Runtime Environment

Blockless Runtime Environment

The Blockless Runtime Environment leverages WebAssembly (Wasm) technology to deliver fast, compatible, and customizable features. This environment supports a variety of programming languages, such as C/C++, Rust, Swift, AssemblyScript, and Kotlin, while also allowing for the integration of these languages (e.g., using Rust to implement a JavaScript API).

Key Features

The Blockless runtime environment provides the following standout features:

  • Speed: Utilizes an optimized code generator for rapid generation of high-quality machine code. The runtime environment is designed for efficient instantiation, low-overhead transitions between the embedder and Wasm, and scalability of concurrent instances.
  • Compatibility: Supports running standard bytecode programs compiled from various programming languages, such as C/C++, Rust, Swift, AssemblyScript, or Kotlin. It also facilitates the mixing of these languages (e.g., using Rust to implement a JavaScript API).
  • Customizability: Offers a configurable file with a range of options, including additional restrictions on WebAssembly beyond its basic guarantees, such as CPU and memory consumption.

Building the Project

To build the project, follow these steps:

  1. Install Rust by visiting the Rust official website (opens in a new tab).
  2. Clone the git repository (opens in a new tab).
  3. Go to your project folder and execute the following command to build the project:
$ cargo build

Supported Languages

Blockless Runtime Environment supports an array of programming languages, including but not limited to:

  • TinyGo
  • Rust
  • AssemblyScript

Runtime Environment Configuration

Below is an example of the runtime environment configuration file:

    "fs_root_path": "/Users/user_name/Downloads",
    "drivers_root_path": "/Users/user_name/Downloads",
    "runtime_logger": "runtime.log",
    "limited_fuel": 200000000,
    "limited_memory": 30,
    "entry": "main",
    "modules": [
            "file": "/Users/user_name/Downloads/test1.wasm",
            "name": "linking2",
            "type": "module",
            "md5": "d41d8cd98f00b204e9800998ecf8427e"
    "permissions": [


fs_root_path: The root file system path of the app. When the app is opened, it will use this file system as its "/".

limited_fuel: The limit of instructions the app can execute. In the example, the limit is 200,000,000.

limited_memory: The maximum size of memory that the app can use. In the example, the maximum is 20 pages, where each page is 64k. So, the app can only use 20 * 64k of physical memory.

entry: The entry is the function name. Please refer to the app example for more information.

permissions: A list of resources that the app is allowed to access. If the app tries to access a resource not in this list, it will receive a "Permission Denied" error.

modules: These are the app's WebAssembly (Wasm) files. The Wasm files have 2 types defined by the type node: module and entry. module is a library in the app, while entry is the entry Wasm, which normally contains the entry function.

  • type: The Wasm files have 2 types defined by the type node.
  • file: The Wasm file.
  • name: This is used to define the linker name, which the app can use for the caller.
  • md5: The checksum of the file.

runtime_logger: Specifies the path to the log file for the runtime environment.

drivers_root_path: Specifies the root path for the drivers used by the runtime environment.

Command Line Interface

The runtime requires input from stdin and also accepts environment variables passed as a list separated by a semicolon through the BLS_LIST_VARS variable. Here's an example of how to run the app:

$ "echo "FOO" | env THIS_IS_MY_VAR=FOO BLS_LIST_VARS=THIS_IS_MY_VAR ~/.bls/runtime/blockless-cli ./build/manifest.json"

data:image/svg+xml,%3csvg%20xmlns=%27 (opens in a new tab)

Exit Code

Exit Code 1Fuel ran out
Exit Code 2Call stack exhausted
Exit Code 3Out of bounds memory access
Exit Code 4Misaligned memory access
Exit Code 5Undefined element: out of bounds table access
Exit Code 6Uninitialized element
Exit Code 7Indirect call type mismatch
Exit Code 8Integer overflow
Exit Code 9Integer divide by zero
Exit Code 10Invalid conversion to integer
Exit Code 11Wasm unreachable instruction executed
Exit Code 12Interrupt
Exit Code 13Degenerate component adapter called
Exit Code 15App timeout
Exit Code 128Configure error