[peerdist] Add support for PeerDist (aka BranchCache) HTTP content encoding

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

src/config/config_http.c

@@ -40,3 +40,6 @@ REQUIRE_OBJECT ( httpbasic );
 #ifdef HTTP_AUTH_DIGEST
 REQUIRE_OBJECT ( httpdigest );
 #endif
+#ifdef HTTP_ENC_PEERDIST
+REQUIRE_OBJECT ( peerdist );
+#endif

src/config/general.h

@@ -75,6 +75,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
  */
 #define HTTP_AUTH_BASIC		/* Basic authentication */
 #define HTTP_AUTH_DIGEST	/* Digest authentication */
+//#define HTTP_ENC_PEERDIST	/* PeerDist content encoding */
 
 /*
  * 802.11 cryptosystems and handshaking protocols

src/net/peerdist.c

@@ -0,0 +1,145 @@
+/*
+ * Copyright (C) 2015 Michael Brown <mbrown@fensystems.co.uk>.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ *
+ * You can also choose to distribute this program under the terms of
+ * the Unmodified Binary Distribution Licence (as given in the file
+ * COPYING.UBDL), provided that you have satisfied its requirements.
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+#include <stdio.h>
+#include <ipxe/http.h>
+#include <ipxe/peermux.h>
+
+/** @file
+ *
+ * Peer Content Caching and Retrieval (PeerDist) protocol
+ *
+ * This is quite possibly the ugliest protocol I have ever had the
+ * misfortune to encounter, and I've encountered multicast TFTP.
+ */
+
+/**
+ * Check whether or not to support PeerDist encoding for this request
+ *
+ * @v http		HTTP transaction
+ * @ret supported	PeerDist encoding is supported for this request
+ */
+static int http_peerdist_supported ( struct http_transaction *http ) {
+
+	/* Support PeerDist encoding only if we can directly access an
+	 * underlying data transfer buffer.  Direct access is required
+	 * in order to support decryption of data received via the
+	 * retrieval protocol (which provides the AES initialisation
+	 * vector only after all of the encrypted data has been
+	 * received).
+	 *
+	 * This test simultaneously ensures that we do not attempt to
+	 * use PeerDist encoding on a request which is itself a
+	 * PeerDist individual block download, since the individual
+	 * block downloads do not themselves provide direct access to
+	 * an underlying data transfer buffer.
+	 */
+	return ( xfer_buffer ( &http->xfer ) != NULL );
+}
+
+/**
+ * Format HTTP "X-P2P-PeerDist" header
+ *
+ * @v http		HTTP transaction
+ * @v buf		Buffer
+ * @v len		Length of buffer
+ * @ret len		Length of header value, or negative error
+ */
+static int http_format_p2p_peerdist ( struct http_transaction *http,
+				      char *buf, size_t len ) {
+	int supported = http_peerdist_supported ( http );
+	int missing;
+
+	/* PeerDist wants us to inform the server whenever we make a
+	 * request for data that was missing from local peers
+	 * (presumably for statistical purposes only).  We use the
+	 * heuristic of assuming that the combination of "this request
+	 * may not itself use PeerDist content encoding" and "this is
+	 * a range request" probably indicates that we are making a
+	 * PeerDist block raw range request for missing data.
+	 */
+	missing = ( http->request.range.len && ( ! supported ) );
+
+	/* Omit header if PeerDist encoding is not supported and we
+	 * are not reporting a missing data request.
+	 */
+	if ( ! ( supported || missing ) )
+		return 0;
+
+	/* Construct header */
+	return snprintf ( buf, len, "Version=1.1%s",
+			  ( missing ? ", MissingDataRequest=true" : "" ) );
+}
+
+/** HTTP "X-P2P-PeerDist" header */
+struct http_request_header http_request_p2p_peerdist __http_request_header = {
+	.name = "X-P2P-PeerDist",
+	.format = http_format_p2p_peerdist,
+};
+
+/**
+ * Format HTTP "X-P2P-PeerDistEx" header
+ *
+ * @v http		HTTP transaction
+ * @v buf		Buffer
+ * @v len		Length of buffer
+ * @ret len		Length of header value, or negative error
+ */
+static int http_format_p2p_peerdistex ( struct http_transaction *http,
+					char *buf, size_t len ) {
+	int supported = http_peerdist_supported ( http );
+
+	/* Omit header if PeerDist encoding is not supported */
+	if ( ! supported )
+		return 0;
+
+	/* Construct header */
+	return snprintf ( buf, len, ( "MinContentInformation=1.0, "
+				      "MaxContentInformation=2.0" ) );
+}
+
+/** HTTP "X-P2P-PeerDist" header */
+struct http_request_header http_request_p2p_peerdistex __http_request_header = {
+	.name = "X-P2P-PeerDistEx",
+	.format = http_format_p2p_peerdistex,
+};
+
+/**
+ * Initialise PeerDist content encoding
+ *
+ * @v http		HTTP transaction
+ * @ret rc		Return status code
+ */
+static int http_peerdist_init ( struct http_transaction *http ) {
+
+	return peermux_filter ( &http->content, &http->transfer, http->uri );
+}
+
+/** PeerDist HTTP content encoding */
+struct http_content_encoding peerdist_encoding __http_content_encoding = {
+	.name = "peerdist",
+	.supported = http_peerdist_supported,
+	.init = http_peerdist_init,
+};