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>

2 files changed, 53 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 --
diff --git a/tests/custom/03_stdlib/57_hexenc b/tests/custom/03_stdlib/57_hexenc
new file mode 100644
index 0000000..235ad66
--- /dev/null
+++ b/tests/custom/03_stdlib/57_hexenc
@@ -0,0 +1,24 @@
+The `hexenc()` function encodes the given byte string into a hexadecimal
+digit string, converting the input value to a string if needed.
+
+Returns the encoded hexadecimal digit string.
+
+-- Testcase --
+{%
+	printf("%.J\n", [
+		hexenc("Hello world!\n"),  	// encoding a simple string
+		hexenc(""),  				// empty input -> empty output
+		hexenc([1, 2, 3]),  		// implicit stringification
+		hexenc(null),  				// null input -> null output
+	]);
+%}
+-- End --
+
+-- Expect stdout --
+[
+	"48656c6c6f20776f726c64210a",
+	"",
+	"5b20312c20322c2033205d",
+	null
+]
+-- End --