implemented HTTP 1.0/1.1 server

internal/string_helper/path.go

@@ -0,0 +1,104 @@
+package string_helper
+
+import (
+	"strings"
+)
+
+// Returns path cleaned from "./", "/./", "//"
+// or empty string if path is not safe.
+// Path is considered unsafe if it:
+// - contains ".." segments
+// - ends with '.'
+// - contains `\:*?"<>|`
+// - contains windows-restricted names COM, CON, ...
+func ResolveSafePath(decodedPath string) string {
+	var sb StringBuilder
+	sb.Grow(len(decodedPath))
+	var seg string
+	for rest := decodedPath; rest != ""; {
+		seg, rest = nextSegment(rest)
+		if seg == "" || seg == "." {
+			continue
+		}
+		if !isSafeSegment(seg) {
+			return ""
+		}
+		sb.AddB('/')
+		sb.AddS(seg)
+	}
+	if sb.Len() == 0 {
+		return "/"
+	}
+	return sb.StringUnsafe()
+}
+
+// nextSegment splits off the first '/'-separated segment of s.
+func nextSegment(s string) (seg, rest string) {
+	seg, rest, _ = strings.Cut(s, "/")
+	return
+}
+
+// isSafeSegment reports whether a single non-empty path segment is safe to
+// use as a file name.
+func isSafeSegment(seg string) bool {
+	if seg == ".." {
+		return false
+	}
+	// Windows strips trailing dots "a.txt." would open "a.txt"
+	if last := seg[len(seg)-1]; last == '.' {
+		return false
+	}
+	for i := 0; i < len(seg); i++ {
+		c := seg[i]
+		if c < 0x20 || c == 0x7F {
+			return false
+		}
+		// invalid in Windows file names, ':' also selects NTFS streams
+		if strings.IndexByte(`\:*?"<>|`, c) >= 0 {
+			return false
+		}
+	}
+	return !isReservedWindowsName(seg)
+}
+
+// isReservedWindowsName reports whether seg names a Windows device:
+// "CON", "con.txt", "COM1.tar.gz", ...
+func isReservedWindowsName(seg string) bool {
+	base := seg
+	if i := strings.IndexByte(seg, '.'); i >= 0 {
+		base = seg[:i]
+	}
+	switch len(base) {
+	case 3:
+		return asciiEqualUpper(base, "CON") || asciiEqualUpper(base, "PRN") ||
+			asciiEqualUpper(base, "AUX") || asciiEqualUpper(base, "NUL")
+	case 4:
+		prefix := base[:3]
+		return (asciiEqualUpper(prefix, "COM") || asciiEqualUpper(prefix, "LPT")) &&
+			'0' <= base[3] && base[3] <= '9'
+	}
+	return false
+}
+
+// asciiUpper upper-cases ASCII letters only (like std::toupper in the "C" locale).
+func asciiUpper(c byte) byte {
+	if 'a' <= c && c <= 'z' {
+		return c - ('a' - 'A')
+	}
+	return c
+}
+
+// asciiEqualUpper compares s with upper (which must be upper-case ASCII), ignoring
+// ASCII case. Unlike strings.EqualFold it does no Unicode folding, so e.g. the
+// Kelvin sign 'K' (U+212A) does not match 'K'.
+func asciiEqualUpper(s, upper string) bool {
+	if len(s) != len(upper) {
+		return false
+	}
+	for i := 0; i < len(s); i++ {
+		if asciiUpper(s[i]) != upper[i] {
+			return false
+		}
+	}
+	return true
+}