refactor: remove forward auth, move module net/http to net/gphttp

internal/net/gphttp/middleware/custom_error_page.go

@@ -0,0 +1,80 @@
+package middleware
+
+import (
+	"bytes"
+	"io"
+	"net/http"
+	"path/filepath"
+	"strconv"
+	"strings"
+
+	"github.com/yusing/go-proxy/internal/logging"
+	gphttp "github.com/yusing/go-proxy/internal/net/gphttp"
+	"github.com/yusing/go-proxy/internal/net/gphttp/httpheaders"
+	"github.com/yusing/go-proxy/internal/net/gphttp/middleware/errorpage"
+)
+
+type customErrorPage struct{}
+
+var CustomErrorPage = NewMiddleware[customErrorPage]()
+
+const StaticFilePathPrefix = "/$gperrorpage/"
+
+// before implements RequestModifier.
+func (customErrorPage) before(w http.ResponseWriter, r *http.Request) (proceed bool) {
+	return !ServeStaticErrorPageFile(w, r)
+}
+
+// modifyResponse implements ResponseModifier.
+func (customErrorPage) modifyResponse(resp *http.Response) error {
+	// only handles non-success status code and html/plain content type
+	contentType := gphttp.GetContentType(resp.Header)
+	if !gphttp.IsSuccess(resp.StatusCode) && (contentType.IsHTML() || contentType.IsPlainText()) {
+		errorPage, ok := errorpage.GetErrorPageByStatus(resp.StatusCode)
+		if ok {
+			logging.Debug().Msgf("error page for status %d loaded", resp.StatusCode)
+			_, _ = io.Copy(io.Discard, resp.Body) // drain the original body
+			resp.Body.Close()
+			resp.Body = io.NopCloser(bytes.NewReader(errorPage))
+			resp.ContentLength = int64(len(errorPage))
+			resp.Header.Set(httpheaders.HeaderContentLength, strconv.Itoa(len(errorPage)))
+			resp.Header.Set(httpheaders.HeaderContentType, "text/html; charset=utf-8")
+		} else {
+			logging.Error().Msgf("unable to load error page for status %d", resp.StatusCode)
+		}
+		return nil
+	}
+	return nil
+}
+
+func ServeStaticErrorPageFile(w http.ResponseWriter, r *http.Request) (served bool) {
+	path := r.URL.Path
+	if path != "" && path[0] != '/' {
+		path = "/" + path
+	}
+	if strings.HasPrefix(path, StaticFilePathPrefix) {
+		filename := path[len(StaticFilePathPrefix):]
+		file, ok := errorpage.GetStaticFile(filename)
+		if !ok {
+			logging.Error().Msg("unable to load resource " + filename)
+			return false
+		}
+		ext := filepath.Ext(filename)
+		switch ext {
+		case ".html":
+			w.Header().Set(httpheaders.HeaderContentType, "text/html; charset=utf-8")
+		case ".js":
+			w.Header().Set(httpheaders.HeaderContentType, "application/javascript; charset=utf-8")
+		case ".css":
+			w.Header().Set(httpheaders.HeaderContentType, "text/css; charset=utf-8")
+		default:
+			logging.Error().Msgf("unexpected file type %q for %s", ext, filename)
+		}
+		if _, err := w.Write(file); err != nil {
+			logging.Err(err).Msg("unable to write resource " + filename)
+			http.Error(w, "Error page failure", http.StatusInternalServerError)
+		}
+		return true
+	}
+	return false
+}