Initial commit: handle email delivery

rsa.go

@@ -0,0 +1,79 @@
+package main
+
+import (
+	"bytes"
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/x509"
+	"encoding/pem"
+	"fmt"
+	"io"
+	"log"
+	"os"
+)
+
+func generateOrRetrieveRSAKeys(name string, size int) (io.Reader, []byte, error) {
+	var pemprvkey bytes.Buffer
+	var prvKey *rsa.PrivateKey
+	fd, err := os.Open(name + ".pem")
+	if os.IsNotExist(err) {
+		log.Println("Private RSA key not found, generating a new one")
+
+		fd, err = os.Create(name + ".pem")
+		if err != nil {
+			return nil, nil, fmt.Errorf("unable to open the file for writing: %w", err)
+		}
+		defer fd.Close()
+
+		prvKey, err = rsa.GenerateKey(rand.Reader, size)
+		if err != nil {
+			return nil, nil, err
+		}
+		pkcs1prvkey := x509.MarshalPKCS1PrivateKey(prvKey)
+
+		var tmpprvkey bytes.Buffer
+		w := io.MultiWriter(&tmpprvkey, &pemprvkey)
+
+		err = pem.Encode(w, &pem.Block{Type: "RSA PRIVATE KEY", Bytes: pkcs1prvkey})
+		if err != nil {
+			return nil, nil, err
+		}
+
+		// Save it!
+		_, err = tmpprvkey.WriteTo(fd)
+		if err != nil {
+			return nil, nil, err
+		}
+	} else if err != nil {
+		return nil, nil, err
+	} else {
+		defer fd.Close()
+
+		var tmpprvkey bytes.Buffer
+		io.Copy(io.MultiWriter(&tmpprvkey, &pemprvkey), fd)
+
+		decodedpem, _ := pem.Decode(tmpprvkey.Bytes())
+		if decodedpem == nil {
+			return nil, nil, fmt.Errorf("unable to decode PEM data")
+		} else if decodedpem.Type != "RSA PRIVATE KEY" {
+			return nil, nil, fmt.Errorf("not the expected PEM type: %s intead of RSA PRIVATE KEY", decodedpem.Type)
+		}
+
+		prvKey, err = x509.ParsePKCS1PrivateKey(decodedpem.Bytes)
+	}
+
+	pubkey := prvKey.Public()
+	pkixpub, err := x509.MarshalPKIXPublicKey(pubkey.(*rsa.PublicKey))
+	if err != nil {
+		return nil, nil, err
+	}
+
+	pempubkey := pem.EncodeToMemory(
+		&pem.Block{
+			Type:  "PUBLIC KEY",
+			Bytes: pkixpub,
+		},
+	)
+
+	return &pemprvkey, pempubkey, nil
+}