Add support for nested json metadata.

lib/mbtiles.js

@@ -229,6 +229,18 @@ MBTiles.prototype.getInfo = function(callback) {
         if (err && err.errno !== 1) return callback(err);
         if (rows) rows.forEach(function(row) {
             switch (row.name) {
+            // The special "json" key/value pair allows JSON to be serialized
+            // and merged into the metadata of an MBTiles based source. This
+            // enables nested properties and non-string datatypes to be
+            // captured by the MBTiles metadata table.
+            case 'json':
+                try { var jsondata = JSON.parse(row.value); }
+                catch (err) { return callback(err); }
+                Object.keys(jsondata).reduce(function(memo, key) {
+                    memo[key] = memo[key] || jsondata[key];
+                    return memo;
+                }, info);
+                break;
             case 'minzoom':
             case 'maxzoom':
                 info[row.name] = parseInt(row.value, 10);
@@ -537,11 +549,21 @@ MBTiles.prototype.putInfo = function(data, callback) {
     if (!this.open) return callback(new Error('MBTiles not yet loaded'));
     if (!this._isWritable) return callback(new Error('MBTiles not in write mode'));
 
+    var jsondata;
     var stmt = this._db.prepare('REPLACE INTO metadata (name, value) VALUES (?, ?)');
     stmt.on('error', callback);
     for (var key in data) {
-        stmt.run(key, String(data[key]));
+        // If a data property is a javascript hash/object, slip it into
+        // the 'json' field which contains stringified JSON to be merged
+        // in at read time. Allows nested/deep metadata to be recorded.
+        if (typeof data[key] === 'object' && !Array.isArray(data[key])) {
+            jsondata = jsondata || {};
+            jsondata[key] = data[key];
+        } else {
+            stmt.run(key, String(data[key]));
+        }
     }
+    if (jsondata) stmt.run('json', JSON.stringify(jsondata));
 
     var mbtiles = this;
     stmt.finalize(function(err) {