[http] Rewrite HTTP core to support content encodings

Rewrite the HTTP core to allow for the addition of arbitrary content
encoding mechanisms, such as PeerDist and gzip.

The core now exposes http_open() which can be used to create requests
with an explicitly selected HTTP method, an optional requested content
range, and an optional request body.  A simple wrapper provides the
preexisting behaviour of creating either a GET request or an
application/x-www-form-urlencoded POST request (if the URI includes
parameters).

The HTTP SAN interface is now implemented using the generic block
device translator.  Individual blocks are requested using http_open()
to create a range request.

Server connections are now managed via a connection pool; this allows
for multiple requests to the same server (e.g. for SAN blocks) to be
completely unaware of each other.  Repeated HTTPS connections to the
same server can reuse a pooled connection, avoiding the per-connection
overhead of establishing a TLS session (which can take several seconds
if using a client certificate).

Support for HTTP SAN booting and for the Basic and Digest
authentication schemes is now optional and can be controlled via the
SANBOOT_PROTO_HTTP, HTTP_AUTH_BASIC, and HTTP_AUTH_DIGEST build
configuration options in config/general.h.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/net/tcp/http.c

@@ -30,26 +30,20 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
  *
  */
 
-#include <stddef.h>
 #include <ipxe/open.h>
 #include <ipxe/http.h>
 #include <ipxe/features.h>
 
 FEATURE ( FEATURE_PROTOCOL, "HTTP", DHCP_EB_FEATURE_HTTP, 1 );
 
-/**
- * Initiate an HTTP connection
- *
- * @v xfer		Data transfer interface
- * @v uri		Uniform Resource Identifier
- * @ret rc		Return status code
- */
-static int http_open ( struct interface *xfer, struct uri *uri ) {
-	return http_open_filter ( xfer, uri, HTTP_PORT, NULL );
-}
-
 /** HTTP URI opener */
 struct uri_opener http_uri_opener __uri_opener = {
 	.scheme	= "http",
-	.open	= http_open,
+	.open	= http_open_uri,
+};
+
+/** HTTP URI scheme */
+struct http_scheme http_scheme __http_scheme = {
+	.name = "http",
+	.port = HTTP_PORT,
 };