Redirect-short-links

.gitignore

@@ -2,4 +2,4 @@
 docker-compose.yml
 .DS_Store
 *bin
-/tmp
+/tmp

main.go

@@ -50,6 +50,8 @@ func main() {
 	r.GET("/", routes.GetHome)
 	r.POST("/", routes.PostHome)
 
+	r.GET("/a/:id", routes.RedirectShortenedOverflowURL)
+
 	r.GET("/questions/:id", func(c *gin.Context) {
 		// redirect user to the question with the title
 		c.Redirect(302, fmt.Sprintf("/questions/%s/placeholder", c.Param("id")))

src/routes/home.go

@@ -35,10 +35,14 @@ func PostHome(c *gin.Context) {
 
 	soLink := body.URL
 
+	// remove the www.
+	soLink = strings.ReplaceAll(soLink, "www.", "")
+
 	// validate URL
 	isStackOverflow := strings.HasPrefix(soLink, "https://stackoverflow.com/questions/")
+	isShortenedStackOverflow := strings.HasPrefix(soLink, "https://stackoverflow.com/a/")
 	isStackExchange := stackExchangeRegex.MatchString(soLink)
-	if !isStackExchange && !isStackOverflow {
+	if !isStackExchange && !isStackOverflow && !isShortenedStackOverflow {
 		c.HTML(400, "home.html", gin.H{
 			"errorMessage": "Invalid stack overflow/exchange URL",
 			"theme":        c.MustGet("theme").(string),
@@ -47,7 +51,7 @@ func PostHome(c *gin.Context) {
 	}
 
 	// if stack overflow, trim https://stackoverflow.com
-	if isStackOverflow {
+	if isStackOverflow || isShortenedStackOverflow {
 		c.Redirect(302, strings.TrimPrefix(soLink, "https://stackoverflow.com"))
 		return
 	}

src/routes/shortened.go

@@ -0,0 +1,44 @@
+package routes
+
+import (
+	"fmt"
+	"net/http"
+	"os"
+
+	"github.com/gin-gonic/gin"
+	"github.com/go-resty/resty/v2"
+)
+
+func RedirectShortenedOverflowURL(c *gin.Context) {
+	id := c.Param("id")
+
+	// fetch the stack overflow URL
+	client := resty.New()
+	client.SetRedirectPolicy(
+		resty.RedirectPolicyFunc(func(req *http.Request, via []*http.Request) error {
+			return http.ErrUseLastResponse
+		}),
+	)
+
+	resp, err := client.R().Get(fmt.Sprintf("https://www.stackoverflow.com/a/%s", id))
+	if err != nil {
+		c.HTML(400, "home.html", gin.H{
+			"errorMessage": "Unable to fetch stack overflow URL",
+			"theme":        c.MustGet("theme").(string),
+		})
+		return
+	}
+
+	if resp.StatusCode() != 302 {
+		c.HTML(400, "home.html", gin.H{
+			"errorMessage": fmt.Sprintf("Unexpected HTTP status from origin: %d", resp.StatusCode()),
+			"theme":        c.MustGet("theme").(string),
+		})
+		return
+	}
+
+	// get the redirect URL
+	location := resp.Header().Get("Location")
+
+	c.Redirect(302, fmt.Sprintf("%s%s", os.Getenv("APP_URL"), location))
+}