chore: feature attemp doc for hurl parser

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Pratham
2025-01-26 18:01:54 +05:30
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### Feature Implementation Writeup: HurlParser Wrapper for API Dash
I initially started with the approach of writing my own parser using `petitparser` and creating a custom implementation. However, after about a week, the maintainer recommended against this approach. They highlighted that building a custom parser would lack future-proofing if `hurl.dev` were to implement changes. While I abandoned this route, the code is still available in a branch. My custom parser had progressed to the point where requests and assertions were working, though it was far from complete.
#### Transition to Hurl Parser Wrapper Using Flutter Rust Bridge
Following the maintainer's suggestion, I began developing a wrapper for the Hurl parser using `flutter_rust_bridge`. Since the documentation for the library can be sparse, Ive documented my steps for clarity:
1. **Creating the Library:**
- I ran the command:
`flutter_rust_bridge_codegen create hurl --template plugin`
- This initialized the project.
2. **Adding the Parse Function:**
- I added the library code and the `parse_hurl` function in `rust/src/api/simple.rs`.
3. **Generating the Flutter Side Code:**
- I ran:
`flutter_rust_bridge_codegen generate`
- This generated all the necessary code for Flutter and all the targeted platforms.
`flutter_rust_bridge` uses a tool called `cargokit` to manage dependencies, acting as a glue layer between Flutter and Rust. Unfortunately, `cargokit` is still experimental, with little documentation available. The [blog post by Matej Knopp](https://matejknopp.com/post/flutter_plugin_in_rust_with_no_prebuilt_binaries/) provided valuable insights. One crucial takeaway was avoiding the Homebrew installation of Rust and instead using `rustup`. This resolved platform compilation issues for me, though the project is still not compiling entirely.
#### Implementing the Wrapper
I postponed multi-platform compilation issues to focus on writing the wrapper code. By reviewing the `hurl.dev` documentation and examples, I identified the required structure:
- `HurlFile` → List of `Entries`
- `Entries``Request` and `Response`
Based on this, I created models in Dart using the `freezed` package. The goal was to convert the JSON output from the Hurl parser into Dart data models. I am confident this part turned out well.
After writing tests for Hurl parsing and model generation, I shifted focus to building the project.
#### Compilation Challenges
During compilation, I encountered an issue, which I reported on the [Hurl repository](https://github.com/Orange-OpenSource/hurl/issues/3603). The Hurl parser depends on the `libxml2` crate for XML parsing. To resolve this, I had to add:
`OTHER_LDFLAGS => -force_load ${BUILT_PRODUCTS_DIR}/libhurl.a -lxml2`
This fixed the macOS build.
However, testing on iOS and Android proved problematic, as I didnt have access to Windows or Linux systems. For iOS, adding similar flags didnt work. I tried various fixes, such as modifying the header search paths, linking frameworks, and changing build phases in Xcode, but none succeeded.
#### Investigation into `libxml2`
I learned that `libxml2` is not a system library but a crate that wraps platform-specific libraries. Unfortunately, `libxml2` does not support Android or iOS, causing persistent errors. After consulting the maintainers of Hurl and `flutter_rust_bridge`, I received the following suggestion from the Hurl maintainer:
> _"I'm not an expert in iOS/Android, but what I would do is try to build something smaller, maybe just calling libxml through a Flutter component, then trying to build with libxml but with the Rust crate wrapper, etc."_ ([GitHub comment](https://github.com/Orange-OpenSource/hurl/issues/3603#issuecomment-2611159759))
#### Current Status and Potential Solutions
At this point, Ive committed all my code to the repository in a fork. Here are some potential solutions I believe might work:
1. **Use Dart Native FFIs**: Currently under an experimental flag, as suggested by the `flutter_rust_bridge` maintainer.
2. **Revert to an Older Version of Hurlfmt**: Use a version of the library from before it transitioned to `libxml` for performance improvements.
3. **Revisit My Custom Parser**: Complete the parser I started building with `petitparser`.
If anyone knows a solution to these challenges or has suggestions, Id appreciate the help!