From bc562d5c06a3c1efab0f0834d7a1fba0145b0adf Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=D0=9B=D0=B5=D0=BE=D0=BD=D0=B8=D0=B4=20=D0=AE=D1=80=D1=8C?=
 =?UTF-8?q?=D0=B5=D0=B2=20=28Leonid=20Yuriev=29?= <leo@yuriev.ru>
Date: Sat, 18 Nov 2023 22:52:13 +0300
Subject: [PATCH] =?UTF-8?q?mdbx:=20=D0=B4=D0=BE=D0=B1=D0=B0=D0=B2=D0=BB?=
 =?UTF-8?q?=D0=B5=D0=BD=D0=B8=D0=B5=20`mdbx=5Fcursor=5Fscan()`=20=D0=B2=20?=
 =?UTF-8?q?API.?=
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---
 mdbx.h     |  8 ++++++++
 src/core.c | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 41 insertions(+)

diff --git a/mdbx.h b/mdbx.h
index 0123a139..c1fdd90e 100644
--- a/mdbx.h
+++ b/mdbx.h
@@ -4929,6 +4929,14 @@ LIBMDBX_API int mdbx_cursor_compare(const MDBX_cursor *left,
  * \retval MDBX_EINVAL    An invalid parameter was specified. */
 LIBMDBX_API int mdbx_cursor_get(MDBX_cursor *cursor, MDBX_val *key,
                                 MDBX_val *data, MDBX_cursor_op op);
+/** FIXME */
+typedef int(MDBX_predicate_func)(void *context, MDBX_val *key, MDBX_val *value,
+                                 void *arg) MDBX_CXX17_NOEXCEPT;
+/** FIXME */
+LIBMDBX_API int mdbx_cursor_scan(MDBX_cursor *cursor,
+                                 MDBX_predicate_func *predicate, void *context,
+                                 MDBX_cursor_op start_op,
+                                 MDBX_cursor_op turn_op, void *arg);
 
 /** \brief Retrieve multiple non-dupsort key/value pairs by cursor.
  * \ingroup c_crud
diff --git a/src/core.c b/src/core.c
index 2e577a93..23eaaa92 100644
--- a/src/core.c
+++ b/src/core.c
@@ -17433,6 +17433,39 @@ int mdbx_cursor_get(MDBX_cursor *mc, MDBX_val *key, MDBX_val *data,
   return cursor_get(mc, key, data, op);
 }
 
+int mdbx_cursor_scan(MDBX_cursor *mc, MDBX_predicate_func *predicate,
+                     void *context, MDBX_cursor_op start_op,
+                     MDBX_cursor_op turn_op, void *arg) {
+  if (unlikely(!predicate))
+    return MDBX_EINVAL;
+
+  const unsigned valid_start_mask =
+      1 << MDBX_FIRST | 1 << MDBX_FIRST_DUP | 1 << MDBX_LAST |
+      1 << MDBX_LAST_DUP | 1 << MDBX_GET_CURRENT | 1 << MDBX_GET_MULTIPLE;
+  if (unlikely(start_op > 30 || ((1 << start_op) & valid_start_mask) == 0))
+    return MDBX_EINVAL;
+
+  const unsigned valid_turn_mask =
+      1 << MDBX_NEXT | 1 << MDBX_NEXT_DUP | 1 << MDBX_NEXT_NODUP |
+      1 << MDBX_PREV | 1 << MDBX_PREV_DUP | 1 << MDBX_PREV_NODUP |
+      1 << MDBX_NEXT_MULTIPLE | 1 << MDBX_PREV_MULTIPLE;
+  if (unlikely(turn_op > 30 || ((1 << turn_op) & valid_turn_mask) == 0))
+    return MDBX_EINVAL;
+
+  MDBX_val key, data;
+  int rc = mdbx_cursor_get(mc, &key, &data, start_op);
+  if (unlikely(rc != MDBX_SUCCESS))
+    return rc;
+  for (;;) {
+    rc = predicate(context, &key, &data, arg);
+    if (rc != MDBX_RESULT_FALSE)
+      return rc;
+    rc = cursor_get(mc, &key, &data, turn_op);
+    if (rc != MDBX_SUCCESS)
+      return (rc == MDBX_NOTFOUND) ? MDBX_RESULT_FALSE : rc;
+  }
+}
+
 static int cursor_first_batch(MDBX_cursor *mc) {
   if (!(mc->mc_flags & C_INITIALIZED) || mc->mc_top) {
     int err = page_search(mc, NULL, MDBX_PS_FIRST);