Support ETag and Last-Modified in Response

[sdavids]

Docker Image used: 6c07143937e57095d8478efc8ab7eab52b44e67c7673285f8c0a2bf4a7b137ad

openapi: 3.0.3
info:
  title: test
  version: '1.0'
servers:
  - url: 'http://localhost:8000'
paths:
  /test:
    get:
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                type: object
                properties:
                  ok:
                    type: boolean
                    default: 'true'
              examples:
                a:
                  value:
                    ok: true
          headers:
            ETag:
              schema:
                type: string
              example: '"c561c68d0ba92bbeb8b0f612a9199f722e3a621a"'
            Last-Modified:
              schema:
                type: string
              example: Mon, 18 Jul 2016 02:36:04 GMT

Will return:

HTTP/1.1 200 OK
Access-Control-Allow-Origin: *
Content-Type: application/json
Etag: string
Last-Modified: string
Date: Thu, 23 Apr 2020 22:38:43 GMT
Content-Length: 16

Either the example values should be provided or (better) real values should be generated.

[sdavids]

This is related to #46.

In the case of:

ETag:
  schema:
    type: string
Last-Modified:
  schema:
    type: string

The output would preferably be:

Etag: ${eTag}
Last-Modified: ${lastModified}

with

const serverStartup = new Date();

// ...

const lastModified = `${serverStartup}`;
const eTag = `"${serverStartup.getTime()}"`;

instead of

Etag: string
Last-Modified: string

You might even return those 2 headers regardless of their inclusion in the OpenAPI file.

[cboitel]

i would use serverStartup only if examples are not provided: after all, apisprout is all about serving examples