1 files changed, 124 insertions, 0 deletions

diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..c31c3a0
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,124 @@
+#[derive(Debug)]
+pub enum HexDecodeError {
+    InvalidByteCount,
+    InvalidHexCharacter,
+}
+
+fn hex_char_byte_to_value(c : u8) -> Result<u8, HexDecodeError> {
+    if !c.is_ascii_hexdigit() {
+        return Err(HexDecodeError::InvalidHexCharacter);
+    }
+    Ok( (c as char).to_digit(16).unwrap() as u8)
+}
+
+fn byte_to_hex_char(b : u8) -> char {
+    assert!(b <= 15);
+    match b {
+        digit if digit < 10 => ('0' as u8 + digit) as char,
+        letter => ('a' as u8 + letter - 10) as char
+    }
+}
+
+fn append_byte_hex_to_string(byte : u8, string : &mut String) {
+    let high = (byte & 0xF0) >> 4;
+    let low = byte & 0x0F;
+    string.push(byte_to_hex_char(high));
+    string.push(byte_to_hex_char(low));
+}
+
+pub fn decode_hex<T : AsRef<[u8]>>(string : T) -> Result<Vec<u8>, HexDecodeError> {
+    let chars = string.as_ref();
+    if chars.len() % 2 != 0 {
+        return Err(HexDecodeError::InvalidByteCount);
+    }
+    let mut data = Vec::new();
+    let mut index = 0;
+    let mut first_digit : u8 = 0;
+    for c in chars.iter() {
+        if index % 2 != 0 {
+            let second_digit = hex_char_byte_to_value(*c)?;
+            let value = first_digit * 16 + second_digit;
+            data.push(value);
+        }else {
+            first_digit = hex_char_byte_to_value(*c)?;
+        }
+        index += 1;
+    }
+    Ok(data)
+}
+
+pub fn encode_hex<T : AsRef<[u8]>>(data : T) -> String {
+    let mut string = String::new();
+    let data_ref = data.as_ref();
+    for b in data_ref.iter() {
+        append_byte_hex_to_string(*b, &mut string);
+    }
+    string
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn decode_zero_bytes_test() {
+        let string = "";
+        let data = decode_hex(string).unwrap();
+        assert_eq!(0, data.len());
+    }
+
+    #[test]
+    fn decode_one_byte_test() {
+        let string = "ff";
+        let data = decode_hex(string).unwrap();
+        assert_eq!(1, data.len());
+        assert_eq!(0xff, data[0]);
+    }
+
+    #[test]
+    fn decode_multiple_bytes_test() {
+        let string = "ffaabbccdd1122";
+        let data = decode_hex(string).unwrap();
+        assert_eq!(7, data.len());
+        assert_eq!(&[0xff, 0xaa, 0xbb, 0xcc, 0xdd, 0x11, 0x22], data.as_slice());
+    }
+
+    #[test]
+    fn decode_invalid_character_test() {
+        let string = "ffaabz";
+        match decode_hex(string) {
+            Err(HexDecodeError::InvalidHexCharacter) => {}
+            _ => panic!("Invalid result returned"),
+        }
+    }
+
+    #[test]
+    fn decode_invalid_character_length() {
+        let string = "ffaab";
+        match decode_hex(string) {
+            Err(HexDecodeError::InvalidByteCount) => {}
+            _ => panic!("Invalid result returned"),
+        }
+    }
+
+    #[test]
+    fn encode_zero_bytes() {
+        let data: &[u8; 0] = &[];
+        let string = encode_hex(&data);
+        assert_eq!(string, "");
+    }
+
+    #[test]
+    fn encode_one_byte() {
+        let data: &[u8; 1] = &[0xa1];
+        let string = encode_hex(&data);
+        assert_eq!(string, "a1");
+    }
+
+    #[test]
+    fn encode_multiple_bytes() {
+        let data: &[u8; 5] = &[0xaa, 0xbb, 0xcc, 0xdd, 0xee];
+        let string = encode_hex(&data);
+        assert_eq!(string, "aabbccddee");
+    }
+}