Add hex2pcap

internal/hexutil/hex.go

@@ -0,0 +1,41 @@
+// Package hexutil decodes hex strings in the loose formats people paste.
+package hexutil
+
+import (
+	"encoding/hex"
+	"fmt"
+	"strings"
+)
+
+// Decode decodes a hex string, tolerating common formatting:
+// whitespace and newlines, ':' '-' ',' '.' separators, and "0x" / "\x" byte prefixes.
+// So "45 00 00 3c", "45:00:00:3c", "0x45,0x00", "\x45\x00" and "4500003c" all work.
+func Decode(s string) ([]byte, error) {
+	s = strings.NewReplacer(`\x`, " ", `\X`, " ", "0x", " ", "0X", " ").Replace(s)
+
+	digits := make([]byte, 0, len(s))
+	for i := 0; i < len(s); i++ {
+		c := s[i]
+		switch {
+		case isHexDigit(c):
+			digits = append(digits, c)
+		case c == ' ' || c == '\t' || c == '\n' || c == '\r' ||
+			c == ':' || c == '-' || c == ',' || c == '.':
+			// separator
+		default:
+			return nil, fmt.Errorf("invalid character %q in hex input", c)
+		}
+	}
+	if len(digits)%2 != 0 {
+		return nil, fmt.Errorf("odd number of hex digits (%d)", len(digits))
+	}
+	out := make([]byte, len(digits)/2)
+	if _, err := hex.Decode(out, digits); err != nil {
+		return nil, err
+	}
+	return out, nil
+}
+
+func isHexDigit(c byte) bool {
+	return '0' <= c && c <= '9' || 'a' <= c && c <= 'f' || 'A' <= c && c <= 'F'
+}