Support duckdb empty path to specify in-memory DB

Closes #41

dburl_test.go

@@ -24,7 +24,6 @@ func TestBadParse(t *testing.T) {
 		{`file+tcp://`, ErrInvalidTransportProtocol},
 		{`file://`, ErrMissingPath},
 		{`ql://`, ErrMissingPath},
-		{`duckdb://`, ErrMissingPath},
 		{`mssql+tcp://user:pass@host/dbname`, ErrInvalidTransportProtocol},
 		{`mssql+foobar://`, ErrInvalidTransportProtocol},
 		{`mssql+unix:/var/run/mssql.sock`, ErrInvalidTransportProtocol},
@@ -787,6 +786,24 @@ func TestParse(t *testing.T) {
 			`/path/to/foo.db?access_mode=read_only&threads=4`,
 			``,
 		},
+		{
+			`duckdb://`,
+			`duckdb`,
+			``,
+			``,
+		},
+		{
+			`duckdb://:memory:`,
+			`duckdb`,
+			`:memory:`,
+			``,
+		},
+		{
+			`duckdb:?threads=4`,
+			`duckdb`,
+			`?threads=4`,
+			``,
+		},
 		{
 			`file:./testdata/test.sqlite3?a=b`,
 			`sqlite3`,

dsn.go

@@ -662,6 +662,12 @@ func GenYDB(u *URL) (string, string, error) {
 	return s + genOptions(u.Query(), "?", "=", "&", ",", true, nil, nil), "", nil
 }
 
+// GenDuckDB generates a duckdb dsn from the passed URL.
+func GenDuckDB(u *URL) (string, string, error) {
+	// Same as GenOpaque but accepts empty path which refers to in-memory DB
+	return u.Opaque + genQueryOptions(u.Query()), "", nil
+}
+
 // convertOptions converts an option value based on name, value pairs.
 func convertOptions(q url.Values, pairs ...string) url.Values {
 	n := make(url.Values)

scheme.go

@@ -202,7 +202,7 @@ func BaseSchemes() []Scheme {
 		},
 		{
 			"duckdb",
-			GenOpaque, 0, true,
+			GenDuckDB, 0, true,
 			[]string{"dk", "ddb", "duck"},
 			"",
 		},