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-rw-r--r--roms/ipxe/src/net/tcp/httpgce.c72
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diff --git a/roms/ipxe/src/net/tcp/httpgce.c b/roms/ipxe/src/net/tcp/httpgce.c
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+/*
+ * Copyright (C) 2017 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 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 );
+
+/**
+ * @file
+ *
+ * Google Compute Engine (GCE) metadata retrieval
+ *
+ * For some unspecified "security" reason, the Google Compute Engine
+ * metadata server will refuse any requests that do not include the
+ * non-standard HTTP header "Metadata-Flavor: Google".
+ */
+
+#include <strings.h>
+#include <stdio.h>
+#include <ipxe/http.h>
+
+/** Metadata host name
+ *
+ * This is used to identify metadata requests, in the absence of any
+ * more robust mechanism.
+ */
+#define GCE_METADATA_HOST_NAME "metadata.google.internal"
+
+/**
+ * Construct HTTP "Metadata-Flavor" 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_metadata_flavor ( struct http_transaction *http,
+ char *buf, size_t len ) {
+
+ /* Do nothing unless this appears to be a Google Compute
+ * Engine metadata request.
+ */
+ if ( strcasecmp ( http->request.host, GCE_METADATA_HOST_NAME ) != 0 )
+ return 0;
+
+ /* Construct host URI */
+ return snprintf ( buf, len, "Google" );
+}
+
+/** HTTP "Metadata-Flavor" header */
+struct http_request_header http_request_metadata_flavor __http_request_header ={
+ .name = "Metadata-Flavor",
+ .format = http_format_metadata_flavor,
+};