Default headers support

[Kronuz]

This adds the feature in #205 by adding the following settings:

• defaultAccept
• defaultAcceptCharset
• defaultAcceptDatetime
• defaultAcceptEncoding
• defaultAcceptLanguage
• defaultAccessControlRequestHeaders
• defaultAccessControlRequestMethod
• defaultAuthorization
• defaultCacheControl
• defaultContentType
• defaultCookie
• defaultHost
• defaultOrigin
• defaultUserAgent

[Huachao]

@Kronuz Thanks for your PR, and I am considering that if we could directly provide a setting like defaultHeaders. And user just needs to place all their expected headers into this setting, even custom headers can be set, not just restricted to the above given headers. What's your opinion?

[Kronuz]

That sounds also good... probably even better! Still, I’d get rid of defaultuseragent nonetheless, so there’s only one way to define that one.

One thing I stumbled upon while making the pull request is I had to create a new instance of the RestClientSettings in the HttpRequestParser, and I wasn’t very happy about it (as it adds new callbacks to and all)... is some other way you can think of to better access it from there?

[Huachao]

I am also considering this question that in current code, every place needs to reference the settings, they have to create a new instance of the RestClientSettings class. My suggestion is that, it seems there's no need to hold many instances of setting class, can we just leverage the singleton pattern. That means add a new public static function which is responsible for creating a setting instance internally if not exists, otherwise return the created one. And the constructor of it can be even made private.

[Kronuz]

@Huachao, I modified and added what you suggested to this pull request (defaultHeaders) 👍

[Huachao]

Please update the comment as well.

[Huachao]

@Kronuz please also update your code related to settings, since I have used the singleton pattern for Settings class. Thanks for your contribution.

[Kronuz]

@Huachao, done! I've changed it to use singleton settings and fixed the comment as well. 👍

[Huachao]

@Kronuz Merged, Thanks!

[Kronuz]

Great! will you make a release any time soon? I can't wait to use the official extension again :)

[Huachao]

@Kronuz Sorry, the release will not happen in the immediate future. However I will notify you as soon as it happens

[Kronuz]

It’s ok, thank you! 👍

[Huachao]

@Kronuz you could test the latest version 0.19.0 to experience this feature, thanks for your contribution.

[aktxyz]

Can variables be used in the settings file for defaultHeaders ??