mDNSResponder/mDNSShared/dnssd_clientlib.c

/* -*- Mode: C; tab-width: 4 -*-
 *
 * Copyright (c) 2004-2018 Apple Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1.  Redistributions of source code must retain the above copyright notice,
 *     this list of conditions and the following disclaimer.
 * 2.  Redistributions in binary form must reproduce the above copyright notice,
 *     this list of conditions and the following disclaimer in the documentation
 *     and/or other materials provided with the distribution.
 * 3.  Neither the name of Apple Inc. ("Apple") nor the names of its
 *     contributors may be used to endorse or promote products derived from this
 *     software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <stdlib.h>
#include <string.h>

#include "dns_sd.h"

#if defined(_WIN32)
// disable warning "conversion from <data> to uint16_t"
#pragma warning(disable:4244)
#define strncasecmp _strnicmp
#define strcasecmp _stricmp
#endif

/*********************************************************************************************
*
*  Supporting Functions
*
*********************************************************************************************/

#define mDNSIsDigit(X)     ((X) >= '0' && (X) <= '9')

// DomainEndsInDot returns 1 if name ends with a dot, 0 otherwise
// (DNSServiceConstructFullName depends this returning 1 for true, rather than any non-zero value meaning true)

static int DomainEndsInDot(const char *dom)
{
    while (dom[0] && dom[1])
    {
        if (dom[0] == '\\') // advance past escaped byte sequence
        {
            if (mDNSIsDigit(dom[1]) && mDNSIsDigit(dom[2]) && mDNSIsDigit(dom[3]))
                dom += 4;           // If "\ddd"    then skip four
            else dom += 2;          // else if "\x" then skip two
        }
        else dom++;                 // else goto next character
    }
    return (dom[0] == '.');
}

static uint8_t *InternalTXTRecordSearch
(
    uint16_t txtLen,
    const void       *txtRecord,
    const char       *key,
    unsigned long    *keylen
)
{
    uint8_t *p = (uint8_t*)txtRecord;
    uint8_t *e = p + txtLen;
    *keylen = (unsigned long) strlen(key);
    while (p<e)
    {
        uint8_t *x = p;
        p += 1 + p[0];
        if (p <= e && *keylen <= x[0] && !strncasecmp(key, (char*)x+1, *keylen))
            if (*keylen == x[0] || x[1+*keylen] == '=') return(x);
    }
    return(NULL);
}

/*********************************************************************************************
*
*  General Utility Functions
*
*********************************************************************************************/

// Note: Need to make sure we don't write more than kDNSServiceMaxDomainName (1009) bytes to fullName
// In earlier builds this constant was defined to be 1005, so to avoid buffer overruns on clients
// compiled with that constant we'll actually limit the output to 1005 bytes.

DNSServiceErrorType DNSSD_API DNSServiceConstructFullName
(
    char       *const fullName,
    const char *const service,      // May be NULL
    const char *const regtype,
    const char *const domain
)
{
    const size_t len = !regtype ? 0 : strlen(regtype) - DomainEndsInDot(regtype);
    char       *fn   = fullName;
    char *const lim  = fullName + 1005;
    const char *s    = service;
    const char *r    = regtype;
    const char *d    = domain;

    // regtype must be at least "x._udp" or "x._tcp"
    if (len < 6 || !domain || !domain[0]) return kDNSServiceErr_BadParam;
    if (strncasecmp((regtype + len - 4), "_tcp", 4) && strncasecmp((regtype + len - 4), "_udp", 4)) return kDNSServiceErr_BadParam;

    if (service && *service)
    {
        while (*s)
        {
            unsigned char c = *s++;             // Needs to be unsigned, or values like 0xFF will be interpreted as < 32
            if (c <= ' ')                       // Escape non-printable characters
            {
                if (fn+4 >= lim) goto fail;
                *fn++ = '\\';
                *fn++ = '0' + (c / 100);
                *fn++ = '0' + (c /  10) % 10;
                c     = '0' + (c      ) % 10;
            }
            else if (c == '.' || (c == '\\'))   // Escape dot and backslash literals
            {
                if (fn+2 >= lim) goto fail;
                *fn++ = '\\';
            }
            else
            if (fn+1 >= lim) goto fail;
            *fn++ = (char)c;
        }
        *fn++ = '.';
    }

    while (*r) if (fn+1 >= lim) goto fail;else *fn++ = *r++;
    if (!DomainEndsInDot(regtype)) { if (fn+1 >= lim) goto fail;else *fn++ = '.';}

    while (*d) if (fn+1 >= lim) goto fail;else *fn++ = *d++;
    if (!DomainEndsInDot(domain)) { if (fn+1 >= lim) goto fail;else *fn++ = '.';}

    *fn = '\0';
    return kDNSServiceErr_NoError;

fail:
    *fn = '\0';
    return kDNSServiceErr_BadParam;
}

/*********************************************************************************************
*
*   TXT Record Construction Functions
*
*********************************************************************************************/

typedef struct _TXTRecordRefRealType
{
    uint8_t  *buffer;       // Pointer to data
    uint16_t buflen;        // Length of buffer
    uint16_t datalen;       // Length currently in use
    uint16_t malloced;  // Non-zero if buffer was allocated via malloc()
} TXTRecordRefRealType;

#define txtRec ((TXTRecordRefRealType*)txtRecord)

// The opaque storage defined in the public dns_sd.h header is 16 bytes;
// make sure we don't exceed that.
struct CompileTimeAssertionCheck_dnssd_clientlib
{
    char assert0[(sizeof(TXTRecordRefRealType) <= 16) ? 1 : -1];
};

void DNSSD_API TXTRecordCreate
(
    TXTRecordRef     *txtRecord,
    uint16_t bufferLen,
    void             *buffer
)
{
    txtRec->buffer   = buffer;
    txtRec->buflen   = buffer ? bufferLen : (uint16_t)0;
    txtRec->datalen  = 0;
    txtRec->malloced = 0;
}

void DNSSD_API TXTRecordDeallocate(TXTRecordRef *txtRecord)
{
    if (txtRec->malloced) free(txtRec->buffer);
}

DNSServiceErrorType DNSSD_API TXTRecordSetValue
(
    TXTRecordRef     *txtRecord,
    const char       *key,
    uint8_t valueSize,
    const void       *value
)
{
    uint8_t *start, *p;
    const char *k;
    unsigned long keysize, keyvalsize;

    for (k = key; *k; k++) if (*k < 0x20 || *k > 0x7E || *k == '=') return(kDNSServiceErr_Invalid);
    keysize = (unsigned long)(k - key);
    keyvalsize = 1 + keysize + (value ? (1 + valueSize) : 0);
    if (keysize < 1 || keyvalsize > 255) return(kDNSServiceErr_Invalid);
    (void)TXTRecordRemoveValue(txtRecord, key);
    if (txtRec->datalen + keyvalsize > txtRec->buflen)
    {
        unsigned char *newbuf;
        unsigned long newlen = txtRec->datalen + keyvalsize;
        if (newlen > 0xFFFF) return(kDNSServiceErr_Invalid);
        newbuf = malloc((size_t)newlen);
        if (!newbuf) return(kDNSServiceErr_NoMemory);
        memcpy(newbuf, txtRec->buffer, txtRec->datalen);
        if (txtRec->malloced) free(txtRec->buffer);
        txtRec->buffer = newbuf;
        txtRec->buflen = (uint16_t)(newlen);
        txtRec->malloced = 1;
    }
    start = txtRec->buffer + txtRec->datalen;
    p = start + 1;
    memcpy(p, key, keysize);
    p += keysize;
    if (value)
    {
        *p++ = '=';
        memcpy(p, value, valueSize);
        p += valueSize;
    }
    *start = (uint8_t)(p - start - 1);
    txtRec->datalen += p - start;
    return(kDNSServiceErr_NoError);
}

DNSServiceErrorType DNSSD_API TXTRecordRemoveValue
(
    TXTRecordRef     *txtRecord,
    const char       *key
)
{
    unsigned long keylen, itemlen, remainder;
    uint8_t *item = InternalTXTRecordSearch(txtRec->datalen, txtRec->buffer, key, &keylen);
    if (!item) return(kDNSServiceErr_NoSuchKey);
    itemlen   = (unsigned long)(1 + item[0]);
    remainder = (unsigned long)((txtRec->buffer + txtRec->datalen) - (item + itemlen));
    // Use memmove because memcpy behaviour is undefined for overlapping regions
    memmove(item, item + itemlen, remainder);
    txtRec->datalen -= itemlen;
    return(kDNSServiceErr_NoError);
}

uint16_t DNSSD_API TXTRecordGetLength  (const TXTRecordRef *txtRecord) { return(txtRec->datalen); }
const void * DNSSD_API TXTRecordGetBytesPtr(const TXTRecordRef *txtRecord) { return(txtRec->buffer); }

/*********************************************************************************************
*
*   TXT Record Parsing Functions
*
*********************************************************************************************/

int DNSSD_API TXTRecordContainsKey
(
    uint16_t txtLen,
    const void       *txtRecord,
    const char       *key
)
{
    unsigned long keylen;
    return (InternalTXTRecordSearch(txtLen, txtRecord, key, &keylen) ? 1 : 0);
}

const void * DNSSD_API TXTRecordGetValuePtr
(
    uint16_t txtLen,
    const void       *txtRecord,
    const char       *key,
    uint8_t          *valueLen
)
{
    unsigned long keylen;
    uint8_t *item = InternalTXTRecordSearch(txtLen, txtRecord, key, &keylen);
    if (!item || item[0] <= keylen) return(NULL);   // If key not found, or found with no value, return NULL
    *valueLen = (uint8_t)(item[0] - (keylen + 1));
    return (item + 1 + keylen + 1);
}

uint16_t DNSSD_API TXTRecordGetCount
(
    uint16_t txtLen,
    const void       *txtRecord
)
{
    uint16_t count = 0;
    uint8_t *p = (uint8_t*)txtRecord;
    uint8_t *e = p + txtLen;
    while (p<e) { p += 1 + p[0]; count++; }
    return((p>e) ? (uint16_t)0 : count);
}

DNSServiceErrorType DNSSD_API TXTRecordGetItemAtIndex
(
    uint16_t txtLen,
    const void       *txtRecord,
    uint16_t itemIndex,
    uint16_t keyBufLen,
    char             *key,
    uint8_t          *valueLen,
    const void       **value
)
{
    uint16_t count = 0;
    uint8_t *p = (uint8_t*)txtRecord;
    uint8_t *e = p + txtLen;
    while (p<e && count<itemIndex) { p += 1 + p[0]; count++; }  // Find requested item
    if (p<e && p + 1 + p[0] <= e)   // If valid
    {
        uint8_t *x = p+1;
        unsigned long len = 0;
        e = p + 1 + p[0];
        while (x+len<e && x[len] != '=') len++;
        if (len >= keyBufLen) return(kDNSServiceErr_NoMemory);
        memcpy(key, x, len);
        key[len] = 0;
        if (x+len<e)        // If we found '='
        {
            *value = x + len + 1;
            *valueLen = (uint8_t)(p[0] - (len + 1));
        }
        else
        {
            *value = NULL;
            *valueLen = 0;
        }
        return(kDNSServiceErr_NoError);
    }
    return(kDNSServiceErr_Invalid);
}

/*********************************************************************************************
*
*   SCCS-compatible version string
*
*********************************************************************************************/

// For convenience when using the "strings" command, this is the last thing in the file

// Note: The C preprocessor stringify operator ('#') makes a string from its argument, without macro expansion
// e.g. If "version" is #define'd to be "4", then STRINGIFY_AWE(version) will return the string "version", not "4"
// To expand "version" to its value before making the string, use STRINGIFY(version) instead
#define STRINGIFY_ARGUMENT_WITHOUT_EXPANSION(s) # s
#define STRINGIFY(s) STRINGIFY_ARGUMENT_WITHOUT_EXPANSION(s)

// The "used" variable attribute prevents a non-exported variable from being stripped, even if its visibility is hidden,
// e.g., when compiling with -fvisibility=hidden.
#if defined(__GNUC__)
#define DNSSD_USED __attribute__((used))
#else
#define DNSSD_USED
#endif

// NOT static -- otherwise the compiler may optimize it out
// The "@(#) " pattern is a special prefix the "what" command looks for
#ifndef MDNS_VERSIONSTR_NODTS
const char VersionString_SCCS_libdnssd[] DNSSD_USED = "@(#) libdns_sd " STRINGIFY(mDNSResponderVersion) " (" __DATE__ " " __TIME__ ")";
#else
const char VersionString_SCCS_libdnssd[] = "@(#) libdns_sd " STRINGIFY(mDNSResponderVersion);
#endif