Mockbox

A flexible HTTP proxy server powered by Rune scripting. Every incoming request is first handled by a Rune script, which can either respond directly or indicate that the request should be proxied to an upstream server.

Table of Contents

• Features
• Installation
  • Pre-Built Binaries (via cargo-binstall)
  • Pre-Built Binaries (manual download)
  • From Source
• Usage
  • Basic Setup
  • Configuration
• Rune Script API
  • Request Object
  • Response Options
    • 1. Return a simple string
    • 2. Return an object
    • 3. Return status and response
    • 4. Proxy to upstream server
• Example Scripts
  • Mock API Endpoints
  • Route-based Handling
  • Conditional Mocking
  • Error Responses
• Architecture
• Use Cases
  • Testing
• Features
  • storage
    • Storage API
    • Storage Example
  • spec
    • Spec API
    • Spec Example

Features

• Rune Scripting: Handle HTTP requests with dynamic Rune scripts
• Upstream Proxy: Automatically proxy unhandled requests to another web server
• Hot-reloadable: Modify scripts without restarting
• Full HTTP Support: Access method, path, headers, and body in scripts

Installation

Pre-Built Binaries (via cargo-binstall)

cargo binstall mockbox

Pre-Built Binaries (manual download)

You can download pre-built binaries from the latest release.

From Source

1. Clone the repository
2. Build the project:

cargo install mockbox

Usage

Basic Setup

1. Generate the an example script (online version):

mockbox example > mockbox.rn

If you want to learn more about rune, check out the rune book.

2. Run the server:

mockbox mock

If no script path is passed to mockbox, it will check for a file called mockbox.rn in the current directory and if it doesn't exist, it will check in $HOME/.local/share/mockbox for a mockbox.rn.

3. The server will start on http://127.0.0.1:3333

Configuration

Configure the upstream server using the MOCKBOX_UPSTREAM environment variable:

MOCKBOX_UPSTREAM=http://localhost:8080 mockbox mock mockbox.rn

or by using the appropriate cli option:

mockbox mock mockbox.rn --upstream http://localhost:8080

Rune Script API

Your mockbox.rn must export a handle_request function that receives a request object and returns either a string, an object, a tuple ((<status_code>, <response>)).

Request Object

The request object passed to your handler contains:

• method: HTTP method (e.g., "GET", "POST")
• path: Request path (e.g., "/api/users")
• body: Request body as a string

Response Options

1. Return a simple string

Return just a string for a 200 OK response:

pub fn handle_request(request) {
    "Hello, World!"
}

2. Return an object

Return an object for a 200 OK response:

pub fn handle_request(request) {
    #{some: 1, values: 2}
}

The object will automatically be converted to json.

3. Return status and response

Return a tuple with status and response (string or object):

pub fn handle_request(request) {
    (200, "Hello, World!")
}

4. Proxy to upstream server

Explicitly return nothing to proxy the request:

pub fn handle_request(request) {
    ()
}

Example Scripts

Mock API Endpoints

pub fn handle_request(request) {
    let path = request.path;
    let method = request.method;

    // Mock user API
    match path {
        "/api/users" if method == "GET" => {
            [#{ "id": 1, "name": "John" }, #{ "id": 2, "name": "Jane" }]
        }

        // Mock authentication
        "/api/login" if method == "POST" => {
            #{ "token": "mock-jwt-token-12345" }
        }
    }
}

Route-based Handling

pub fn handle_request(request) {
    let path = request.path;

    match path {
        // Echo endpoint
        "/echo" => request.body,

        // Handle all /mock/* routes
        _ if path.starts_with("/mock/") => #{mocked: true, path: path},
    }
}

Conditional Mocking

pub fn handle_request(request) {
    let path = request.path;
    let body = request.body;

    // Mock only if body contains "test"
    if body.contains("test") {
        return #{ "message": "Test mode response" };
    }
}

Error Responses

pub fn handle_request(request) {
    let path = request.path;

    // Simulate errors for testing
    match path {
        "/error/500" => (500, "Internal Server Error"),
        "/error/404" => (404, "Not Found"),
    }
}

Architecture

1. Request Reception: Axum receives the HTTP request
2. Rune Execution: The handle_request function in mockbox.rn is called
3. Response Decision:
   • If the script returns a string, object or response tuple → respond directly
   • If the script doesn't return anything or explicitly returns () → proxy to upstream server
4. Upstream Proxy: Forward the original request to the configured upstream URL
5. Response: Return the response from either Rune or the upstream server

Use Cases

• Mock APIs: Create mock responses for testing frontend applications
• Request Interception: Log, modify, or reject requests based on conditions
• A/B Testing: Route requests to different backends based on rules
• Development Environment: Override specific endpoints while keeping others real

Testing

Test your Rune scripts by making HTTP requests:

# Test a mocked endpoint

curl http://localhost:3333/demo


# Test the upstream proxy

curl http://localhost:3333/some/unhandled/path

Features

storage

Enables the storage API to persist data between requests.

This is enabled by default

Storage API

// store a rune value
storage::set(key: &str, value: rune::Value) -> Result<()>;

// load a stored value
storage::get(key: &str) -> Result<rune::Value>;

// delete a stored value
storage::delete(key: &str) -> Result<()>;

// check if a value exists
storage::has(key: &str) -> bool;

// clear the whole storage
storage::clear() -> Result<()>;

// get keys of all stored values
storage::keys() -> Result<()>;

Storage Example

["demo"] => {
    let demo_count = storage::get("demo_count")?.unwrap_or(0);
    let new_demo_count = demo_count + 1;
    storage::set("demo_count", new_demo_count)?;
    #{ message: `This demo endpoint has been called ${new_demo_count} times` }
},

spec

Enables the spec API to build descriptions for generating random data.

This is enabled by default

Spec API

// creates a spec that evaluates to the passed value
spec::just(value: rune::Value) -> Spec;

// creates a spec that evaluates to a random boolean
spec::bool() -> Spec;

// creates a spec that evaluates to a random u128 between <min> and <max> (exclusive)
spec::uint(min: u128, max:  u128) -> Spec;

// creates a spec that evaluates to a random i128 between <min> and <max> (exclusive)
spec::int(min: i128, max:  i128) -> Spec;

// creates a spec that evaluates to a random f64 between <min> and <max> (exclusive)
spec::float(min: f32, max: f32) -> Spec;

// creates a spec that evaluates to a string of random alpha numeric characters that is <len> long
spec::alphanumeric(len: Spec) -> Spec;

// creates a spec that evaluates to a string of random characters between <min> and <max> (exclusive)
spec::string(min: usize, max: usize) -> Spec;

// creates a spec that evaluates to a random value from the passed vec
spec::one_of(values: Vec<Spec>) -> Spec;

// creates a spec that evaluates to a weighted random value from the passed vec
spec::weighted(values: Vec<(u32, Spec)>) -> Spec;

// creates a spec that evaluates to a vec of length <len>, filled with values defined by <item>
spec::array(len: Spec, item: Spec) -> Spec;

// creates a spec that evaluates to a an object
spec::object(fields: HashMap<String, Spec>) -> Spec;

// creates a spec that has a 0.0 < p < 1.0 chance to evaluate to an optional value defined by <item>
spec::optional(p: Spec, item: Spec) -> Spec;

// creates a spec that takes all items in a vec and evaluates them to values, according to their spec
spec::tuple(items: Vec<Spec>) -> Spec;

// evaluates a given spec
Spec::generate(&self) -> Result<rune::Value>;

Spec Example

use spec as s;

match path.parts() {
    ["demo"] => object(
            #{
                asdf: s::uint(1, 10),
                values: s::array(s::just(5), s::float(55.0, 128.0)),
                choice: s::one_of(
                    [
                        s::object(#{ A: s::uint(100, 200) }),
                        s::object(#{ B: s::int(-100, 100) }),
                        s::object(#{ C: s::float(0.5, 2.5) }),
                        s::object(#{ D: s::alphanumeric(s::just(10)) }),
                    ],
                ),
            },
        )
        .generate()?,
}