Added OpenApi spec

openapi.yaml

+openapi: 3.0.2
+info:
+  title: Mailer service
+  version: 0.2.0
+
+paths:
+  /{template}:
+    post:
+      summary: Send message with specified template
+      parameters:
+        - name: template
+          in: path
+          description: Template name
+          schema:
+            type: string
+            required: true
+      requestBody:
+        description: Message to be sent
+        required: true
+        content:
+          application/json:
+            schema:
+              type: object
+              required: true
+              properties:
+                to:
+                  description: Recipient's address
+                  type: string
+                  format: email
+                  required: true
+                subject:
+                  description: Message subject
+                  type: string
+                  required: true
+                vars:
+                  description: Map between variables used in template and their values
+                  type: object
+                  required: false
+                  default: {}
+            example:
+              {
+                "to": "john.doe@example.com",
+                "subject": "Hello John!",
+                "vars": {
+                  "name": "John Doe"
+                }
+              }
+      responses:
+        200:
+          description: Message has been sent to server
+          content:
+            application/json:
+              schema:
+                description: Result of sending
+                type: object
+                required: true
+                properties:
+                  messageId:
+                    description: Most servers *should* return the final Message-Id value used
+                    type: string
+                  accepted:
+                    description: Recipients' addresses that were accepted by server
+                    type: array
+                    items:
+                      description: Recipient's address
+                      type: string
+                  rejected:
+                    description: Recipients' addresses that were rejected by server
+                    type: array
+                    items:
+                      description: Recipient's address
+                      type: string
+                  message:
+                    description: Sent message
+                    type: object
+                    properties:
+                      from:
+                        description: Sender's address
+                        type: string
+                        format: email
+                      to:
+                        description: Recipient's address
+                        type: string
+                        format: email
+                      subject:
+                        description: Message subject
+                        type: string
+                      html:
+                        description: Sent message text, specified template compiled with provided variables
+                        type: string
+              example:
+                {
+                  "messageId": "<b6cb2a56-03b3-e782-acaf-480865b8d8b5@example.com>",
+                  "accepted": ["john.doe@example.com"],
+                  "rejected": [],
+                  "message": {
+                   "from": "mail@example.com",
+                   "to": "john.doe@example.com",
+                   "subject": "Hello John!",
+                   "html": "Hello John Doe!"
+                  }
+                }
+        400:
+          description: Invalid template name or parameters