1 files changed, 305 insertions, 0 deletions
diff --git a/pkg/ascii/ascii.go b/pkg/ascii/ascii.go
new file mode 100644
index 0000000..350890c
--- /dev/null
+++ b/pkg/ascii/ascii.go
@@ -0,0 +1,305 @@
+// package ascii implements an ASCII key-value parser.
+//
+// The top-most (de)serialize must operate on a struct pointer.  A struct may
+// contain other structs, in which case all tag names should be unique.  Public
+// fields without tag names are ignored.  Private fields are also ignored.
+//
+// The supported field types are:
+// - struct
+// - string (no empty strings)
+// - uint64 (only digits in ASCII representation)
+// - byte array (only lower-case hex in ASCII representation)
+// - slice of uint64 (no empty slices)
+// - slice of byte array (no empty slices)
+//
+// A key must not contain an encoding's end-of-key value.
+// A value must not contain an encoding's end-of-value value.
+//
+// For additional details, please refer to the Sigsum v0 API documentation.
+//
+package ascii
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"reflect"
+	"strconv"
+	"strings"
+
+	"git.sigsum.org/sigsum-lib-go/pkg/hex"
+)
+
+var StdEncoding = NewEncoding("ascii", "=", "\n")
+
+type Encoding struct {
+	identifier string
+	endOfKey   string
+	endOfValue string
+}
+
+func NewEncoding(id, eok, eov string) *Encoding {
+	return &Encoding{
+		identifier: id,
+		endOfKey:   eok,
+		endOfValue: eov,
+	}
+}
+
+type someValue struct {
+	v  reflect.Value
+	ok bool
+}
+
+// Serialize tries to serialize an interface as ASCII key-value pairs
+func (e *Encoding) Serialize(w io.Writer, i interface{}) error {
+	v, err := dereferenceStructPointer(i)
+	if err != nil {
+		return err
+	}
+
+	t := v.Type()
+	for i := 0; i < t.NumField(); i++ {
+		switch v.Field(i).Type().Kind() {
+		case reflect.Struct:
+			if err := e.Serialize(w, v.Field(i).Addr().Interface()); err != nil {
+				return err
+			}
+		default:
+			if t.Field(i).PkgPath != "" {
+				continue // skip private field
+			}
+			key, ok := t.Field(i).Tag.Lookup(e.identifier)
+			if !ok {
+				continue // skip public field without tag
+			}
+
+			if strings.Contains(key, e.endOfKey) {
+				return fmt.Errorf("ascii: key %q contains end-of-key character", key)
+			}
+			if err := e.write(w, key, v.Field(i)); err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
+func (e *Encoding) write(w io.Writer, key string, v reflect.Value) error {
+	t := v.Type()
+	switch t {
+	case reflect.TypeOf(uint64(0)):
+		val := fmt.Sprintf("%d", v.Uint())
+		return e.writeOne(w, key, val)
+	}
+
+	k := t.Kind()
+	switch k {
+	case reflect.Array:
+		if kind := t.Elem().Kind(); kind != reflect.Uint8 {
+			return fmt.Errorf("ascii: array kind not supported: %v", kind)
+		}
+
+		arrayLen := v.Len()
+		array := make([]byte, arrayLen, arrayLen)
+		for i := 0; i < arrayLen; i++ {
+			array[i] = uint8(v.Index(i).Uint())
+		}
+
+		val := hex.Serialize(array)
+		return e.writeOne(w, key, val)
+
+	case reflect.Slice:
+		kind := t.Elem().Kind()
+		if kind != reflect.Array && kind != reflect.Uint64 {
+			return fmt.Errorf("ascii: slice kind not supported: %v", kind)
+		}
+		if v.Len() == 0 {
+			return fmt.Errorf("ascii: slice must not be empty")
+		}
+
+		var err error
+		for i := 0; i < v.Len(); i++ {
+			err = e.write(w, key, v.Index(i))
+		}
+		return err
+
+	case reflect.String:
+		if v.Len() == 0 {
+			return fmt.Errorf("ascii: string must not be empty")
+		}
+		return e.writeOne(w, key, v.String())
+	}
+
+	return fmt.Errorf("ascii: unsupported type %v and kind %v", t, k)
+}
+
+func (e *Encoding) writeOne(w io.Writer, key, value string) error {
+	_, err := w.Write([]byte(key + e.endOfKey + value + e.endOfValue))
+	return err
+}
+
+// Deserialize tries to deserialize a buffer of ASCII key-value pairs
+func (e *Encoding) Deserialize(r io.Reader, i interface{}) error {
+	m := make(map[string]*someValue)
+	if err := e.mapKeys(i, m); err != nil {
+		return err
+	}
+
+	buf, err := io.ReadAll(r)
+	if err != nil {
+		return fmt.Errorf("ascii: failed reading incoming buffer")
+	}
+
+	// trim end of buffer so that loop does not run on an empty line
+	if len(buf) <= len(e.endOfValue) {
+		return fmt.Errorf("ascii: buffer contains no key-value pair")
+	}
+	offset := len(buf) - len(e.endOfValue)
+	if !bytes.Equal(buf[offset:], []byte(e.endOfValue)) {
+		return fmt.Errorf("ascii: buffer must end with endOfValue")
+	}
+	buf = buf[:offset]
+
+	for _, kv := range bytes.Split(buf, []byte(e.endOfValue)) {
+		split := bytes.Split(kv, []byte(e.endOfKey))
+		if len(split) == 1 {
+			return fmt.Errorf("ascii: missing key-value pair in %q", string(kv))
+		}
+
+		key := string(split[0])
+		value := string(bytes.Join(split[1:], nil))
+		ref, ok := m[key]
+		if !ok {
+			return fmt.Errorf("ascii: unexpected key %q", key)
+		}
+		if len(value) == 0 {
+			fmt.Errorf("ascii: missing value for key %q", key)
+		}
+		if err := setKey(ref, key, value); err != nil {
+			return err
+		}
+	}
+	return requireValues(m)
+}
+
+func (e *Encoding) mapKeys(i interface{}, m map[string]*someValue) error {
+	v, err := dereferenceStructPointer(i)
+	if err != nil {
+		return err
+	}
+
+	t := v.Type()
+	for i := 0; i < t.NumField(); i++ {
+		switch v.Field(i).Type().Kind() {
+		case reflect.Struct:
+			i := v.Field(i).Addr().Interface()
+			e.mapKeys(i, m) // return is always nil
+		default:
+			if t.Field(i).PkgPath != "" {
+				continue // skip private field
+			}
+			key, ok := t.Field(i).Tag.Lookup(e.identifier)
+			if !ok {
+				continue // skip public field without tag
+			}
+			m[key] = &someValue{
+				v: v.Field(i),
+			}
+		}
+	}
+	return nil
+}
+
+func setKey(ref *someValue, key, value string) error {
+	v := ref.v
+	if v.Kind() == reflect.Ptr && !v.IsNil() {
+		v = v.Elem()
+	}
+
+	t := v.Type()
+	switch t {
+	case reflect.TypeOf(uint64(0)):
+		num, err := strconv.ParseUint(value, 10, 64)
+		if err != nil {
+			return err
+		}
+
+		ref.ok = true
+		v.SetUint(num)
+		return nil
+	}
+
+	k := t.Kind()
+	switch k {
+	case reflect.Array:
+		arrayLen := v.Len()
+		b, err := hex.Deserialize(value)
+		if err != nil {
+			return err
+		}
+		if len(b) != arrayLen {
+			return fmt.Errorf("ascii: invalid array size for key %q", key)
+		}
+
+		ref.ok = true
+		reflect.Copy(v, reflect.ValueOf(b))
+		return nil
+
+	case reflect.Slice:
+		sliceType := t
+		kind := sliceType.Elem().Kind()
+		if kind != reflect.Array && kind != reflect.Uint64 {
+			return fmt.Errorf("ascii: slice kind not supported: %v", kind)
+		}
+
+		if v.IsNil() {
+			v.Set(reflect.MakeSlice(sliceType, 0, 0))
+		}
+		sv := &someValue{
+			v: reflect.New(sliceType.Elem()),
+		}
+		if err := setKey(sv, key, value); err != nil {
+			return err
+		}
+
+		ref.ok = true
+		v.Set(reflect.Append(v, sv.v.Elem()))
+		return nil
+
+	case reflect.String:
+		if len(value) == 0 {
+			return fmt.Errorf("ascii: string must not be empty")
+		}
+
+		ref.ok = true
+		v.SetString(value)
+		return nil
+	}
+
+	return fmt.Errorf("ascii: unsupported type %v and kind %v", t, k)
+}
+
+func requireValues(m map[string]*someValue) error {
+	for k, v := range m {
+		if !v.ok {
+			return fmt.Errorf("ascii: missing value for key %q", k)
+		}
+	}
+	return nil
+}
+
+func dereferenceStructPointer(i interface{}) (*reflect.Value, error) {
+	v := reflect.ValueOf(i)
+	if v.Kind() != reflect.Ptr {
+		return nil, fmt.Errorf("ascii: interface value must be pointer")
+	}
+	if v.IsNil() {
+		return nil, fmt.Errorf("ascii: interface value must be non-nil pointer")
+	}
+	v = v.Elem()
+	if v.Type().Kind() != reflect.Struct {
+		return nil, fmt.Errorf("ascii: interface value must point to struct")
+	}
+	return &v, nil
+}