http-client

Is your feature request related to a problem? Please describe.

I try to execute my first GET request and get this result:

I think the first-time-user experience could get improved here.

The hint to F12 vanishes soon, and I think accessing the error message via F12 is not a

🐣 Is your feature request related to a problem? Please describe.
We had a report in aiohttp-session (see aio-libs/aiohttp-session#574) that a user submitting a 'large' cookie had the cookie dropped by the receiving browser.

According to RFC 6265 - section 6.1:

General-use user agents SHOULD
provide each of the following minimum

From time to time i see ppl using data instead of body which is wrong.
happened just recently in node-fetch/node-fetch#481 (comment)

how do you feel about adding a little warning message that can only appear once. (kinda like node reports that you are using experimental apis)

if ('data' in bodyInit && notWarned) {
  console.warn('use body i

For some reason Amazon REST api's require the content-type to be set to "application/x-amz-json-1.1" instead of the standard "application/json"

Currently the content-type header is set automatically for json data overriding any headers passed in to the request.

It would be useful to first check if the header is set before overriding it:

if (!this.request.headers.set('content-type')) {

Currently, UnframedGrpcService returns an error message as plain text.
https://github.com/line/armeria/blob/54b70906bcd813f0b9b2c6715ad4086160ac49b2/grpc/src/main/java/com/linecorp/armeria/server/grpc/UnframedGrpcService.java#L255-L272
It would be nice to return a JSON object if the content type is JSON compatible.

{ 
   "code": "FAILED_PRECONDITION",
   "message": "Input validatio