@instana/core/src/tracing/instrumentation/frameworks/fastify.js

Core library for Instana's Node.js packages

/*
 * (c) Copyright IBM Corp. 2021
 * (c) Copyright Instana Inc. and contributors 2018
 */

'use strict';

const hook = require('../../../util/hook');
const httpServer = require('../protocols/httpServer');
const cls = require('../../cls');

let logger;
let active = false;

exports.activate = function activate() {
  active = true;
};

exports.deactivate = function deactivate() {
  active = false;
};

exports.init = function init(config) {
  logger = config.logger;
  hook.onModuleLoad('fastify', instrument);
};

/**
 * Fastify is auto instrumend by our http server instrumention.
 *
 * In this instrumentation, we want to capture extra data on top.
 * We register a custom hook via the framework API and add this data to the
 * target http entry span.
 *
 * See https://www.fastify.io/docs/latest/Hooks
 */
function instrument(build) {
  if (typeof build !== 'function') {
    return build;
  }

  // copy further exported properties
  Object.keys(build).forEach(k => {
    overwrittenBuild[k] = build[k];
  });

  return overwrittenBuild;

  function overwrittenBuild() {
    const app = build.apply(this, arguments);

    // NOTE: all major versions support `addHook` - this is just a safe protection
    if (!app.addHook) {
      logger.warn('Instana was not able to instrument Fastify. The instrumention of http requests is still working.');
      return app;
    }

    app.addHook('onRequest', function onRequest(request, reply, done) {
      try {
        // NOTE: v1 uses _context https://github.com/fastify/fastify/blob/1.x/fastify.js#L276
        //       v2/v3/v4 uses context https://github.com/fastify/fastify/blob/2.x/test/handler-context.test.js#L41
        //       v5 uses reply.routeOptions and no longer exposes `.context`
        //       https://fastify.dev/docs/latest/Guides/Migration-Guide-V5/#streamlined-access-to-route-definition
        let url;

        if (reply?.routeOptions?.config?.url) {
          url = reply.routeOptions.config.url;
        } else {
          url = reply._context ? reply._context.config.url : reply.context.config.url;
        }

        annotateHttpEntrySpanWithPathTemplate(app, url);
      } catch (err) {
        logger.warn(
          'Instana was not able to retrieve the path template. The instrumention of http requests is still working.'
        );
      }

      done();
    });

    return app;
  }
}

/**
 * A request comes in GET /foo/22
 * We want to trace GET /foo/:id
 */
function annotateHttpEntrySpanWithPathTemplate(app, url) {
  if (!active) {
    return;
  }

  const span = cls.getCurrentEntrySpan();
  if (!span || span.n !== httpServer.spanName || span.pathTplFrozen) {
    return;
  }

  const basePathDescriptor = Object.getOwnPropertyDescriptor(app, 'basePath');
  const basePathOrPrefix = basePathDescriptor && basePathDescriptor.get ? app.prefix : app.basePath;
  span.data.http.path_tpl = (basePathOrPrefix || '') + (url || '/');
}