Fastify wont capture body - fix proposed

[ddoice]

Fastify

When instrumenting a fastify server the captureBody option wont work, it seems that the function getContextFromRequest is not able to recover the body.

To Reproduce

Steps to reproduce the behavior:

1. Start the fastify server
2. Then call some endpoint (tried both with and without error)
3. Check kibana APM module and look for that transaction

Expected behavior

To have the body available in the transaction.

Environment (please complete the following information)

• OS: Linux
• Node.js version: 18.14.2
• APM Server version: 7.6.1
• Agent version: 3.43.0
• Fastify version 4.13.0

How are you starting the agent? (please tick one of the boxes)

• Calling agent.start() directly (e.g. require('elastic-apm-node').start(...))
• Requiring elastic-apm-node/start from within the source code
• Starting node with -r elastic-apm-node/start

Additional context

Agent config options:

Click to expand

    serverUrl: 'http://localhost:8200',
    logLevel: 'trace',
    verifyServerCert: false,
    captureBody: 'all',

package.json dependencies:

Click to expand

    "@fastify/sensible": "5.2.0",
    "@fastify/swagger": "8.3.1",
    "@fastify/swagger-ui": "1.5.0",
    "@prisma/client": "4.10.1",
    "@types/pg": "8.6.6",
    "elastic-apm-node": "^3.43.0",
    "fastify": "4.13.0",
    "fastify-plugin": "4.5.0",
    "fluent-json-schema": "4.1.0",
    "pg": "8.10.0"

[ddoice]

Looks like fastify wont expose the body in the onRequest hook.

fastify/fastify#1546

I managed a way to fix it, but to be honest I do not have sufficient knowledge of the APM internals to know if this is a good idea, looks a bit hacky to me.

This is the hook that I have added, and with it the body is captured.

ddoice/apm-agent-nodejs@main...ddoice:apm-agent-nodejs:fix/missing-captured-body-with-fastify

[trentm]

@ddoice Thanks very much for the issue and the patch and my apologies for taking so long to respond. There was an old PR to do almost exactly this that had languished (partly my fault). #2681 I think that will solve the issue for you. I am hoping to get that PR merged very soon. I'll update this issue when that is done.