From 085cf20de98c8b7008434f4fb3287fa6c5a16195b32c4e58f2cbd95bc3caac1d Mon Sep 17 00:00:00 2001
From: Sergey Matveev <stargrave@stargrave.org>
Date: Thu, 9 Jan 2025 18:02:23 +0300
Subject: [PATCH] Initial commit

---
 go.mod  |   3 ++
 main.go | 136 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 139 insertions(+)
 create mode 100644 go.mod
 create mode 100644 main.go

diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..bfc15c6
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,3 @@
+module go.stargrave.org/pgpmaildecryptor
+
+go 1.23.4
diff --git a/main.go b/main.go
new file mode 100644
index 0000000..50dd1d9
--- /dev/null
+++ b/main.go
@@ -0,0 +1,136 @@
+package main
+
+import (
+	"bufio"
+	"bytes"
+	"io"
+	"log"
+	"mime"
+	"net/mail"
+	"net/textproto"
+	"os"
+	"os/exec"
+	"strings"
+)
+
+func main() {
+	log.SetFlags(log.Lshortfile)
+	rawEnc, err := io.ReadAll(bufio.NewReader(os.Stdin))
+	if err != nil {
+		log.Fatal(err)
+	}
+	msgEnc, err := mail.ReadMessage(bytes.NewReader(rawEnc))
+	if err != nil {
+		log.Fatal(err)
+	}
+	{
+		ct := msgEnc.Header.Get("Content-Type")
+		if ct == "" {
+			log.Fatal("no Content-Type")
+		}
+		mt, params, errParse := mime.ParseMediaType(ct)
+		if errParse != nil {
+			log.Fatal(errParse)
+		}
+		if mt != "multipart/encrypted" {
+			log.Fatal("not multipart/encrypted")
+		}
+		if proto := params["protocol"]; proto != "application/pgp-encrypted" {
+			log.Fatal("not application/pgp-encrypted")
+		}
+	}
+	var rawDec []byte
+	{
+		cmd := exec.Command("gpg", "--batch", "--decrypt", "--status-fd", "3")
+		cmd.Stderr = os.Stderr
+		var stdin io.WriteCloser
+		stdin, err = cmd.StdinPipe()
+		if err != nil {
+			log.Fatal(err)
+		}
+		var stdout io.ReadCloser
+		stdout, err = cmd.StdoutPipe()
+		if err != nil {
+			log.Fatal(err)
+		}
+		var statusR, statusW *os.File
+		statusR, statusW, err = os.Pipe()
+		if err != nil {
+			log.Fatal(err)
+		}
+		cmd.ExtraFiles = append(cmd.ExtraFiles, statusW)
+
+		err = cmd.Start()
+		if err != nil {
+			log.Fatal(err)
+		}
+		go func() {
+			_, errStdin := io.Copy(stdin, msgEnc.Body)
+			if err != nil {
+				log.Print(errStdin)
+			}
+			if errStdin = stdin.Close(); err != nil {
+				log.Print(errStdin)
+			}
+		}()
+		var goodDec bool
+		go func() {
+			s := bufio.NewScanner(statusR)
+			var t string
+			for s.Scan() {
+				t = s.Text()
+				if t == "[GNUPG:] DECRYPTION_OKAY" {
+					goodDec = true
+				}
+				log.Print(t)
+			}
+			if s.Err() != nil {
+				log.Print(s.Err())
+			}
+		}()
+		rawDec, err = io.ReadAll(stdout)
+		if err != nil {
+			log.Fatal(err)
+		}
+		err = cmd.Wait()
+		if err != nil {
+			log.Fatal(err)
+		}
+		if !goodDec {
+			log.Fatal("no DECRYPTION_OKAY received")
+		}
+	}
+	msgDec, err := mail.ReadMessage(bytes.NewReader(rawDec))
+	if err != nil {
+		log.Fatal(err)
+	}
+	stdout := bufio.NewWriter(os.Stdout)
+	r := textproto.NewReader(bufio.NewReader(bytes.NewReader(rawEnc)))
+	var t string
+	var hdr string
+	for {
+		t, err = r.ReadContinuedLine()
+		if err != nil {
+			log.Fatal(err)
+		}
+		if t == "" {
+			break
+		}
+		hdr = t[:strings.Index(t, ":")]
+		if msgDec.Header.Get(hdr) != "" {
+			continue
+		}
+		if _, err = stdout.WriteString(t); err != nil {
+			log.Fatal(err)
+		}
+		if _, err = stdout.WriteString("\n"); err != nil {
+			log.Fatal(err)
+		}
+	}
+	if _, err = io.Copy(stdout, bytes.NewReader(rawDec)); err != nil {
+		log.Fatal(err)
+	}
+	if err = stdout.Flush(); err != nil {
+		log.Fatal(err)
+	}
+}
-- 
2.48.1