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HTTP FAQ

For HTTP we model the message to maximize flexibility of implementation strategies while allowing familiar verbs such as read and write. The HTTP interface is further driven by the needs of the WebSocket module, as a WebSocket session requires a HTTP Upgrade handshake exchange at the start. Other design goals:

"Some more advanced examples, e.g. including TLS with client/server certificates would help."

The HTTP interface doesn't try to reinvent the wheel, it just uses the boost::asio::ip::tcp::socket or boost::asio::ssl::stream that you set up beforehand. Callers use the interfaces already existing on those objects to make outgoing connections, accept incoming connections, or establish TLS sessions with certificates. We find the available Asio examples for performing these tasks sufficient.

"A built-in router?"

We presume this means a facility to match expressions against the URI in HTTP requests, and dispatch them to calling code. The authors feel that this is a responsibility of higher level code. Beast.HTTP does not try to offer a web server.

"Cookies? Forms/File Uploads?"

Cookies, or managing these types of HTTP headers in general, is the responsibility of higher levels. Beast.HTTP just tries to get complete messages to and from the calling code. It deals in the HTTP headers just enough to process the message body and leaves the rest to callers. However, for forms and file uploads the symmetric interface of the message class allows HTTP requests to include arbitrary body types including those needed to upload a file or fill out a form.

"...supporting TLS (is this a feature? If not this would be a show-stopper), etc."

Beast.HTTP does not provide direct facilities for implementing TLS connections; however, the interfaces already existing on the boost::asio::ssl::stream are available and can be used to establish secure connections. Then, functions like http::read or http::async_write can work with those encrypted connections with no problem.

"There should also be more examples of how to integrate the http service with getting files from the file system, generating responses CGI-style"

The design goal for the library is to not try to invent a web server. We feel that there is a strong need for a basic implementation that models the HTTP message and provides functions to send and receive them over Asio. Such an implementation should serve as a building block upon which higher abstractions such as the aforementioned HTTP service or cgi-gateway can be built.

One of the example programs implements a simple HTTP server that delivers files from the filesystem.

"You should send a 100-continue to ask for the rest of the body if required."

The Beast interface needs to support this functionality (by allowing this special case of partial message parsing and serialization). Specifically, it should let callers read the request up to just before the body, and let callers write the request up to just before the body. However, making use of this behavior should be up to callers (since Beast is low level).

"What about HTTP/2?"

Many reviewers feel that HTTP/2 support is an essential feature of a HTTP library. The authors agree that HTTP/2 is important but also feel that the most sensible implementation is one that does not re-use the same network reading and writing interface for 2 as that for 1.0 and 1.1.

The Beast.HTTP message model is suitable for HTTP/2 and can be re-used. The IETF HTTP Working Group adopted message compatiblity with HTTP/1.x as an explicit goal. A parser can simply emit full headers after decoding the compressed HTTP/2 headers. The stream ID is not logically part of the message but rather message metadata and should be communicated out-of-band (see below). HTTP/2 sessions begin with a traditional HTTP/1.1 Upgrade similar in fashion to the WebSocket upgrade. An HTTP/2 implementation can use existing Beast.HTTP primitives to perform this handshake.

Free functions for HTTP/2 sessions are not possible because of the requirement to maintain per-session state. For example, to decode the compressed headers. Or to remember and respect the remote peer's window settings. The authors propose that a HTTP/2 implementation be written as a separate class template, similar to the websocket::stream but with additional interfaces to support version 2 features. We feel that Beast.HTTP offers enough useful functionality to justify inclusion, so that developers can take advantage of it right away instead of waiting.


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