Your business needs you to generate an automated email report containing data from your app. In this example we will use the SendGrid web API to email a .csv file.

Get a SendGrid API key

First, you need to get a SendGrid API key. I'm not going to cover this in any more detail as there is plenty of documentation available on their website.

Once you have your API key, you can pass it into your app as an environment variable.

Set up the example data

We want to send some data in .csv format as an attachment. We are just using a list of maps in this case. However, in a real-world application, this could be data you get back from a database query. Here's the data.

(def data
  [{:name "Bob" :age 27 :favourite-food "bagels"}
   {:name "Sarah" :age 23 :favourite-food "apples"}
   {:name "John" :age 41 :favourite-food "pasta"}])

Next, we need a function to convert this data into csv format.

(defn escape-csv-value [value]
  (str "\"" value "\""))

(defn row->csv-row [row]
  (->> (map escape-csv-value row)
       (str/join ",")))

(defn ms->csv-string [ms]
  (let [columns (keys (first ms))
        headers (map name columns)
        rows    (map #(map % columns) ms)]
    (->> (into [headers] rows)
         (map row->csv-row)
         (str/join "\n"))))

Sendgrid Rest API

First lets look at the SendGrid Web API documentation. From the documentation, we can see that we need to make the following request.

POST https://api.sendgrid.com/v3/mail/send
content-type: application/json
Authorization: Bearer YOUR_API_KEY

{
  "personalizations": [
    {
      "to": [
        {
          "email": "john@example.com"
        }
      ],
      "subject": "Hello, World!"
    }
  ],
  "from": {
    "email": "from_address@example.com"
  },
  "content": [
    {
      "type": "text/plain",
      "value": "Hello, World!"
    }
  ]
  "attachements": [
    {
      "filename": "helloworld.csv",
      "content": "The Base64 encoded content of the attachment."
    }
  ]
}

Before we translate this request into Clojure, we need to be able to convert our csv string into a base64 encoded string. We can do this with java.util.Base64.

(defn encode-string-to-base64 [string]
  (.encodeToString
   (java.util.Base64/getEncoder)
   (.getBytes string)))

Finally, we write a function to make the request to the SendGrid API.

(defn send-email-with-csv [to-email csv-string]
  (http/post
   "https://api.sendgrid.com/v3/mail/send"
   {:headers      {:authorization
                   (str "Bearer "
                        (System/getenv "SENGRID_API_KEY"))}
    :content-type :json
    :form-params
    {:personalizations [{:to      [{:email to-email}]
                         :subject "Hello, World!"}]
     :from             {:email "from_address@exampl.com"}
     :content          [{:type  "text/plain"
                         :value "Hello, World!"}]
     :attachments
     [{:filename "helloworld.csv"
       :content  (encode-string-to-base64 csv-string)}]}}))

That's all there is to it. Here's all the code.

(ns clj-sendgrid-example.core
  (:require [clj-http.client :as http]
            [clojure.string :as str]))

(def data
  [{:name "Bob" :age 27 :favourite-food "bagels"}
   {:name "Sarah" :age 23 :favourite-food "apples"}
   {:name "John" :age 41 :favourite-food "pasta"}])

(defn escape-csv-value [value]
  (str "\"" value "\""))

(defn row->csv-row [row]
  (->> (map escape-csv-value row)
       (str/join ",")))

(defn ms->csv-string [ms]
  (let [columns (keys (first ms))
        headers (map name columns)
        rows    (map #(map % columns) ms)]
    (->> (into [headers] rows)
         (map row->csv-row)
         (str/join "\n"))))

(defn encode-string-to-base64 [string]
  (.encodeToString
   (java.util.Base64/getEncoder)
   (.getBytes string)))

(defn send-email-with-csv [to-email csv-string]
  (http/post
   "https://api.sendgrid.com/v3/mail/send"
   {:headers      {:authorization
                   (str "Bearer "
                        (System/getenv "SENGRID_API_KEY"))}
    :content-type :json
    :form-params
    {:personalizations [{:to      [{:email to-email}]
                         :subject "Hello, World!"}]
     :from             {:email "from_address@exampl.com"}
     :content          [{:type  "text/plain"
                         :value "Hello, World!"}]
     :attachments
     [{:filename "helloworld.csv"
       :content  (encode-string-to-base64 csv-string)}]}}))

(comment
  (->> data
       ms->csv-string
       (send-email-with-csv "john@example.com")))

The full example project can be found here.