From 1dd351d18223577c1ba83550f1b0dbeae0a9cdbb Mon Sep 17 00:00:00 2001
From: Kris Zyp <kriszyp@gmail.com>
Date: Wed, 7 Jul 2021 16:24:02 -0600
Subject: [PATCH] Fix for doing reverse range query, #69

---
 src/cursor.cpp     | 35 ++++++++++++++---------------------
 test/index.test.js | 26 ++++++++++++++++++++++++++
 2 files changed, 40 insertions(+), 21 deletions(-)

diff --git a/src/cursor.cpp b/src/cursor.cpp
index 7534bcbf94..5b8de5a43c 100644
--- a/src/cursor.cpp
+++ b/src/cursor.cpp
@@ -389,7 +389,7 @@ int CursorWrap::returnEntry(int lastRC, MDB_val &key, MDB_val &data) {
             comparison = mdb_dcmp(tw->txn, dw->dbi, &endKey, &data);
         else
             comparison = mdb_cmp(tw->txn, dw->dbi, &endKey, &key);
-        if ((flags & 0x400) ? comparison >= 0 : (comparison <=0)) {
+        if ((flags & 0x400) ? comparison >= 0 : (comparison <= 0)) {
             return 0;
         }
     }
@@ -438,34 +438,27 @@ uint32_t CursorWrap::doPosition(uint32_t offset, uint32_t keySize, uint64_t endK
             data.mv_size = endKeyAddress ? *((uint32_t*)startValueBuffer) : 0;
             data.mv_data = startValueBuffer + 1;
             rc = mdb_cursor_get(cursor, &key, &data, data.mv_size ? MDB_GET_BOTH_RANGE : MDB_SET_KEY);
+            if (rc == MDB_NOTFOUND)
+                return 0;
             if (flags & 0x1000 && !endKeyAddress) {
-                if (rc == MDB_NOTFOUND)
-                    return 0;
                 size_t count;
                 rc = mdb_cursor_count(cursor, &count);
                 if (rc)
                     throwLmdbError(rc);
                 return count;
             }
-        } else
-            rc = mdb_cursor_get(cursor, &key, &data, MDB_SET_RANGE);
-        if (flags & 0x400) {// reverse
-            MDB_val firstKey = key; // save it for comparison
-            if (rc) { // not found
-                if (flags & 0x800) {// only values for this key
-                    // nothing to do, not found
-                } else if (true) {// MDB_SET_RANGE, not found, go to end
+            if (flags & 0x400) // reverse, get last dup
+                rc = mdb_cursor_get(cursor, &key, &data, MDB_LAST_DUP);
+        } else {
+            if (flags & 0x400) {// reverse
+                MDB_val firstKey = key; // save it for comparison
+                rc = mdb_cursor_get(cursor, &key, &data, MDB_SET_RANGE);
+                if (rc)
                     rc = mdb_cursor_get(cursor, &key, &data, MDB_LAST);
-                }
-            } else {
-                if (flags & 0x800) {// only values for this key
-                    // compare data
-                    rc = mdb_cursor_get(cursor, &key, &data, MDB_LAST_DUP);
-                } else  {// MDB_SET_RANGE
-                    if (mdb_cmp(tw->txn, dw->dbi, &firstKey, &key))
-                        rc = mdb_cursor_get(cursor, &key, &data, MDB_PREV);
-                }
-            }
+                if (mdb_cmp(tw->txn, dw->dbi, &firstKey, &key) && !rc)
+                    rc = mdb_cursor_get(cursor, &key, &data, MDB_PREV);
+            } else // forward, just do a get by range
+                rc = mdb_cursor_get(cursor, &key, &data, MDB_SET_RANGE);
         }
     }
     while (offset-- > 0 && !rc) {
diff --git a/test/index.test.js b/test/index.test.js
index a17084ff31..78b6edb9aa 100644
--- a/test/index.test.js
+++ b/test/index.test.js
@@ -115,6 +115,32 @@ describe('lmdb-store', function() {
         value.should.equal(db.get(key))
       }
       keys.should.deep.equal(returnedKeys)
+
+      returnedKeys = []
+      for (let { key, value } of db.getRange({
+        reverse: true,
+      })) {
+        returnedKeys.unshift(key)
+        value.should.equal(db.get(key))
+      }
+      keys.should.deep.equal(returnedKeys)
+    });
+    it('reverse query range', async function() {
+      const keys = [
+        [ 'Test', 100, 1 ],
+        [ 'Test', 10010, 2 ],
+        [ 'Test', 10010, 3 ],
+      ]
+      for (let key of keys)
+        await db.put(key, 3);
+      let returnedKeys = []
+      for (let { key, value } of db.getRange({
+        start: ['Test', null],
+        end: ['Test', null],
+        reverse: true
+      })) {
+        throw new Error('Should not return any results')
+      }
     });
     it('string', async function() {
       await db.put('key1', 'Hello world!');