Fix Unbounded Memory Usage in Image Proxy

- Added `maxImageProxySize` constant (10MB) to limit memory usage.
- Used `io.LimitReader` in `imageProxyHandler` to enforce the limit.
- Added regression test `web/proxy_limit_test.go` to verify the fix.

Co-authored-by: adammathes <868470+adammathes@users.noreply.github.com>

2 files changed, 47 insertions, 1 deletions

diff --git a/web/proxy_limit_test.go b/web/proxy_limit_test.go
new file mode 100644
index 0000000..2bd0637
--- /dev/null
+++ b/web/proxy_limit_test.go
@@ -0,0 +1,44 @@
+package web
+
+import (
+	"encoding/base64"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+)
+
+// TestImageProxyHandlerUnboundedRead attempts to reproduce the issue by
+// serving a large response and checking if the handler reads it all.
+// Since we can't easily check memory usage in a test without potentially crashing,
+// this test will serve as a baseline.
+//
+// After the fix, we will modify this test or add a new one to verify that
+// the handler stops reading after a certain limit.
+func TestImageProxyHandlerLargeResponse(t *testing.T) {
+	// Create a mock server that returns a large response
+	largeContent := strings.Repeat("A", 1024*1024*15) // 15MB
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "image/jpeg")
+		w.Write([]byte(largeContent))
+	}))
+	defer ts.Close()
+
+	// Encode the URL
+	encodedURL := base64.URLEncoding.EncodeToString([]byte(ts.URL))
+	// The handler expects the path to be the encoded URL (after StripPrefix)
+	req := httptest.NewRequest("GET", "/"+encodedURL, nil)
+	rr := httptest.NewRecorder()
+
+	// Call the handler directly (skipping auth/routing middleware for simplicity)
+	http.HandlerFunc(imageProxyHandler).ServeHTTP(rr, req)
+
+	if rr.Code != http.StatusOK {
+		t.Errorf("Expected status 200, got %d", rr.Code)
+	}
+
+	// With the fix, the handler should read only up to the limit.
+	if len(rr.Body.Bytes()) != maxImageProxySize {
+		t.Errorf("Expected response body length %d, got %d", maxImageProxySize, len(rr.Body.Bytes()))
+	}
+}
diff --git a/web/web.go b/web/web.go
index 245f844..4f111a3 100644
--- a/web/web.go
+++ b/web/web.go
@@ -31,6 +31,8 @@ var gzPool = sync.Pool{
 	},
 }
 
+const maxImageProxySize = 10 * 1024 * 1024 // 10 MB
+
 var (
 	//go:embed static/*
 	staticFiles embed.FS
@@ -89,7 +91,7 @@ func imageProxyHandler(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	bts, err := io.ReadAll(resp.Body)
+	bts, err := io.ReadAll(io.LimitReader(resp.Body, maxImageProxySize))
 	if err != nil {
 		http.Error(w, "failed to read proxy image", http.StatusNotFound)
 		return