Add easy way to set date header.

I want to put the date header (https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Date) on all my requests.

static final ThreadLocal<DateFormat> DATE_HEADER_FORMAT =
      new ThreadLocal<DateFormat>() {
        @Override protected DateFormat initialValue() {
          DateFormat format = new SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss 'GMT'", Locale.US);
          format.setTimeZone(TimeZone.getTimeZone("GMT"));
          return format;
        }
      };
...
requestBuilder.addHeader("Date", DATE_HEADER_FORMAT.get().format(new Date())

I’d like to remove this code in favor of perhaps okhttp3.Headers.setDate(Date).

The downside is that it opens up discussion about other general headers that could be added to the Headers API. Is this general-purpose enough?

[swankjesse]

I think we’ve opened the door to java.time overloads, kicked off in OkHttpClient.

@jjshanks if you’d like to add more overloads, please do!

[yschimke]

+1 I think OkHttp could usefully provide constants and formatters for more headers. Would it be worth a sweep through https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers?

Date is also pretty common in responses.