lib: introduce hexenc() and hexdec()

Add two new functions to deal with encoding and decoding of hexadecimal
digit strings:

 - hexenc() - convert the given input value into a lower case hex digit
   string, implicitely converting the input argument to a string value
   if needed

 - hexdec() - decode the given input hex digit string into a byte string,
   skipping whitespace or optionally specified characters in the input

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

1 files changed, 29 insertions, 0 deletions

diff --git a/tests/custom/03_stdlib/56_hexdec b/tests/custom/03_stdlib/56_hexdec
new file mode 100644
index 0000000..cb842ca
--- /dev/null
+++ b/tests/custom/03_stdlib/56_hexdec
@@ -0,0 +1,29 @@
+The `hexdec()` function decodes the given hexadecimal digit string into
+a byte string, optionally skipping specified characters.
+
+Returns null if the input string contains invalid characters or an uneven
+amount of hex digits.
+
+Returns the decoded byte string on success.
+
+-- Testcase --
+{%
+	printf("%.J\n", [
+		hexdec("44 55 66 77 33 44\n"),   	// whitespace is skipped by default
+		hexdec("44-55-66:77-33-44", ":-"),	// skip specified characters
+		hexdec("abc"),						// error; uneven amount of digits
+		hexdec("ab cd !"),					// error; non-whitespace, non-hex, non-skipped char
+		hexdec(1234),						// error; non-string input
+	]);
+%}
+-- End --
+
+-- Expect stdout --
+[
+	"DUfw3D",
+	"DUfw3D",
+	null,
+	null,
+	null
+]
+-- End --