Fix date/time format for SQLite, use RFC 3339

We implement `ToSql` and `FromSql` for `time::Timespec` values.  Our
documentation indicates that we store the value in the same format
used by SQLite's built-in date/time functions, but this was not
correct.

We were using the format:

    %Y-%m-%d %H:%M:%S:%f %Z

This format cannot be interpreted at all by SQLite's built-in
date/time functions.  There are three reasons for this:

- SQLite supports only two timezone formats: `[+-]HH:MM` and the
  literal character `Z` (indicating UTC)

- SQLite does not support a space before the timezone indicator

- SQLite supports a period (`.`) between the seconds field and the
  fractional seconds field, but not a colon (`:`)

SQLite does support the RFC 3339 date/time format, which is standard
in many other places.  As we're always storing a UTC value, we'll
simply use a trailing `Z` to indicate the timezone, as allowed by RFC
3339.  The new format is:

    %Y-%m-%dT%H:%M:%S.%fZ

To avoid breaking applications using databases with values in the old
format, we'll continue to support it as a fallback for `FromSql`.

[1] https://www.sqlite.org/lang_datefunc.html
[2] https://tools.ietf.org/html/rfc3339

src/types/time.rs

@@ -3,7 +3,8 @@ extern crate time;
 use Result;
 use types::{FromSql, FromSqlError, FromSqlResult, ToSql, ToSqlOutput, ValueRef};
 
-const SQLITE_DATETIME_FMT: &str = "%Y-%m-%d %H:%M:%S:%f %Z";
+const SQLITE_DATETIME_FMT: &str = "%Y-%m-%dT%H:%M:%S.%fZ";
+const SQLITE_DATETIME_FMT_LEGACY: &str = "%Y-%m-%d %H:%M:%S:%f %Z";
 
 impl ToSql for time::Timespec {
     fn to_sql(&self) -> Result<ToSqlOutput> {
@@ -19,10 +20,12 @@ impl FromSql for time::Timespec {
     fn column_result(value: ValueRef) -> FromSqlResult<Self> {
         value
             .as_str()
-            .and_then(|s| match time::strptime(s, SQLITE_DATETIME_FMT) {
-                          Ok(tm) => Ok(tm.to_timespec()),
-                          Err(err) => Err(FromSqlError::Other(Box::new(err))),
-                      })
+            .and_then(|s| {
+                time::strptime(s, SQLITE_DATETIME_FMT)
+                    .or_else(|err| {
+                        time::strptime(s, SQLITE_DATETIME_FMT_LEGACY)
+                            .or(Err(FromSqlError::Other(Box::new(err))))})})
+            .map(|tm| tm.to_timespec())
     }
 }