openpgp: Fix Signature::get_issuer to return set of issuers.

  - A signature can contain multiple hints as to who created the
    signature.  Return all those hints to the caller.

  - Adapt all callers accordingly.

  - Fixes #264.

4 files changed, 34 insertions, 22 deletions

diff --git a/openpgp/examples/web-of-trust.rs b/openpgp/examples/web-of-trust.rs
index 754a7b13..34cbe289 100644
--- a/openpgp/examples/web-of-trust.rs
+++ b/openpgp/examples/web-of-trust.rs
@@ -10,6 +10,7 @@
 use std::env;
 
 extern crate sequoia_openpgp as openpgp;
+use crate::openpgp::KeyID;
 use crate::openpgp::tpk::TPKParser;
 use crate::openpgp::parse::Parse;
 
@@ -39,14 +40,12 @@ fn main() {
                     let keyid = tpk.keyid();
                     for uidb in tpk.userids() {
                         for tps in uidb.certifications() {
-                            if let Some(issuer) = tps.get_issuer() {
+                            for issuer in tps.get_issuers() {
                                 println!("{}, {:?}, {}",
-                                         issuer.as_u64().unwrap(),
+                                         KeyID::from(issuer).as_u64().unwrap(),
                                          String::from_utf8_lossy(
                                              uidb.userid().value()),
                                          keyid.as_u64().unwrap());
-                            } else {
-                                eprintln!("No issuer!?");
                             }
                         }
                     }
diff --git a/openpgp/src/packet/signature/mod.rs b/openpgp/src/packet/signature/mod.rs
index 4fb15d18..a754bec7 100644
--- a/openpgp/src/packet/signature/mod.rs
+++ b/openpgp/src/packet/signature/mod.rs
@@ -19,7 +19,6 @@ use crate::packet::{
     key,
     Key,
 };
-use crate::KeyID;
 use crate::packet::UserID;
 use crate::packet::UserAttribute;
 use crate::Packet;
@@ -476,13 +475,25 @@ impl Signature4 {
         ::std::mem::replace(&mut self.level, level)
     }
 
-    /// Gets the issuer.
-    pub fn get_issuer(&self) -> Option<KeyID> {
-        if let Some(id) = self.issuer() {
-            Some(id)
-        } else {
-            None
-        }
+    /// Collects all the issuers.
+    ///
+    /// A signature can contain multiple hints as to who issued the
+    /// signature.
+    pub fn get_issuers(&self) -> std::collections::HashSet<crate::KeyHandle> {
+        use crate::packet::signature::subpacket:: SubpacketValue;
+
+        self.hashed_area().iter()
+            .chain(self.unhashed_area().iter())
+            .filter_map(|(_, _, subpacket)| {
+                match subpacket.value() {
+                    SubpacketValue::Issuer(i) =>
+                        Some(crate::KeyHandle::KeyID(i.clone())),
+                    SubpacketValue::IssuerFingerprint(i) =>
+                        Some(crate::KeyHandle::Fingerprint(i.clone())),
+                    _ => None,
+                }
+            })
+            .collect()
     }
 
     /// Normalizes the signature.
@@ -1098,6 +1109,7 @@ impl From<Signature4> for super::Signature {
 #[cfg(test)]
 mod test {
     use super::*;
+    use crate::KeyID;
     use crate::conversions::Time;
     use crate::crypto;
     use crate::crypto::mpis::MPI;
diff --git a/openpgp/src/parse/stream.rs b/openpgp/src/parse/stream.rs
index cca238dc..43120f87 100644
--- a/openpgp/src/parse/stream.rs
+++ b/openpgp/src/parse/stream.rs
@@ -606,8 +606,8 @@ impl<'a, H: VerificationHelper> Verifier<'a, H> {
                 //
                 // In this case, we get the issuer from the
                 // signature itself.
-                if let Some(issuer) = sig.get_issuer() {
-                    issuers.push(issuer);
+                if let Some(issuer) = sig.get_issuers().iter().next() {
+                    issuers.push(issuer.clone().into());
                 } else {
                     issuers.push(KeyID::wildcard());
                 }
@@ -656,9 +656,9 @@ impl<'a, H: VerificationHelper> Verifier<'a, H> {
                 IMessageLayer::SignatureGroup { sigs, .. } => {
                     results.new_signature_group();
                     for sig in sigs.into_iter() {
-                        if let Some(issuer) = sig.get_issuer() {
+                        if let Some(issuer) = sig.get_issuers().iter().next() {
                             let r =  if let Some((i, j)) =
-                                self.keys.get(&issuer)
+                                self.keys.get(&issuer.clone().into())
                             {
                                 let tpk = &self.tpks[*i];
                                 let (binding, revoked, key)
@@ -1421,8 +1421,8 @@ impl<'a, H: VerificationHelper + DecryptionHelper> Decryptor<'a, H> {
                         //
                         // In this case, we get the issuer from the
                         // signature itself.
-                        if let Some(issuer) = sig.get_issuer() {
-                            issuers.push(issuer);
+                        if let Some(issuer) = sig.get_issuers().iter().next() {
+                            issuers.push(issuer.clone().into());
                         } else {
                             issuers.push(KeyID::wildcard());
                         }
@@ -1518,9 +1518,9 @@ impl<'a, H: VerificationHelper + DecryptionHelper> Decryptor<'a, H> {
                 IMessageLayer::SignatureGroup { sigs, .. } => {
                     results.new_signature_group();
                     for sig in sigs.into_iter() {
-                        if let Some(issuer) = sig.get_issuer() {
+                        if let Some(issuer) = sig.get_issuers().iter().next() {
                             results.push_verification_result(
-                                if let Some((i, j)) = self.keys.get(&issuer) {
+                                if let Some((i, j)) = self.keys.get(&issuer.clone().into()) {
                                     let tpk = &self.tpks[*i];
                                     let (binding, revoked, key)
                                         = tpk.keys_all().nth(*j).unwrap();
diff --git a/tool/src/commands/mod.rs b/tool/src/commands/mod.rs
index 6da5f56b..a7b76038 100644
--- a/tool/src/commands/mod.rs
+++ b/tool/src/commands/mod.rs
@@ -238,8 +238,9 @@ impl<'a> VHelper<'a> {
         use self::VerificationResult::*;
         for result in results {
             if let MissingKey { sig } = result {
-                let issuer = sig.get_issuer()
-                    .expect("missing key checksum has an issuer");
+                let issuer = sig.get_issuers().iter().nth(0)
+                    .expect("missing key checksum has an issuer")
+                    .to_string();
                 let what = match sig.level() {
                     0 => "checksum".into(),
                     n => format!("level {} notarizing checksum", n),