init simple crate for doing base64 encoding/decoding

.gitignore

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+/target

Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "base64"
+version = "0.1.0"

Cargo.toml

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+[package]
+name = "base64"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]

src/lib.rs

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+
+const BASE64_ALPHABET: [u8; 64] = *b"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
+
+pub fn encode(bytes: Vec<u8>) -> String {
+    let mut output : Vec<char> = Vec::new();
+    for chunk in bytes.chunks(3) {
+        let b0 = chunk.get(0).copied().unwrap_or(0) as u32;
+        let b1 = chunk.get(1).copied().unwrap_or(0) as u32;
+        let b2 = chunk.get(2).copied().unwrap_or(0) as u32;
+
+        // 24-bit number
+        let triple = (b0 << 16) | (b1 << 8) | b2;
+
+        // in 6-bit indices
+        let i0 = ((triple >> 18) & 0x3F) as usize;
+        let i1 = ((triple >> 12) & 0x3F) as usize;
+        let i2 = ((triple >> 6) & 0x3F) as usize;
+        let i3 = (triple & 0x3F) as usize;
+
+        // at least 1 chunk of 8-bit input
+        // so at least 2 chunks of 6-bit window is valid
+        output.push(BASE64_ALPHABET[i0] as char);
+        output.push(BASE64_ALPHABET[i1] as char);
+
+        match chunk.len() {
+            1 => { 
+                output.push('=');
+                output.push('=');
+            },
+            2 => {
+                output.push(BASE64_ALPHABET[i2] as char);
+                output.push('=');
+            },
+            3 => { 
+                output.push(BASE64_ALPHABET[i2] as char);
+                output.push(BASE64_ALPHABET[i3] as char);
+            },
+            _ => unreachable!()
+        }
+    }
+    output.into_iter().collect()
+}
+
+pub fn decode(_b64_str: &String) -> Option<Vec<u8>> {
+    // todo
+    Some(vec!()) // dummy
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_encode() {
+        let input = "f";
+        let bytes = input.as_bytes().to_vec();
+        let base64 = encode(bytes);
+        assert_eq!(base64, String::from("Zg=="));
+    }
+}