cli/show: produce "email" element in sigstatus

When the certificate that signs a message is known to be valid, GMime
is capable of reporting on the e-mail address embedded in the
certificate.

We pass this information along to the caller of "notmuch show", as
often only the e-mail address of the certificate has actually been
checked/verified.

Furthermore, signature verification should probably at some point
compare the e-mail address of the caller against the sender address of
the message itself.  Having to parse what gmime thinks is a "userid"
to extract an e-mail address seems clunky and unnecessary if gmime
already thinks it knows what the e-mail address is.

See id:878s41ax6t.fsf@fifthhorseman.net for more motivation and discussion.

Signed-off-by: Daniel Kahn Gillmor <dkg@fifthhorseman.net>

1 files changed, 4 insertions, 0 deletions

diff --git a/util/gmime-extra.h b/util/gmime-extra.h
index 094309ec..889e91f3 100644
--- a/util/gmime-extra.h
+++ b/util/gmime-extra.h
@@ -69,6 +69,10 @@ gint64 g_mime_utils_header_decode_date_unix (const char *date);
  * Return string for valid User ID (or NULL if no valid User ID exists)
  */
 const char *g_mime_certificate_get_valid_userid (GMimeCertificate *cert);
+/**
+ * Return string for valid e-mail address (or NULL if no valid e-mail address exists)
+ */
+const char *g_mime_certificate_get_valid_email (GMimeCertificate *cert);
 
 #ifdef __cplusplus
 }