Integrating Sentry and Elastic APM in Buffalo

Question

I am trying to integrate Elastic APM and Sentry into my website using Buffalo. The interesting files are as follows:

handlers/sentryHandler.go

package handlers

import (
    sentryhttp "github.com/getsentry/sentry-go/http"
    "github.com/gobuffalo/buffalo"
)

func SentryHandler(next buffalo.Handler) buffalo.Handler {
    handler := buffalo.WrapBuffaloHandler(next)
    sentryHandler := sentryhttp.New(sentryhttp.Options{})

    return buffalo.WrapHandler(sentryHandler.Handle(handler))
}

handlers/elasticAPMHandler.go

package handlers

import (
    "fmt"

    "github.com/gobuffalo/buffalo"
    "go.elastic.co/apm/module/apmhttp"
)

func ElasticAPMHandler(next buffalo.Handler) buffalo.Handler {
    fmt.Println("AAA")
    handler := apmhttp.Wrap(buffalo.WrapBuffaloHandler(next))
    return buffalo.WrapHandler(handler)
}

actions/app.go

package actions

import (
    "github.com/gobuffalo/buffalo"
    "github.com/gobuffalo/envy"
    forcessl "github.com/gobuffalo/mw-forcessl"
    paramlogger "github.com/gobuffalo/mw-paramlogger"
    "github.com/unrolled/secure"

    "my_website/handlers"
    "my_website/models"

    "github.com/gobuffalo/buffalo-pop/pop/popmw"
    csrf "github.com/gobuffalo/mw-csrf"
    i18n "github.com/gobuffalo/mw-i18n"
    "github.com/gobuffalo/packr/v2"
)

func App() *buffalo.App {
    if app == nil {
        app = buffalo.New(buffalo.Options{
            Env:         ENV,
            SessionName: "_my_website_session",
        })

        // Automatically redirect to SSL
        app.Use(forceSSL())

        // Catch errors and send them to Sentry.
        app.Use(handlers.SentryHandler)

        // Get tracing information and send it to Elastic.
        app.Use(handlers.ElasticAPMHandler)

        // Other Buffalo middleware stuff goes here...

        // Routing stuff goes here...
    }

    return app
}

The problem I'm running into is if I have the Sentry/APM handlers at the top, then I get errors like application.html: line 24: "showPagePath": unknown identifier. However, if I move it to just before I set up the routes, then I get a no transaction found error. So, I'm guessing that the handler wrappers are dropping the buffalo.Context information. So, what would I need to do to be able to integrate Sentry and Elastic in Buffalo asides from trying to reimplement their wrappers?

Answer 1

So, I'm guessing that the handler wrappers are dropping the buffalo.Context information.

That's correct. The problem is that buffalo.WrapHandler (Source) throws away all of the context other than the underlying http.Request/http.Response:

// WrapHandler wraps a standard http.Handler and transforms it
// into a buffalo.Handler.
func WrapHandler(h http.Handler) Handler {
    return func(c Context) error {
        h.ServeHTTP(c.Response(), c.Request())
        return nil
    }
}

So, what would I need to do to be able to integrate Sentry and Elastic in Buffalo asides from trying to reimplement their wrappers?

I can see two options:

• Reimplement buffalo.WrapHandler/buffalo.WrapBuffaloHandler to stop throwing away the buffalo.Context. This would involve storing the buffalo.Context in the underlying http.Request's context, and then pulling it out again on the other side instead of creating a whole new context.
• Implement Buffalo-specific middleware for Sentry and Elastic APM without using the Wrap* functions.

There's an open issue in the Elastic APM agent for the latter option: elastic/apm#39.