internal/postgres: merge latest and versioned handling

getLatestPackage and getLatestVersionInfo are removed, with their
functionality inlined into GetPackage and GetVersionInfo, respectively.

Additionally, the following cleanup is applied:
 + sql values are scanned directly into the returned struct
 + a new helper type is added to support scanning null values into empty
   strings

Fixes b/140558033

Change-Id: I101a475bb4a4a3d70075396d60473e0df0d6c8b0
Reviewed-on: https://team-review.git.corp.google.com/c/golang/discovery/+/544272
Reviewed-by: Julie Qiu <julieqiu@google.com>

1 files changed, 21 insertions, 0 deletions

diff --git a/internal/postgres/postgres.go b/internal/postgres/postgres.go
index f50c229c..6027d3df 100644
--- a/internal/postgres/postgres.go
+++ b/internal/postgres/postgres.go
@@ -198,3 +198,24 @@ func (db *DB) runQuery(ctx context.Context, query string, f func(*sql.Rows) erro
 	}
 	return rows.Err()
 }
+
+// emptyStringScanner wraps the functionality of sql.NullString to just write
+// an empty string if the value is NULL.
+type emptyStringScanner struct {
+	ptr *string
+}
+
+func (e emptyStringScanner) Scan(value interface{}) error {
+	var ns sql.NullString
+	if err := ns.Scan(value); err != nil {
+		return err
+	}
+	*e.ptr = ns.String
+	return nil
+}
+
+// nullIsEmpty returns a sql.Scanner that writes the empty string to s if the
+// sql.Value is NULL.
+func nullIsEmpty(s *string) sql.Scanner {
+	return emptyStringScanner{s}
+}