Add function to comment HN story

.env.template

@@ -1 +1,2 @@
-AUTH_COOKIE=
+SN_AUTH_COOKIE=
+HN_AUTH_COOKIE=

hn.go

@@ -3,8 +3,16 @@ package main
 import (
 	"encoding/json"
 	"fmt"
+	"io/ioutil"
 	"log"
 	"net/http"
+	"net/url"
+	"regexp"
+	"strconv"
+	"strings"
+
+	"github.com/joho/godotenv"
+	"github.com/namsral/flag"
 )
 
 type ItemID = int
@@ -23,11 +31,21 @@ type Story struct {
 var (
 	HackerNewsUrl         string
 	HackerNewsFirebaseUrl string
+	HnAuthCookie          string
 )
 
 func init() {
 	HackerNewsUrl = "https://news.ycombinator.com"
 	HackerNewsFirebaseUrl = "https://hacker-news.firebaseio.com/v0"
+	err := godotenv.Load()
+	if err != nil {
+		log.Fatal("Error loading .env file")
+	}
+	flag.StringVar(&HnAuthCookie, "HN_AUTH_COOKIE", "", "Cookie required for authorizing requests to news.ycombinator.com")
+	flag.Parse()
+	if HnAuthCookie == "" {
+		log.Fatal("HN_AUTH_COOKIE not set")
+	}
 }
 
 func FetchHackerNewsTopStories() []Story {
@@ -79,6 +97,61 @@ func FetchStoryById(id ItemID) Story {
 	return story
 }
 
+func FetchHackerNewsItemHMAC(id ItemID) string {
+	hnUrl := fmt.Sprintf("%s/item?id=%d", HackerNewsUrl, id)
+	req, err := http.NewRequest("GET", hnUrl, nil)
+	if err != nil {
+		panic(err)
+	}
+	// Cookie header must be set to fetch the correct HMAC for posting comments
+	req.Header.Set("Cookie", HnAuthCookie)
+	client := http.DefaultClient
+	resp, err := client.Do(req)
+	if err != nil {
+		panic(err)
+	}
+	log.Printf("GET %s %d\n", hnUrl, resp.StatusCode)
+
+	body, err := ioutil.ReadAll(resp.Body)
+	if err != nil {
+		log.Fatal("Failed to read response body:", err)
+	}
+
+	// Find HMAC in body
+	re := regexp.MustCompile(`name="hmac" value="([a-z0-9]+)"`)
+	match := re.FindStringSubmatch(string(body))
+	if len(match) == 0 {
+		log.Fatal("No HMAC found")
+	}
+	hmac := match[1]
+
+	return hmac
+}
+
+func CommentHackerNewsStory(text string, id ItemID) {
+	hmac := FetchHackerNewsItemHMAC(id)
+
+	hnUrl := fmt.Sprintf("%s/comment", HackerNewsUrl)
+	data := url.Values{}
+	data.Set("parent", strconv.Itoa(id))
+	data.Set("goto", fmt.Sprintf("item?id=%d", id))
+	data.Set("text", text)
+	data.Set("hmac", hmac)
+	req, err := http.NewRequest("POST", hnUrl, strings.NewReader(data.Encode()))
+	if err != nil {
+		panic(err)
+	}
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+	req.Header.Set("Cookie", HnAuthCookie)
+	client := http.DefaultClient
+	resp, err := client.Do(req)
+	if err != nil {
+		panic(err)
+	}
+	defer resp.Body.Close()
+	log.Printf("POST %s %d\n", hnUrl, resp.StatusCode)
+}
+
 func HackerNewsUserLink(user string) string {
 	return fmt.Sprintf("%s/user?id=%s", HackerNewsUrl, user)
 }

sn.go

@@ -51,10 +51,10 @@ func init() {
 	if err != nil {
 		log.Fatal("Error loading .env file")
 	}
-	flag.StringVar(&SnAuthCookie, "AUTH_COOKIE", "", "Cookie required for authorizing requests to stacker.news/api/graphql")
+	flag.StringVar(&SnAuthCookie, "SN_AUTH_COOKIE", "", "Cookie required for authorizing requests to stacker.news/api/graphql")
 	flag.Parse()
 	if SnAuthCookie == "" {
-		log.Fatal("AUTH_COOKIE not set")
+		log.Fatal("SN_AUTH_COOKIE not set")
 	}
 }