fix: ensure enough data for skip and limit

lib/index.js

@@ -29,7 +29,13 @@ function createMergedReadStream(db, options) {
 
   var sources = options.ranges.map(function (range) {
     // Force keys for comparator
-    return db.createReadStream(extend(options, range, { keys: true }));
+    var overrides = { keys: true };
+    // Increase per-stream limit to guarantee enough results for merged limit to
+    // be reached
+    if (options.limit && options.skip) {
+      overrides.limit = options.limit + options.skip;
+    }
+    return db.createReadStream(extend(options, range, overrides));
   });
   var stream = merge(makeComparator(options), sources);
   if (options.skip) {

test/test.js

@@ -246,6 +246,25 @@ describe('level-merged-stream', function () {
           });
       });
     });
+
+    it('should provide enough source stream results to meet skip & limit', function (done) {
+      var results = [];
+      db.mergedReadStream({
+        ranges: ranges,
+        comparator: comparator,
+        skip: 3,
+        limit: 1
+      })
+        .on('data', function (data) {
+          results.push(data.value);
+        })
+        .on('end', function () {
+          // If createReadStream limit was set to 1 and not 3 + 1, we'd get []
+          // and not ['3'] because the 'b' stream would already have ended
+          expect(results).to.deep.equal(['3']);
+          done();
+        });
+    });
   });
 
   describe('createMergedKeyStream', function () {