Add support for use of the system timezone database, rather
than embedding a copy.  Discussed upstream but was not desired.

History:
r7: per Sean Finney's review: simpler lat/long rounding,
    use stat() not access() to check existence of timezone,
    improve comments throughout.
r6: fix fd leak in r5, fix country code/BC flag use in 
    timezone_identifiers_list() using system db,
    fix use of PECL timezonedb to override system db,
r5: reverts addition of "System/Localtime" fake tzname.
    updated for 5.3.0, parses zone.tab to pick up mapping between
    timezone name, country code and long/lat coords
r4: added "System/Localtime" tzname which uses /etc/localtime
r3: fix a crash if /usr/share/zoneinfo doesn't exist (Raphael Geissert)
r2: add filesystem trawl to set up name alias index
r1: initial revision

--- a/ext/date/lib/parse_tz.c
+++ b/ext/date/lib/parse_tz.c
@@ -24,6 +24,16 @@
 
 #include "timelib.h"
 
+#ifdef HAVE_SYSTEM_TZDATA
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <limits.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+#include "php_scandir.h"
+#endif
+
 #include <stdio.h>
 
 #ifdef HAVE_LOCALE_H
@@ -35,7 +45,12 @@
 #else
 #include <strings.h>
 #endif
+
+#ifndef HAVE_SYSTEM_TZDATA
 #include "timezonedb.h"
+#endif
+
+#include <ctype.h>
 
 #if (defined(__APPLE__) || defined(__APPLE_CC__)) && (defined(__BIG_ENDIAN__) || defined(__LITTLE_ENDIAN__))
 # if defined(__LITTLE_ENDIAN__)
@@ -55,6 +70,11 @@
 
 static void read_preamble(const unsigned char **tzf, timelib_tzinfo *tz)
 {
+	if (memcmp(tzf, "TZif", 4) == 0) {
+		*tzf += 20;
+		return;
+	}
+    
 	/* skip ID */
 	*tzf += 4;
 	
@@ -257,7 +277,435 @@ void timelib_dump_tzinfo(timelib_tzinfo
 	}
 }
 
-static int seek_to_tz_position(const unsigned char **tzf, char *timezone, const timelib_tzdb *tzdb)
+#ifdef HAVE_SYSTEM_TZDATA
+
+#ifdef HAVE_SYSTEM_TZDATA_PREFIX
+#define ZONEINFO_PREFIX HAVE_SYSTEM_TZDATA_PREFIX
+#else
+#define ZONEINFO_PREFIX "/usr/share/zoneinfo"
+#endif
+
+/* Hash table entry for the cache of the zone.tab mapping table. */
+struct location_info {
+	char code[2]; /* Country code. */
+	double latitude, longitude;
+	char name[64];
+	char *comment;
+	struct location_info *next;
+};
+
+/* System timezone database pointer. */
+static const timelib_tzdb *timezonedb_system = NULL;
+
+/* Cache of zone.tab location data. */
+static struct location_info **system_location_table;
+
+/* Size of the zone.tab hash table; a random-ish prime big enough to
+ * prevent too many collisions. */
+#define LOCINFO_HASH_SIZE (1021)
+
+/* Hash function for indexing the location_info hash table. */
+static uint32_t tz_hash(const char *str)
+{
+	const unsigned char *p = (const unsigned char *)str;
+	uint32_t hash = 5381;
+	int c;
+	
+	while ((c = *p++) != '\0') {
+		hash = (hash << 5) ^ hash ^ c;
+	}
+	
+	return hash % LOCINFO_HASH_SIZE;
+}
+
+/* Parse an ISO-6709 co-ordinate as used in zone.tab. Returns end of
+ * the parsed string on success, or NULL on parse error.  On success,
+ * writes the parsed number to *result. */
+static char *parse_iso6709(char *p, double *result)
+{
+	double v, sign;
+	char *pend;
+	size_t len;
+
+	if (*p == '+')
+		sign = 1.0;
+	else if (*p == '-')
+		sign = -1.0;
+	else
+		return NULL;
+
+	p++;
+	for (pend = p; *pend >= '0' && *pend <= '9'; pend++)
+		;;
+
+	/* Annoying encoding used by zone.tab has no decimal point, so use
+	 * the length to determine the format:
+	 * 
+	 * 4 = DDMM
+	 * 5 = DDDMM
+	 * 6 = DDMMSS
+	 * 7 = DDDMMSS
+	 */
+	len = pend - p;
+	if (len < 4 || len > 7) {
+		return NULL;
+	}
+
+	/* p => [D]DD */
+	v = (p[0] - '0') * 10.0 + (p[1] - '0');
+	p += 2;
+	if (len == 5 || len == 7)
+		v = v * 10.0 + (*p++ - '0');
+	/* p => MM[SS] */
+	v += (10.0 * (p[0] - '0')
+		  + p[1] - '0') / 60.0;
+	p += 2;
+	/* p => [SS] */
+	if (len > 5) {
+		v += (10.0 * (p[0] - '0')
+			  + p[1] - '0') / 3600.0;
+		p += 2;
+	}
+
+	/* Round to five decimal place, not because it's a good idea,
+	 * but, because the builtin data uses rounded data, so, match
+	 * that. */
+	*result = sign * (int)(v * 100000.0 + 0.5) / 100000.0;
+
+	return p;
+}
+
+/* This function parses the zone.tab file to build up the mapping of
+ * timezone to country code and geographic location, and returns a
+ * hash table.	The hash table is indexed by the function:
+ *
+ *	 tz_hash(timezone-name)
+ */
+static struct location_info **create_location_table(void)
+{
+	struct location_info **li, *i;
+	char zone_tab[PATH_MAX];
+	char line[512];
+	FILE *fp;
+
+	strncpy(zone_tab, ZONEINFO_PREFIX "/zone.tab", sizeof zone_tab);
+
+	fp = fopen(zone_tab, "r");
+	if (!fp) {
+		return NULL;
+	}
+
+	li = calloc(LOCINFO_HASH_SIZE, sizeof *li);
+
+	while (fgets(line, sizeof line, fp)) {
+		char *p = line, *code, *name, *comment;
+		uint32_t hash;
+		double latitude, longitude;
+
+		while (isspace(*p))
+			p++;
+
+		if (*p == '#' || *p == '\0' || *p == '\n')
+			continue;
+		
+		if (!isalpha(p[0]) || !isalpha(p[1]) || p[2] != '\t')
+			continue;
+		
+		/* code => AA */
+		code = p;
+		p[2] = 0;
+		p += 3;
+
+		/* coords => [+-][D]DDMM[SS][+-][D]DDMM[SS] */
+		p = parse_iso6709(p, &latitude);
+		if (!p) {
+			continue;
+		}
+		p = parse_iso6709(p, &longitude);
+		if (!p) {
+			continue;
+		}
+
+		if (!p || *p != '\t') {
+			continue;
+		}
+
+		/* name = string */
+		name = ++p;
+		while (*p != '\t' && *p && *p != '\n')
+			p++;
+
+		*p++ = '\0';
+
+		/* comment = string */
+		comment = p;
+		while (*p != '\t' && *p && *p != '\n')
+			p++;
+
+		if (*p == '\n' || *p == '\t')
+			*p = '\0';
+		
+		hash = tz_hash(name);
+		i = malloc(sizeof *i);
+		memcpy(i->code, code, 2);
+		strncpy(i->name, name, sizeof i->name);
+		i->comment = strdup(comment);
+		i->longitude = longitude;
+		i->latitude = latitude;
+		i->next = li[hash];
+		li[hash] = i;
+		/* printf("%s [%u, %f, %f]\n", name, hash, latitude, longitude); */
+	}
+
+	fclose(fp);
+
+	return li;
+}
+
+/* Return location info from hash table, using given timezone name.
+ * Returns NULL if the name could not be found. */
+const struct location_info *find_zone_info(struct location_info **li, 
+										   const char *name)
+{
+	uint32_t hash = tz_hash(name);
+	const struct location_info *l;
+
+	if (!li) {
+		return NULL;
+	}
+
+	for (l = li[hash]; l; l = l->next) {
+		if (strcasecmp(l->name, name) == 0)
+			return l;
+	}
+
+	return NULL;
+}	 
+
+/* Filter out some non-tzdata files and the posix/right databases, if
+ * present. */
+static int index_filter(const struct dirent *ent)
+{
+	return strcmp(ent->d_name, ".") != 0
+		&& strcmp(ent->d_name, "..") != 0
+		&& strcmp(ent->d_name, "posix") != 0
+		&& strcmp(ent->d_name, "posixrules") != 0
+		&& strcmp(ent->d_name, "right") != 0
+		&& strstr(ent->d_name, ".tab") == NULL;
+}
+
+/* Comparison callback for qsort(), used to alpha-sort the index
+ * array by timezone name. */
+static int sysdbcmp(const void *first, const void *second)
+{
+	const timelib_tzdb_index_entry *alpha = first, *beta = second;
+	
+	return strcmp(alpha->id, beta->id);
+}
+
+
+/* Create the zone identifier index by trawling the filesystem. */
+static void create_zone_index(timelib_tzdb *db)
+{
+	size_t dirstack_size,  dirstack_top;
+	size_t index_size, index_next;
+	timelib_tzdb_index_entry *db_index;
+	char **dirstack;
+
+	/* LIFO stack to hold directory entries to scan; each slot is a
+	 * directory name relative to the zoneinfo prefix. */
+	dirstack_size = 32;
+	dirstack = malloc(dirstack_size * sizeof *dirstack);
+	dirstack_top = 1;
+	dirstack[0] = strdup("");
+	
+	/* Index array. */
+	index_size = 64;
+	db_index = malloc(index_size * sizeof *db_index);
+	index_next = 0;
+
+	do {
+		struct dirent **ents;
+		char name[PATH_MAX], *top;
+		int count;
+
+		/* Pop the top stack entry, and iterate through its contents. */
+		top = dirstack[--dirstack_top];
+		snprintf(name, sizeof name, ZONEINFO_PREFIX "/%s", top);
+
+		count = php_scandir(name, &ents, index_filter, php_alphasort);
+
+		while (count > 0) {
+			struct stat st;
+			const char *leaf = ents[count - 1]->d_name;
+
+			snprintf(name, sizeof name, ZONEINFO_PREFIX "/%s/%s", 
+				 top, leaf);
+			
+			if (strlen(name) && stat(name, &st) == 0) {
+				/* Name, relative to the zoneinfo prefix. */
+				const char *root = top;
+
+				if (root[0] == '/') root++;
+
+				snprintf(name, sizeof name, "%s%s%s", root, 
+					 *root ? "/": "", leaf);
+
+				if (S_ISDIR(st.st_mode)) {
+					if (dirstack_top == dirstack_size) {
+						dirstack_size *= 2;
+						dirstack = realloc(dirstack, 
+										   dirstack_size * sizeof *dirstack);
+					}
+					dirstack[dirstack_top++] = strdup(name);
+				}
+				else {
+					if (index_next == index_size) {
+						index_size *= 2;
+						db_index = realloc(db_index,
+										   index_size * sizeof *db_index);
+					}
+
+					db_index[index_next++].id = strdup(name);
+				}
+			}
+
+			free(ents[--count]);
+		}
+		
+		if (count != -1) free(ents);
+		free(top);
+	} while (dirstack_top);
+
+	/* Alpha-sort the index array; shouldn't be technically necessary
+	 * but some of the test cases rely on this, and, it matches the
+	 * builtin database. */
+	qsort(db_index, index_next, sizeof *db_index, sysdbcmp);
+	
+	db->index = db_index;
+	db->index_size = index_next;
+
+	free(dirstack);
+}
+
+#define FAKE_HEADER "1234\0??\1??"
+#define FAKE_BC_POS (0)
+#define FAKE_UTC_POS (7 - 4)
+
+/* Create a fake data segment for database 'sysdb'.   This mocks
+ * up a fake ->data segment for the given timezone database. 
+ * php_date.c::timezone_identifiers_list() looks at data[pos + 4]
+ * through data[pos + 6] to compare the country code and BC flag, 
+ * which are stored in the builtin data array like:
+ *
+ *    (pos + 4) => BC flag
+ *    (pos + 5, pos + 6) => Two chars of country code
+ *
+ * where pos is the index corresponding to the timezone name.
+ *
+ * Timezone names are classified here into three types:
+ *    1) UTC, which is special
+ *    2) "normal" zone names
+ *    3) "backwards-compat" zone names
+ *
+ * (boolean logic of the BC flag seems to be inverted, but hey)
+ *
+ * UTC is special since it has BC=\1, code = "??"
+ * "normal" zones exist in zone.tab and have the given c-code and BC=\1
+ * "backwards-compat" zones don't exist in zone.tab and have BC=\0
+ *
+ * Since UTC and the BC zones are constant, they are encoded in the
+ * FAKE_HEADER prefix, and pos pointers index into that.
+ *
+ * FAKE_HEADER is hence four random bytes, then the BC zone segment
+ * (three bytes), then the UTC zone segment (another three).
+ *
+ * For all "normal" zones, three bytes are appended to the data array;
+ * the BC flag, always 1, and the two bytes of country code.
+ */
+static void fake_data_segment(timelib_tzdb *sysdb,
+							  struct location_info **info)
+{
+	size_t n;
+	char *data, *p;
+	
+	/* Worst case maximum is 3 bytes per zone, plus the header. */
+	data = malloc((3 * sysdb->index_size) + sizeof(FAKE_HEADER) - 1);
+	
+	/* Append the fake header, p then = next byte */
+	p = mempcpy(data, FAKE_HEADER, sizeof(FAKE_HEADER) - 1);
+	
+	for (n = 0; n < sysdb->index_size; n++) {
+		const struct location_info *li;
+		timelib_tzdb_index_entry *ent;
+		
+		/* Lost const'ness since we're modifying the pos pointer. */
+		ent = (timelib_tzdb_index_entry *)&sysdb->index[n];
+		
+		/* Lookup the timezone name in the hash table. */
+		if (strcmp(ent->id, "UTC") == 0) {
+			ent->pos = FAKE_UTC_POS;
+			continue;
+		}
+		
+		li = find_zone_info(info, ent->id);
+		if (li) {
+			/* If found, append the BC byte and the country code; set
+			 * the position index for the timezone to point to
+			 * this.  */
+			ent->pos = (p - data) - 4;
+			*p++ = '\x01';
+			*p++ = li->code[0];
+			*p++ = li->code[1];
+		}
+		else {
+			/* If not found, the timezone data can
+			 * point at the header. */
+			ent->pos = 0;
+		}
+	}
+	
+	/* Store the fake data array */
+	sysdb->data = (unsigned char *)data;
+}
+
+/* Evaluates to true if given timezone name is valid. */
+#define is_valid_tz_name(tz_) (tz_[0] && strstr(tz_, "..") == NULL)
+
+/* Return the mmap()ed tzfile if found, else NULL.	On success, the
+ * length of the mapped data is placed in *length. */
+static char *map_tzfile(const char *timezone, size_t *length)
+{
+	char fname[PATH_MAX];
+	struct stat st;
+	char *p;
+	int fd;
+	
+	if (!is_valid_tz_name(timezone)) {
+		return NULL;
+	}
+
+	snprintf(fname, sizeof fname, ZONEINFO_PREFIX "/%s", timezone);
+	
+	fd = open(fname, O_RDONLY);
+	if (fd == -1) {
+		return NULL;
+	} else if (fstat(fd, &st) != 0 || st.st_size < 21) {
+		close(fd);
+		return NULL;
+	}
+
+	*length = st.st_size;
+	p = mmap(NULL, st.st_size, PROT_READ, MAP_SHARED, fd, 0);
+	close(fd);
+	
+	return p != MAP_FAILED ? p : NULL;
+}
+#endif
+
+/* seek_to_tz_position() for a builtin/external database. */
+static int inmem_seek_to_tz_position(const unsigned char **tzf, 
+									 char *timezone, const timelib_tzdb *tzdb)
 {
 	int left = 0, right = tzdb->index_size - 1;
 #ifdef HAVE_SETLOCALE
@@ -296,36 +744,131 @@ static int seek_to_tz_position(const uns
 	return 0;
 }
 
+/* Modified seek_to_tz_position wrapper which handles the system
+ * database and the builtin/external databases in the same way.
+ * Returns zero on failure on non-zero on success.  On success, (*map,
+ * *maplen) is an mmap'ed region if *map is non-NULL, and must be
+ * munmaped after use.  */
+static int seek_to_tz_position(const unsigned char **tzf, char *timezone, 
+							   char **map, size_t *maplen,
+							   const timelib_tzdb *tzdb)
+{
+#ifdef HAVE_SYSTEM_TZDATA
+	if (tzdb == timezonedb_system) {
+		char *orig;
+
+		orig = map_tzfile(timezone, maplen);
+		if (orig == NULL) {
+			return 0;
+		}
+		
+		(*tzf) = (unsigned char *)orig ;
+		*map = orig;
+				
+		return 1;
+	}
+	else 
+#endif
+	{
+		return inmem_seek_to_tz_position(tzf, timezone, tzdb);
+	}
+}
+
 const timelib_tzdb *timelib_builtin_db(void)
 {
+#ifdef HAVE_SYSTEM_TZDATA
+	if (timezonedb_system == NULL) {
+		timelib_tzdb *tmp = malloc(sizeof *tmp);
+
+		tmp->version = "0.system";
+		tmp->data = NULL;
+		create_zone_index(tmp);
+		system_location_table = create_location_table();
+		fake_data_segment(tmp, system_location_table);
+		timezonedb_system = tmp;
+	}
+			
+	return timezonedb_system;
+#else
 	return &timezonedb_builtin;
+#endif
 }
 
 const timelib_tzdb_index_entry *timelib_timezone_builtin_identifiers_list(int *count)
 {
+#ifdef HAVE_SYSTEM_TZDATA
+	*count = timezonedb_system->index_size;
+	return timezonedb_system->index;
+#else
 	*count = sizeof(timezonedb_idx_builtin) / sizeof(*timezonedb_idx_builtin);
 	return timezonedb_idx_builtin;
+#endif
 }
 
 int timelib_timezone_id_is_valid(char *timezone, const timelib_tzdb *tzdb)
 {
 	const unsigned char *tzf;
-	return (seek_to_tz_position(&tzf, timezone, tzdb));
+
+#ifdef HAVE_SYSTEM_TZDATA
+	if (tzdb == timezonedb_system) {
+		char fname[PATH_MAX];
+		struct stat st;
+		
+		if (!is_valid_tz_name(timezone)) {
+			return 0;
+		}
+        
+		snprintf(fname, sizeof fname, ZONEINFO_PREFIX "/%s", timezone);
+        
+		return stat(fname, &st) == 0 && S_ISREG(st.st_mode);
+	}
+#endif
+
+	return (inmem_seek_to_tz_position(&tzf, timezone, tzdb));
 }
 
 timelib_tzinfo *timelib_parse_tzfile(char *timezone, const timelib_tzdb *tzdb)
 {
 	const unsigned char *tzf;
+	char *memmap = NULL;
+	size_t maplen;
 	timelib_tzinfo *tmp;
 
-	if (seek_to_tz_position(&tzf, timezone, tzdb)) {
+	if (seek_to_tz_position(&tzf, timezone, &memmap, &maplen, tzdb)) {
 		tmp = timelib_tzinfo_ctor(timezone);
 
 		read_preamble(&tzf, tmp);
 		read_header(&tzf, tmp);
 		read_transistions(&tzf, tmp);
 		read_types(&tzf, tmp);
-		read_location(&tzf, tmp);
+
+#ifdef HAVE_SYSTEM_TZDATA
+		if (memmap) {
+			const struct location_info *li;
+			
+			/* TZif-style - grok the location info from the system database,
+			 * if possible. */
+			if ((li = find_zone_info(system_location_table, timezone)) != NULL) {
+				tmp->location.comments = strdup(li->comment);
+				strncpy(tmp->location.country_code, li->code, 2);
+				tmp->location.longitude = li->longitude;
+				tmp->location.latitude = li->latitude;
+				tmp->bc = 1;
+			}
+			else {
+				strcpy(tmp->location.country_code, "??");
+				tmp->bc = 0;
+				tmp->location.comments = strdup("");
+			}
+
+			/* Now done with the mmap segment - discard it. */
+			munmap(memmap, maplen);
+#endif
+		}
+		else {
+			/* PHP-style - use the embedded info. */
+			read_location(&tzf, tmp);
+		}
 	} else {
 		tmp = NULL;
 	}
--- a/ext/date/lib/timelib.m4
+++ b/ext/date/lib/timelib.m4
@@ -78,3 +78,17 @@ stdlib.h
 
 dnl Check for strtoll, atoll
 AC_CHECK_FUNCS(strtoll atoll strftime)
+
+PHP_ARG_WITH(system-tzdata, for use of system timezone data,
+[  --with-system-tzdata[=DIR]      to specify use of system timezone data],
+no, no)
+
+if test "$PHP_SYSTEM_TZDATA" != "no"; then
+   AC_DEFINE(HAVE_SYSTEM_TZDATA, 1, [Define if system timezone data is used])
+
+   if test "$PHP_SYSTEM_TZDATA" != "yes"; then
+      AC_DEFINE_UNQUOTED(HAVE_SYSTEM_TZDATA_PREFIX, "$PHP_SYSTEM_TZDATA",
+                         [Define for location of system timezone data])
+   fi
+fi
+