this.res._headers has changed in node master

[ilkkao]

Just compiled Node from the master branch and tried to use koa. It failed because the property values in this.res._headers are now arrays instead of strings.

$ node
> http = require('http');
> resp = new http.ServerResponse({});
> resp.setHeader('Content-Type', 'foo');
> result = resp._headers

In Node 7.x, result is { 'content-type': 'foo' }

In Node master (pre-8.0), result is { 'content-type': [ 'Content-Type', 'foo' ] }

The change was made here: nodejs/node@c00e4ad#diff-286202fdbdd74ede6f5f5334b6176b5cR406 (Node PR: nodejs/node#10558)

@mscdex noticed that it broke express and provided a fix https://github.com/jshttp/fresh/pull/20/files Something similar would be needed for koa.

I'll open this issue to make sure this issue is solved for koa in some way.

[mscdex]

I would probably wait until nodejs/node#10805 lands, which will provide more public API functions around accessing HTTP headers (there is a separate PR to deprecate _headers) for outgoing messages. Then you can do feature detection and use the new public API if it's available.

For some use cases though using functions such as the existing getHeader() is already enough.

[ilkkao]

I can prepare a PR when response.getHeaders from nodejs/node#10805 has landed

[mscdex]

Just a heads up, the PR has landed now in nodejs/node@3e6f103.

Additionally, nodejs/node#10941 will re-add _headers and _headerNames, but will result in runtime deprecation warnings.

[ilkkao]

Koa PR open: #907

[ilkkao]

Code in the master branch still uses this.res._headers directly. Shouldn't the fix go to master too?

[jonathanong]

@ilkkao yes, that would be great!

[ilkkao]

I'll send a PR in few days

[JasonBoy]

@ilkkao getHeaders and getHeaderNames are added in node-v7.7, the comment Node < 8 in #907 could be updated to Node < 7.7?

[jonathanong]

released in 2.1.0 and 1.3.0 thank you @ilkkao !!