Base implementation of new /message/from_id route

! Requires unit testing
! Written with max response length in mind, (still ignores mem limits howevr)

server-api/db/src/messages.rs

@@ -190,5 +190,44 @@ impl Message {
         }
     }
 
+    pub async fn get_from_id(p: &Pool, channel_id: UBigInt, start: UBigInt, limit: Option<UBigInt>) -> Result<Response<Self>, SqlError> {
+        //! @returns on success : Set(Vec<Messages>)
+        //! @returns on failure : Err(SqlError)
+        let conn = p.get_conn().await?;
+        const MAX: u64 = 1000;
+        let limit = if let Some(limit) = limit{
+            match limit {
+                1 ..= MAX => limit,
+                _ => MAX
+            }
+        } else {
+            MAX // messages at a time
+        };
+
+        let q = "SELECT id, time, content, author_id FROM messages WHERE
+            channel_id = :channel AND id >= :start LIMIT :limit";
+
+        let params = params!{
+            "channel" => channel_id,
+            "start" => start,
+            "limit" => limit
+        };
+
+        let select_result = conn.prep_exec(q, params).await?;
+
+        let (_conn, messages) = select_result.map_and_drop(|row| {
+            type Tuple = (UBigInt, BigInt, String, UBigInt);
+            let (id, time, content, author_id): Tuple = mysql_async::from_row(row);
+            Self {
+                id,
+                time,
+                content,
+                author_id,
+                channel_id
+            }
+        }).await?;
+
+        Ok(Response::Set(messages))
+    }
 }