path: root/src/cursor/cur_json.c

/*-
 * Copyright (c) 2014-2016 MongoDB, Inc.
 * Copyright (c) 2008-2014 WiredTiger, Inc.
 *	All rights reserved.
 *
 * See the file LICENSE for redistribution information.
 */

#include "wt_internal.h"

static size_t __json_unpack_put(WT_SESSION_IMPL *, void *, u_char *, size_t,
    WT_CONFIG_ITEM *);
static inline int __json_struct_size(WT_SESSION_IMPL *, const void *, size_t,
    const char *, WT_CONFIG_ITEM *, bool, size_t *);
static inline int __json_struct_unpackv(WT_SESSION_IMPL *, const void *, size_t,
    const char *, WT_CONFIG_ITEM *, u_char *, size_t, bool, va_list);
static int json_string_arg(WT_SESSION_IMPL *, const char **, WT_ITEM *);
static int json_int_arg(WT_SESSION_IMPL *, const char **, int64_t *);
static int json_uint_arg(WT_SESSION_IMPL *, const char **, uint64_t *);
static int __json_pack_struct(WT_SESSION_IMPL *, void *, size_t, const char *,
    const char *);
static int __json_pack_size(WT_SESSION_IMPL *, const char *, WT_CONFIG_ITEM *,
    bool, const char *, size_t *);

#define	WT_PACK_JSON_GET(session, pv, jstr) do {			\
	switch (pv.type) {						\
	case 'x':							\
		break;							\
	case 's':							\
	case 'S':							\
		WT_RET(json_string_arg(session, &jstr, &pv.u.item));	\
		pv.type = pv.type == 's' ? 'j' : 'J';			\
		break;							\
	case 'b':							\
	case 'h':							\
	case 'i':							\
	case 'l':							\
	case 'q':							\
		WT_RET(json_int_arg(session, &jstr, &pv.u.i));		\
		break;							\
	case 'B':							\
	case 'H':							\
	case 'I':							\
	case 'L':							\
	case 'Q':							\
	case 'r':							\
	case 'R':							\
	case 't':							\
		WT_RET(json_uint_arg(session, &jstr, &pv.u.u));		\
		break;							\
	case 'u':							\
		WT_RET(json_string_arg(session, &jstr, &pv.u.item));	\
		pv.type = 'K';						\
		break;							\
	/* User format strings have already been validated. */		\
	WT_ILLEGAL_VALUE(session);					\
	}								\
} while (0)

/*
 * __json_unpack_put --
 *	Calculate the size of a packed byte string as formatted for JSON.
 */
static size_t
__json_unpack_put(WT_SESSION_IMPL *session, void *voidpv,
    u_char *buf, size_t bufsz, WT_CONFIG_ITEM *name)
{
	WT_PACK_VALUE *pv;
	const u_char *p, *end;
	size_t s, n;

	pv = (WT_PACK_VALUE *)voidpv;
	s = (size_t)snprintf((char *)buf, bufsz, "\"%.*s\" : ",
	    (int)name->len, name->str);
	if (s <= bufsz) {
		bufsz -= s;
		buf += s;
	}
	else
		bufsz = 0;

	switch (pv->type) {
	case 'x':
		return (0);
	case 's':
	case 'S':
		/* Account for '"' quote in front and back. */
		s += 2;
		p = (const u_char *)pv->u.s;
		if (bufsz > 0) {
			*buf++ = '"';
			bufsz--;
		}
		if (pv->type == 's' || pv->havesize) {
			end = p + pv->size;
			for (; p < end; p++) {
				n = __wt_json_unpack_char(
				    *p, buf, bufsz, false);
				if (n > bufsz)
					bufsz = 0;
				else {
					bufsz -= n;
					buf += n;
				}
				s += n;
			}
		} else
			for (; *p; p++) {
				n = __wt_json_unpack_char(
				    *p, buf, bufsz, false);
				if (n > bufsz)
					bufsz = 0;
				else {
					bufsz -= n;
					buf += n;
				}
				s += n;
			}
		if (bufsz > 0)
			*buf++ = '"';
		return (s);
	case 'U':
	case 'u':
		s += 2;
		p = (const u_char *)pv->u.item.data;
		end = p + pv->u.item.size;
		if (bufsz > 0) {
			*buf++ = '"';
			bufsz--;
		}
		for (; p < end; p++) {
			n = __wt_json_unpack_char(*p, buf, bufsz, true);
			if (n > bufsz)
				bufsz = 0;
			else {
				bufsz -= n;
				buf += n;
			}
			s += n;
		}
		if (bufsz > 0)
			*buf++ = '"';
		return (s);
	case 'b':
	case 'h':
	case 'i':
	case 'l':
	case 'q':
		return (s +
		    (size_t)snprintf((char *)buf, bufsz, "%" PRId64, pv->u.i));
	case 'B':
	case 't':
	case 'H':
	case 'I':
	case 'L':
	case 'Q':
	case 'r':
	case 'R':
		return (s +
		    (size_t)snprintf((char *)buf, bufsz, "%" PRId64, pv->u.u));
	}
	__wt_err(session, EINVAL, "unknown pack-value type: %c", (int)pv->type);
	return ((size_t)-1);
}

/*
 * __json_struct_size --
 *	Calculate the size of a packed byte string as formatted for JSON.
 */
static inline int
__json_struct_size(WT_SESSION_IMPL *session, const void *buffer,
    size_t size, const char *fmt, WT_CONFIG_ITEM *names, bool iskey,
    size_t *presult)
{
	WT_CONFIG_ITEM name;
	WT_DECL_PACK_VALUE(pv);
	WT_DECL_RET;
	WT_PACK pack;
	WT_PACK_NAME packname;
	size_t result;
	bool needcr;
	const uint8_t *p, *end;

	p = buffer;
	end = p + size;
	result = 0;
	needcr = false;

	__pack_name_init(session, names, iskey, &packname);
	WT_RET(__pack_init(session, &pack, fmt));
	while ((ret = __pack_next(&pack, &pv)) == 0) {
		if (needcr)
			result += 2;
		needcr = true;
		WT_RET(__unpack_read(session, &pv, &p, (size_t)(end - p)));
		WT_RET(__pack_name_next(&packname, &name));
		result += __json_unpack_put(session, &pv, NULL, 0, &name);
	}
	if (ret == WT_NOTFOUND)
		ret = 0;

	/* Be paranoid - __pack_write should never overflow. */
	WT_ASSERT(session, p <= end);

	*presult = result;
	return (ret);
}

/*
 * __json_struct_unpackv --
 *	Unpack a byte string to JSON (va_list version).
 */
static inline int
__json_struct_unpackv(WT_SESSION_IMPL *session,
    const void *buffer, size_t size, const char *fmt, WT_CONFIG_ITEM *names,
    u_char *jbuf, size_t jbufsize, bool iskey, va_list ap)
{
	WT_CONFIG_ITEM name;
	WT_DECL_PACK_VALUE(pv);
	WT_DECL_RET;
	WT_PACK pack;
	WT_PACK_NAME packname;
	size_t jsize;
	bool needcr;
	const uint8_t *p, *end;

	p = buffer;
	end = p + size;
	needcr = false;

	/* Unpacking a cursor marked as json implies a single arg. */
	*va_arg(ap, const char **) = (char *)jbuf;

	__pack_name_init(session, names, iskey, &packname);
	WT_RET(__pack_init(session, &pack, fmt));
	while ((ret = __pack_next(&pack, &pv)) == 0) {
		if (needcr) {
			WT_ASSERT(session, jbufsize >= 3);
			strncat((char *)jbuf, ",\n", jbufsize);
			jbuf += 2;
			jbufsize -= 2;
		}
		needcr = true;
		WT_RET(__unpack_read(session, &pv, &p, (size_t)(end - p)));
		WT_RET(__pack_name_next(&packname, &name));
		jsize = __json_unpack_put(session,
		    (u_char *)&pv, jbuf, jbufsize, &name);
		WT_ASSERT(session, jsize <= jbufsize);
		jbuf += jsize;
		jbufsize -= jsize;
	}
	if (ret == WT_NOTFOUND)
		ret = 0;

	/* Be paranoid - __unpack_read should never overflow. */
	WT_ASSERT(session, p <= end);

	WT_ASSERT(session, jbufsize == 1);

	return (ret);
}

/*
 * __wt_json_alloc_unpack --
 *	Allocate space for, and unpack an entry into JSON format.
 */
int
__wt_json_alloc_unpack(WT_SESSION_IMPL *session, const void *buffer,
    size_t size, const char *fmt, WT_CURSOR_JSON *json,
    bool iskey, va_list ap)
{
	WT_CONFIG_ITEM *names;
	WT_DECL_RET;
	size_t needed;
	char **json_bufp;

	if (iskey) {
		names = &json->key_names;
		json_bufp = &json->key_buf;
	} else {
		names = &json->value_names;
		json_bufp = &json->value_buf;
	}
	needed = 0;
	WT_RET(__json_struct_size(session, buffer, size, fmt, names,
	    iskey, &needed));
	WT_RET(__wt_realloc(session, NULL, needed + 1, json_bufp));
	WT_RET(__json_struct_unpackv(session, buffer, size, fmt,
	    names, (u_char *)*json_bufp, needed + 1, iskey, ap));

	return (ret);
}

/*
 * __wt_json_close --
 *	Release any json related resources.
 */
void
__wt_json_close(WT_SESSION_IMPL *session, WT_CURSOR *cursor)
{
	WT_CURSOR_JSON *json;

	if ((json = (WT_CURSOR_JSON *)cursor->json_private) != NULL) {
		__wt_free(session, json->key_buf);
		__wt_free(session, json->value_buf);
		__wt_free(session, json);
	}
	return;
}

/*
 * __wt_json_unpack_char --
 *	Unpack a single character into JSON escaped format.
 *	Can be called with null buf for sizing.
 */
size_t
__wt_json_unpack_char(u_char ch, u_char *buf, size_t bufsz, bool force_unicode)
{
	u_char abbrev;

	if (!force_unicode) {
		if (__wt_isprint(ch) && ch != '\\' && ch != '"') {
			if (bufsz >= 1)
				*buf = ch;
			return (1);
		} else {
			abbrev = '\0';
			switch (ch) {
			case '\\':
			case '"':
				abbrev = ch;
				break;
			case '\f':
				abbrev = 'f';
				break;
			case '\n':
				abbrev = 'n';
				break;
			case '\r':
				abbrev = 'r';
				break;
			case '\t':
				abbrev = 't';
				break;
			}
			if (abbrev != '\0') {
				if (bufsz >= 2) {
					*buf++ = '\\';
					*buf = abbrev;
				}
				return (2);
			}
		}
	}
	if (bufsz >= 6) {
		*buf++ = '\\';
		*buf++ = 'u';
		*buf++ = '0';
		*buf++ = '0';
		*buf++ = __wt_hex((ch & 0xf0) >> 4);
		*buf++ = __wt_hex(ch & 0x0f);
	}
	return (6);
}

/*
 * __wt_json_column_init --
 *	Set json_key_names, json_value_names to comma separated lists
 *	of column names.
 */
void
__wt_json_column_init(WT_CURSOR *cursor, const char *keyformat,
    const WT_CONFIG_ITEM *idxconf, const WT_CONFIG_ITEM *colconf)
{
	WT_CURSOR_JSON *json;
	const char *p, *end, *beginkey;
	uint32_t keycnt, nkeys;

	json = (WT_CURSOR_JSON *)cursor->json_private;
	beginkey = colconf->str;
	end = beginkey + colconf->len;

	if (idxconf != NULL) {
		json->key_names.str = idxconf->str;
		json->key_names.len = idxconf->len;
	} else if (colconf->len > 0 && *beginkey == '(') {
		beginkey++;
		if (end[-1] == ')')
			end--;
	}

	for (nkeys = 0; *keyformat; keyformat++)
		if (!__wt_isdigit((u_char)*keyformat))
			nkeys++;

	p = beginkey;
	keycnt = 0;
	while (p < end && keycnt < nkeys) {
		if (*p == ',')
			keycnt++;
		p++;
	}
	json->value_names.str = p;
	json->value_names.len = WT_PTRDIFF(end, p);
	if (idxconf == NULL) {
		if (p > beginkey)
			p--;
		json->key_names.str = beginkey;
		json->key_names.len = WT_PTRDIFF(p, beginkey);
	}
}

#define	MATCH_KEYWORD(session, in, result, keyword, matchval) 	do {	\
	size_t _kwlen = strlen(keyword);				\
	if (strncmp(in, keyword, _kwlen) == 0 &&			\
	    !__wt_isalnum((u_char)in[_kwlen])) {			\
		in += _kwlen;						\
		result = matchval;					\
	} else {							\
		const char *_bad = in;					\
		while (__wt_isalnum((u_char)*in))			\
			in++;						\
		WT_RET_MSG(session, EINVAL,				\
		    "unknown keyword \"%.*s\" in JSON",			\
		    (int)(in - _bad), _bad);				\
	}								\
} while (0)

/*
 * __wt_json_token --
 *	Return the type, start position and length of the next JSON
 *	token in the input.  String tokens include the quotes.  JSON
 *	can be entirely parsed using calls to this tokenizer, each
 *	call using a src pointer that is the previously returned
 *	tokstart + toklen.
 *
 *	The token type returned is one of:
 *		0	:  EOF
 *		's'	:  string
 *		'i'	:  intnum
 *		'f'	:  floatnum
 *		':'	:  colon
 *		','	:  comma
 *		'{'	:  lbrace
 *		'}'	:  rbrace
 *		'['	:  lbracket
 *		']'	:  rbracket
 *		'N'	:  null
 *		'T'	:  true
 *		'F'	:  false
 */
int
__wt_json_token(WT_SESSION *wt_session, const char *src, int *toktype,
    const char **tokstart, size_t *toklen)
{
	WT_SESSION_IMPL *session;
	int result;
	bool backslash, isalph, isfloat;
	const char *bad;
	char ch;

	result = -1;
	session = (WT_SESSION_IMPL *)wt_session;
	while (__wt_isspace((u_char)*src))
		src++;
	*tokstart = src;

	if (*src == '\0') {
		*toktype = 0;
		*toklen = 0;
		return (0);
	}

	/* JSON is specified in RFC 4627. */
	switch (*src) {
	case '"':
		backslash = false;
		src++;
		while ((ch = *src) != '\0') {
			if (!backslash) {
				if (ch == '"') {
					src++;
					result = 's';
					break;
				}
				if (ch == '\\')
					backslash = true;
			} else {
				/* We validate Unicode on this pass. */
				if (ch == 'u') {
					u_char ignored;
					const u_char *uc;

					uc = (const u_char *)src;
					if (__wt_hex2byte(&uc[1], &ignored) ||
					    __wt_hex2byte(&uc[3], &ignored))
						WT_RET_MSG(session, EINVAL,
				    "invalid Unicode within JSON string");
					src += 4;
				}
				backslash = false;
			}
			src++;
		}
		if (result == 's')
			break;
		WT_RET_MSG(session, EINVAL, "unterminated string in JSON");
	case '-':
	case '0':
	case '1':
	case '2':
	case '3':
	case '4':
	case '5':
	case '6':
	case '7':
	case '8':
	case '9':
		isfloat = false;
		if (*src == '-')
			src++;
		while ((ch = *src) != '\0' && __wt_isdigit((u_char)ch))
			src++;
		if (*src == '.') {
			isfloat = true;
			src++;
			while ((ch = *src) != '\0' && __wt_isdigit((u_char)ch))
				src++;
		}
		if (*src == 'e' || *src == 'E') {
			isfloat = true;
			src++;
			if (*src == '+' || *src == '-')
				src++;
			while ((ch = *src) != '\0' && __wt_isdigit((u_char)ch))
				src++;
		}
		result = isfloat ? 'f' : 'i';
		break;
	case ':':
	case ',':
	case '{':
	case '}':
	case '[':
	case ']':
		result = *src++;
		break;
	case 'n':
		MATCH_KEYWORD(session, src, result, "null", 'N');
		break;
	case 't':
		MATCH_KEYWORD(session, src, result, "true", 'T');
		break;
	case 'f':
		MATCH_KEYWORD(session, src, result, "false", 'F');
		break;
	default:
		/* An illegal token, move past it anyway */
		bad = src;
		isalph = __wt_isalnum((u_char)*src);
		src++;
		if (isalph)
			while (*src != '\0' && __wt_isalnum((u_char)*src))
				src++;
		WT_RET_MSG(session, EINVAL,
		    "unknown token \"%.*s\" in JSON", (int)(src - bad), bad);
		/* NOTREACHED */
	}
	WT_ASSERT(session, result != -1);

	*toklen = (size_t)(src - *tokstart);
	*toktype = result;
	return (0);
}

/*
 * __wt_json_tokname --
 *	Return a descriptive name from the token type returned by
 *	__wt_json_token.
 */
const char *
__wt_json_tokname(int toktype)
{
	switch (toktype) {
	case 0:		return ("<EOF>");
	case 's':	return ("<string>");
	case 'i':	return ("<integer>");
	case 'f':	return ("<float>");
	case ':':	return ("':'");
	case ',':	return ("','");
	case '{':	return ("'{'");
	case '}':	return ("'}'");
	case '[':	return ("'['");
	case ']':	return ("']'");
	case 'N':	return ("'null'");
	case 'T':	return ("'true'");
	case 'F':	return ("'false'");
	default:	return ("<UNKNOWN>");
	}
}

/*
 * json_string_arg --
 *	Returns a first cut of the needed string in item.
 *	The result has not been stripped of escapes.
 */
static int
json_string_arg(WT_SESSION_IMPL *session, const char **jstr, WT_ITEM *item)
{
	int tok;
	const char *tokstart;

	WT_RET(__wt_json_token(
	    (WT_SESSION *)session, *jstr, &tok, &tokstart, &item->size));
	if (tok == 's') {
		*jstr = tokstart + item->size;
		/* The tokenizer includes the '"' chars */
		item->data = tokstart + 1;
		item->size -= 2;
	} else
		WT_RET_MSG(session, EINVAL,
		    "expected JSON <string>, got %s", __wt_json_tokname(tok));
	return (0);
}

/*
 * json_int_arg --
 *	Returns a signed integral value from the current position
 *	in the JSON string.
 */
static int
json_int_arg(WT_SESSION_IMPL *session, const char **jstr, int64_t *ip)
{
	char *end;
	const char *tokstart;
	size_t toksize;
	int tok;

	WT_RET(__wt_json_token((WT_SESSION *)session, *jstr, &tok, &tokstart,
		&toksize));
	if (tok == 'i') {
		/* JSON only allows decimal */
		*ip = strtoll(tokstart, &end, 10);
		if (end != tokstart + toksize)
			WT_RET_MSG(session, EINVAL,
			    "JSON <int> extraneous input");
		*jstr = tokstart + toksize;
	} else
		WT_RET_MSG(session, EINVAL,
		    "expected JSON <int>, got %s", __wt_json_tokname(tok));
	return (0);
}

/*
 * json_uint_arg --
 *	Returns an unsigned integral value from the current position
 *	in the JSON string.
 */
static int
json_uint_arg(WT_SESSION_IMPL *session, const char **jstr, uint64_t *up)
{
	size_t toksize;
	int tok;
	const char *tokstart;
	char *end;

	WT_RET(__wt_json_token((WT_SESSION *)session, *jstr, &tok, &tokstart,
		&toksize));
	if (tok == 'i' && *tokstart != '-') {
		/* JSON only allows decimal */
		*up = strtoull(tokstart, &end, 10);
		if (end != tokstart + toksize)
			WT_RET_MSG(session, EINVAL,
			    "JSON <int> extraneous input");
		*jstr = tokstart + toksize;
	} else
		WT_RET_MSG(session, EINVAL,
		    "expected unsigned JSON <int>, got %s",
		    __wt_json_tokname(tok));
	return (0);
}

#define	JSON_EXPECT_TOKEN_GET(session, jstr, tokval, start, sz) do {	\
    int __tok;								\
    WT_RET(__wt_json_token((WT_SESSION *)session, jstr, &__tok, &start, &sz));\
    if (__tok != tokval)						\
	    WT_RET_MSG(session, EINVAL,					\
		"expected JSON %s, got %s",				\
		__wt_json_tokname(tokval), __wt_json_tokname(__tok));	\
    jstr = start + sz;							\
} while (0)

#define	JSON_EXPECT_TOKEN(session, jstr, tokval) do {			\
    const char *__start;						\
    size_t __sz;							\
    JSON_EXPECT_TOKEN_GET(session, jstr, tokval, __start, __sz);	\
} while (0)

/*
 * __json_pack_struct --
 *	Pack a byte string from a JSON string.
 */
static int
__json_pack_struct(WT_SESSION_IMPL *session, void *buffer, size_t size,
    const char *fmt, const char *jstr)
{
	WT_DECL_PACK_VALUE(pv);
	WT_DECL_RET;
	WT_PACK pack;
	size_t toksize;
	bool multi;
	uint8_t *p, *end;
	const char *tokstart;

	p = buffer;
	end = p + size;
	multi = false;

	if (fmt[0] != '\0' && fmt[1] == '\0') {
		JSON_EXPECT_TOKEN_GET(session, jstr, 's', tokstart, toksize);
		/* the key name was verified in __json_pack_size */
		JSON_EXPECT_TOKEN(session, jstr, ':');
		pv.type = fmt[0];
		WT_PACK_JSON_GET(session, pv, jstr);
		return (__pack_write(session, &pv, &p, size));
	}

	WT_RET(__pack_init(session, &pack, fmt));
	while ((ret = __pack_next(&pack, &pv)) == 0) {
		if (multi)
			JSON_EXPECT_TOKEN(session, jstr, ',');
		JSON_EXPECT_TOKEN_GET(session, jstr, 's', tokstart, toksize);
		/* the key name was verified in __json_pack_size */
		JSON_EXPECT_TOKEN(session, jstr, ':');
		WT_PACK_JSON_GET(session, pv, jstr);
		WT_RET(__pack_write(session, &pv, &p, (size_t)(end - p)));
		multi = true;
	}

	/* Be paranoid - __pack_write should never overflow. */
	WT_ASSERT(session, p <= end);

	if (ret != WT_NOTFOUND)
		return (ret);

	return (0);
}

/*
 * __json_pack_size --
 *	Calculate the size of a packed byte string from a JSON string.
 *	We verify that the names and value types provided in JSON match
 *	the column names and type from the schema format, returning error
 *	if not.
 */
static int
__json_pack_size(
    WT_SESSION_IMPL *session, const char *fmt, WT_CONFIG_ITEM *names,
	bool iskey, const char *jstr, size_t *sizep)
{
	WT_CONFIG_ITEM name;
	WT_DECL_PACK_VALUE(pv);
	WT_PACK pack;
	WT_PACK_NAME packname;
	size_t toksize, total;
	bool multi;
	const char *tokstart;

	__pack_name_init(session, names, iskey, &packname);
	multi = false;
	WT_RET(__pack_init(session, &pack, fmt));
	for (total = 0; __pack_next(&pack, &pv) == 0;) {
		if (multi)
			JSON_EXPECT_TOKEN(session, jstr, ',');
		JSON_EXPECT_TOKEN_GET(session, jstr, 's', tokstart, toksize);
		WT_RET(__pack_name_next(&packname, &name));
		if (toksize - 2 != name.len ||
		    strncmp(tokstart + 1, name.str, toksize - 2) != 0)
			WT_RET_MSG(session, EINVAL,
			    "JSON expected %s name: \"%.*s\"",
			    iskey ? "key" : "value", (int)name.len, name.str);
		JSON_EXPECT_TOKEN(session, jstr, ':');
		WT_PACK_JSON_GET(session, pv, jstr);
		total += __pack_size(session, &pv);
		multi = true;
	}
	/* check end of string */
	JSON_EXPECT_TOKEN(session, jstr, 0);

	*sizep = total;
	return (0);
}

/*
 * __wt_json_to_item --
 *	Convert a JSON input string for either key/value to a raw WT_ITEM.
 *	Checks that the input matches the expected format.
 */
int
__wt_json_to_item(WT_SESSION_IMPL *session, const char *jstr,
    const char *format, WT_CURSOR_JSON *json, bool iskey, WT_ITEM *item)
{
	size_t sz;
	sz = 0; /* Initialize because GCC 4.1 is paranoid */

	WT_RET(__json_pack_size(session, format,
	    iskey ? &json->key_names : &json->value_names, iskey, jstr, &sz));
	WT_RET(__wt_buf_initsize(session, item, sz));
	WT_RET(__json_pack_struct(session, item->mem, sz, format, jstr));
	return (0);
}

/*
 * __wt_json_strlen --
 *	Return the number of bytes represented by a string in JSON format,
 *	or -1 if the format is incorrect.
 */
ssize_t
__wt_json_strlen(const char *src, size_t srclen)
{
	const char *srcend;
	size_t dstlen;
	u_char hi, lo;

	dstlen = 0;
	srcend = src + srclen;
	while (src < srcend) {
		/* JSON can include any UTF-8 expressed in 4 hex chars. */
		if (*src == '\\') {
			if (*++src == 'u') {
				if (__wt_hex2byte((const u_char *)++src, &hi))
					return (-1);
				src += 2;
				if (__wt_hex2byte((const u_char *)src, &lo))
					return (-1);
				src += 2;
				if (hi != 0)
					/*
					 * For our dump representation,
					 * every Unicode character on input
					 * represents a single byte.
					 */
					return (-1);
			}
		} else
			src++;
		dstlen++;
	}
	if (src != srcend)
		return (-1);   /* invalid input, e.g. final char is '\\' */
	return ((ssize_t)dstlen);
}

/*
 * __wt_json_strncpy --
 *	Copy bytes of string in JSON format to a destination, up to dstlen
 * bytes. If dstlen is greater than the needed size, the result if zero padded.
 */
int
__wt_json_strncpy(WT_SESSION *wt_session, char **pdst, size_t dstlen,
    const char *src, size_t srclen)
{
	WT_SESSION_IMPL *session;
	char ch, *dst;
	const char *dstend, *srcend;
	u_char hi, lo;

	session = (WT_SESSION_IMPL *)wt_session;

	dst = *pdst;
	dstend = dst + dstlen;
	srcend = src + srclen;
	while (src < srcend && dst < dstend) {
		/* JSON can include any UTF-8 expressed in 4 hex chars. */
		if ((ch = *src++) == '\\')
			switch (ch = *src++) {
			case 'u':
				if (__wt_hex2byte((const u_char *)src, &hi) ||
				    __wt_hex2byte((const u_char *)src + 2, &lo))
					WT_RET_MSG(session, EINVAL,
				    "invalid Unicode within JSON string");
				src += 4;
				if (hi != 0)
					WT_RET_MSG(session, EINVAL,
					    "Unicode \"%6.6s\" byte out of "
					    "range in JSON",
					    src - 6);
				*dst++ = (char)lo;
				break;
			case 'f':
				*dst++ = '\f';
				break;
			case 'n':
				*dst++ = '\n';
				break;
			case 'r':
				*dst++ = '\r';
				break;
			case 't':
				*dst++ = '\t';
				break;
			case '"':
			case '\\':
				*dst++ = ch;
				break;
			WT_ILLEGAL_VALUE(session);
			}
		else
			*dst++ = ch;
	}
	if (src != srcend)
		WT_RET_MSG(session,
		    ENOMEM, "JSON string copy destination buffer too small");
	*pdst = dst;
	while (dst < dstend)
		*dst++ = '\0';
	return (0);
}