iPXE
httpgce.c
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1 /*
2  * Copyright (C) 2017 Michael Brown <mbrown@fensystems.co.uk>.
3  *
4  * This program is free software; you can redistribute it and/or
5  * modify it under the terms of the GNU General Public License as
6  * published by the Free Software Foundation; either version 2 of the
7  * License, or any later version.
8  *
9  * This program is distributed in the hope that it will be useful, but
10  * WITHOUT ANY WARRANTY; without even the implied warranty of
11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12  * General Public License for more details.
13  *
14  * You should have received a copy of the GNU General Public License
15  * along with this program; if not, write to the Free Software
16  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
17  * 02110-1301, USA.
18  *
19  * You can also choose to distribute this program under the terms of
20  * the Unmodified Binary Distribution Licence (as given in the file
21  * COPYING.UBDL), provided that you have satisfied its requirements.
22  */
23 
24 FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
25 
26 /**
27  * @file
28  *
29  * Google Compute Engine (GCE) metadata retrieval
30  *
31  * For some unspecified "security" reason, the Google Compute Engine
32  * metadata server will refuse any requests that do not include the
33  * non-standard HTTP header "Metadata-Flavor: Google".
34  */
35 
36 #include <strings.h>
37 #include <stdio.h>
38 #include <ipxe/http.h>
39 
40 /** Metadata host name
41  *
42  * This is used to identify metadata requests, in the absence of any
43  * more robust mechanism.
44  */
45 #define GCE_METADATA_HOST_NAME "metadata.google.internal"
46 
47 /**
48  * Construct HTTP "Metadata-Flavor" header
49  *
50  * @v http HTTP transaction
51  * @v buf Buffer
52  * @v len Length of buffer
53  * @ret len Length of header value, or negative error
54  */
56  char *buf, size_t len ) {
57 
58  /* Do nothing unless this appears to be a Google Compute
59  * Engine metadata request.
60  */
61  if ( strcasecmp ( http->request.host, GCE_METADATA_HOST_NAME ) != 0 )
62  return 0;
63 
64  /* Construct host URI */
65  return snprintf ( buf, len, "Google" );
66 }
67 
68 /** HTTP "Metadata-Flavor" header */
69 struct http_request_header http_request_metadata_flavor __http_request_header ={
70  .name = "Metadata-Flavor",
72 };
const char * host
Server host name.
Definition: http.h:218
const char * name
Header name (e.g.
Definition: http.h:230
int strcasecmp(const char *first, const char *second)
Compare case-insensitive strings.
Definition: string.c:192
An HTTP request header.
Definition: http.h:228
struct http_request_header http_request_metadata_flavor __http_request_header
HTTP "Metadata-Flavor" header.
Definition: httpgce.c:69
#define GCE_METADATA_HOST_NAME
Metadata host name.
Definition: httpgce.c:45
struct http_request request
Request.
Definition: http.h:436
An HTTP transaction.
Definition: http.h:417
Hyper Text Transport Protocol.
FILE_LICENCE(GPL2_OR_LATER_OR_UBDL)
static int http_format_metadata_flavor(struct http_transaction *http, char *buf, size_t len)
Construct HTTP "Metadata-Flavor" header.
Definition: httpgce.c:55
uint32_t len
Length.
Definition: ena.h:14
int snprintf(char *buf, size_t size, const char *fmt,...)
Write a formatted string to a buffer.
Definition: vsprintf.c:382
String functions.