Add simple from_hex() helper

src/daemon.rs

@@ -40,10 +40,9 @@ impl Daemon {
 
     fn get_headers(&self) -> (HeaderMap, Bytes) {
         let mut headers = HashMap::new();
-        let mut blockhash: Bytes = vec![
-            111, 226, 140, 10, 182, 241, 179, 114, 193, 166, 162, 70, 174, 99, 247, 79, 147, 30,
-            131, 101, 225, 90, 8, 156, 104, 214, 25, 0, 0, 0, 0, 0,
-        ]; // genesis block hash
+        let mut blockhash: Bytes = util::from_hex(
+            "6fe28c0ab6f1b372c1a6a246ae63f74f931e8365e15a089c68d6190000000000",
+        ).unwrap(); // genesis block hash
         loop {
             let data = self.get(&format!("headers/2000/{}.bin", util::revhex(&blockhash)));
             assert!(!data.is_empty());

src/util.rs

@@ -8,3 +8,33 @@ pub fn revhex(data: &[u8]) -> String {
     }
     ret
 }
+
+pub fn from_hex(s: &str) -> Option<Vec<u8>> {
+    let mut b = Vec::with_capacity(s.len() / 2);
+    let mut modulus = 0;
+    let mut buf = 0;
+
+    for byte in s.bytes() {
+        buf <<= 4;
+
+        match byte {
+            b'A'...b'F' => buf |= byte - b'A' + 10,
+            b'a'...b'f' => buf |= byte - b'a' + 10,
+            b'0'...b'9' => buf |= byte - b'0',
+            _ => {
+                return None;
+            }
+        }
+
+        modulus += 1;
+        if modulus == 2 {
+            modulus = 0;
+            b.push(buf);
+        }
+    }
+
+    match modulus {
+        0 => Some(b),
+        _ => None,
+    }
+}