openpgp: Change CertBuilder to use a relative expiration time.

  - `CertBuilder::set_expiration_time` takes an absolute time.

    - Most callers use a relative time.

    - Internally, we need a relative time (that's what the Key
      Expiration Time packet takes).

    - Converting the absolute time to a relative time is error prone:
      should it be relative to the creation time when called or when
      `CertBuilder` is finalized?

  - KISS: Change it to just take a relative time.

  - To better reflect the new semantics, also change the name to
    `CertBuilder::set_validity_period`.

1 files changed, 2 insertions, 2 deletions

diff --git a/openpgp/src/types/timestamp.rs b/openpgp/src/types/timestamp.rs
index 3a9a0e4c..59b903d1 100644
--- a/openpgp/src/types/timestamp.rs
+++ b/openpgp/src/types/timestamp.rs
@@ -267,11 +267,11 @@ impl Arbitrary for Timestamp {
 /// let p = &StandardPolicy::new();
 ///
 /// let now = Timestamp::now();
-/// let then = now.checked_add(Duration::days(365)?).unwrap();
+/// let validity_period = Duration::days(365)?;
 ///
 /// let (cert,_) = CertBuilder::new()
 ///     .set_creation_time(now)
-///     .set_expiration_time(then)
+///     .set_validity_period(validity_period)
 ///     .generate()?;
 ///
 /// let vc = cert.with_policy(p, now)?;