dc_receive_imf: simplify timestamp calculation

Reduce the number of mutable variables and out parameters in
`add_parts`.

Also don't call `dc_create_smeared_timestamp` if there is no `Date`
header. Timestamps are only supposed to be "created" when the message
is sent, not received, to make sure sent messages are sorted properly
in MUAs that only use the date for sorting. Delta Chat uses database
IDs for sorting in addition to timestamps, so it can sort messages
with equal timestamps properly.

Update `dc_smeared_time` documentation.

Turn `dc_smeared_time` and `dc_create_smeared_timestamp` comments into
documentation comments.

Author: link2xt

src/dc_receive_imf.rs

@@ -1,5 +1,6 @@
 //! Internet Message Format reception pipeline.
 
+use std::cmp::min;
 use std::convert::TryFrom;
 
 use anyhow::{bail, ensure, Result};
@@ -18,9 +19,7 @@ use crate::constants::{
 };
 use crate::contact::{addr_cmp, normalize_name, Contact, Origin, VerifiedStatus};
 use crate::context::Context;
-use crate::dc_tools::{
-    dc_create_smeared_timestamp, dc_extract_grpid_from_rfc724_mid, dc_smeared_time,
-};
+use crate::dc_tools::{dc_extract_grpid_from_rfc724_mid, dc_smeared_time};
 use crate::download::DownloadState;
 use crate::ephemeral::{stock_ephemeral_timer_changed, Timer as EphemeralTimer};
 use crate::events::EventType;
@@ -106,15 +105,6 @@ pub(crate) async fn dc_receive_imf_inner(
         return Ok(());
     }
 
-    let mut sent_timestamp = if let Some(value) = mime_parser
-        .get_header(HeaderDef::Date)
-        .and_then(|value| mailparse::dateparse(value).ok())
-    {
-        value
-    } else {
-        dc_create_smeared_timestamp(context).await
-    };
-
     let rfc724_mid = mime_parser.get_rfc724_mid().unwrap_or_else(||
         // missing Message-IDs may come if the mail was set from this account with another
         // client that relies in the SMTP server to generate one.
@@ -193,6 +183,12 @@ pub(crate) async fn dc_receive_imf_inner(
         .await?,
     );
 
+    let rcvd_timestamp = dc_smeared_time(context).await;
+    let sent_timestamp = mime_parser
+        .get_header(HeaderDef::Date)
+        .and_then(|value| mailparse::dateparse(value).ok())
+        .map_or(rcvd_timestamp, |value| min(value, rcvd_timestamp));
+
     // Add parts
     let chat_id = add_parts(
         context,
@@ -204,7 +200,8 @@ pub(crate) async fn dc_receive_imf_inner(
         server_uid,
         &to_ids,
         rfc724_mid,
-        &mut sent_timestamp,
+        sent_timestamp,
+        rcvd_timestamp,
         from_id,
         &mut hidden,
         seen || replace_partial_download,
@@ -406,7 +403,8 @@ async fn add_parts(
     server_uid: u32,
     to_ids: &ContactIds,
     rfc724_mid: String,
-    sent_timestamp: &mut i64,
+    sent_timestamp: i64,
+    rcvd_timestamp: i64,
     from_id: u32,
     hidden: &mut bool,
     seen: bool,
@@ -455,9 +453,6 @@ async fn add_parts(
         }
     }
 
-    let rcvd_timestamp = dc_smeared_time(context).await;
-    *sent_timestamp = std::cmp::min(*sent_timestamp, rcvd_timestamp);
-
     // check if the message introduces a new chat:
     // - outgoing messages introduce a chat with the first to: address if they are sent by a messenger
     // - incoming messages introduce a chat only for known contacts if they are sent by a messenger
@@ -531,7 +526,7 @@ async fn add_parts(
             if let Some((new_chat_id, new_chat_id_blocked)) = create_or_lookup_group(
                 context,
                 &mut mime_parser,
-                *sent_timestamp,
+                sent_timestamp,
                 if test_normal_chat.is_none() {
                     allow_creation
                 } else {
@@ -761,7 +756,7 @@ async fn add_parts(
                 if let Some((new_chat_id, new_chat_id_blocked)) = create_or_lookup_group(
                     context,
                     &mut mime_parser,
-                    *sent_timestamp,
+                    sent_timestamp,
                     allow_creation,
                     Blocked::Not,
                     from_id,
@@ -857,7 +852,7 @@ async fn add_parts(
     // correct message_timestamp, it should not be used before,
     // however, we cannot do this earlier as we need chat_id to be set
     let in_fresh = state == MessageState::InFresh;
-    let sort_timestamp = calc_sort_timestamp(context, *sent_timestamp, chat_id, in_fresh).await?;
+    let sort_timestamp = calc_sort_timestamp(context, sent_timestamp, chat_id, in_fresh).await?;
 
     // Apply ephemeral timer changes to the chat.
     //
@@ -896,7 +891,7 @@ async fn add_parts(
                 chat_id
             );
         } else if chat_id
-            .update_timestamp(context, Param::EphemeralSettingsTimestamp, *sent_timestamp)
+            .update_timestamp(context, Param::EphemeralSettingsTimestamp, sent_timestamp)
             .await?
         {
             if let Err(err) = chat_id
@@ -967,7 +962,7 @@ async fn add_parts(
                         .update_timestamp(
                             context,
                             Param::ProtectionSettingsTimestamp,
-                            *sent_timestamp,
+                            sent_timestamp,
                         )
                         .await?
                     {
@@ -1047,7 +1042,6 @@ async fn add_parts(
         Vec::new()
     };
 
-    let sent_timestamp = *sent_timestamp;
     let is_hidden = *hidden;
 
     let mut is_hidden = is_hidden;
@@ -1304,11 +1298,7 @@ async fn calc_sort_timestamp(
         }
     }
 
-    if sort_timestamp >= dc_smeared_time(context).await {
-        sort_timestamp = dc_create_smeared_timestamp(context).await;
-    }
-
-    Ok(sort_timestamp)
+    Ok(min(sort_timestamp, dc_smeared_time(context).await))
 }
 
 async fn lookup_chat_by_reply(

src/dc_tools.rs

@@ -84,9 +84,9 @@ pub(crate) fn dc_gm2local_offset() -> i64 {
 //   but at max `MAX_SECONDS_TO_LEND_FROM_FUTURE`
 const MAX_SECONDS_TO_LEND_FROM_FUTURE: i64 = 5;
 
-// returns the currently smeared timestamp,
-// may be used to check if call to dc_create_smeared_timestamp() is needed or not.
-// the returned timestamp MUST NOT be used to be sent out or saved in the database!
+/// Returns the current smeared timestamp,
+///
+/// The returned timestamp MUST NOT be sent out.
 pub(crate) async fn dc_smeared_time(context: &Context) -> i64 {
     let mut now = time();
     let ts = *context.last_smeared_timestamp.read().await;
@@ -97,7 +97,7 @@ pub(crate) async fn dc_smeared_time(context: &Context) -> i64 {
     now
 }
 
-// returns a timestamp that is guaranteed to be unique.
+/// Returns a timestamp that is guaranteed to be unique.
 pub(crate) async fn dc_create_smeared_timestamp(context: &Context) -> i64 {
     let now = time();
     let mut ret = now;