chore(sn_api): switch from chrono to time

Due to the active security advisory against chrono (RUSTSEC-2020-0159)
is makes sense to switch to a library that is not affected (though we
are not using the affected APIs in `chrono`).

sn_api/Cargo.toml

@@ -14,7 +14,6 @@ edition = "2018"
 [dependencies]
 async-recursion = "0.3.2"
 bincode = "1.3.1"
-chrono = "~0.4"
 color-eyre = "~0.5"
 dirs-next = "2.0.0"
 env_logger = "~0.8"
@@ -35,6 +34,7 @@ serde_json = "1.0.62"
 sha3 = "~0.9"
 safe_network = { path = "../sn", version = "0.36.3" }
 thiserror = "1.0.23"
+time = "0.3.4"
 uhttp_uri = "~0.5"
 url = "2.2.0"
 urlencoding = "1.1.1"

sn_api/src/app/helpers.rs

@@ -9,7 +9,7 @@
 
 #[cfg(feature = "app")]
 use crate::{Error, Result};
-use chrono::{DateTime, SecondsFormat, Utc};
+use ::time::{format_description::well_known::Rfc3339, OffsetDateTime};
 
 use safe_network::types::{Error as SafeNdError, PublicKey, Token};
 use std::{
@@ -53,10 +53,12 @@ pub fn parse_tokens_amount(amount_str: &str) -> Result<Token> {
 }
 
 pub fn systemtime_to_rfc3339(t: time::SystemTime) -> String {
-    let datetime: DateTime<Utc> = t.into();
-    datetime.to_rfc3339_opts(SecondsFormat::Secs, true)
+    let datetime: OffsetDateTime = t.into();
+    datetime
+        .format(&Rfc3339)
+        .expect("formatting OffsetDateTime to RFC 3339 should be infallible")
 }
 
 pub fn gen_timestamp_secs() -> String {
-    Utc::now().to_rfc3339_opts(SecondsFormat::Secs, true)
+    OffsetDateTime::now_utc().unix_timestamp().to_string()
 }