[#155] Added s3 url encoder

Signed-off-by: Denis Kirillov <denis@nspcc.ru>

api/handler/s3encoder.go

@@ -0,0 +1,111 @@
+package handler
+
+import (
+	"strings"
+)
+
+type encoding int
+
+const (
+	encodePathSegment encoding = iota
+	encodeQueryComponent
+)
+
+const (
+	urlEncodingType = "url"
+	upperhex        = "0123456789ABCDEF"
+)
+
+func shouldEscape(c byte) bool {
+	if 'A' <= c && c <= 'Z' || 'a' <= c && c <= 'z' || '0' <= c && c <= '9' {
+		return false
+	}
+
+	switch c {
+	case '-', '_', '.', '/', '*':
+		return false
+	}
+	return true
+}
+
+// s3URLEncode is based on url.QueryEscape() code,
+// while considering some S3 exceptions.
+func s3URLEncode(s string, mode encoding) string {
+	spaceCount, hexCount := 0, 0
+	for i := 0; i < len(s); i++ {
+		c := s[i]
+		if shouldEscape(c) {
+			if c == ' ' && mode == encodeQueryComponent {
+				spaceCount++
+			} else {
+				hexCount++
+			}
+		}
+	}
+
+	if spaceCount == 0 && hexCount == 0 {
+		return s
+	}
+
+	var buf [64]byte
+	var t []byte
+
+	required := len(s) + 2*hexCount
+	if required <= len(buf) {
+		t = buf[:required]
+	} else {
+		t = make([]byte, required)
+	}
+
+	if hexCount == 0 {
+		copy(t, s)
+		for i := 0; i < len(s); i++ {
+			if s[i] == ' ' {
+				t[i] = '+'
+			}
+		}
+		return string(t)
+	}
+
+	j := 0
+	for i := 0; i < len(s); i++ {
+		switch c := s[i]; {
+		case c == ' ' && mode == encodeQueryComponent:
+			t[j] = '+'
+			j++
+		case shouldEscape(c):
+			t[j] = '%'
+			t[j+1] = upperhex[c>>4]
+			t[j+2] = upperhex[c&15]
+			j += 3
+		default:
+			t[j] = s[i]
+			j++
+		}
+	}
+	return string(t)
+}
+
+func s3QueryEncode(name string, encodingType string) (result string) {
+	if encodingType == "" {
+		return name
+	}
+	encodingType = strings.ToLower(encodingType)
+	switch encodingType {
+	case urlEncodingType:
+		return s3URLEncode(name, encodeQueryComponent)
+	}
+	return name
+}
+
+func s3PathEncode(name string, encodingType string) (result string) {
+	if encodingType == "" {
+		return name
+	}
+	encodingType = strings.ToLower(encodingType)
+	switch encodingType {
+	case urlEncodingType:
+		return s3URLEncode(name, encodePathSegment)
+	}
+	return name
+}