Add readable ZXYStream and createZXYStream method. Refs #42.

lib/mbtiles.js

@@ -8,6 +8,7 @@ var Buffer = require('buffer').Buffer;
 var sm = new (require('sphericalmercator'));
 var sqlite3 = require('sqlite3');
 var tiletype = require('tiletype');
+var ZXYStream = require('./zxystream');
 
 function noop(err) {
     if (err) throw err;
@@ -740,3 +741,8 @@ MBTiles.prototype.geocoderCentroid = function(id, zxy, callback) {
         ], mid[0]));
     });
 };
+
+MBTiles.prototype.createZXYStream = function(options) {
+    return new ZXYStream(this, options);
+};
+

lib/zxystream.js

@@ -0,0 +1,41 @@
+var stream = require('stream');
+var util = require('util');
+
+module.exports = ZXYStream;
+util.inherits(ZXYStream, stream.Readable);
+
+// Readable stream of line-delimited z/x/y coordinates
+// contained within the MBTiles `tiles` table/view.
+function ZXYStream(source, options) {
+    if (!source) throw new TypeError('MBTiles source required');
+
+    options = options || {};
+
+    if (options.batch !== undefined && typeof options.batch !== 'number')
+        throw new TypeError('options.batch must be a positive integer');
+
+    this.source = source;
+    this.batch = options.batch || 10000;
+    this.offset = 0;
+
+    stream.Readable.call(this);
+}
+
+ZXYStream.prototype._read = function() {
+    var stream = this;
+    this.source._db.all('SELECT zoom_level AS z, tile_column AS x, tile_row AS y FROM tiles LIMIT ' + this.batch + ' OFFSET ' + this.offset, function(err, rows) {
+        if (err) return stream.emit('error', err);
+        if (!rows.length) return stream.push(null);
+        stream.offset += stream.batch;
+        var chunk = '';
+        for (var i = 0; i < rows.length; i++) chunk += toLine(rows[i]);
+        stream.push(chunk);
+    });
+};
+
+function toLine(row) {
+    // Flip Y coordinate because MBTiles files are TMS.
+    var y = row.y = (1 << row.z) - 1 - row.y;
+    return row.z + '/' + row.x + '/' + y + '\n';
+}
+