Implemented flagd-specific JSONLogic operators

[m-olko]

This PR

Implements all flagd-specific JSONLogic operators: starts_with, ends_with, semver and fractional.

The semver operator supports out of the box the v and V prefixes, partial versions and correctly returns on parse errors according to open-feature/flagd#1873

The fractional operator supports out of the box the high precision bucketing according to open-feature/flagd#1800
The PR also introduces testcases copied from flagd-testbed, as we don't have Gherkin suite introduced here, but written in C++ to ensure that the hashing is consistent.

Third-party Code: MurmurHash3

The MurmurHash3 implementation in providers/flagd/src/evaluator/murmur_hash/ has been copied from the aappleby/smhasher (https://github.com/aappleby/smhasher/blob/master/src/MurmurHash3.cpp) repository.

License & Attribution:

• Author: Austin Appleby
• License: Public Domain. The author disclaims all copyright to this source code.
• Reasoning: This approach was chosen to avoid unnecessary dependencies and a large repository download, as there is no official Bazel package for MurmurHash3. This is a common practice for projects requiring this specific hashing function.

Related Issues

Fixes #19

How to test

bazelisk test //...

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances flagd's evaluation capabilities by introducing a suite of new JSONLogic operators. These operators, including starts_with, ends_with, sem_ver, and fractional, enable more sophisticated and precise flag targeting logic, allowing for advanced string comparisons, semantic versioning checks, and weighted fractional distributions. This expansion provides developers with greater flexibility in defining complex flag rules.

Highlights

• New JSONLogic Operators: Added four new flagd-specific JSONLogic operators: "starts_with", "ends_with", "sem_ver", and "fractional" to enhance flag evaluation capabilities.
• Operator Integration: Integrated the newly implemented operators into the JsonLogicEvaluator to make them available for use in flag evaluation logic.
• Hashing Algorithm Inclusion: Included a MurmurHash3 implementation to support the advanced bucketing logic required by the "fractional" operator.

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[gemini-code-assist]

Code Review

This pull request introduces new JsonLogic operations (starts_with, ends_with, sem_ver, fractional) to the flagd evaluator, along with their implementation, a SemanticVersion class, and integration of MurmurHash3. Review feedback highlights several issues: the SemVer parsing needs to enforce leading zero rules for version components and pre-release identifiers as per SemVer 2.0.0, the Fractional operation requires validation for non-negative weights to prevent underflow, and its sum_of_weights limit should be adjusted for broader compatibility. Additionally, it's recommended to use Abseil's StartsWith and EndsWith for idiomatic code and to refine an unreachable return statement in the Fractional operation.

[m-olko]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces new JSON logic operations (starts_with, ends_with, sem_ver, fractional) to the flagd evaluator, implemented within a new flagd_ops library. These operations include semantic version comparison and fractional bucketing using MurmurHash3. Feedback suggests refactoring duplicated SemVer parsing logic, using int32_t for weight in fractional evaluation for consistency, and adding a newline to the fractional ops test file.

[tangenti]

IIUC the hash code is copied from https://github.com/aappleby/smhasher/blob/master/src/MurmurHash3.cpp

Is this best way we can do to import it?

[m-olko]

This library is public domain and doesn't have any library with it's implementation in bazel registry nor any other known to me c++ resources. If we would like to download it from the source, we would also download multiple different hashing functions and whole smhasher test suite which is completely unnecessary for our usecase. This way of using this library is common for numerous projects I inspected and best solution according to gemini. As the code is public domain, I don't think there will be any issues with using it like this. From official source:

All MurmurHash versions are public domain software, and the author disclaims all copyright to their code.

[tangenti]

This library is public domain and doesn't have any library with it's implementation in bazel registry nor any other known to me c++ resources. If we would like to download it from the source, we would also download multiple different hashing functions and whole smhasher test suite which is completely unnecessary for our usecase. This way of using this library is common for numerous projects I inspected and best solution according to gemini. As the code is public domain, I don't think there will be any issues with using it like this. From official source:

All MurmurHash versions are public domain software, and the author disclaims all copyright to their code.

Thanks. Could you document this in the directory and also in the PR description?

[m-olko]

Thanks. Could you document this in the directory and also in the PR description?

Done