Canonical form of 'ETag' header is incorrect

[rickb777]

Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

1.7.4

What operating system and processor architecture are you using (go env)?

GOARCH="amd64"
GOOS="linux"

What did you do?

This was found by code inspection.

The 'ETag' header's canonical form has a capital 'T' (https://tools.ietf.org/html/rfc7232#section-2.3).

But the Go apis use lowercase 't' in 'Etag' instead.

This is in

• net/http/fs.go:300 - literal string
• net/textproto/reader.go:562 - CanonicalMIMEHeaderKey doesn't handle this case.

Consequence

No adverse effects of this have been observed. It's impact will be limited to rare cross-compatibility problems with other systems that don't correctly handle canonicalisation and/or case-insensitivity of header keys.

[bradfitz]

We don't intend to change this. It would be too many special cases everywhere for something that's already working correctly and would only exist to encourage other's broken implementations.

And in http2, you can't send capital letters on the wire anyway, so this is even more irrelevant with modern HTTP.