initial import, barely working

did.go

@@ -0,0 +1,93 @@
+package did
+
+import (
+	"fmt"
+	"strings"
+	"sync"
+)
+
+// Decoder is a function decoding an identifier ("foo" in "did:example:foo") into a DID.
+type Decoder func(identifier string) (DID, error)
+
+var (
+	decodersMu sync.RWMutex
+	decoders   = map[string]Decoder{}
+)
+
+// RegisterMethod registers a DID decoder for a given DID method..
+// Method must be the DID method (for example "key" in did:key).
+func RegisterMethod(method string, decoder Decoder) {
+	decodersMu.Lock()
+	defer decodersMu.Unlock()
+	if !checkMethod(method) {
+		panic("invalid method")
+	}
+	if decoders[method] != nil {
+		panic("did decoder already registered")
+	}
+	decoders[method] = decoder
+}
+
+// Parse returns the DID from the string representation or an error if
+// the prefix and method are incorrect, if an unknown encryption algorithm
+// is specified or if the method-specific-identifier's bytes don't
+// represent a public key for the specified encryption algorithm.
+func Parse(str string) (DID, error) {
+	decodersMu.RLock()
+	defer decodersMu.RUnlock()
+
+	if !strings.HasPrefix(str, "did:") {
+		return nil, fmt.Errorf("%w: must start with \"did:\"", ErrInvalidDid)
+	}
+
+	method, identifier, ok := strings.Cut(str[len("did:"):], ":")
+	if !ok {
+		return nil, fmt.Errorf("%w: must have a method and an identifier", ErrInvalidDid)
+	}
+
+	if !checkIdentifier(identifier) {
+		return nil, fmt.Errorf("%w: invalid identifier characters", ErrInvalidDid)
+	}
+
+	decoder, ok := decoders[method]
+	if !ok {
+		return nil, fmt.Errorf("%w: %s", ErrMethodNotSupported, method)
+	}
+
+	return decoder(identifier)
+}
+
+// MustParse is like Parse but panics instead of returning an error.
+func MustParse(str string) DID {
+	did, err := Parse(str)
+	if err != nil {
+		panic(err)
+	}
+	return did
+}
+
+func checkMethod(method string) bool {
+	if len(method) == 0 {
+		return false
+	}
+	for _, char := range method {
+		isAlpha := 'a' <= char && char <= 'z'
+		isDigit := '0' <= char && char <= '9'
+		if !isAlpha && !isDigit {
+			return false
+		}
+	}
+	return true
+}
+
+func checkIdentifier(identifier string) bool {
+	if len(identifier) == 0 {
+		return false
+	}
+	// TODO
+	// for _, char := range identifier {
+	//
+	// }
+
+	return true
+}