feat: Implement proxy functionality

server/api/proxy.go

@@ -0,0 +1,124 @@
+package api
+
+import (
+	"encoding/base64"
+	"encoding/json"
+	"io"
+	"log/slog"
+	"net/http"
+	"net/url"
+	"nysoure/server/cache"
+	"nysoure/server/model"
+	"os"
+	"regexp"
+	"strings"
+	"time"
+
+	"github.com/gofiber/fiber/v3"
+)
+
+var (
+	allowedUrlRegexps []*regexp.Regexp
+)
+
+type proxyResponse struct {
+	Content     string `json:"content"`
+	ContentType string `json:"content_type"`
+}
+
+func init() {
+	regexps := os.Getenv("ALLOWED_URL_REGEXPS")
+	for _, expr := range strings.Split(regexps, ",") {
+		if expr == "" {
+			continue
+		}
+		re, err := regexp.Compile(expr)
+		if err != nil {
+			panic("Invalid regex in ALLOWED_URL_REGEXPS: " + expr)
+		}
+		allowedUrlRegexps = append(allowedUrlRegexps, re)
+	}
+}
+
+func handleProxyCall(c fiber.Ctx) error {
+	uriBase64 := c.Query("uri")
+	if uriBase64 == "" {
+		return model.NewRequestError("Missing uri parameter")
+	}
+	uriStr, err := base64.URLEncoding.DecodeString(uriBase64)
+	if err != nil {
+		return model.NewRequestError("Invalid base64 encoding")
+	}
+	uri, err := url.Parse(string(uriStr))
+	if err != nil {
+		return model.NewRequestError("Invalid URL")
+	}
+	allowed := false
+	for _, re := range allowedUrlRegexps {
+		if re.MatchString(uri.String()) {
+			allowed = true
+			break
+		}
+	}
+	if !allowed {
+		return model.NewRequestError("URL not allowed")
+	}
+
+	var resp *proxyResponse
+
+	rawVal, err := cache.Get("proxy:" + uri.String())
+	if err == nil {
+		var r proxyResponse
+		err = json.Unmarshal([]byte(rawVal), &r)
+		if err != nil {
+			slog.ErrorContext(c, "Failed to unmarshal cached proxy response", "error", err)
+			return model.NewInternalServerError("Error")
+		}
+		resp = &r
+	} else {
+		resp, err = proxy(uri)
+		if err != nil {
+			slog.ErrorContext(c, "Proxy request failed", "error", err)
+			return model.NewInternalServerError("Error")
+		}
+	}
+
+	c.Response().Header.SetContentType(resp.ContentType)
+	return c.Send([]byte(rawVal))
+}
+
+func proxy(uri *url.URL) (*proxyResponse, error) {
+	client := http.Client{}
+	req, err := http.NewRequest("GET", uri.String(), nil)
+	if err != nil {
+		return nil, err
+	}
+	resp, err := client.Do(req)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+	contentType := resp.Header.Get("Content-Type")
+	data, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return nil, err
+	}
+	proxyResp := &proxyResponse{
+		Content:     string(data),
+		ContentType: contentType,
+	}
+
+	j, err := json.Marshal(proxyResp)
+	if err != nil {
+		return nil, err
+	}
+	err = cache.Set("proxy:"+uri.String(), string(j), 24*time.Hour)
+	if err != nil {
+		slog.Error("Failed to cache proxy response", "error", err)
+	}
+	return proxyResp, nil
+}
+
+func AddProxyRoutes(router fiber.Router) {
+	router.Get("/proxy", handleProxyCall)
+}