 7900 8093 +193
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This is really cool! Have we considered to use new line delimited JSON instead of a big JSON array as the primary output format? |
I feel that since we already have the text format for more readable output, the JSON format can be a bit more condensed since it's meant to be consumed by tools anyway? Using new-line delimited JSON would kind of force tools to be able to deal with that instead of just parsing it directly, and also not sure where the version field should go in that case, if we want to reuse the probes (because many hits can come from the same probe) they have to maintain some states to collect the probes first then collect the events, which means the tools all have to add specialized state management to parse it instead of just using whatever JSON parser they have. |
I was thinking about this less from a human readable perspective and more from an "incremental parsing by tools". But that can also be done by a (slightly more complicated) parser in the consuming tool. Starting with one big JSON blob is perfectly reasonable I think. The format flag is open to extension if anybody ever asks for something more incremental. 👍 |
|
@hybrist Thanks for the review, yeah I think we can leave an incremental output (or technically streaming output?) as a follow-up if it turns out to be useful. I fixed the linter issue, can you re-approve again? Thanks! |
3 participants
Add a non-interactive probe mode to
node inspectfor inspecting runtime values in a run-to-completion application. This allows users to perform printf-style debugging without having to modify the application code and clean up afterwards, it also supports structured output to be consumed by tools.This is proposed to be experimental first, so that we can iterate on the interface. There are a few features that would be nice to have but better left for follow-ups to avoid bloating the diff:
In this patch, probe mode launches the application, sets one or more source breakpoints, evaluates one expression at each hit, and prints a single text or JSON report containing all the evaluated values when execution ends.
Interface:
For example, to inspect a string in an application without modifying the source:
(Prettified JSON to fit in commit message restrictions).