Add Performance Monitoring (transactions) support

[Hugo-C]

Hello, this PR add support for performance/transaction.
It requires sentry_transaction_sample_rate to be set with a value above 0, else transactions are not enabled.

A downside is that raw URI are used and so for a common route (with an id as parameter for example), transaction will not be aggregated. To fix it, we need to set the transaction name in the on_response callback as the routing is not yet done in on_request. But I didn't find a way to set a name to an existing transaction.
A solution might be to start a span in the on_request and then create later the transaction with sentry::continue_from_span. I didn't test it though.

Anyway let me know your thoughts and if there is anything you would like I change.

[intgr]

Hi! Thanks for the contribution. Sorry, the notification about this PR got lost among others.

This expands the scope of rocket-sentry beyond what I need it for (some background here). My knowledge of neither Rust nor Sentry are that strong.

Would you be interested in taking over the maintainership of this crate? I can still continue as a co-maintainer and help with reviews, if you want.

[intgr]

I imagine users may want to customize the transaction name. So possibly as a follow-up, it may make sense to provide a "request to transaction name" hook.

[Hugo-C]

I am not sure how it would looks like but nice idea. Some sentry sdk propose out of the box for transactions names to be returned as url or endpoint/function name. A custom hook could accomplish the same thing.

[intgr]

A downside is that raw URI are used and so for a common route (with an id as parameter for example), transaction will not be aggregated. To fix it, we need to set the transaction name in the on_response callback as the routing is not yet done in on_request. But I didn't find a way to set a name to an existing transaction.

A solution might be to start a span in the on_request and then create later the transaction with sentry::continue_from_span. I didn't test it though.

I agree, that's worth trying out and fixing.

But feel free to leave it to a follow-up PR.

[intgr]

Also README needs updating, this is no longer true:

Currently rocket-sentry is very basic, it only enables the Rust panic handler.
There is no integration with the Rocket request lifecycle.

• We should document which Transaction fields we fill.

[Hugo-C]

Hi! Thanks for the contribution. Sorry, the notification about this PR got lost among others.

This expands the scope of rocket-sentry beyond what I need it for (some background here). My knowledge of neither Rust nor Sentry are that strong.

Would you be interested in taking over the maintainership of this crate? I can still continue as a co-maintainer and help with reviews, if you want.

Hi, thanks for taking the time to review the PR.
I would gladly help maintaining the crate although I am not very proficient in Rust. But let's first try to merge this PR 😃 .

Also README needs updating, this is no longer true:

Currently rocket-sentry is very basic, it only enables the Rust panic handler.
There is no integration with the Rocket request lifecycle.

* [ ]  We should document which `Transaction` fields we fill.

I tried to list the transaction's fields. Let me know what you think of the changes.

[Hugo-C]

@intgr I have added headers as well as I have the need for it.
Once everything is good for you, I should probably squash the commits in a single one.

[intgr]

Sorry for so many rounds of back-and-forth, I don't feel very competent reviewing this stuff yet. :)

Once everything is good for you, I should probably squash the commits in a single one.

No need, I'll use GitHub's "squash and merge"

[intgr]

Thanks, looks good! Sorry again for procrastinating on this.

[Hugo-C]

Great ! Don't forget to release it on crates.io, so I can switch back to using the crate. Cheers!

[intgr]

@Hugo-C It's released! https://github.com/intgr/rocket-sentry/releases/tag/v0.16.0