iPXE
httpgce.c
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00001 /*
00002  * Copyright (C) 2017 Michael Brown <mbrown@fensystems.co.uk>.
00003  *
00004  * This program is free software; you can redistribute it and/or
00005  * modify it under the terms of the GNU General Public License as
00006  * published by the Free Software Foundation; either version 2 of the
00007  * License, or any later version.
00008  *
00009  * This program is distributed in the hope that it will be useful, but
00010  * WITHOUT ANY WARRANTY; without even the implied warranty of
00011  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00012  * General Public License for more details.
00013  *
00014  * You should have received a copy of the GNU General Public License
00015  * along with this program; if not, write to the Free Software
00016  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
00017  * 02110-1301, USA.
00018  *
00019  * You can also choose to distribute this program under the terms of
00020  * the Unmodified Binary Distribution Licence (as given in the file
00021  * COPYING.UBDL), provided that you have satisfied its requirements.
00022  */
00023 
00024 FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
00025 
00026 /**
00027  * @file
00028  *
00029  * Google Compute Engine (GCE) metadata retrieval
00030  *
00031  * For some unspecified "security" reason, the Google Compute Engine
00032  * metadata server will refuse any requests that do not include the
00033  * non-standard HTTP header "Metadata-Flavor: Google".
00034  */
00035 
00036 #include <strings.h>
00037 #include <stdio.h>
00038 #include <ipxe/http.h>
00039 
00040 /** Metadata host name
00041  *
00042  * This is used to identify metadata requests, in the absence of any
00043  * more robust mechanism.
00044  */
00045 #define GCE_METADATA_HOST_NAME "metadata.google.internal"
00046 
00047 /**
00048  * Construct HTTP "Metadata-Flavor" header
00049  *
00050  * @v http              HTTP transaction
00051  * @v buf               Buffer
00052  * @v len               Length of buffer
00053  * @ret len             Length of header value, or negative error
00054  */
00055 static int http_format_metadata_flavor ( struct http_transaction *http,
00056                                          char *buf, size_t len ) {
00057 
00058         /* Do nothing unless this appears to be a Google Compute
00059          * Engine metadata request.
00060          */
00061         if ( strcasecmp ( http->request.host, GCE_METADATA_HOST_NAME ) != 0 )
00062                 return 0;
00063 
00064         /* Construct host URI */
00065         return snprintf ( buf, len, "Google" );
00066 }
00067 
00068 /** HTTP "Metadata-Flavor" header */
00069 struct http_request_header http_request_metadata_flavor __http_request_header ={
00070         .name = "Metadata-Flavor",
00071         .format = http_format_metadata_flavor,
00072 };