FIX: Uploading File With Unkown Catagory Id

cms/internal/handlers/errors.go

@@ -0,0 +1,16 @@
+package handlers
+
+import "errors"
+
+// Sentinel errors the handlers branch on with errors.Is to decide which
+// problem response a failure deserves. They exist to separate a client's
+// mistake from a server fault where the code that detects both is the same
+// code — the repositories return plain errors, so without these every failure
+// out of a lookup would have to be answered as a 500.
+
+// errUnknownCatagoryID reports that a submitted category id is not in the
+// category table. It is kept distinct from the error the lookup itself
+// returns because the two are not the same kind of failure: an id nobody has
+// is the client's mistake and answers 404, while a lookup that could not run
+// is the server's and answers 500.
+var errUnknownCatagoryID = errors.New("unknown catagory id")