Maxmind DB support for scripting engine

README.md

@@ -442,6 +442,8 @@ Following builtin functions are addionally available within JS scripts:
 
 * `print(val)` - print arbitrary values *val* into dumbproxy log for debugging purposes.
 * `readFile(path: string): string` - read file from *path* and return its content as a string.
+* `mmdbOpen(path: string): mmdbReaderObject` - opens MaxMind database and returns a reader object which has only one method:
+  * `lookup(IP: string): mmdbRecordObject` - returns JS object with information about IP address or throws an exception if record was not found. See detailed example in the project's wiki.
 * `newStopAddressIteration(): Exception` - create an exception which, once `throw`n, halts further invocations of JS function with different resolved addresses for that request. Useful to cut excess JS calls of access filter scripts which can conclude access denial without looking further into remaining resolved addresses.
 
 Following objects are additionally available in global scope of JS scripts:

go.mod

@@ -10,6 +10,7 @@ require (
 	github.com/hashicorp/go-multierror v1.1.1
 	github.com/libp2p/go-reuseport v0.4.0
 	github.com/ncruces/go-dns v1.3.3
+	github.com/oschwald/maxminddb-golang/v2 v2.3.0
 	github.com/pires/go-proxyproto v0.12.0
 	github.com/redis/go-redis/v9 v9.19.0
 	github.com/refraction-networking/utls v1.8.2

go.sum

@@ -39,6 +39,8 @@ github.com/libp2p/go-reuseport v0.4.0 h1:nR5KU7hD0WxXCJbmw7r2rhRYruNRl2koHw8fQsc
 github.com/libp2p/go-reuseport v0.4.0/go.mod h1:ZtI03j/wO5hZVDFo2jKywN6bYKWLOy8Se6DrI2E1cLU=
 github.com/ncruces/go-dns v1.3.3 h1:59OV7XoJrTCoUMZjWRVs4GOjtntMTZqiQ5Mn+BT13hk=
 github.com/ncruces/go-dns v1.3.3/go.mod h1:tuzixNY8PY/M7yUzcvRbUaeLs3ifIdydpi5H2bfRU+s=
+github.com/oschwald/maxminddb-golang/v2 v2.3.0 h1:PnXjMGjkSQlwOBSyZ7hk6Fd75t7erkAhJNJgEhA3MQU=
+github.com/oschwald/maxminddb-golang/v2 v2.3.0/go.mod h1:NSQvgFwPxODpBTJI5+5Ns1AAucnx7ggW9PSRRifAT1s=
 github.com/pires/go-proxyproto v0.12.0 h1:TTCxD66dU898tahivkqc3hoceZp7P44FnorWyo9d5vM=
 github.com/pires/go-proxyproto v0.12.0/go.mod h1:qUvfqUMEoX7T8g0q7TQLDnhMjdTrxnG0hvpMn+7ePNI=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=

jsext/jsext.go

@@ -10,6 +10,9 @@ func ConfigureRuntime(vm *goja.Runtime) error {
 	if err := AddStopAddressIteration(vm); err != nil {
 		return err
 	}
+	if err := AddMMDBReader(vm); err != nil {
+		return err
+	}
 	if err := ExportEnv(vm); err != nil {
 		return err
 	}

jsext/mmdb.go

@@ -0,0 +1,98 @@
+package jsext
+
+import (
+	"net/netip"
+	"runtime"
+
+	"github.com/dop251/goja"
+	"github.com/oschwald/maxminddb-golang/v2"
+)
+
+type mmdbReaderObject struct {
+	reader *maxminddb.Reader
+	vm     *goja.Runtime
+}
+
+func (ro *mmdbReaderObject) Get(key string) goja.Value {
+	switch key {
+	case "lookup":
+		return ro.vm.ToValue(ro.jsLookup)
+	default:
+		return goja.Undefined()
+	}
+}
+
+func (ro *mmdbReaderObject) Set(_ string, _ goja.Value) bool {
+	return false
+}
+
+func (ro *mmdbReaderObject) Has(key string) bool {
+	return key == "lookup"
+}
+
+func (ro *mmdbReaderObject) Delete(key string) bool {
+	return false
+}
+
+func (ro *mmdbReaderObject) Keys() []string {
+	return []string{"lookup"}
+}
+
+func (ro *mmdbReaderObject) lookup(ip netip.Addr) (any, error) {
+	var record any
+	err := ro.reader.Lookup(ip).Decode(&record)
+	if err != nil {
+		return nil, err
+	}
+	return record, nil
+}
+
+func (ro *mmdbReaderObject) jsLookup(call goja.FunctionCall, vm *goja.Runtime) goja.Value {
+	if len(call.Arguments) != 1 {
+		panic(vm.NewTypeError("lookup expects exactly 1 argument, IP address string"))
+	}
+	ip, err := netip.ParseAddr(call.Argument(0).String())
+	if err != nil {
+		panic(vm.NewGoError(err))
+	}
+	record, err := ro.lookup(ip)
+	if err != nil {
+		panic(vm.NewGoError(err))
+	}
+	return vm.ToValue(record)
+}
+
+func newMMDBReaderObject(reader *maxminddb.Reader, vm *goja.Runtime) *mmdbReaderObject {
+	o := &mmdbReaderObject{
+		reader: reader,
+		vm:     vm,
+	}
+	runtime.AddCleanup(o, func(r *maxminddb.Reader) {
+		r.Close()
+	}, reader)
+	return o
+}
+
+func mmdbOpen(filename string, vm *goja.Runtime) (*mmdbReaderObject, error) {
+	reader, err := maxminddb.Open(filename)
+	if err != nil {
+		return nil, err
+	}
+	return newMMDBReaderObject(reader, vm), nil
+}
+
+func AddMMDBReader(vm *goja.Runtime) error {
+	return vm.Set("mmdbOpen", func(call goja.FunctionCall) goja.Value {
+		if len(call.Arguments) != 1 {
+			panic(vm.NewTypeError("mmdbOpen expects exactly 1 argument, a filename"))
+		}
+
+		filename := call.Argument(0).String()
+		ro, err := mmdbOpen(filename, vm)
+		if err != nil {
+			panic(vm.NewGoError(err))
+		}
+
+		return vm.NewDynamicObject(ro)
+	})
+}