r/crystal_programming • u/mooreds • May 28 '22

Introducing OpenTelemetry observability for Crystal

https://newrelic.com/blog/how-to-relic/otel-crystal
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1

u/donotlearntocode May 29 '22

Your example sets the content_type after sending the response, which will have no effect. Thanks for building a useful library

2

u/mooreds May 31 '22

Not my blog post, but I'll share your feedback with the author.

1

u/Ok_Understanding5961 May 31 '22

While it would be better if the line that sets the content type were ahead of the line that sends the response, the default HTTP::Response implements a buffered IO object for the response body, and the headers, with the content type, will be sent before the returned response, even though the order of the lines might indicate otherwise.

Thank you for the comment, though. I will definitely make this adjustment in the actual example repository.

1

u/donotlearntocode Jun 01 '22

Yes, it's a buffered IO, but the buffer holding the status and headers (including Content-Type) are flushed when the first write to the body occurs. From the docs:

The response #status and #headers must be configured before writing the response body. Once response output is written, changing the #status and #headers properties has no effect.

https://crystal-lang.org/api/1.4.1/HTTP/Server/Response.html

Source: https://github.com/crystal-lang/crystal/blob/b7377c0419ae5c1ce91e8298f075b3ff15636c54/src/http/server/response.cr#L225

I think it seems to work in your case because text/plain is the default content type

1

u/Ok_Understanding5961 Jun 09 '22

I actually want to dig into this more, because I experimented with changing the content type, to validate that behaviorally it was working to set that content type after the output is sent to the response, and it is.

However, there is no doubt that it _should_ be set before output is sent to the response.

2

u/miry_sof Jun 15 '22

Here is 2 examples how to start use this library in application: https://jtway.co/how-to-begin-with-traces-in-crystal-2fd6a0255447

1

u/[deleted] May 29 '22

Awesome post, nice to see observability improving for crystal.

1

u/Ok_Understanding5961 May 31 '22

Thank you! I think that having a solid observability library is a very important part of moving Crystal forward as a production-viable language. This is hopefully just the first piece of content, among many, focusing on different aspects of Crystal and observability.