putty/misc.c

/*
 * Platform-independent routines shared between all PuTTY programs.
 */

#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <limits.h>
#include <ctype.h>
#include <assert.h>
#include "putty.h"
#include "misc.h"

/*
 * Parse a string block size specification. This is approximately a
 * subset of the block size specs supported by GNU fileutils:
 *  "nk" = n kilobytes
 *  "nM" = n megabytes
 *  "nG" = n gigabytes
 * All numbers are decimal, and suffixes refer to powers of two.
 * Case-insensitive.
 */
unsigned long parse_blocksize(const char *bs)
{
    char *suf;
    unsigned long r = strtoul(bs, &suf, 10);
    if (*suf != '\0') {
	while (*suf && isspace((unsigned char)*suf)) suf++;
	switch (*suf) {
	  case 'k': case 'K':
	    r *= 1024ul;
	    break;
	  case 'm': case 'M':
	    r *= 1024ul * 1024ul;
	    break;
	  case 'g': case 'G':
	    r *= 1024ul * 1024ul * 1024ul;
	    break;
	  case '\0':
	  default:
	    break;
	}
    }
    return r;
}

/*
 * Parse a ^C style character specification.
 * Returns NULL in `next' if we didn't recognise it as a control character,
 * in which case `c' should be ignored.
 * The precise current parsing is an oddity inherited from the terminal
 * answerback-string parsing code. All sequences start with ^; all except
 * ^<123> are two characters. The ones that are worth keeping are probably:
 *   ^?		    127
 *   ^@A-Z[\]^_	    0-31
 *   a-z	    1-26
 *   <num>	    specified by number (decimal, 0octal, 0xHEX)
 *   ~		    ^ escape
 */
char ctrlparse(char *s, char **next)
{
    char c = 0;
    if (*s != '^') {
	*next = NULL;
    } else {
	s++;
	if (*s == '\0') {
	    *next = NULL;
	} else if (*s == '<') {
	    s++;
	    c = (char)strtol(s, next, 0);
	    if ((*next == s) || (**next != '>')) {
		c = 0;
		*next = NULL;
	    } else
		(*next)++;
	} else if (*s >= 'a' && *s <= 'z') {
	    c = (*s - ('a' - 1));
	    *next = s+1;
	} else if ((*s >= '@' && *s <= '_') || *s == '?' || (*s & 0x80)) {
	    c = ('@' ^ *s);
	    *next = s+1;
	} else if (*s == '~') {
	    c = '^';
	    *next = s+1;
	}
    }
    return c;
}

/*
 * Find a character in a string, unless it's a colon contained within
 * square brackets. Used for untangling strings of the form
 * 'host:port', where host can be an IPv6 literal.
 *
 * We provide several variants of this function, with semantics like
 * various standard string.h functions.
 */
static const char *host_strchr_internal(const char *s, const char *set,
                                        int first)
{
    int brackets = 0;
    const char *ret = NULL;

    while (1) {
        if (!*s)
            return ret;

        if (*s == '[')
            brackets++;
        else if (*s == ']' && brackets > 0)
            brackets--;
        else if (brackets && *s == ':')
            /* never match */ ;
        else if (strchr(set, *s)) {
            ret = s;
            if (first)
                return ret;
        }

        s++;
    }
}
size_t host_strcspn(const char *s, const char *set)
{
    const char *answer = host_strchr_internal(s, set, TRUE);
    if (answer)
        return answer - s;
    else
        return strlen(s);
}
char *host_strchr(const char *s, int c)
{
    char set[2];
    set[0] = c;
    set[1] = '\0';
    return (char *) host_strchr_internal(s, set, TRUE);
}
char *host_strrchr(const char *s, int c)
{
    char set[2];
    set[0] = c;
    set[1] = '\0';
    return (char *) host_strchr_internal(s, set, FALSE);
}

#ifdef TEST_HOST_STRFOO
int main(void)
{
    int passes = 0, fails = 0;

#define TEST1(func, string, arg2, suffix, result) do                    \
    {                                                                   \
        const char *str = string;                                       \
        unsigned ret = func(string, arg2) suffix;                       \
        if (ret == result) {                                            \
            passes++;                                                   \
        } else {                                                        \
            printf("fail: %s(%s,%s)%s = %u, expected %u\n",             \
                   #func, #string, #arg2, #suffix, ret, result);        \
            fails++;                                                    \
        }                                                               \
} while (0)

    TEST1(host_strchr, "[1:2:3]:4:5", ':', -str, 7);
    TEST1(host_strrchr, "[1:2:3]:4:5", ':', -str, 9);
    TEST1(host_strcspn, "[1:2:3]:4:5", "/:",, 7);
    TEST1(host_strchr, "[1:2:3]", ':', == NULL, 1);
    TEST1(host_strrchr, "[1:2:3]", ':', == NULL, 1);
    TEST1(host_strcspn, "[1:2:3]", "/:",, 7);
    TEST1(host_strcspn, "[1:2/3]", "/:",, 4);
    TEST1(host_strcspn, "[1:2:3]/", "/:",, 7);

    printf("passed %d failed %d total %d\n", passes, fails, passes+fails);
    return fails != 0 ? 1 : 0;
}
/* Stubs to stop the rest of this module causing compile failures. */
void modalfatalbox(const char *fmt, ...) {}
int conf_get_int(Conf *conf, int primary) { return 0; }
char *conf_get_str(Conf *conf, int primary) { return NULL; }
#endif /* TEST_HOST_STRFOO */

/*
 * Trim square brackets off the outside of an IPv6 address literal.
 * Leave all other strings unchanged. Returns a fresh dynamically
 * allocated string.
 */
char *host_strduptrim(const char *s)
{
    if (s[0] == '[') {
        const char *p = s+1;
        int colons = 0;
        while (*p && *p != ']') {
            if (isxdigit((unsigned char)*p))
                /* OK */;
            else if (*p == ':')
                colons++;
            else
                break;
            p++;
        }
        if (*p == ']' && !p[1] && colons > 1) {
            /*
             * This looks like an IPv6 address literal (hex digits and
             * at least two colons, contained in square brackets).
             * Trim off the brackets.
             */
            return dupprintf("%.*s", (int)(p - (s+1)), s+1);
        }
    }

    /*
     * Any other shape of string is simply duplicated.
     */
    return dupstr(s);
}

prompts_t *new_prompts(void *frontend)
{
    prompts_t *p = snew(prompts_t);
    p->prompts = NULL;
    p->n_prompts = 0;
    p->frontend = frontend;
    p->data = NULL;
    p->to_server = TRUE; /* to be on the safe side */
    p->name = p->instruction = NULL;
    p->name_reqd = p->instr_reqd = FALSE;
    return p;
}
void add_prompt(prompts_t *p, char *promptstr, int echo)
{
    prompt_t *pr = snew(prompt_t);
    pr->prompt = promptstr;
    pr->echo = echo;
    pr->result = NULL;
    pr->resultsize = 0;
    p->n_prompts++;
    p->prompts = sresize(p->prompts, p->n_prompts, prompt_t *);
    p->prompts[p->n_prompts-1] = pr;
}
void prompt_ensure_result_size(prompt_t *pr, int newlen)
{
    if ((int)pr->resultsize < newlen) {
        char *newbuf;
        newlen = newlen * 5 / 4 + 512; /* avoid too many small allocs */

        /*
         * We don't use sresize / realloc here, because we will be
         * storing sensitive stuff like passwords in here, and we want
         * to make sure that the data doesn't get copied around in
         * memory without the old copy being destroyed.
         */
        newbuf = snewn(newlen, char);
        memcpy(newbuf, pr->result, pr->resultsize);
        smemclr(pr->result, pr->resultsize);
        sfree(pr->result);
        pr->result = newbuf;
        pr->resultsize = newlen;
    }
}
void prompt_set_result(prompt_t *pr, const char *newstr)
{
    prompt_ensure_result_size(pr, strlen(newstr) + 1);
    strcpy(pr->result, newstr);
}
void free_prompts(prompts_t *p)
{
    size_t i;
    for (i=0; i < p->n_prompts; i++) {
	prompt_t *pr = p->prompts[i];
	smemclr(pr->result, pr->resultsize); /* burn the evidence */
	sfree(pr->result);
	sfree(pr->prompt);
	sfree(pr);
    }
    sfree(p->prompts);
    sfree(p->name);
    sfree(p->instruction);
    sfree(p);
}

/* ----------------------------------------------------------------------
 * String handling routines.
 */

char *dupstr(const char *s)
{
    char *p = NULL;
    if (s) {
        int len = strlen(s);
        p = snewn(len + 1, char);
        strcpy(p, s);
    }
    return p;
}

/* Allocate the concatenation of N strings. Terminate arg list with NULL. */
char *dupcat(const char *s1, ...)
{
    int len;
    char *p, *q, *sn;
    va_list ap;

    len = strlen(s1);
    va_start(ap, s1);
    while (1) {
	sn = va_arg(ap, char *);
	if (!sn)
	    break;
	len += strlen(sn);
    }
    va_end(ap);

    p = snewn(len + 1, char);
    strcpy(p, s1);
    q = p + strlen(p);

    va_start(ap, s1);
    while (1) {
	sn = va_arg(ap, char *);
	if (!sn)
	    break;
	strcpy(q, sn);
	q += strlen(q);
    }
    va_end(ap);

    return p;
}

void burnstr(char *string)             /* sfree(str), only clear it first */
{
    if (string) {
        smemclr(string, strlen(string));
        sfree(string);
    }
}

int toint(unsigned u)
{
    /*
     * Convert an unsigned to an int, without running into the
     * undefined behaviour which happens by the strict C standard if
     * the value overflows. You'd hope that sensible compilers would
     * do the sensible thing in response to a cast, but actually I
     * don't trust modern compilers not to do silly things like
     * assuming that _obviously_ you wouldn't have caused an overflow
     * and so they can elide an 'if (i < 0)' test immediately after
     * the cast.
     *
     * Sensible compilers ought of course to optimise this entire
     * function into 'just return the input value'!
     */
    if (u <= (unsigned)INT_MAX)
        return (int)u;
    else if (u >= (unsigned)INT_MIN)   /* wrap in cast _to_ unsigned is OK */
        return INT_MIN + (int)(u - (unsigned)INT_MIN);
    else
        return INT_MIN; /* fallback; should never occur on binary machines */
}

/*
 * Do an sprintf(), but into a custom-allocated buffer.
 * 
 * Currently I'm doing this via vsnprintf. This has worked so far,
 * but it's not good, because vsnprintf is not available on all
 * platforms. There's an ifdef to use `_vsnprintf', which seems
 * to be the local name for it on Windows. Other platforms may
 * lack it completely, in which case it'll be time to rewrite
 * this function in a totally different way.
 * 
 * The only `properly' portable solution I can think of is to
 * implement my own format string scanner, which figures out an
 * upper bound for the length of each formatting directive,
 * allocates the buffer as it goes along, and calls sprintf() to
 * actually process each directive. If I ever need to actually do
 * this, some caveats:
 * 
 *  - It's very hard to find a reliable upper bound for
 *    floating-point values. %f, in particular, when supplied with
 *    a number near to the upper or lower limit of representable
 *    numbers, could easily take several hundred characters. It's
 *    probably feasible to predict this statically using the
 *    constants in <float.h>, or even to predict it dynamically by
 *    looking at the exponent of the specific float provided, but
 *    it won't be fun.
 * 
 *  - Don't forget to _check_, after calling sprintf, that it's
 *    used at most the amount of space we had available.
 * 
 *  - Fault any formatting directive we don't fully understand. The
 *    aim here is to _guarantee_ that we never overflow the buffer,
 *    because this is a security-critical function. If we see a
 *    directive we don't know about, we should panic and die rather
 *    than run any risk.
 */
char *dupprintf(const char *fmt, ...)
{
    char *ret;
    va_list ap;
    va_start(ap, fmt);
    ret = dupvprintf(fmt, ap);
    va_end(ap);
    return ret;
}
char *dupvprintf(const char *fmt, va_list ap)
{
    char *buf;
    int len, size;

    buf = snewn(512, char);
    size = 512;

    while (1) {
#if defined _WINDOWS && _MSC_VER < 1900 /* 1900 == VS2015 has real snprintf */
#define vsnprintf _vsnprintf
#endif
#ifdef va_copy
	/* Use the `va_copy' macro mandated by C99, if present.
	 * XXX some environments may have this as __va_copy() */
	va_list aq;
	va_copy(aq, ap);
	len = vsnprintf(buf, size, fmt, aq);
	va_end(aq);
#else
	/* Ugh. No va_copy macro, so do something nasty.
	 * Technically, you can't reuse a va_list like this: it is left
	 * unspecified whether advancing a va_list pointer modifies its
	 * value or something it points to, so on some platforms calling
	 * vsnprintf twice on the same va_list might fail hideously
	 * (indeed, it has been observed to).
	 * XXX the autoconf manual suggests that using memcpy() will give
	 *     "maximum portability". */
	len = vsnprintf(buf, size, fmt, ap);
#endif
	if (len >= 0 && len < size) {
	    /* This is the C99-specified criterion for snprintf to have
	     * been completely successful. */
	    return buf;
	} else if (len > 0) {
	    /* This is the C99 error condition: the returned length is
	     * the required buffer size not counting the NUL. */
	    size = len + 1;
	} else {
	    /* This is the pre-C99 glibc error condition: <0 means the
	     * buffer wasn't big enough, so we enlarge it a bit and hope. */
	    size += 512;
	}
	buf = sresize(buf, size, char);
    }
}

/*
 * Read an entire line of text from a file. Return a buffer
 * malloced to be as big as necessary (caller must free).
 */
char *fgetline(FILE *fp)
{
    char *ret = snewn(512, char);
    int size = 512, len = 0;
    while (fgets(ret + len, size - len, fp)) {
	len += strlen(ret + len);
	if (len > 0 && ret[len-1] == '\n')
	    break;		       /* got a newline, we're done */
	size = len + 512;
	ret = sresize(ret, size, char);
    }
    if (len == 0) {		       /* first fgets returned NULL */
	sfree(ret);
	return NULL;
    }
    ret[len] = '\0';
    return ret;
}

/*
 * Perl-style 'chomp', for a line we just read with fgetline. Unlike
 * Perl chomp, however, we're deliberately forgiving of strange
 * line-ending conventions. Also we forgive NULL on input, so you can
 * just write 'line = chomp(fgetline(fp));' and not bother checking
 * for NULL until afterwards.
 */
char *chomp(char *str)
{
    if (str) {
        int len = strlen(str);
        while (len > 0 && (str[len-1] == '\r' || str[len-1] == '\n'))
            len--;
        str[len] = '\0';
    }
    return str;
}

/* ----------------------------------------------------------------------
 * Core base64 encoding and decoding routines.
 */

void base64_encode_atom(const unsigned char *data, int n, char *out)
{
    static const char base64_chars[] =
	"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

    unsigned word;

    word = data[0] << 16;
    if (n > 1)
	word |= data[1] << 8;
    if (n > 2)
	word |= data[2];
    out[0] = base64_chars[(word >> 18) & 0x3F];
    out[1] = base64_chars[(word >> 12) & 0x3F];
    if (n > 1)
	out[2] = base64_chars[(word >> 6) & 0x3F];
    else
	out[2] = '=';
    if (n > 2)
	out[3] = base64_chars[word & 0x3F];
    else
	out[3] = '=';
}

int base64_decode_atom(const char *atom, unsigned char *out)
{
    int vals[4];
    int i, v, len;
    unsigned word;
    char c;

    for (i = 0; i < 4; i++) {
	c = atom[i];
	if (c >= 'A' && c <= 'Z')
	    v = c - 'A';
	else if (c >= 'a' && c <= 'z')
	    v = c - 'a' + 26;
	else if (c >= '0' && c <= '9')
	    v = c - '0' + 52;
	else if (c == '+')
	    v = 62;
	else if (c == '/')
	    v = 63;
	else if (c == '=')
	    v = -1;
	else
	    return 0;		       /* invalid atom */
	vals[i] = v;
    }

    if (vals[0] == -1 || vals[1] == -1)
	return 0;
    if (vals[2] == -1 && vals[3] != -1)
	return 0;

    if (vals[3] != -1)
	len = 3;
    else if (vals[2] != -1)
	len = 2;
    else
	len = 1;

    word = ((vals[0] << 18) |
	    (vals[1] << 12) | ((vals[2] & 0x3F) << 6) | (vals[3] & 0x3F));
    out[0] = (word >> 16) & 0xFF;
    if (len > 1)
	out[1] = (word >> 8) & 0xFF;
    if (len > 2)
	out[2] = word & 0xFF;
    return len;
}

/* ----------------------------------------------------------------------
 * Generic routines to deal with send buffers: a linked list of
 * smallish blocks, with the operations
 * 
 *  - add an arbitrary amount of data to the end of the list
 *  - remove the first N bytes from the list
 *  - return a (pointer,length) pair giving some initial data in
 *    the list, suitable for passing to a send or write system
 *    call
 *  - retrieve a larger amount of initial data from the list
 *  - return the current size of the buffer chain in bytes
 */

#define BUFFER_MIN_GRANULE  512

struct bufchain_granule {
    struct bufchain_granule *next;
    char *bufpos, *bufend, *bufmax;
};

void bufchain_init(bufchain *ch)
{
    ch->head = ch->tail = NULL;
    ch->buffersize = 0;
}

void bufchain_clear(bufchain *ch)
{
    struct bufchain_granule *b;
    while (ch->head) {
	b = ch->head;
	ch->head = ch->head->next;
	sfree(b);
    }
    ch->tail = NULL;
    ch->buffersize = 0;
}

int bufchain_size(bufchain *ch)
{
    return ch->buffersize;
}

void bufchain_add(bufchain *ch, const void *data, int len)
{
    const char *buf = (const char *)data;

    if (len == 0) return;

    ch->buffersize += len;

    while (len > 0) {
	if (ch->tail && ch->tail->bufend < ch->tail->bufmax) {
	    int copylen = min(len, ch->tail->bufmax - ch->tail->bufend);
	    memcpy(ch->tail->bufend, buf, copylen);
	    buf += copylen;
	    len -= copylen;
	    ch->tail->bufend += copylen;
	}
	if (len > 0) {
	    int grainlen =
		max(sizeof(struct bufchain_granule) + len, BUFFER_MIN_GRANULE);
	    struct bufchain_granule *newbuf;
	    newbuf = smalloc(grainlen);
	    newbuf->bufpos = newbuf->bufend =
		(char *)newbuf + sizeof(struct bufchain_granule);
	    newbuf->bufmax = (char *)newbuf + grainlen;
	    newbuf->next = NULL;
	    if (ch->tail)
		ch->tail->next = newbuf;
	    else
		ch->head = newbuf;
	    ch->tail = newbuf;
	}
    }
}

void bufchain_consume(bufchain *ch, int len)
{
    struct bufchain_granule *tmp;

    assert(ch->buffersize >= len);
    while (len > 0) {
	int remlen = len;
	assert(ch->head != NULL);
	if (remlen >= ch->head->bufend - ch->head->bufpos) {
	    remlen = ch->head->bufend - ch->head->bufpos;
	    tmp = ch->head;
	    ch->head = tmp->next;
	    if (!ch->head)
		ch->tail = NULL;
	    sfree(tmp);
	} else
	    ch->head->bufpos += remlen;
	ch->buffersize -= remlen;
	len -= remlen;
    }
}

void bufchain_prefix(bufchain *ch, void **data, int *len)
{
    *len = ch->head->bufend - ch->head->bufpos;
    *data = ch->head->bufpos;
}

void bufchain_fetch(bufchain *ch, void *data, int len)
{
    struct bufchain_granule *tmp;
    char *data_c = (char *)data;

    tmp = ch->head;

    assert(ch->buffersize >= len);
    while (len > 0) {
	int remlen = len;

	assert(tmp != NULL);
	if (remlen >= tmp->bufend - tmp->bufpos)
	    remlen = tmp->bufend - tmp->bufpos;
	memcpy(data_c, tmp->bufpos, remlen);

	tmp = tmp->next;
	len -= remlen;
	data_c += remlen;
    }
}

/* ----------------------------------------------------------------------
 * My own versions of malloc, realloc and free. Because I want
 * malloc and realloc to bomb out and exit the program if they run
 * out of memory, realloc to reliably call malloc if passed a NULL
 * pointer, and free to reliably do nothing if passed a NULL
 * pointer. We can also put trace printouts in, if we need to; and
 * we can also replace the allocator with an ElectricFence-like
 * one.
 */

#ifdef MINEFIELD
void *minefield_c_malloc(size_t size);
void minefield_c_free(void *p);
void *minefield_c_realloc(void *p, size_t size);
#endif

#ifdef MALLOC_LOG
static FILE *fp = NULL;

static char *mlog_file = NULL;
static int mlog_line = 0;

void mlog(char *file, int line)
{
    mlog_file = file;
    mlog_line = line;
    if (!fp) {
	fp = fopen("putty_mem.log", "w");
	setvbuf(fp, NULL, _IONBF, BUFSIZ);
    }
    if (fp)
	fprintf(fp, "%s:%d: ", file, line);
}
#endif

void *safemalloc(size_t n, size_t size)
{
    void *p;

    if (n > INT_MAX / size) {
	p = NULL;
    } else {
	size *= n;
	if (size == 0) size = 1;
#ifdef MINEFIELD
	p = minefield_c_malloc(size);
#else
	p = malloc(size);
#endif
    }

    if (!p) {
	char str[200];
#ifdef MALLOC_LOG
	sprintf(str, "Out of memory! (%s:%d, size=%d)",
		mlog_file, mlog_line, size);
	fprintf(fp, "*** %s\n", str);
	fclose(fp);
#else
	strcpy(str, "Out of memory!");
#endif
	modalfatalbox("%s", str);
    }
#ifdef MALLOC_LOG
    if (fp)
	fprintf(fp, "malloc(%d) returns %p\n", size, p);
#endif
    return p;
}

void *saferealloc(void *ptr, size_t n, size_t size)
{
    void *p;

    if (n > INT_MAX / size) {
	p = NULL;
    } else {
	size *= n;
	if (!ptr) {
#ifdef MINEFIELD
	    p = minefield_c_malloc(size);
#else
	    p = malloc(size);
#endif
	} else {
#ifdef MINEFIELD
	    p = minefield_c_realloc(ptr, size);
#else
	    p = realloc(ptr, size);
#endif
	}
    }

    if (!p) {
	char str[200];
#ifdef MALLOC_LOG
	sprintf(str, "Out of memory! (%s:%d, size=%d)",
		mlog_file, mlog_line, size);
	fprintf(fp, "*** %s\n", str);
	fclose(fp);
#else
	strcpy(str, "Out of memory!");
#endif
	modalfatalbox("%s", str);
    }
#ifdef MALLOC_LOG
    if (fp)
	fprintf(fp, "realloc(%p,%d) returns %p\n", ptr, size, p);
#endif
    return p;
}

void safefree(void *ptr)
{
    if (ptr) {
#ifdef MALLOC_LOG
	if (fp)
	    fprintf(fp, "free(%p)\n", ptr);
#endif
#ifdef MINEFIELD
	minefield_c_free(ptr);
#else
	free(ptr);
#endif
    }
#ifdef MALLOC_LOG
    else if (fp)
	fprintf(fp, "freeing null pointer - no action taken\n");
#endif
}

/* ----------------------------------------------------------------------
 * Debugging routines.
 */

#ifdef DEBUG
extern void dputs(const char *); /* defined in per-platform *misc.c */

void debug_printf(const char *fmt, ...)
{
    char *buf;
    va_list ap;

    va_start(ap, fmt);
    buf = dupvprintf(fmt, ap);
    dputs(buf);
    sfree(buf);
    va_end(ap);
}


void debug_memdump(const void *buf, int len, int L)
{
    int i;
    const unsigned char *p = buf;
    char foo[17];
    if (L) {
	int delta;
	debug_printf("\t%d (0x%x) bytes:\n", len, len);
	delta = 15 & (uintptr_t)p;
	p -= delta;
	len += delta;
    }
    for (; 0 < len; p += 16, len -= 16) {
	dputs("  ");
	if (L)
	    debug_printf("%p: ", p);
	strcpy(foo, "................");	/* sixteen dots */
	for (i = 0; i < 16 && i < len; ++i) {
	    if (&p[i] < (unsigned char *) buf) {
		dputs("   ");	       /* 3 spaces */
		foo[i] = ' ';
	    } else {
		debug_printf("%c%02.2x",
			&p[i] != (unsigned char *) buf
			&& i % 4 ? '.' : ' ', p[i]
		    );
		if (p[i] >= ' ' && p[i] <= '~')
		    foo[i] = (char) p[i];
	    }
	}
	foo[i] = '\0';
	debug_printf("%*s%s\n", (16 - i) * 3 + 2, "", foo);
    }
}

#endif				/* def DEBUG */

/*
 * Determine whether or not a Conf represents a session which can
 * sensibly be launched right now.
 */
int conf_launchable(Conf *conf)
{
    if (conf_get_int(conf, CONF_protocol) == PROT_SERIAL)
	return conf_get_str(conf, CONF_serline)[0] != 0;
    else
	return conf_get_str(conf, CONF_host)[0] != 0;
}

char const *conf_dest(Conf *conf)
{
    if (conf_get_int(conf, CONF_protocol) == PROT_SERIAL)
	return conf_get_str(conf, CONF_serline);
    else
	return conf_get_str(conf, CONF_host);
}

#ifndef PLATFORM_HAS_SMEMCLR
/*
 * Securely wipe memory.
 *
 * The actual wiping is no different from what memset would do: the
 * point of 'securely' is to try to be sure over-clever compilers
 * won't optimise away memsets on variables that are about to be freed
 * or go out of scope. See
 * https://buildsecurityin.us-cert.gov/bsi-rules/home/g1/771-BSI.html
 *
 * Some platforms (e.g. Windows) may provide their own version of this
 * function.
 */
void smemclr(void *b, size_t n) {
    volatile char *vp;

    if (b && n > 0) {
        /*
         * Zero out the memory.
         */
        memset(b, 0, n);

        /*
         * Perform a volatile access to the object, forcing the
         * compiler to admit that the previous memset was important.
         *
         * This while loop should in practice run for zero iterations
         * (since we know we just zeroed the object out), but in
         * theory (as far as the compiler knows) it might range over
         * the whole object. (If we had just written, say, '*vp =
         * *vp;', a compiler could in principle have 'helpfully'
         * optimised the memset into only zeroing out the first byte.
         * This should be robust.)
         */
        vp = b;
        while (*vp) vp++;
    }
}
#endif

/*
 * Validate a manual host key specification (either entered in the
 * GUI, or via -hostkey). If valid, we return TRUE, and update 'key'
 * to contain a canonicalised version of the key string in 'key'
 * (which is guaranteed to take up at most as much space as the
 * original version), suitable for putting into the Conf. If not
 * valid, we return FALSE.
 */
int validate_manual_hostkey(char *key)
{
    char *p, *q, *r, *s;

    /*
     * Step through the string word by word, looking for a word that's
     * in one of the formats we like.
     */
    p = key;
    while ((p += strspn(p, " \t"))[0]) {
        q = p;
        p += strcspn(p, " \t");
        if (*p) *p++ = '\0';

        /*
         * Now q is our word.
         */

        if (strlen(q) == 16*3 - 1 &&
            q[strspn(q, "0123456789abcdefABCDEF:")] == 0) {
            /*
             * Might be a key fingerprint. Check the colons are in the
             * right places, and if so, return the same fingerprint
             * canonicalised into lowercase.
             */
            int i;
            for (i = 0; i < 16; i++)
                if (q[3*i] == ':' || q[3*i+1] == ':')
                    goto not_fingerprint; /* sorry */
            for (i = 0; i < 15; i++)
                if (q[3*i+2] != ':')
                    goto not_fingerprint; /* sorry */
            for (i = 0; i < 16*3 - 1; i++)
                key[i] = tolower(q[i]);
            key[16*3 - 1] = '\0';
            return TRUE;
        }
      not_fingerprint:;

        /*
         * Before we check for a public-key blob, trim newlines out of
         * the middle of the word, in case someone's managed to paste
         * in a public-key blob _with_ them.
         */
        for (r = s = q; *r; r++)
            if (*r != '\n' && *r != '\r')
                *s++ = *r;
        *s = '\0';

        if (strlen(q) % 4 == 0 && strlen(q) > 2*4 &&
            q[strspn(q, "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"
                     "abcdefghijklmnopqrstuvwxyz+/=")] == 0) {
            /*
             * Might be a base64-encoded SSH-2 public key blob. Check
             * that it starts with a sensible algorithm string. No
             * canonicalisation is necessary for this string type.
             *
             * The algorithm string must be at most 64 characters long
             * (RFC 4251 section 6).
             */
            unsigned char decoded[6];
            unsigned alglen;
            int minlen;
            int len = 0;

            len += base64_decode_atom(q, decoded+len);
            if (len < 3)
                goto not_ssh2_blob;    /* sorry */
            len += base64_decode_atom(q+4, decoded+len);
            if (len < 4)
                goto not_ssh2_blob;    /* sorry */

            alglen = GET_32BIT_MSB_FIRST(decoded);
            if (alglen > 64)
                goto not_ssh2_blob;    /* sorry */

            minlen = ((alglen + 4) + 2) / 3;
            if (strlen(q) < minlen)
                goto not_ssh2_blob;    /* sorry */

            strcpy(key, q);
            return TRUE;
        }
      not_ssh2_blob:;
    }

    return FALSE;
}

int smemeq(const void *av, const void *bv, size_t len)
{
    const unsigned char *a = (const unsigned char *)av;
    const unsigned char *b = (const unsigned char *)bv;
    unsigned val = 0;

    while (len-- > 0) {
        val |= *a++ ^ *b++;
    }
    /* Now val is 0 iff we want to return 1, and in the range
     * 0x01..0xFF iff we want to return 0. So subtracting from 0x100
     * will clear bit 8 iff we want to return 0, and leave it set iff
     * we want to return 1, so then we can just shift down. */
    return (0x100 - val) >> 8;
}

int match_ssh_id(int stringlen, const void *string, const char *id)
{
    int idlen = strlen(id);
    return (idlen == stringlen && !memcmp(string, id, idlen));
}

void *get_ssh_string(int *datalen, const void **data, int *stringlen)
{
    void *ret;
    unsigned int len;

    if (*datalen < 4)
        return NULL;
    len = GET_32BIT_MSB_FIRST((const unsigned char *)*data);
    if (*datalen < len+4)
        return NULL;
    ret = (void *)((const char *)*data + 4);
    *datalen -= len + 4;
    *data = (const char *)*data + len + 4;
    *stringlen = len;
    return ret;
}

int get_ssh_uint32(int *datalen, const void **data, unsigned *ret)
{
    if (*datalen < 4)
        return FALSE;
    *ret = GET_32BIT_MSB_FIRST((const unsigned char *)*data);
    *datalen -= 4;
    *data = (const char *)*data + 4;
    return TRUE;
}

int strstartswith(const char *s, const char *t)
{
    return !memcmp(s, t, strlen(t));
}

int strendswith(const char *s, const char *t)
{
    size_t slen = strlen(s), tlen = strlen(t);
    return slen >= tlen && !strcmp(s + (slen - tlen), t);
}