Adding diagnostics channels to Fetch #2701
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With the addition of the try block the indentations were necessary, excluding them the commit will result in lint errors. |
Yes, I can add the finally to the promise, though the initial start event is placed in the first try block |
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Can you resolve the conflicts with |
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@mcollina conflicts have been resolved 👍🏼 |
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Since your work started, we have migrated the tests to |
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My proposed suggestion would migrate the test from tap to node:test ;) |
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@Uzlopak committed the changes, thanks for that! |
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Interesting. The unit fests found a valid bug. |
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Thanks for the great work and keeping up with us! |
| @@ -135,114 +191,115 @@ function fetch (input, init = undefined) { | |||
| try { | |||
| requestObject = new Request(input, init) | |||
| } catch (e) { | |||
| p.reject(e) | |||
| return p.promise | |||
| return Promise.reject(e) | |||
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@tsctx I am not sure what you mean by this, can you elaborate?
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new Promise((_, reject) => reject(v)) is rejected synchronously, while Promise.reject(v) is rejected asynchronously (after one microtask). It must be rejected synchronously as per the spec.
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looking forward to this :) |
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@tsctx ptal |
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Please answer this. #2701 (comment) |
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This looks cool, should we not maybe prefix the new channel with Also looking at the code it looks like we don't capture the start of fetching when it actually occurs? As in we perform all the trace calls when the promise is settled. |
@tsctx Which document are you referring to? |
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@tsctx ptal
This PR changes around 80 lines of code in the actual algorithm. It doesn't seem this is making |
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@jasnell can you take a quick look too? |
| @@ -114,6 +122,75 @@ if (undiciDebugLog.enabled || fetchDebuglog.enabled) { | |||
| isClientSet = true | |||
| } | |||
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| // Track fetch requests | |||
| if (fetchDebuglog.enabled && diagnosticsChannel.tracingChannel) { | |||
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Shouldn't this code be placed by users instead of having a helper inside undici core?
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| // subscribersCheck will be called at the beginning of the fetch call | ||
| // and will check if we have subscribers | ||
| function subscribersCheck () { |
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AFAIK tracingChannel.hasSubscribers will do all these checks for you. No need to do it manually.
https://github.com/nodejs/node/blob/main/lib/diagnostics_channel.js#L280
cc: @Qard
| if (hasSubscribers) { | ||
| const context = { req, input, init, result: null, error: null } | ||
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| return channels.start.runStores(context, () => { |
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Shouldn't it run traceSync or tracePromise instead?
cc: @Qard
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It absolutely will make maintaining fetch harder. |
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How? For the most part this is just an indentation level change. |
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It's not the code itself, it's how intrusive it is. We are taking a web spec and shoving node-specific things into it, things that are not entirely compatible with the spec (I assume that's why you said "for the most part"). There are steps that are rewritten and things added to fetch itself. Every, every single time we have even slightly deviated from the spec it always comes back to bite us in the ass later on, even the smallest change to the spec makes maintaining it harder. I can find specific examples but I hope you'll trust me on that... |
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@crysmags I think it could be implemented with fewer changes. In the way... tsctx@56c36f7 |
Documentation of how to use the added debuglog's. |
This relates to...
This is a follow up to a previous PR [Added diagnostics channels on fetch] (#2210) , this includes [proposed changes] (#2210 (comment)) to emit the start event synchronously at the beginning of the function, and emit the end event right before returning, on all paths.
Rationale
We added five diagnostics channels on fetch to trace the same information as would tracingChannel.tracePromise. Some channels won't make perfect sense but we want to stay consistent with TracingChannel as we want to use it to trace fetch and maybe other functions when TracingChannel become available in the most commonly used versions of node.js. The descriptions of each channel and what gets published to them are detailed in DiagnosticsChannel.md
Use case: enable APM tools to trace fetch
Changes
Added diagnostics channel to fetch
Added tests to diagnostics channel for fetch
Status