From f3fdc33c9efcbe5c83e99751eac7097df95c4973 Mon Sep 17 00:00:00 2001
From: Filippo Valsorda <hi@filippo.io>
Date: Tue, 9 Mar 2021 20:42:20 -0500
Subject: [PATCH] cmd/age-keygen: add -y mode to convert identity file to
 recipients

Copied -y from ssh-keygen. Copied the INPUT as only optional argument
from cmd/age.

Fixes #122
Closes #146
---
 cmd/age-keygen/keygen.go | 57 +++++++++++++++++++++++++++++++++++-----
 1 file changed, 51 insertions(+), 6 deletions(-)

diff --git a/cmd/age-keygen/keygen.go b/cmd/age-keygen/keygen.go
index cf6972a4..c744b484 100644
--- a/cmd/age-keygen/keygen.go
+++ b/cmd/age-keygen/keygen.go
@@ -9,6 +9,7 @@ package main
 import (
 	"flag"
 	"fmt"
+	"io"
 	"log"
 	"os"
 	"runtime/debug"
@@ -20,9 +21,11 @@ import (
 
 const usage = `Usage:
     age-keygen [-o OUTPUT]
+    age-keygen -y [-o OUTPUT] [INPUT]
 
 Options:
-    -o, --output OUTPUT       Write the key to the file at path OUTPUT.
+    -o, --output OUTPUT       Write the result to the file at path OUTPUT.
+    -y                        Convert an identity file to a recipients file.
 
 age-keygen generates a new standard X25519 key pair, and outputs it to
 standard output or to the OUTPUT file.
@@ -30,6 +33,10 @@ standard output or to the OUTPUT file.
 If an OUTPUT file is specified, the public key is printed to standard error.
 If OUTPUT already exists, it is not overwritten.
 
+In -y mode, age-keygen reads an identity file from INPUT or from standard
+input and writes the corresponding recipient(s) to OUTPUT or to standard
+output, one per line, with no comments.
+
 Examples:
 
     $ age-keygen
@@ -38,7 +45,10 @@ Examples:
     AGE-SECRET-KEY-1N9JEPW6DWJ0ZQUDX63F5A03GX8QUW7PXDE39N8UYF82VZ9PC8UFS3M7XA9
 
     $ age-keygen -o key.txt
-    Public key: age1ql3z7hjy54pw3hyww5ayyfg7zqgvc7w3j2elw8zmrj2kg5sfn9aqmcac8p`
+    Public key: age1ql3z7hjy54pw3hyww5ayyfg7zqgvc7w3j2elw8zmrj2kg5sfn9aqmcac8p
+
+    $ age-keygen -y key.txt
+    age1ql3z7hjy54pw3hyww5ayyfg7zqgvc7w3j2elw8zmrj2kg5sfn9aqmcac8p`
 
 // Version can be set at link time to override debug.BuildInfo.Main.Version,
 // which is "(devel)" when building from within the module. See
@@ -50,17 +60,21 @@ func main() {
 	flag.Usage = func() { fmt.Fprintf(os.Stderr, "%s\n", usage) }
 
 	var (
-		versionFlag bool
-		outFlag     string
+		versionFlag, convertFlag bool
+		outFlag                  string
 	)
 
 	flag.BoolVar(&versionFlag, "version", false, "print the version")
+	flag.BoolVar(&convertFlag, "y", false, "convert identities to recipients")
 	flag.StringVar(&outFlag, "o", "", "output to `FILE` (default stdout)")
 	flag.StringVar(&outFlag, "output", "", "output to `FILE` (default stdout)")
 	flag.Parse()
-	if len(flag.Args()) != 0 {
+	if len(flag.Args()) != 0 && !convertFlag {
 		log.Fatalf("age-keygen takes no arguments")
 	}
+	if len(flag.Args()) > 1 && convertFlag {
+		log.Fatalf("Too many arguments")
+	}
 	if versionFlag {
 		if Version != "" {
 			fmt.Println(Version)
@@ -90,7 +104,21 @@ func main() {
 		}
 	}
 
-	generate(out)
+	in := os.Stdin
+	if inFile := flag.Arg(0); inFile != "" && inFile != "-" {
+		f, err := os.Open(inFile)
+		if err != nil {
+			log.Fatalf("Failed to open input file %q: %v", inFile, err)
+		}
+		defer f.Close()
+		in = f
+	}
+
+	if convertFlag {
+		convert(in, out)
+	} else {
+		generate(out)
+	}
 }
 
 func generate(out *os.File) {
@@ -107,3 +135,20 @@ func generate(out *os.File) {
 	fmt.Fprintf(out, "# public key: %s\n", k.Recipient())
 	fmt.Fprintf(out, "%s\n", k)
 }
+
+func convert(in io.Reader, out io.Writer) {
+	ids, err := age.ParseIdentities(in)
+	if err != nil {
+		log.Fatalf("Failed to parse input: %v", err)
+	}
+	if len(ids) == 0 {
+		log.Fatalf("No identities found in the input")
+	}
+	for _, id := range ids {
+		id, ok := id.(*age.X25519Identity)
+		if !ok {
+			log.Fatalf("Internal error: unexpected identity type: %T", id)
+		}
+		fmt.Fprintf(out, "%s\n", id.Recipient())
+	}
+}