path: root/libs/libssh2/src/misc.c

/* Copyright (C) Sara Golemon <sarag@libssh2.org>
 * Copyright (C) Daniel Stenberg
 * Copyright (C) Simon Josefsson
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms,
 * with or without modification, are permitted provided
 * that the following conditions are met:
 *
 *   Redistributions of source code must retain the above
 *   copyright notice, this list of conditions and the
 *   following disclaimer.
 *
 *   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.
 *
 *   Neither the name of the copyright holder nor the names
 *   of any other contributors may be used to endorse or
 *   promote products derived from this software without
 *   specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
 * 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 THE COPYRIGHT OWNER OR
 * 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.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

#include "libssh2_priv.h"

#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif

#include <errno.h>
#include <assert.h>

#ifdef _WIN32
/* Force parameter type. */
#define recv(s, b, l, f)  recv((s), (b), (int)(l), (f))
#define send(s, b, l, f)  send((s), (b), (int)(l), (f))
#endif

/* snprintf not in Visual Studio CRT and _snprintf dangerously incompatible.
   We provide a safe wrapper if snprintf not found */
#ifdef LIBSSH2_SNPRINTF
#include <stdarg.h>

/* Want safe, 'n += snprintf(b + n ...)' like function. If cp_max_len is 1
* then assume cp is pointing to a null char and do nothing. Returns number
* number of chars placed in cp excluding the trailing null char. So for
* cp_max_len > 0 the return value is always < cp_max_len; for cp_max_len
* <= 0 the return value is 0 (and no chars are written to cp). */
int _libssh2_snprintf(char *cp, size_t cp_max_len, const char *fmt, ...)
{
    va_list args;
    int n;

    if(cp_max_len < 2)
        return 0;
    va_start(args, fmt);
#ifdef __clang__
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wformat-nonliteral"
#endif
    n = vsnprintf(cp, cp_max_len, fmt, args);
#ifdef __clang__
#pragma clang diagnostic pop
#endif
    va_end(args);
    return (n < (int)cp_max_len) ? n : (int)(cp_max_len - 1);
}
#endif

int _libssh2_error_flags(LIBSSH2_SESSION* session, int errcode,
                         const char *errmsg, int errflags)
{
    if(!session) {
        if(errmsg)
            fprintf(stderr, "Session is NULL, error: %s\n", errmsg);
        return errcode;
    }

    if(session->err_flags & LIBSSH2_ERR_FLAG_DUP)
        LIBSSH2_FREE(session, (char *)session->err_msg);

    session->err_code = errcode;
    session->err_flags = 0;

    if(errmsg && ((errflags & LIBSSH2_ERR_FLAG_DUP) != 0)) {
        size_t len = strlen(errmsg);
        char *copy = LIBSSH2_ALLOC(session, len + 1);
        if(copy) {
            memcpy(copy, errmsg, len + 1);
            session->err_flags = LIBSSH2_ERR_FLAG_DUP;
            session->err_msg = copy;
        }
        else
            /* Out of memory: this code path is very unlikely */
            session->err_msg = "former error forgotten (OOM)";
    }
    else
        session->err_msg = errmsg;

#ifdef LIBSSH2DEBUG
    if((errcode == LIBSSH2_ERROR_EAGAIN) && !session->api_block_mode)
        /* if this is EAGAIN and we're in non-blocking mode, don't generate
           a debug output for this */
        return errcode;
    _libssh2_debug((session, LIBSSH2_TRACE_ERROR, "%d - %s", session->err_code,
                   session->err_msg));
#endif

    return errcode;
}

int _libssh2_error(LIBSSH2_SESSION* session, int errcode, const char *errmsg)
{
    return _libssh2_error_flags(session, errcode, errmsg, 0);
}

#ifdef _WIN32
int _libssh2_wsa2errno(void)
{
    switch(WSAGetLastError()) {
    case WSAEWOULDBLOCK:
        return EAGAIN;

    case WSAENOTSOCK:
        return EBADF;

    case WSAEINTR:
        return EINTR;

    default:
        /* It is most important to ensure errno does not stay at EAGAIN
         * when a different error occurs so just set errno to a generic
         * error */
        return EIO;
    }
}
#endif

/* _libssh2_recv
 *
 * Replacement for the standard recv, return -errno on failure.
 */
ssize_t
_libssh2_recv(libssh2_socket_t sock, void *buffer, size_t length,
              int flags, void **abstract)
{
    ssize_t rc;

    (void)abstract;

    rc = recv(sock, buffer, length, flags);
    if(rc < 0) {
        int err;
#ifdef _WIN32
        err = _libssh2_wsa2errno();
#else
        err = errno;
#endif
        /* Profiling tools that use SIGPROF can cause EINTR responses.
           recv() does not modify its arguments when it returns EINTR,
           but there may be data waiting, so the caller should try again */
        if(err == EINTR)
            return -EAGAIN;
        /* Sometimes the first recv() function call sets errno to ENOENT on
           Solaris and HP-UX */
        if(err == ENOENT)
            return -EAGAIN;
#ifdef EWOULDBLOCK /* For VMS and other special unixes */
        else if(err == EWOULDBLOCK)
            return -EAGAIN;
#endif
        else
            return -err;
    }
    return rc;
}

/* _libssh2_send
 *
 * Replacement for the standard send, return -errno on failure.
 */
ssize_t
_libssh2_send(libssh2_socket_t sock, const void *buffer, size_t length,
              int flags, void **abstract)
{
    ssize_t rc;

    (void)abstract;

    rc = send(sock, buffer, length, flags);
    if(rc < 0) {
        int err;
#ifdef _WIN32
        err = _libssh2_wsa2errno();
#else
        err = errno;
#endif
        /* Profiling tools that use SIGPROF can cause EINTR responses.
           send() is defined as not yet sending any data when it returns EINTR,
           so the caller should try again */
        if(err == EINTR)
            return -EAGAIN;
#ifdef EWOULDBLOCK /* For VMS and other special unixes */
        if(err == EWOULDBLOCK)
            return -EAGAIN;
#endif
        return -err;
    }
    return rc;
}

/* libssh2_ntohu32
 */
uint32_t
_libssh2_ntohu32(const unsigned char *buf)
{
    return ((uint32_t)buf[0] << 24)
         | ((uint32_t)buf[1] << 16)
         | ((uint32_t)buf[2] << 8)
         | ((uint32_t)buf[3]);
}


/* _libssh2_ntohu64
 */
libssh2_uint64_t
_libssh2_ntohu64(const unsigned char *buf)
{
    return ((libssh2_uint64_t)buf[0] << 56)
         | ((libssh2_uint64_t)buf[1] << 48)
         | ((libssh2_uint64_t)buf[2] << 40)
         | ((libssh2_uint64_t)buf[3] << 32)
         | ((libssh2_uint64_t)buf[4] << 24)
         | ((libssh2_uint64_t)buf[5] << 16)
         | ((libssh2_uint64_t)buf[6] <<  8)
         | ((libssh2_uint64_t)buf[7]);
}

/* _libssh2_htonu32
 */
void
_libssh2_htonu32(unsigned char *buf, uint32_t value)
{
    buf[0] = (unsigned char)((value >> 24) & 0xFF);
    buf[1] = (value >> 16) & 0xFF;
    buf[2] = (value >> 8) & 0xFF;
    buf[3] = value & 0xFF;
}

/* _libssh2_store_u32
 */
void _libssh2_store_u32(unsigned char **buf, uint32_t value)
{
    _libssh2_htonu32(*buf, value);
    *buf += sizeof(uint32_t);
}

/* _libssh2_store_str
 */
int _libssh2_store_str(unsigned char **buf, const char *str, size_t len)
{
    uint32_t len_stored = (uint32_t)len;

    _libssh2_store_u32(buf, len_stored);
    if(len_stored) {
        memcpy(*buf, str, len_stored);
        *buf += len_stored;
    }

    assert(len_stored == len);
    return len_stored == len;
}

/* _libssh2_store_bignum2_bytes
 */
int _libssh2_store_bignum2_bytes(unsigned char **buf,
                                 const unsigned char *bytes,
                                 size_t len)
{
    uint32_t len_stored;
    uint32_t extraByte;
    const unsigned char *p;

    for(p = bytes; len > 0 && *p == 0; --len, ++p) {}

    extraByte = (len > 0 && (p[0] & 0x80) != 0);
    len_stored = (uint32_t)len;
    if(extraByte && len_stored == 0xffffffff)
        len_stored--;
    _libssh2_store_u32(buf, len_stored + extraByte);

    if(extraByte) {
        *buf[0] = 0;
        *buf += 1;
    }

    if(len_stored) {
        memcpy(*buf, p, len_stored);
        *buf += len_stored;
    }

    assert(len_stored == len);
    return len_stored == len;
}

/* Base64 Conversion */

static const short base64_reverse_table[256] = {
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63,
    52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1,
    -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,
    15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1,
    -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
    41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1
};

/* libssh2_base64_decode
 *
 * Legacy public function. DEPRECATED.
 */
LIBSSH2_API int
libssh2_base64_decode(LIBSSH2_SESSION *session, char **data,
                      unsigned int *datalen, const char *src,
                      unsigned int src_len)
{
    int rc;
    size_t dlen;

    rc = _libssh2_base64_decode(session, data, &dlen, src, src_len);

    if(datalen)
        *datalen = (unsigned int)dlen;

    return rc;
}

/* _libssh2_base64_decode
 *
 * Decode a base64 chunk and store it into a newly alloc'd buffer
 */
int _libssh2_base64_decode(LIBSSH2_SESSION *session,
                           char **data, size_t *datalen,
                           const char *src, size_t src_len)
{
    unsigned char *d;
    const char *s;
    short v;
    ssize_t i = 0, len = 0;

    *data = LIBSSH2_ALLOC(session, ((src_len / 4) * 3) + 1);
    d = (unsigned char *) *data;
    if(!d) {
        return _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
                              "Unable to allocate memory for base64 decoding");
    }

    for(s = src; s < (src + src_len); s++) {
        v = base64_reverse_table[(unsigned char)*s];
        if(v < 0)
            continue;
        switch(i % 4) {
        case 0:
            d[len] = (unsigned char)(v << 2);
            break;
        case 1:
            d[len++] |= (unsigned char)(v >> 4);
            d[len] = (unsigned char)(v << 4);
            break;
        case 2:
            d[len++] |= (unsigned char)(v >> 2);
            d[len] = (unsigned char)(v << 6);
            break;
        case 3:
            d[len++] |= (unsigned char)v;
            break;
        }
        i++;
    }
    if((i % 4) == 1) {
        /* Invalid -- We have a byte which belongs exclusively to a partial
           octet */
        LIBSSH2_FREE(session, *data);
        *data = NULL;
        return _libssh2_error(session, LIBSSH2_ERROR_INVAL, "Invalid base64");
    }

    *datalen = len;
    return 0;
}

/* ---- Base64 Encoding/Decoding Table --- */
static const char table64[]=
    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

/*
 * _libssh2_base64_encode
 *
 * Returns the length of the newly created base64 string. The third argument
 * is a pointer to an allocated area holding the base64 data. If something
 * went wrong, 0 is returned.
 *
 */
size_t _libssh2_base64_encode(LIBSSH2_SESSION *session,
                              const char *inp, size_t insize, char **outptr)
{
    unsigned char ibuf[3];
    unsigned char obuf[4];
    int i;
    int inputparts;
    char *output;
    char *base64data;
    const char *indata = inp;

    *outptr = NULL; /* set to NULL in case of failure before we reach the
                       end */

    if(insize == 0)
        insize = strlen(indata);

    base64data = output = LIBSSH2_ALLOC(session, insize * 4 / 3 + 4);
    if(!output)
        return 0;

    while(insize > 0) {
        for(i = inputparts = 0; i < 3; i++) {
            if(insize > 0) {
                inputparts++;
                ibuf[i] = *indata;
                indata++;
                insize--;
            }
            else
                ibuf[i] = 0;
        }

        obuf[0] = (unsigned char)  ((ibuf[0] & 0xFC) >> 2);
        obuf[1] = (unsigned char) (((ibuf[0] & 0x03) << 4) | \
                                   ((ibuf[1] & 0xF0) >> 4));
        obuf[2] = (unsigned char) (((ibuf[1] & 0x0F) << 2) | \
                                   ((ibuf[2] & 0xC0) >> 6));
        obuf[3] = (unsigned char)   (ibuf[2] & 0x3F);

        switch(inputparts) {
        case 1: /* only one byte read */
            output[0] = table64[obuf[0]];
            output[1] = table64[obuf[1]];
            output[2] = '=';
            output[3] = '=';
            break;
        case 2: /* two bytes read */
            output[0] = table64[obuf[0]];
            output[1] = table64[obuf[1]];
            output[2] = table64[obuf[2]];
            output[3] = '=';
            break;
        default:
            output[0] = table64[obuf[0]];
            output[1] = table64[obuf[1]];
            output[2] = table64[obuf[2]];
            output[3] = table64[obuf[3]];
            break;
        }
        output += 4;
    }
    *output = 0;
    *outptr = base64data; /* make it return the actual data memory */

    return strlen(base64data); /* return the length of the new data */
}
/* ---- End of Base64 Encoding ---- */

LIBSSH2_API void
libssh2_free(LIBSSH2_SESSION *session, void *ptr)
{
    LIBSSH2_FREE(session, ptr);
}

#ifdef LIBSSH2DEBUG
#include <stdarg.h>

LIBSSH2_API int
libssh2_trace(LIBSSH2_SESSION * session, int bitmask)
{
    session->showmask = bitmask;
    return 0;
}

LIBSSH2_API int
libssh2_trace_sethandler(LIBSSH2_SESSION *session, void *handler_context,
                         libssh2_trace_handler_func callback)
{
    session->tracehandler = callback;
    session->tracehandler_context = handler_context;
    return 0;
}

void
_libssh2_debug_low(LIBSSH2_SESSION * session, int context, const char *format,
                   ...)
{
    char buffer[1536];
    int len, msglen, buflen = sizeof(buffer);
    va_list vargs;
    struct timeval now;
    static long firstsec;
    static const char *const contexts[] = {
        "Unknown",
        "Transport",
        "Key Ex",
        "Userauth",
        "Conn",
        "SCP",
        "SFTP",
        "Failure Event",
        "Publickey",
        "Socket",
    };
    const char *contexttext = contexts[0];
    unsigned int contextindex;

    if(!(session->showmask & context)) {
        /* no such output asked for */
        return;
    }

    /* Find the first matching context string for this message */
    for(contextindex = 0; contextindex < ARRAY_SIZE(contexts);
         contextindex++) {
        if((context & (1 << contextindex)) != 0) {
            contexttext = contexts[contextindex];
            break;
        }
    }

    gettimeofday(&now, NULL);
    if(!firstsec) {
        firstsec = now.tv_sec;
    }
    now.tv_sec -= firstsec;

    len = snprintf(buffer, buflen, "[libssh2] %d.%06d %s: ",
                   (int)now.tv_sec, (int)now.tv_usec, contexttext);

    if(len >= buflen)
        msglen = buflen - 1;
    else {
        buflen -= len;
        msglen = len;
        va_start(vargs, format);
#ifdef __clang__
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wformat-nonliteral"
#endif
        len = vsnprintf(buffer + msglen, buflen, format, vargs);
#ifdef __clang__
#pragma clang diagnostic pop
#endif
        va_end(vargs);
        msglen += len < buflen ? len : buflen - 1;
    }

    if(session->tracehandler)
        (session->tracehandler)(session, session->tracehandler_context, buffer,
                                msglen);
    else
        fprintf(stderr, "%s\n", buffer);
}

#else
LIBSSH2_API int
libssh2_trace(LIBSSH2_SESSION * session, int bitmask)
{
    (void)session;
    (void)bitmask;
    return 0;
}

LIBSSH2_API int
libssh2_trace_sethandler(LIBSSH2_SESSION *session, void *handler_context,
                         libssh2_trace_handler_func callback)
{
    (void)session;
    (void)handler_context;
    (void)callback;
    return 0;
}
#endif

/* init the list head */
void _libssh2_list_init(struct list_head *head)
{
    head->first = head->last = NULL;
}

/* add a node to the list */
void _libssh2_list_add(struct list_head *head,
                       struct list_node *entry)
{
    /* store a pointer to the head */
    entry->head = head;

    /* we add this entry at the "top" so it has no next */
    entry->next = NULL;

    /* make our prev point to what the head thinks is last */
    entry->prev = head->last;

    /* and make head's last be us now */
    head->last = entry;

    /* make sure our 'prev' node points to us next */
    if(entry->prev)
        entry->prev->next = entry;
    else
        head->first = entry;
}

/* return the "first" node in the list this head points to */
void *_libssh2_list_first(struct list_head *head)
{
    return head->first;
}

/* return the next node in the list */
void *_libssh2_list_next(struct list_node *node)
{
    return node->next;
}

/* return the prev node in the list */
void *_libssh2_list_prev(struct list_node *node)
{
    return node->prev;
}

/* remove this node from the list */
void _libssh2_list_remove(struct list_node *entry)
{
    if(entry->prev)
        entry->prev->next = entry->next;
    else
        entry->head->first = entry->next;

    if(entry->next)
        entry->next->prev = entry->prev;
    else
        entry->head->last = entry->prev;
}

#if 0
/* insert a node before the given 'after' entry */
void _libssh2_list_insert(struct list_node *after, /* insert before this */
                          struct list_node *entry)
{
    /* 'after' is next to 'entry' */
    bentry->next = after;

    /* entry's prev is then made to be the prev after current has */
    entry->prev = after->prev;

    /* the node that is now before 'entry' was previously before 'after'
       and must be made to point to 'entry' correctly */
    if(entry->prev)
        entry->prev->next = entry;
    else
      /* there was no node before this, so we make sure we point the head
         pointer to this node */
      after->head->first = entry;

    /* after's prev entry points back to entry */
    after->prev = entry;

    /* after's next entry is still the same as before */

    /* entry's head is the same as after's */
    entry->head = after->head;
}

#endif

/* Defined in libssh2_priv.h for the correct platforms */
#ifdef LIBSSH2_GETTIMEOFDAY
/*
 * _libssh2_gettimeofday
 * Implementation according to:
 * The Open Group Base Specifications Issue 6
 * IEEE Std 1003.1, 2004 Edition
 */

/*
 *  THIS SOFTWARE IS NOT COPYRIGHTED
 *
 *  This source code is offered for use in the public domain. You may
 *  use, modify or distribute it freely.
 *
 *  This code is distributed in the hope that it will be useful but
 *  WITHOUT ANY WARRANTY. ALL WARRANTIES, EXPRESS OR IMPLIED ARE HEREBY
 *  DISCLAIMED. This includes but is not limited to warranties of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 *
 *  Contributed by:
 *  Danny Smith <dannysmith@users.sourceforge.net>
 */

int _libssh2_gettimeofday(struct timeval *tp, void *tzp)
{
    (void)tzp;
    if(tp) {
#ifdef _WIN32
        /* Offset between 1601-01-01 and 1970-01-01 in 100 nanosec units */
        #define _WIN32_FT_OFFSET (116444736000000000)

        union {
            libssh2_uint64_t ns100; /* time since 1 Jan 1601 in 100ns units */
            FILETIME ft;
        } _now;
        GetSystemTimeAsFileTime(&_now.ft);
        tp->tv_usec = (long)((_now.ns100 / 10) % 1000000);
        tp->tv_sec = (long)((_now.ns100 - _WIN32_FT_OFFSET) / 10000000);
#else
        /* Platforms without a native implementation or local replacement */
        tp->tv_usec = 0;
        tp->tv_sec = 0;
#endif
    }
    /* Always return 0 as per Open Group Base Specifications Issue 6.
       Do not set errno on error.  */
    return 0;
}
#endif

void *_libssh2_calloc(LIBSSH2_SESSION* session, size_t size)
{
    void *p = LIBSSH2_ALLOC(session, size);
    if(p) {
        memset(p, 0, size);
    }
    return p;
}

/* XOR operation on buffers input1 and input2, result in output.
   It is safe to use an input buffer as the output buffer. */
void _libssh2_xor_data(unsigned char *output,
                       const unsigned char *input1,
                       const unsigned char *input2,
                       size_t length)
{
    size_t i;

    for(i = 0; i < length; i++)
        *output++ = *input1++ ^ *input2++;
}

/* Increments an AES CTR buffer to prepare it for use with the
   next AES block. */
void _libssh2_aes_ctr_increment(unsigned char *ctr,
                                size_t length)
{
    unsigned char *pc;
    unsigned int val, carry;

    pc = ctr + length - 1;
    carry = 1;

    while(pc >= ctr) {
        val = (unsigned int)*pc + carry;
        *pc-- = val & 0xFF;
        carry = val >> 8;
    }
}

#ifdef LIBSSH2_MEMZERO
static void * (* const volatile memset_libssh)(void *, int, size_t) = memset;

void _libssh2_memzero(void *buf, size_t size)
{
    memset_libssh(buf, 0, size);
}
#endif

/* String buffer */

struct string_buf *_libssh2_string_buf_new(LIBSSH2_SESSION *session)
{
    struct string_buf *ret;

    ret = _libssh2_calloc(session, sizeof(*ret));
    if(!ret)
        return NULL;

    return ret;
}

void _libssh2_string_buf_free(LIBSSH2_SESSION *session, struct string_buf *buf)
{
    if(!buf)
        return;

    if(buf->data)
        LIBSSH2_FREE(session, buf->data);

    LIBSSH2_FREE(session, buf);
    buf = NULL;
}

int _libssh2_get_byte(struct string_buf *buf, unsigned char *out)
{
    if(!_libssh2_check_length(buf, 1)) {
        return -1;
    }

    *out = buf->dataptr[0];
    buf->dataptr += 1;
    return 0;
}

int _libssh2_get_boolean(struct string_buf *buf, unsigned char *out)
{
    if(!_libssh2_check_length(buf, 1)) {
        return -1;
    }


    *out = buf->dataptr[0] == 0 ? 0 : 1;
    buf->dataptr += 1;
    return 0;
}

int _libssh2_get_u32(struct string_buf *buf, uint32_t *out)
{
    if(!_libssh2_check_length(buf, 4)) {
        return -1;
    }

    *out = _libssh2_ntohu32(buf->dataptr);
    buf->dataptr += 4;
    return 0;
}

int _libssh2_get_u64(struct string_buf *buf, libssh2_uint64_t *out)
{
    if(!_libssh2_check_length(buf, 8)) {
        return -1;
    }

    *out = _libssh2_ntohu64(buf->dataptr);
    buf->dataptr += 8;
    return 0;
}

int _libssh2_match_string(struct string_buf *buf, const char *match)
{
    unsigned char *out;
    size_t len = 0;
    if(_libssh2_get_string(buf, &out, &len) || len != strlen(match) ||
        strncmp((char *)out, match, strlen(match)) != 0) {
        return -1;
    }
    return 0;
}

int _libssh2_get_string(struct string_buf *buf, unsigned char **outbuf,
                        size_t *outlen)
{
    uint32_t data_len;
    if(!buf || _libssh2_get_u32(buf, &data_len) != 0) {
        return -1;
    }
    if(!_libssh2_check_length(buf, data_len)) {
        return -1;
    }
    *outbuf = buf->dataptr;
    buf->dataptr += data_len;

    if(outlen)
        *outlen = (size_t)data_len;

    return 0;
}

int _libssh2_copy_string(LIBSSH2_SESSION *session, struct string_buf *buf,
                         unsigned char **outbuf, size_t *outlen)
{
    size_t str_len;
    unsigned char *str;

    if(_libssh2_get_string(buf, &str, &str_len)) {
        return -1;
    }

    if(str_len) {
        *outbuf = LIBSSH2_ALLOC(session, str_len);
        if(*outbuf) {
            memcpy(*outbuf, str, str_len);
        }
        else {
            return -1;
        }
    }
    else {
        *outbuf = NULL;
    }

    if(outlen)
        *outlen = str_len;

    return 0;
}

int _libssh2_get_bignum_bytes(struct string_buf *buf, unsigned char **outbuf,
                              size_t *outlen)
{
    uint32_t data_len;
    uint32_t bn_len;
    unsigned char *bnptr;

    if(_libssh2_get_u32(buf, &data_len)) {
        return -1;
    }
    if(!_libssh2_check_length(buf, data_len)) {
        return -1;
    }

    bn_len = data_len;
    bnptr = buf->dataptr;

    /* trim leading zeros */
    while(bn_len > 0 && *bnptr == 0x00) {
        bn_len--;
        bnptr++;
    }

    *outbuf = bnptr;
    buf->dataptr += data_len;

    if(outlen)
        *outlen = (size_t)bn_len;

    return 0;
}

/* Given the current location in buf, _libssh2_check_length ensures
   callers can read the next len number of bytes out of the buffer
   before reading the buffer content */

int _libssh2_check_length(struct string_buf *buf, size_t len)
{
    unsigned char *endp = &buf->data[buf->len];
    size_t left = endp - buf->dataptr;
    return (len <= left) && (left <= buf->len);
}

int _libssh2_eob(struct string_buf *buf)
{
    unsigned char *endp = &buf->data[buf->len];
    return buf->dataptr >= endp;
}