Add regex (#10)

regex.go

@@ -0,0 +1,70 @@
+package bson
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"regexp"
+)
+
+// Regex represents BSON regular expression.
+type Regex struct {
+	Pattern string
+	Options string
+}
+
+// String returns a hex string representation of the id.
+func (re Regex) String() string {
+	return fmt.Sprintf(`Regex('%s', '%s')`, re.Pattern, re.Options)
+}
+
+// MarshalBSON implements [bson.Marshaler].
+func (re *Regex) MarshalBSON() ([]byte, error) {
+	b := make([]byte, 0, len(re.Pattern)+1+len(re.Options)+1)
+	b = append(b, re.Pattern...)
+	b = append(b, 0)
+	b = append(b, re.Options...)
+	b = append(b, 0)
+	return b, nil
+}
+
+// UnmarshalBSON implements [bson.Unmarshaler].
+func (re *Regex) UnmarshalBSON(b []byte) error {
+	idx := bytes.IndexByte(b, 0)
+	if idx == -1 {
+		return errors.New("malformed regex")
+	}
+	re.Pattern = string(b[0:idx])
+	b = b[idx+1:]
+
+	idx = bytes.IndexByte(b, 0)
+	if idx == -1 {
+		return errors.New("malformed regex")
+	}
+	re.Options = string(b[:idx])
+
+	return nil
+}
+
+// Compile returns [regexp.Regexp].
+func (r Regex) Compile() (*regexp.Regexp, error) {
+	var opts string
+	for _, o := range r.Options {
+		switch o {
+		case 'i', 'm', 's':
+			opts += string(o)
+		default:
+		}
+	}
+
+	expr := r.Pattern
+	if opts != "" {
+		expr = "(?" + opts + ")" + expr
+	}
+
+	re, err := regexp.Compile(expr)
+	if err != nil {
+		return nil, err
+	}
+	return re, nil
+}

regex_test.go

@@ -0,0 +1,31 @@
+package bson
+
+import "testing"
+
+func TestRegex(t *testing.T) {
+	re := Regex{
+		Pattern: "h.ll?ow(or)ld",
+		Options: "i",
+	}
+
+	b, err := re.MarshalBSON()
+	mustOk(t, err)
+	wantBytes(t, b, "682e6c6c3f6f77286f72296c64006900")
+
+	var re2 Regex
+	err = re2.UnmarshalBSON(b)
+	mustOk(t, err)
+	mustEqual(t, re2.Pattern, re.Pattern)
+	mustEqual(t, re2.Options, re.Options)
+}
+
+func TestRegexCompile(t *testing.T) {
+	re := Regex{
+		Pattern: "h.ll?ow(or)ld",
+		Options: "i",
+	}
+
+	r, err := re.Compile()
+	mustOk(t, err)
+	mustEqual(t, r.String(), `(?i)h.ll?ow(or)ld`)
+}