From 3cdcac64e8a9d9112fe5288c0413c0b92eb429f6 Mon Sep 17 00:00:00 2001
From: Denis K <kalantaevskii@gmail.com>
Date: Wed, 9 Oct 2024 23:06:13 +0200
Subject: [PATCH] fix:bug in bitpos function for the clear bit mode

- fakeredis returns the number of bits instead of -1 if it doesn't find 0.
- It returns 0 if the key doesn't exist.
---
 fakeredis/_commands.py                    |  8 ++++++++
 fakeredis/commands_mixins/bitmap_mixin.py | 24 +++++++++++++++++++----
 test/test_mixins/test_bitmap_commands.py  | 13 ++++++++++++
 3 files changed, 41 insertions(+), 4 deletions(-)

diff --git a/fakeredis/_commands.py b/fakeredis/_commands.py
index aafbf176..46b6b262 100644
--- a/fakeredis/_commands.py
+++ b/fakeredis/_commands.py
@@ -519,6 +519,14 @@ def delete_keys(*keys: CommandItem) -> int:
             ans += 1
     return ans
 
+def positive_range(start: int, end: int, length: int) -> Tuple[int, int]:
+    # Redis handles negative slightly differently for zrange
+    if start < 0:
+        start = max(0, start + length)
+    if end < 0:
+        end += length
+    end = min(end, length - 1)
+    return start, end + 1
 
 def fix_range(start: int, end: int, length: int) -> Tuple[int, int]:
     # Redis handles negative slightly differently for zrange
diff --git a/fakeredis/commands_mixins/bitmap_mixin.py b/fakeredis/commands_mixins/bitmap_mixin.py
index bed7d973..a49229f8 100644
--- a/fakeredis/commands_mixins/bitmap_mixin.py
+++ b/fakeredis/commands_mixins/bitmap_mixin.py
@@ -10,6 +10,7 @@
     BitValue,
     fix_range_string,
     fix_range,
+    positive_range,
     CommandItem,
 )
 from fakeredis._helpers import SimpleError, casematch
@@ -54,6 +55,13 @@ def bitpos(self, key: CommandItem, bit: int, *args: bytes) -> int:
             bit_mode = casematch(args[2], b"bit")
             if not bit_mode and not casematch(args[2], b"byte"):
                 raise SimpleError(msgs.SYNTAX_ERROR_MSG)
+
+        # Redis treats non-existent key as an infinite array of 0 bits.
+        # If the user is looking for the first clear bit return 0,
+        # If the user is looking for the first set bit, return -1.
+        if not key.value:
+            return -1 if bit == 1 else 0
+
         start = 0 if len(args) == 0 else Int.decode(args[0])
         bit_chr = str(bit)
         key_value = key.value if key.value else b""
@@ -61,16 +69,24 @@ def bitpos(self, key: CommandItem, bit: int, *args: bytes) -> int:
         if bit_mode:
             value = self._bytes_as_bin_string(key_value)
             end = len(value) if len(args) <= 1 else Int.decode(args[1])
-            start, end = fix_range(start, end, len(value))
-            value = value[start:end]
+            length = len(value)
         else:
             end = len(key_value) if len(args) <= 1 else Int.decode(args[1])
-            start, end = fix_range(start, end, len(key_value))
-            value = self._bytes_as_bin_string(key_value[start:end])
+            length = len(key_value)
+
+        start, end = positive_range(start, end, length)
+
+        if start > end or start >= length:
+            return -1
 
+        value  = value[start:end] if bit_mode else self._bytes_as_bin_string(key_value[start:end])
         result = value.find(bit_chr)
         if result != -1:
             result += start if bit_mode else (start * 8)
+        # Redis treats the value as padded with zero bytes to an infinity
+        # if the user is looking for the first clear bit and no end is set.
+        elif bit == 0 and len(args) <= 1:
+            result = len(key_value) * 8
         return result
 
     @command(name="BITCOUNT", fixed=(Key(bytes),), repeat=(bytes,), flags=msgs.FLAG_DO_NOT_CREATE)
diff --git a/test/test_mixins/test_bitmap_commands.py b/test/test_mixins/test_bitmap_commands.py
index e0b5457a..67d8a576 100644
--- a/test/test_mixins/test_bitmap_commands.py
+++ b/test/test_mixins/test_bitmap_commands.py
@@ -197,7 +197,20 @@ def test_bitpos(r: redis.Redis):
     assert r.bitpos(key, 1, 1) == 8
     r.set(key, b"\x00\x00\x00")
     assert r.bitpos(key, 1) == -1
+    r.set(key, b"\xff\xff\xff")
+    assert r.bitpos(key, 1) == 0
+    assert r.bitpos(key, 1, 1) == 8
+    assert r.bitpos(key, 1, 3) == -1
+    assert r.bitpos(key, 0) == 24
+    assert r.bitpos(key, 0, 1) == 24
+    assert r.bitpos(key, 0, 3) == -1
+    assert r.bitpos(key, 0, 0, -1) == -1
     r.set(key, b"\xff\xf0\x00")
+    assert r.bitpos("nokey:bitpos", 0) == 0
+    assert r.bitpos("nokey:bitpos", 1) == -1
+    assert r.bitpos("nokey:bitpos", 0, 1) == 0
+    assert r.bitpos("nokey:bitpos", 1, 1) == -1
+
 
 
 @pytest.mark.min_server("7")