go-whosonfirst-validate-wasm

README

go-whosonfirst-validate-wasm

Go package for compiling the Validate method of the go-whosonfirst-validate package to a JavaScript-compatible WebAssembly (wasm) binary. It also provides a net/http middleware packages for appending the necessary static assets and HTML resources to use the wasm binary in web applications.

Build

To build the validate_feature WebAssembly binary for use in your applications run the following command:

GOOS=js GOARCH=wasm go build -mod vendor -o validate_feature.wasm cmd/validate_feature/main.go

Use

To use the validate_feature WebAssembly binary in your applications a JSON-encoded GeoJSON string to the validate_feature function.

The function returns a JavaScript Promise that will return a JSON-encoded Who's On First (WOF) GeoJSON string on success or an error message if there was a problem.

	var str_f = '{"type": "Feature" ... }'	// A valid GeoJSON Feature
	
	validate_feature().then(rsp => {
	    console.log("WOF feature is valid.");
	}).catch(err => {
	    console.log("Failed to validate feature: ", err);
	});

In order to load the validate_feature function you will need to include the wasm_exec.js and whosonfirst.validate.feature.js JavaScript files, or functional equivalents. Both scripts are bundled with this package in the static/javascript folder.

Middleware

The go-whosonfirst-validate-wasm/http package provides methods for appending static assets and HTML resources to existing web applications to facilitate the use of the validate_feature WebAssembly binary. For example:

Note the use of the sfomuseum/go-http-wasm package which is an HTTP middleware package for serving and appending resources to the wasm_exec.js JavaScript library.

package main

import (
	"embed"
	"flag"
	"fmt"
	"log"
	"net/http"

	validate_wasm "github.com/whosonfirst/go-whosonfirst-validate-wasm/http"
	"github.com/sfomuseum/go-http-wasm"	
)

//go:embed index.html example.*
var FS embed.FS

func main() {

	host := flag.String("host", "localhost", "The host name to listen for requests on")
	port := flag.Int("port", 8080, "The host port to listen for requests on")

	flag.Parse()

	mux := http.NewServeMux()

	wasm.AppendAssetHandlers(mux)
	validate_wasm.AppendAssetHandlers(mux)

	http_fs := http.FS(FS)
	example_handler := http.FileServer(http_fs)

	wasm_opts := wasm.DefaultWASMOptions()
	example_handler = wasm.AppendResourcesHandler(example_handler, wasm_opts)

	mux.Handle("/", example_handler)

	addr := fmt.Sprintf("%s:%d", *host, *port)
	log.Printf("Listening for requests on %s\n", addr)

	http.ListenAndServe(addr, mux)
}

Error handling omitted for brevity.

Example

There is a full working example of this application in the cmd/example folder. To run this application type the following command:

$> make example
go run -mod vendor cmd/example/main.go
2023/01/31 15:11:48 Listening for requests on localhost:8080

Then open http://localhost:8080 in a web browser. You should see something like this:

The default document included in the example is invalid so when you click the "Validate" button you should see an error like this:

If you add a "wof:repo":"whosonfirst-data-example" property and resubmit the document the validation will succeed.

See also

• https://github.com/whosonfirst/go-whosonfirst-validate
• https://github.com/sfomuseum/go-http-wasm
• https://github.com/golang/go/wiki/WebAssembly