Failed to convert header keys to lower case due to field name conflict: x-request-id

stack":["Error: Failed to convert header keys to lower case due to field name conflict: x-request-id","    at /usr/src/node_modules/nock/lib/common.js:247:13","    at /usr/src/node_modules/nock/node_modules/lodash/lodash.js:4925:15","    at baseForOwn (/usr/src/node_modules/nock/node_modules/lodash/lodash.js:3010:24)","    at Function.forOwn (/usr/src/node_modules/nock/node_modules/lodash/lodash.js:13013:24)","    at Object.headersFieldNamesToLowerCase (/usr/src/node_modules/nock/lib/common.js:244:5)","    at RequestOverrider (/usr/src/node_modules/nock/lib/request_overrider.js:104:30)","    at new OverriddenClientRequest (/usr/src/node_modules/nock/lib/intercept.js:260:23)","    at /usr/src/node_modules/nock/lib/intercept.js:395:13","    at Object.module.request (/usr/src/node_modules/nock/lib/common.js:140:14)",

I saw there was a PR related to that? @gr2m

[gkatsanos]

We fixed it by just changing our code because and sticking with one casing for our requests. Fingers crossed it won’t fail elsewhere 😃 but indeed I don’t think nock should care about header casing or there should be an option a switch or a regexp we can use to accept both. An option ideally for case sensitive or insensitive headers. Or just what @krekkied suggested

[KrekkieD]

Checked it a bit more. It throws the error when the request has the same header name in different casing. Formally headers should be case insensitive, but technically it’s possible to send in the same header with different casing.

I’m not sure nock should be throwing errors when this occurs. I mean sure it’s not desirable to have the same header names on the consuming side (because which of the variations is the one that should be used…?), but it’ll complicate consuming nock if it throws errors on it.

Also an actual server would not error on it by default, which could mean nock shouldn’t either. I’m not sure if there are rules that state which of the headers should be used.

Maybe nock should use the first value instead:

var headersFieldNamesToLowerCase = function(headers) {
  if(!_.isObject(headers)) {
    return headers;
  }

  //  For each key in the headers, delete its value and reinsert it with lower-case key.
  //  Keys represent headers field names.
  var lowerCaseHeaders = {};
  _.forOwn(headers, function(fieldVal, fieldName) {
    var lowerCaseFieldName = fieldName.toLowerCase();
    // use the value of the first occurrence of the header name
    if(!_.isUndefined(lowerCaseHeaders[lowerCaseFieldName])) {
      lowerCaseHeaders[lowerCaseFieldName] = fieldVal;
    }
  });

  return lowerCaseHeaders;
};

or the last;

var headersFieldNamesToLowerCase = function(headers) {
  if(!_.isObject(headers)) {
    return headers;
  }

  //  For each key in the headers, delete its value and reinsert it with lower-case key.
  //  Keys represent headers field names.
  var lowerCaseHeaders = {};
  _.forOwn(headers, function(fieldVal, fieldName) {
    var lowerCaseFieldName = fieldName.toLowerCase();
    // use the value of the last occurrence of the header name
    lowerCaseHeaders[lowerCaseFieldName] = fieldVal;
  });

  return lowerCaseHeaders;
};