Our drop-in replacement for File.readAsBinaryString wasn't entirely drop-in, in

that if it encountered any bytes > 127, it would fail with an

InvalidCharacterError, which would get translated into a fake ajax error that

said "HTTP 0" (which I don't have to tell you is completely useless). The

problem here was that we were using Int8Array instead of Uint8Array to convert

each byte into a String.

Made a diff that added a BOM to a utf-8 file. Tried to upload that diff and got

the same mysterious HTTP errors that appeared before any HTTP request got made.

After this change, the diff uploads correctly and I can see the added BOM in

the diff viewer.