From 0f7dc3262e558e9b5e6d2c9cc231a5f8a26f6cce Mon Sep 17 00:00:00 2001
From: Eryn Wells <eryn@erynwells.me>
Date: Sun, 25 Mar 2018 12:49:33 -0400
Subject: [PATCH] 1.1: Non-padding base64 encoder

---
 src/lib.rs | 65 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 65 insertions(+)
 create mode 100644 src/lib.rs

diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..8b74d77
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,65 @@
+static B64: &'static str = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+\\";
+
+pub fn base64(hex: &str) -> Result<String, String> {
+    let mut out = String::from("");
+    let mut acc: u32 = 0;
+    for (idx, c) in hex.char_indices() {
+        if let Some(c_digit) = c.to_digit(16) {
+            // Accumulate bytes until we have 24 of them. (We can do this with any number of bytes % 6.
+            acc = (acc << 4) + c_digit;
+            println!("idx={}, c='{}'({:2}), acc={:024b}", idx, c, c_digit, acc);
+            if idx % 6 != 5 {
+                continue;
+            }
+        
+            // Read out bytes in chunks of 6.
+            for i in (0..4).rev() {
+                let out_char_idx = ((acc >> (6 * i)) & 0x3F) as usize;
+                println!("  i:{}, shift:{}, out_char_idx:{:08b}", i, 6*i, out_char_idx); 
+                // TODO: I don't like this nth() call.
+                if let Some(out_char) = B64.chars().nth(out_char_idx) {
+                    out.push(out_char);
+                } else {
+                    return Err(format!("Couldn't make output char from {} (shifted: {})", out_char_idx, 6 * i));
+                }
+            }
+            acc = 0;
+        } else {
+            return Err(format!("Invalid input: {}", c));
+        }
+    }
+
+    Ok(out)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::base64;
+
+    #[test]
+    fn simple_single() {
+        let input = "4d616e";
+        let ex_output = "TWFu";
+        println!("");
+        let output = base64(input).expect("Error converting to base64");
+        assert_eq!(output, ex_output);
+    }
+
+    #[test]
+    fn padding() {
+        let input = "6f6d";
+        let ex_output = "b20=";
+        println!("");
+        let output = base64(input).expect("Error converting to base64");
+        assert_eq!(output, ex_output);
+    }
+
+    #[test]
+    fn cryptopals_input() {
+        let input = "49276d206b696c6c696e6720796f757220627261696e206c696b65206120706f69736f6e6f7573206d757368726f6f6d";
+        let ex_output = "SSdtIGtpbGxpbmcgeW91ciBicmFpbiBsaWtlIGEgcG9pc29ub3VzIG11c2hyb29t";
+        println!("");
+        let output = base64(input).expect("Error converting to base64");
+        assert_eq!(output, ex_output);
+    }
+}