openpgp: Improve and document encryption example.

  - Encrypt to multiple recipients.

  - Add comments.

1 files changed, 26 insertions, 7 deletions

diff --git a/openpgp/examples/encrypt-for.rs b/openpgp/examples/encrypt-for.rs
index 8d704296..fa5f81c1 100644
--- a/openpgp/examples/encrypt-for.rs
+++ b/openpgp/examples/encrypt-for.rs
@@ -1,3 +1,5 @@
+/// This program demonstrates how to encrypt a stream of data.
+
 use std::env;
 use std::io;
 
@@ -9,21 +11,38 @@ use openpgp::serialize::stream::{
 
 fn main() {
     let args: Vec<String> = env::args().collect();
-    if args.len() != 2 {
+    if args.len() < 2 {
         panic!("A simple encryption filter.\n\n\
-                Usage: {} <keyfile> <input >output\n", args[0]);
+                Usage: {} <keyfile> [<keyfile>...] <input >output\n", args[0]);
     }
 
-    let keyfile = &args[1];
-    let tpk = openpgp::TPK::from_reader(
-        openpgp::Reader::from_file(keyfile).expect("Failed to open file"))
-        .expect("Failed to read key");
+    // Read the transferable public keys from the given files.
+    let tpks: Vec<openpgp::TPK> = args[1..].iter().map(|f| {
+        openpgp::TPK::from_reader(
+            // Use an openpgp::Reader so that we accept both armored
+            // and plain PGP data.
+            openpgp::Reader::from_file(f)
+                .expect("Failed to open file"))
+            .expect("Failed to read key")
+    }).collect();
+    // Build a vector of references to hand to Encryptor.
+    let recipients: Vec<&openpgp::TPK> = tpks.iter().collect();
+
+    // Compose a writer stack corresponding to the output format and
+    // packet structure we want.  First, we want the output to be as
+    // armored.
     let sink = armor::Writer::new(io::stdout(), armor::Kind::Message);
-    let encryptor = Encryptor::new(wrap(sink), &[], &[&tpk],
+
+    // We want to encrypt a literal data packet.
+    let encryptor = Encryptor::new(wrap(sink),
+                                   &[], // No symmetric encryption.
+                                   &recipients,
                                    EncryptionMode::AtRest)
         .expect("Failed to create encryptor");
     let mut literal_writer = LiteralWriter::new(encryptor, 't', None, 0)
         .expect("Failed to create literal writer");
+
+    // Finally, copy stdin to our writer stack to encrypt the data.
     io::copy(&mut io::stdin(), &mut literal_writer)
         .expect("Failed to encrypt");
 }