### Networking Libraries

A new class TS3WebFile has been introduced. The new class TS3WebFile is an extension of TWebFile and belongs to the net module. The name TS3WebFile reflects better the fact that this solution is intended to be generic to several S3 servers and not limited to Amazon's, in addition to the fact that it actually extends the capabilities of TWebFile.

Compared to the current support of S3 in ROOT (basically the class TAS3File), the modifications include the improvements below:

- add support for using HTTPS : you can use different schemas for specifying the underlying transport protocol to use "s3:", "s3http:", "s3https:" ["s3" uses HTTPS]. The current schema, namely "as3:", is supported for backwards compatibility.
- extend support for other S3 service providers that do not offer the virtual hosting functionality (currently only Amazon offers this).
- support the possibility of specifying user credentials on a per-file basis or for all S3 files via environment variables.
- honor the "NOPROXY" option when specified in the constructor.
- exploit the capability of the S3 file server to provide partial content responses to multi-range HTTP requests.

Here are some examples of usages from the end user perspective:

       TFile* f = TFile::Open("s3://s3.amazonaws.com/mybucket/path/to/my/file", "AUTH=<accessKey>:<secretKey> NOPROXY")
       TFile* f = TFile::Open("s3://s3.amazonaws.com/mybucket/path/to/my/file")   // Uses environmental variables for retrieving credentials

Limitations:

- we cannot efficiently detect that a S3 server is able to respond to multi-range HTTP GET requests. Some servers, such as Amazon's, respond to such kind of requests with the whole file contents. Other servers, such as Huawei's, respond with the exact partial content requested. Therefore, I added the possibility of configuring the behavior via the ROOT configuration file: the identity of the servers known to correctly support multi-range requests is configurable. If the server is known to support this feature, ROOT will send multi-range requests, otherwise it will issue multiple single-range GET requests, which is also the default behavior.
- currently the virtual host syntax: "s3://mybucket.s3.amazonaws.com/path/to/my/file" is not supported but can be added if this is considered useful.

The TAS3File class will be removed and should not have been used directly by users anyway as it was only accessed via the plugin manager in TFile::Open().

### New HTTP Server package

A new HTTP Server package has been introduced. The idea behind such server is to provide direct access to the data from a running ROOT application. Any object can be streamed when requested and delivered to the browser.

#### Starting the HTTP server

To start the http server, at any time create instance of the `THttpServer` class like:

`serv = new THttpServer("http:8080");`

This will start civetweb-based http server on port 8080. Then, one should be able to open address "http://localhost:8080" in any modern browser and browse objects created in application. By default, the server can access files, canvases and histograms via gROOT. All such objects can be displayed with JSRootIO graphics.

At any time one could register other objects with the command:

`TGraph* gr = new TGraph(10); gr->SetName("gr1"); serv->Register("graphs/subfolder", gr);`

If the object content is changing in the application, like for example histograms being continuously filled, one could enable the monitoring flag in the browser, then the object view will be regularly updated.