From 9a34a60df931358d35ea88c32afe3f044548d3c0 Mon Sep 17 00:00:00 2001
From: "Neal H. Walfield" <neal@pep.foundation>
Date: Fri, 31 Jul 2020 17:43:30 +0200
Subject: openpgp: Add variants to SignatureBuilder to add issuer subpackets.

  - `SignatureBuilder::set_issuer` and
    `SignatureBuilder::set_issuer_fingerprint` first clear the
    unhashed area of any existing Issuer or Issuer Fingerprint
    subpackets, respectively.

  - Add a variant to add an additional Issuer or Issuer Fingerprint
    subpacket.
---
 openpgp/src/packet/signature/subpacket.rs | 36 +++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/openpgp/src/packet/signature/subpacket.rs b/openpgp/src/packet/signature/subpacket.rs
index 158202ee..4d33377b 100644
--- a/openpgp/src/packet/signature/subpacket.rs
+++ b/openpgp/src/packet/signature/subpacket.rs
@@ -2595,6 +2595,25 @@ impl signature::SignatureBuilder {
         Ok(self)
     }
 
+    /// Adds an Issuer subpacket.
+    ///
+    /// Adds an [Issuer subpacket] to the unhashed subpacket area.
+    /// Unlike [`set_issuer`], this function does not first remove any
+    /// Issuer subpackets from the unhashed subpacket area.
+    ///
+    /// Caution: By default, the issuer is set correctly when creating
+    /// the signature. Only use this function to override it.
+    ///
+    /// [Issuer subpacket]: https://tools.ietf.org/html/rfc4880#section-5.2.3.5
+    /// [`set_issuer`]: #method.set_issuer
+    pub fn add_issuer(mut self, id: KeyID) -> Result<Self> {
+        self.unhashed_area.add(Subpacket::new(
+            SubpacketValue::Issuer(id),
+            false)?)?;
+
+        Ok(self)
+    }
+
     /// Sets the value of the Notation Data subpacket with the given
     /// name.
     ///
@@ -2828,6 +2847,23 @@ impl signature::SignatureBuilder {
         Ok(self)
     }
 
+    /// Adds an Issuer Fingerprint subpacket.
+    ///
+    /// Adds an [Issuer Fingerprint subpacket] to the unhashed
+    /// subpacket area.  Unlike [`set_issuer_fingerprint`], this
+    /// function does not first remove any existing Issuer Fingerprint
+    /// subpackets from the unhashed subpacket area.
+    ///
+    ///   [Issuer Fingerprint subpacket]: https://www.ietf.org/id/draft-ietf-openpgp-rfc4880bis-09.html#section-5.2.3.28
+    ///   [`set_issuer_fingerprint`]: #method.set_issuer_fingerprint
+    pub fn add_issuer_fingerprint(mut self, fp: Fingerprint) -> Result<Self> {
+        self.unhashed_area.add(Subpacket::new(
+            SubpacketValue::IssuerFingerprint(fp),
+            false)?)?;
+
+        Ok(self)
+    }
+
     /// Sets the value of the Preferred AEAD Algorithms subpacket,
     /// which contains the list of AEAD algorithms that the key holder
     /// prefers, ordered according by the key holder's preference.
-- 
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