readstat-wasm Bun Demo

Demonstrates reading SAS .sas7bdat file metadata and data from JavaScript using the readstat-wasm package compiled to WebAssembly via Emscripten. The demo parses a .sas7bdat file entirely in-memory via WASM and converts it to CSV.

Quick start

If you already have Rust, Emscripten SDK, libclang, and Bun installed:

macOS / Linux:

# Activate Emscripten (first time per terminal session)
source /path/to/emsdk/emsdk_env.sh

# Add the wasm target (first time only)
rustup target add wasm32-unknown-emscripten

# Initialize submodules (first time only)
git submodule update --init --recursive

# Build the wasm package
cd crates/readstat-wasm
cargo build --target wasm32-unknown-emscripten --release
cp target/wasm32-unknown-emscripten/release/readstat_wasm.wasm pkg/

# Run the demo
cd ../../examples/bun-demo
bun install
bun run index.ts

Windows (Git Bash):

# Activate Emscripten (first time per terminal session)
/c/path/to/emsdk/emsdk.bat activate latest
export EMSDK=C:/path/to/emsdk

# Add the wasm target (first time only)
rustup target add wasm32-unknown-emscripten

# Initialize submodules (first time only)
git submodule update --init --recursive

# Build the wasm package
cd crates/readstat-wasm
cargo build --target wasm32-unknown-emscripten --release
cp target/wasm32-unknown-emscripten/release/readstat_wasm.wasm pkg/

# Run the demo
cd ../../examples/bun-demo
bun install
bun run index.ts

Windows (PowerShell):

# Activate Emscripten (first time per terminal session)
C:\path\to\emsdk\emsdk.bat activate latest
$env:EMSDK = "C:\path\to\emsdk"

# Add the wasm target (first time only)
rustup target add wasm32-unknown-emscripten

# Initialize submodules (first time only)
git submodule update --init --recursive

# Build the wasm package
cd crates\readstat-wasm
cargo build --target wasm32-unknown-emscripten --release
copy target\wasm32-unknown-emscripten\release\readstat_wasm.wasm pkg\

# Run the demo
cd ..\..\examples\bun-demo
bun install
bun run index.ts

1. Install dependencies

Rust + wasm target

# Install Rust (if not already installed)
# macOS / Linux
curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh

# Windows — download and run rustup-init.exe from https://rustup.rs

# Add the Emscripten wasm target (all platforms)
rustup target add wasm32-unknown-emscripten

Emscripten SDK

# Clone the SDK
git clone https://github.com/emscripten-core/emsdk.git
cd emsdk

# Install and activate the latest toolchain
./emsdk install latest
./emsdk activate latest

Activate in your shell (run every new terminal session, or add to your profile):

Platform	Command
macOS / Linux	`source ./emsdk_env.sh`
Windows (cmd)	`emsdk_env.bat`
Windows (PowerShell)	`emsdk_env.bat` (then set `$env:EMSDK = "C:\path\to\emsdk"` if needed)
Windows (Git Bash)	`source ./emsdk_env.sh` (then `export EMSDK=C:/path/to/emsdk` if needed)

Note: On Windows, emsdk_env.sh / emsdk_env.bat may update PATH without exporting the EMSDK variable. If the build fails with “EMSDK must be set”, set it manually as shown above. The build script will also attempt to auto-detect the emsdk root from PATH.

libclang (required by bindgen)

Platform	Command
macOS	`brew install llvm`
Ubuntu / Debian	`sudo apt-get install libclang-dev`
Fedora	`sudo dnf install clang-devel`
Windows	Install LLVM from https://releases.llvm.org/download.html and set `LIBCLANG_PATH` to the `lib` directory (e.g., `C:\Program Files\LLVM\lib`)

Bun

# macOS / Linux
curl -fsSL https://bun.sh/install | bash

# Windows (PowerShell)
powershell -c "irm bun.sh/install.ps1 | iex"

2. Initialize git submodules

From the repository root:

git submodule update --init --recursive

3. Build the WASM package

# Make sure Emscripten is activated in your shell (see table above)

# From the readstat-wasm crate directory
cd crates/readstat-wasm

# Build with Emscripten target (release mode)
cargo build --target wasm32-unknown-emscripten --release

# Copy the .wasm binary into the pkg/ directory
# macOS / Linux
cp target/wasm32-unknown-emscripten/release/readstat_wasm.wasm pkg/
# Windows (PowerShell)
# copy target\wasm32-unknown-emscripten\release\readstat_wasm.wasm pkg\

4. Run the demo

cd examples/bun-demo
bun install
bun run index.ts

Expected output

=== SAS7BDAT Metadata ===
Table name:    CARS
File encoding: WINDOWS-1252
Row count:     1081
Variable count:13
Compression:   None
Endianness:    Little
Created:       2008-09-30 12:55:01
Modified:      2008-09-30 12:55:01

=== Variables ===
  [0] Brand (String, )
  [1] Model (String, )
  [2] Minivan (Double, )
  [3] Wagon (Double, )
  [4] Pickup (Double, )
  [5] Automatic (Double, )
  [6] EngineSize (Double, )
  [7] Cylinders (Double, )
  [8] CityMPG (Double, )
  [9] HwyMPG (Double, )
  [10] SUV (Double, )
  [11] AWD (Double, )
  [12] Hybrid (Double, )

=== CSV Data (preview) ===
Brand,Model,Minivan,Wagon,Pickup,Automatic,EngineSize,Cylinders,CityMPG,HwyMPG,SUV,AWD,Hybrid
TOYOTA,Prius,0.0,0.0,0.0,1.0,1.5,4.0,60.0,51.0,0.0,0.0,1.0
HONDA,Civic Hybrid,0.0,0.0,0.0,1.0,1.3,4.0,48.0,47.0,0.0,0.0,1.0
HONDA,Civic Hybrid,0.0,0.0,0.0,1.0,1.3,4.0,47.0,48.0,0.0,0.0,1.0
HONDA,Civic Hybrid,0.0,0.0,0.0,0.0,1.3,4.0,46.0,51.0,0.0,0.0,1.0
HONDA,Civic Hybrid,0.0,0.0,0.0,0.0,1.3,4.0,45.0,51.0,0.0,0.0,1.0
... (1081 total data rows)

Wrote 1081 rows to cars.csv

How it works

The readstat-wasm crate compiles the ReadStat C library and the Rust readstat parsing library to WebAssembly using the wasm32-unknown-emscripten target. Emscripten is required because the underlying ReadStat C code needs a C standard library (libc, iconv) — which Emscripten provides for wasm. (Note: zlib is only needed for SPSS zsav support, which is not included in the current wasm build.)

The crate exports eight C-compatible functions:

Export	Signature	Purpose
`read_metadata`	`(ptr, len) -> *char`	Parse metadata as JSON from a byte buffer
`read_metadata_fast`	`(ptr, len) -> *char`	Same, but skips full row count
`read_data`	`(ptr, len) -> *char`	Parse data and return as CSV string
`read_data_ndjson`	`(ptr, len) -> *char`	Parse data and return as NDJSON string
`read_data_parquet`	`(ptr, len, out_len) -> *u8`	Parse data and return as Parquet bytes
`read_data_feather`	`(ptr, len, out_len) -> *u8`	Parse data and return as Feather bytes
`free_string`	`(ptr)`	Free a string returned by the string functions
`free_binary`	`(ptr, len)`	Free binary data returned by parquet/feather

The data functions perform a two-pass parse over the same byte buffer: first to extract metadata (schema, row count), then to read row values into an Arrow RecordBatch, which is serialized to CSV or NDJSON in memory.

The JS wrapper in pkg/readstat_wasm.js handles:

Loading the .wasm module
Providing minimal WASI and Emscripten import stubs
Memory management (malloc/free for input bytes, free_string for output)
Converting between JS types and wasm pointers

Troubleshooting

EMSDK must be set for Emscripten builds Set the EMSDK environment variable to point to your emsdk installation directory. On macOS/Linux: export EMSDK=/path/to/emsdk. On Windows (PowerShell): $env:EMSDK = "C:\path\to\emsdk". On Windows (Git Bash): export EMSDK=C:/path/to/emsdk. The build script also attempts to auto-detect the emsdk root from your PATH, so simply having Emscripten activated may be sufficient.

error: linking with emcc failed / undefined symbol: main Make sure you’re building from crates/readstat-wasm/ (not the repo root). The .cargo/config.toml in that directory provides the necessary linker flags.

The command line is too long (Windows) This was a known issue when building all ReadStat C source files for the Emscripten target. It has been fixed — the build script now compiles only the SAS format sources for Emscripten builds, keeping the archiver command within Windows’ command-line length limit.

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