pccrd.c File Reference

Peer Content Caching and Retrieval: Discovery Protocol [MS-PCCRD]. More...

#include <stddef.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include <errno.h>
#include <assert.h>
#include <ipxe/pccrd.h>

Go to the source code of this file.

Macros
#define	PEERDIST_DISCOVERY_REQUEST
	Discovery request format. More...

Functions
	FILE_LICENCE (GPL2_OR_LATER_OR_UBDL)
char *	peerdist_discovery_request (const char *uuid, const char *id)
	Construct discovery request. More...
static char *	peerdist_discovery_reply_tag (char *data, size_t len, const char *tag)
	Locate discovery reply tag. More...
static char *	peerdist_discovery_reply_values (char *data, size_t len, const char *name)
	Locate discovery reply values. More...
int	peerdist_discovery_reply (char *data, size_t len, struct peerdist_discovery_reply *reply)
	Parse discovery reply. More...

Detailed Description

Peer Content Caching and Retrieval: Discovery Protocol [MS-PCCRD].

This protocol manages to ingeniously combine the excessive verbosity of XML with a paucity of actual information. For example: even in version 2.0 of the protocol it is still not possible to discover which peers hold a specific block within a given segment.

For added bonus points, version 1.0 of the protocol is specified to use a case-sensitive string comparison (for SHA2 digest values) but nothing specifies whether the strings in question should be in upper or lower case. There are example strings given in the specification, but the author skilfully manages to leave the issue unresolved by using the somewhat implausible digest value of "0200000000000000000000000000000000000000000000000000000000000000".

Just in case you were thinking that the silver lining of the choice to use an XML-based protocol would be the ability to generate and process messages with standard tools, version 2.0 of the protocol places most of the critical information inside a Base64-encoded custom binary data structure. Within an XML element, naturally.

I hereby announce this specification to be the 2015 winner of the prestigious "UEFI HII API" award for incompetent design.

Definition in file pccrd.c.

Macro Definition Documentation

PEERDIST_DISCOVERY_REQUEST

#define PEERDIST_DISCOVERY_REQUEST

Value:

"<?xml version=\"1.0\" encoding=\"utf-8\"?>"                          \
        "<soap:Envelope "                                                     \
            "xmlns:soap=\"http://www.w3.org/2003/05/soap-envelope\" "         \
            "xmlns:wsa=\"http://schemas.xmlsoap.org/ws/2004/08/addressing\" " \
            "xmlns:wsd=\"http://schemas.xmlsoap.org/ws/2005/04/discovery\" "  \
            "xmlns:PeerDist=\"http://schemas.microsoft.com/p2p/"              \
                             "2007/09/PeerDistributionDiscovery\">"           \
          "<soap:Header>"                                                     \
            "<wsa:To>"                                                        \
              "urn:schemas-xmlsoap-org:ws:2005:04:discovery"                  \
            "</wsa:To>"                                                       \
            "<wsa:Action>"                                                    \
              "http://schemas.xmlsoap.org/ws/2005/04/discovery/Probe"         \
            "</wsa:Action>"                                                   \
            "<wsa:MessageID>"                                                 \
              "urn:uuid:%s"                                                   \
            "</wsa:MessageID>"                                                \
          "</soap:Header>"                                                    \
          "<soap:Body>"                                                       \
            "<wsd:Probe>"                                                     \
              "<wsd:Types>"                                                   \
                "PeerDist:PeerDistData"                                       \
              "</wsd:Types>"                                                  \
              "<wsd:Scopes MatchBy=\"http://schemas.xmlsoap.org/ws/"          \
                                    "2005/04/discovery/strcmp0\">"            \
                "%s"                                                          \
              "</wsd:Scopes>"                                                 \
            "</wsd:Probe>"                                                    \
          "</soap:Body>"                                                      \
        "</soap:Envelope>"

Discovery request format.

Definition at line 64 of file pccrd.c.

Function Documentation

FILE_LICENCE()

FILE_LICENCE

(

GPL2_OR_LATER_OR_UBDL

)

peerdist_discovery_request()

char* peerdist_discovery_request	(	const char *	uuid,
		const char *	id
	)

Construct discovery request.

Parameters

uuid	Message UUID string
id	Segment identifier string

Return values

request

Discovery request, or NULL on failure

The request is dynamically allocated; the caller must eventually free() the request.

Definition at line 106 of file pccrd.c.

                                                                       {
        char *request;
        int len;

        /* Construct request */
        len = asprintf ( &request, PEERDIST_DISCOVERY_REQUEST, uuid, id );
        if ( len < 0 )
                return NULL;

        return request;
}

References asprintf(), len, NULL, PEERDIST_DISCOVERY_REQUEST, and request.

Referenced by peerdisc_socket_tx().

peerdist_discovery_reply_tag()

static char* peerdist_discovery_reply_tag ( char *  data, size_t  len, const char *  tag  )

static

Locate discovery reply tag.

Parameters

data	Reply data (not NUL-terminated)
len	Length of reply data
tag	XML tag

Return values

found

Found tag (or NULL if not found)

Definition at line 126 of file pccrd.c.

                                                               {
        size_t tag_len = strlen ( tag );

        /* Search, allowing for the fact that the reply data is not
         * cleanly NUL-terminated and may contain embedded NULs due to
         * earlier parsing.
         */
        for ( ; len >= tag_len ; data++, len-- ) {
                if ( strncmp ( data, tag, tag_len ) == 0 )
                        return data;
        }
        return NULL;
}

References data, len, NULL, strlen(), strncmp(), and tag.

Referenced by peerdist_discovery_reply_values().

peerdist_discovery_reply_values()

static char* peerdist_discovery_reply_values ( char *  data, size_t  len, const char *  name  )

static

Locate discovery reply values.

Parameters

data	Reply data (not NUL-terminated, will be modified)
len	Length of reply data
name	XML tag name

Return values

values

Tag values (or NULL if not found)

The reply data is modified by adding NULs and moving characters as needed to produce a NUL-separated list of values, terminated with a zero-length string.

This is not supposed to be a full XML parser; it's supposed to include just enough functionality to allow PeerDist discovery to work with existing implementations.

Definition at line 157 of file pccrd.c.

                                                                   {
        char buf[ 2 /* "</" */ + strlen ( name ) + 1 /* ">" */ + 1 /* NUL */ ];
        char *open;
        char *close;
        char *start;
        char *end;
        char *in;
        char *out;
        char c;

        /* Locate opening tag */
        snprintf ( buf, sizeof ( buf ), "<%s>", name );
        open = peerdist_discovery_reply_tag ( data, len, buf );
        if ( ! open )
                return NULL;
        start = ( open + strlen ( buf ) );
        len -= ( start - data );
        data = start;

        /* Locate closing tag */
        snprintf ( buf, sizeof ( buf ), "</%s>", name );
        close = peerdist_discovery_reply_tag ( data, len, buf );
        if ( ! close )
                return NULL;
        assert ( close >= open );
        end = close;

        /* Strip initial whitespace, convert other whitespace
         * sequences to single NULs, add terminating pair of NULs.
         * This will probably overwrite part of the closing tag.
         */
        for ( in = start, out = start ; in < end ; in++ ) {
                c = *in;
                if ( isspace ( c ) ) {
                        if ( ( out > start ) && ( out[-1] != '\0' ) )
                                *(out++) = '\0';
                } else {
                        *(out++) = c;
                }
        }
        *(out++) = '\0';
        *(out++) = '\0';
        assert ( out < ( close + strlen ( buf ) ) );

        return start;
}

References assert(), c, close, data, end, in, isspace(), len, name, NULL, open(), out, peerdist_discovery_reply_tag(), snprintf(), start, and strlen().

Referenced by peerdist_discovery_reply().

peerdist_discovery_reply()

int peerdist_discovery_reply	(	char *	data,
		size_t	len,
		struct peerdist_discovery_reply *	reply
	)

Parse discovery reply.

Parameters

data	Reply data (not NUL-terminated, will be modified)
len	Length of reply data
reply	Discovery reply to fill in

Return values

rc	Return status code

The discovery reply includes pointers to strings within the modified reply data.

Definition at line 216 of file pccrd.c.

                                                                        {
        static const struct peerdist_discovery_block_count zcount = {
                .hex = "00000000",
        };
        struct peerdist_discovery_block_count *count;
        unsigned int max;
        unsigned int i;
        char *scopes;
        char *xaddrs;
        char *blockcount;
        char *in;
        char *out;
        size_t skip;

        /* Find <wsd:Scopes> tag */
        scopes = peerdist_discovery_reply_values ( data, len, "wsd:Scopes" );
        if ( ! scopes ) {
                DBGC ( reply, "PCCRD %p missing <wsd:Scopes> tag\n", reply );
                return -ENOENT;
        }

        /* Find <wsd:XAddrs> tag */
        xaddrs = peerdist_discovery_reply_values ( data, len, "wsd:XAddrs" );
        if ( ! xaddrs ) {
                DBGC ( reply, "PCCRD %p missing <wsd:XAddrs> tag\n", reply );
                return -ENOENT;
        }

        /* Find <PeerDist:BlockCount> tag */
        blockcount = peerdist_discovery_reply_values ( data, len,
                                                       "PeerDist:BlockCount" );
        if ( ! blockcount ) {
                DBGC ( reply, "PCCRD %p missing <PeerDist:BlockCount> tag\n",
                       reply );
                return -ENOENT;
        }

        /* Determine maximum number of segments (according to number
         * of entries in the block count list).
         */
        max = ( strlen ( blockcount ) / sizeof ( *count ) );
        count = container_of ( blockcount,
                               struct peerdist_discovery_block_count, hex[0] );

        /* Eliminate any segments with a zero block count */
        for ( i = 0, in = scopes, out = scopes ; *in ; i++, in += skip ) {

                /* Fail if we have overrun the maximum number of segments */
                if ( i >= max ) {
                        DBGC ( reply, "PCCRD %p too many segment IDs\n",
                               reply );
                        return -EPROTO;
                }

                /* Delete segment if block count is zero */
                skip = ( strlen ( in ) + 1 /* NUL */ );
                if ( memcmp ( count[i].hex, zcount.hex,
                              sizeof ( zcount.hex ) ) == 0 )
                        continue;
                strcpy ( out, in );
                out += skip;
        }
        out[0] = '\0'; /* Ensure list is terminated with a zero-length string */

        /* Fill in discovery reply */
        reply->ids = scopes;
        reply->locations = xaddrs;

        return 0;
}

References container_of, count, data, DBGC, ENOENT, EPROTO, hex, peerdist_discovery_block_count::hex, peerdist_discovery_reply::ids, in, len, peerdist_discovery_reply::locations, max, memcmp(), out, peerdist_discovery_reply_values(), strcpy(), and strlen().