⚡️ Speed up method AuthService._add_padding by 17% in PR #11639 (docs-chat-refactor-and-screenshots)

[codeflash-ai]

⚡️ This pull request contains optimizations for PR #11639

If you approve this dependent PR, these changes will be merged into the original PR branch docs-chat-refactor-and-screenshots.

This PR will be automatically closed if the original PR is merged.

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📄 17% (0.17x) speedup for AuthService._add_padding in src/backend/base/langflow/services/auth/service.py

⏱️ Runtime : 16.0 microseconds → 13.7 microseconds (best of 42 runs)

📝 Explanation and details

The optimized code achieves a 16% speedup through two micro-optimizations in the _add_padding method:

Key Changes

1. Precomputed padding strings: A module-level tuple _PADS = ("", "=", "==", "===", "====") eliminates repeated string allocations. Instead of computing "=" * padding_needed on every call (which allocates a new string), the code now performs a simple tuple lookup _PADS[padding_needed].

2. Bitwise operation: Replaced len(value) % 4 with len(value) & 3. Since modulo 4 is equivalent to keeping only the last 2 bits, the bitwise AND operation is faster than the modulo operator in Python.

Why This Is Faster

From line profiler data:

• The return statement dropped from 1148.4 ns/hit to 1012.3 ns/hit (~12% faster)
• This improvement comes from avoiding string multiplication and allocation on each call
• The bitwise operation provides a marginal gain in the padding calculation line

String allocation overhead: In Python, "=" * n creates a new string object each time. By pre-allocating all possible padding strings (only 5 variants exist), the optimized version performs a constant-time array lookup instead of a string multiplication operation.

Impact on Workloads

This optimization is particularly beneficial when _add_padding is called frequently in authentication/token processing flows. The test results show consistent performance improvements across all test cases—from basic padding scenarios to large-scale strings near 1000 characters. Since padding is typically needed for base64 encoding in authentication tokens, services handling many authentication requests will see cumulative benefits from these per-call savings.

The changes preserve exact behavior (including the quirk where strings divisible by 4 get 4 padding characters) and require no updates to calling code.

✅ Correctness verification report:

Test	Status
⚙️ Existing Unit Tests	🔘 None Found
🌀 Generated Regression Tests	✅ 30 Passed
⏪ Replay Tests	🔘 None Found
🔎 Concolic Coverage Tests	🔘 None Found
📊 Tests Coverage	100.0%

🌀 Click to see Generated Regression Tests

import pytest  # used for our unit tests
from langflow.services.auth.service import AuthService


def test_basic_padding_for_each_remainder_case():
    """
    Basic Test Cases:
    Verify the function's behavior for inputs whose lengths produce remainders 0,1,2,3 when divided by 4.
    The current implementation adds (4 - (len % 4)) '=' characters even when the remainder is 0
    (i.e., it adds 4 '=' characters for lengths divisible by 4). The tests assert that current behavior.
    """
    svc = AuthService(settings_service=None)  # settings_service is not used internally

    # remainder 0: len=4 -> padding_needed = 4 -> expect four '=' appended
    codeflash_output = svc._add_padding("abcd")  # 'abcd' length 4 -> adds 4 '='

    # remainder 1: len=5 -> padding_needed = 3 -> expect three '=' appended
    codeflash_output = svc._add_padding("abcde")

    # remainder 2: len=2 -> padding_needed = 2 -> expect two '=' appended
    codeflash_output = svc._add_padding("ab")

    # remainder 3: len=3 -> padding_needed = 1 -> expect one '=' appended
    codeflash_output = svc._add_padding("abc")


def test_empty_string_and_already_padded_values():
    """
    Edge Test Cases:
    - Empty string should receive four '=' according to the current implementation.
    - Strings that already include '=' characters are treated the same: padding is appended
      based solely on length, not content.
    """
    svc = AuthService(settings_service=None)

    # empty string length 0 -> padding_needed = 4
    codeflash_output = svc._add_padding("")

    # string that already contains '=' characters; length determines padding only
    # "a=" length is 2 -> padding_needed = 2 -> append '=='
    codeflash_output = svc._add_padding("a=")

    # multiple existing '='; "===" length 3 -> padding_needed = 1 -> append '='
    codeflash_output = svc._add_padding("===")  # original '===' + one '=' -> '===='


def test_unicode_and_multibyte_characters_counted_by_len():
    """
    Edge Test Case:
    Ensure that Unicode characters are counted by Python's len() (number of code points),
    and padding is computed accordingly.
    """
    svc = AuthService(settings_service=None)

    # single non-ASCII character: length 1 -> padding_needed = 3
    codeflash_output = svc._add_padding("ñ")

    # combination of characters where len() yields expected counts
    sample = "λβ"  # length 2 -> padding_needed = 2
    codeflash_output = svc._add_padding(sample)

    # emoji (single code point in many cases)
    emoji = "🙂"  # often length 1
    codeflash_output = svc._add_padding(emoji)


def test_invalid_input_types_raise_type_error():
    """
    Edge Test Case:
    If a non-string is passed, len(value) will raise a TypeError. The function does not
    perform type checks itself (as per the original implementation), so we assert that
    TypeError is raised for invalid inputs.
    """
    svc = AuthService(settings_service=None)

    with pytest.raises(TypeError):
        svc._add_padding(None)  # None has no length

    with pytest.raises(TypeError):
        svc._add_padding(12345)  # integers have no length


def test_output_length_is_always_multiple_of_four_for_various_lengths():
    """
    Property Test:
    According to the implementation, the resulting string length should always be divisible
    by 4 because padding_needed = 4 - (len % 4) and that is appended regardless of remainder.
    Test a range of lengths to ensure this invariant holds.
    """
    svc = AuthService(settings_service=None)

    # test a variety of representative lengths; avoid large loops per instructions
    samples = [
        "",       # 0
        "a",      # 1
        "ab",     # 2
        "abc",    # 3
        "abcd",   # 4
        "abcde",  # 5
        "abcdef", # 6
        "abcdefg" # 7
    ]
    for s in samples:
        codeflash_output = svc._add_padding(s); res = codeflash_output


def test_large_scale_near_upper_size_limits():
    """
    Large Scale Test Case:
    Use large strings near the suggested size constraints to ensure performance and correctness.
    - We avoid loops > 1000 and data structures > 1000 elements.
    - We construct two large strings with lengths below 1000.
    - Confirm exact expected padding behavior according to the current implementation.
    """
    svc = AuthService(settings_service=None)

    # length 996 is divisible by 4 -> padding_needed = 4 (current implementation)
    s_divisible = "a" * 996
    codeflash_output = svc._add_padding(s_divisible); result_divisible = codeflash_output

    # length 997 has remainder 1 -> padding_needed = 3
    s_remainder1 = "b" * 997
    codeflash_output = svc._add_padding(s_remainder1); result_remainder1 = codeflash_output


def test_mutation_detection_example_behavior_difference():
    """
    Mutation Detection:
    This test encodes the (intentionally peculiar) behavior that when the input length is already
    divisible by 4, _add_padding still adds four '=' characters. If someone "fixes" the function
    to not add padding when length % 4 == 0, this test will fail and thus detect the mutation.
    """
    svc = AuthService(settings_service=None)

    base = "WXYZ"  # length 4
    # We assert the current behavior (add four '='); a "corrected" implementation that adds 0 '='
    # for len % 4 == 0 would fail this assertion.
    codeflash_output = svc._add_padding(base)
# codeflash_output is used to check that the output of the original code is the same as that of the optimized code.
#------------------------------------------------
import pytest
from langflow.services.auth.service import AuthService
from lfx.services.settings.service import SettingsService


@pytest.fixture
def settings_service():
    """Fixture to provide a SettingsService instance for testing."""
    return SettingsService()


@pytest.fixture
def auth_service(settings_service):
    """Fixture to provide an AuthService instance for testing."""
    return AuthService(settings_service)


class TestBasicFunctionality:
    """Basic test cases for AuthService._add_padding function."""

To edit these changes git checkout codeflash/optimize-pr11639-2026-02-07T00.09.09 and push.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (docs-chat-refactor-and-screenshots@de09fdb). Learn more about missing BASE report.

Additional details and impacted files

@@                          Coverage Diff                          @@
##             docs-chat-refactor-and-screenshots   #11642   +/-   ##
=====================================================================
  Coverage                                      ?   35.22%           
=====================================================================
  Files                                         ?     1521           
  Lines                                         ?    72924           
  Branches                                      ?    10936           
=====================================================================
  Hits                                          ?    25688           
  Misses                                        ?    45842           
  Partials                                      ?     1394           

Flag	Coverage Δ
backend	55.71% <100.00%> (?)
lfx	42.12% <ø> (?)

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Files with missing lines	Coverage Δ
src/backend/base/langflow/services/auth/service.py	66.58% <100.00%> (ø)

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