express-opentracing/dist/middleware.js

opentracing middleware for express-js

"use strict";

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.default = middleware;

var _opentracing = require("opentracing");

var opentracing = _interopRequireWildcard(_opentracing);

var _url = require("url");

var url = _interopRequireWildcard(_url);

function _interopRequireWildcard(obj) { if (obj && obj.__esModule) { return obj; } else { var newObj = {}; if (obj != null) { for (var key in obj) { if (Object.prototype.hasOwnProperty.call(obj, key)) newObj[key] = obj[key]; } } newObj.default = obj; return newObj; } }

function middleware() {
  var options = arguments.length > 0 && arguments[0] !== undefined ? arguments[0] : {};

  var tracer = options.tracer || opentracing.globalTracer();

  return function (req, res, next) {
    var wireCtx = tracer.extract(opentracing.FORMAT_HTTP_HEADERS, req.headers);
    var pathname = url.parse(req.url).pathname;
    var span = tracer.startSpan(pathname, { childOf: wireCtx });
    span.logEvent("request_received");

    // include some useful tags on the trace
    span.setTag("http.method", req.method);
    span.setTag("span.kind", "server");
    span.setTag("http.url", req.url);

    // include trace ID in headers so that we can debug slow requests we see in
    // the browser by looking up the trace ID found in response headers
    var responseHeaders = {};
    tracer.inject(span, opentracing.FORMAT_TEXT_MAP, responseHeaders);
    Object.keys(responseHeaders).forEach(function (key) {
      return res.setHeader(key, responseHeaders[key]);
    });

    // add the span to the request object for handlers to use
    Object.assign(req, { span: span });

    // finalize the span when the response is completed
    var finishSpan = function finishSpan() {
      span.logEvent("request_finished");
      // Route matching often happens after the middleware is run. Try changing the operation name
      // to the route matcher.
      var opName = req.route && req.route.path || pathname;
      span.setOperationName(opName);
      span.setTag("http.status_code", res.statusCode);
      if (res.statusCode >= 500) {
        span.setTag("error", true);
        span.setTag("sampling.priority", 1);
      }
      span.finish();
    };
    res.on('close', finishSpan);
    res.on('finish', finishSpan);

    next();
  };
}