Support of PGTARGETSESSIONATTRS ENV variable

Signed-off-by: Artemiy Ryabinkov <getlag@ya.ru>

conn.go

@@ -1016,6 +1016,7 @@ func ParseURI(uri string) (ConnConfig, error) {
 	if cp.Password == "" {
 		pgpass(&cp)
 	}
+
 	return cp, nil
 }
 
@@ -1181,7 +1182,7 @@ func ParseConnectionString(s string) (ConnConfig, error) {
 // PGSSLROOTCERT
 // PGAPPNAME
 // PGCONNECT_TIMEOUT
-// TODO: PGTARGETSESSIONATTRS support
+// PGTARGETSESSIONATTRS
 // @see: https://www.postgresql.org/docs/10/libpq-envars.html
 //
 // Important TLS Security Notes:
@@ -1228,6 +1229,11 @@ func ParseEnvLibpq() (ConnConfig, error) {
 		}
 	}
 
+	cc.TargetSessionAttrs = TargetSessionType(os.Getenv("PGTARGETSESSIONATTRS"))
+	if err := cc.TargetSessionAttrs.isValid(); err != nil {
+		return cc, err
+	}
+
 	tlsArgs := configTLSArgs{
 		sslMode:     os.Getenv("PGSSLMODE"),
 		sslKey:      os.Getenv("PGSSLKEY"),

pgpass.go

@@ -57,7 +57,6 @@ func parsepgpass(line, cfgHost, cfgPort, cfgDatabase, cfgUsername string) *strin
 	return &parts[4]
 }
 
-// TODO: Multi-host support
 func pgpass(cfg *ConnConfig) (found bool) {
 	passfile := os.Getenv("PGPASSFILE")
 	if passfile == "" {