1 files changed, 59 insertions, 0 deletions

diff --git a/echo/controller/content_type_negotiator.go b/echo/controller/content_type_negotiator.go
new file mode 100644
index 0000000..273a118
--- /dev/null
+++ b/echo/controller/content_type_negotiator.go
@@ -0,0 +1,59 @@
+package controller
+
+import (
+        "errors"
+        "net/http"
+        "sync"
+
+        "github.com/elnormous/contenttype"
+        "github.com/labstack/echo/v4"
+)
+
+type ContentTypeNegotiatingHandler struct {
+        Handlers       map[string]echo.HandlerFunc
+        DefaultHandler echo.HandlerFunc
+        mediaTypes     []contenttype.MediaType
+        once           sync.Once
+}
+
+func errorIsNotAcceptable(err error) bool {
+        return errors.Is(err, contenttype.ErrNoAcceptableTypeFound) ||
+                errors.Is(err, contenttype.ErrNoAvailableTypeGiven)
+}
+
+func errorIsBadRequest(err error) bool {
+        return errors.Is(err, contenttype.ErrInvalidMediaType) ||
+                errors.Is(err, contenttype.ErrInvalidMediaRange) ||
+                errors.Is(err, contenttype.ErrInvalidParameter) ||
+                errors.Is(err, contenttype.ErrInvalidExtensionParameter) ||
+                errors.Is(err, contenttype.ErrInvalidWeight)
+}
+
+func (h *ContentTypeNegotiatingHandler) Handle(c echo.Context) error {
+        h.once.Do(func() {
+                h.mediaTypes = []contenttype.MediaType{}
+                for k, _ := range h.Handlers {
+                        h.mediaTypes = append(h.mediaTypes, contenttype.NewMediaType(k))
+                }
+        })
+
+        handler := h.DefaultHandler
+        ct, _, err := contenttype.GetAcceptableMediaType(c.Request(), h.mediaTypes)
+        if err == nil {
+                handler = h.Handlers[ct.String()]
+        } else if errorIsNotAcceptable(err) {
+                return echo.NewHTTPError(http.StatusNotAcceptable)
+        } else if errorIsBadRequest(err) {
+                return echo.NewHTTPError(http.StatusBadRequest)
+        }
+
+        // If negotiation failed but it wasn't an error and there is no default
+        // handler then the request is still not acceptable
+        if handler == nil {
+                return echo.NewHTTPError(http.StatusNotAcceptable)
+        }
+
+        // Don't force each handler to do this itself to eliminate redundant code
+        c.Response().Header().Set("Content-Type", ct.String())
+        return handler(c)
+}