diff --git a/src/decode.rs b/src/decode.rs
index 0988833..8c6c82a 100644
--- a/src/decode.rs
+++ b/src/decode.rs
@@ -1,8 +1,6 @@
 pub use {
     super::B64Alphabet,
-    std::{
-        io::{self, Read, Write, ErrorKind},
-    },
+    std::io::{self, ErrorKind, Read, Write},
 };
 
 #[derive(Debug)]
@@ -33,4 +31,3 @@ pub struct Decoder<R: Read, W: Write> {
 mod tests {
     use super::*;
 }
-
diff --git a/src/encode.rs b/src/encode.rs
index fa02faf..dd08d12 100644
--- a/src/encode.rs
+++ b/src/encode.rs
@@ -2,7 +2,7 @@ pub use {
     super::B64Alphabet,
     std::{
         fmt::{self, Write},
-        io::{self, Read, ErrorKind},
+        io::{self, ErrorKind, Read},
     },
 };
 
@@ -50,11 +50,57 @@ pub struct Encoder<R: Read, W: Write> {
 
 impl<R: Read, W: Write> Encoder<R, W> {
     pub fn new(reader: R, writer: W, alphabet: B64Alphabet) -> Self {
-        Self { reader, writer, alphabet }
+        Self {
+            reader,
+            writer,
+            alphabet,
+        }
     }
 
     pub fn encode(&mut self) -> Result<(), Error> {
-        todo!()
+        loop {
+            let mut ibuf = [0; 3];
+            let mut obuf = [self.alphabet.pad(); 4];
+            let mut n_bytes = 0;
+            let mut num: u64 = 0;
+            loop {
+                n_bytes += match self.reader.read(&mut ibuf) {
+                    Ok(n) => n,
+                    Err(e) if e.kind() == ErrorKind::Interrupted => continue,
+                    Err(e) => return Err(e.into()),
+                };
+                break;
+            }
+            if n_bytes == 0 {
+                break;
+            }
+            for (idx, n) in ibuf.iter().enumerate() {
+                num <<= 8;
+                if idx < n_bytes {
+                    num |= *n as u64;
+                }
+            }
+            let pad = n_bytes * 8 % 6;
+            for idx in (0..4).rev() {
+                if pad == 0 || idx < 4 - pad {
+                    let b = num & 0b111111;
+                    obuf[idx] = self.alphabet.items[b as usize];
+                }
+                num >>= 6;
+            }
+            write!(
+                self.writer,
+                "{}{}{}{}",
+                char::try_from(obuf[0]).unwrap(),
+                char::try_from(obuf[1]).unwrap(),
+                char::try_from(obuf[2]).unwrap(),
+                char::try_from(obuf[3]).unwrap()
+            )?;
+            if pad > 0 {
+                break;
+            }
+        }
+        Ok(())
     }
 }
 
diff --git a/src/lib.rs b/src/lib.rs
index 6e3dc9e..d349fca 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,9 +1,9 @@
-mod encode;
 mod decode;
+mod encode;
 
 pub use {
-    encode::{Error as B64EncoderError, Encoder as B64Encoder},
-    decode::{Error as B64DecoderError, Decoder as B64Decoder},
+    decode::{Decoder as B64Decoder, Error as B64DecoderError},
+    encode::{Encoder as B64Encoder, Error as B64EncoderError},
 };
 
 #[derive(Clone, Copy)]
@@ -14,11 +14,10 @@ pub struct B64Alphabet {
 
 pub static B64_RFC4648_ALPHABET: B64Alphabet = B64Alphabet {
     items: [
-        'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O',
-        'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd',
-        'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's',
-        't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7',
-        '8', '9', '+', '/',
+        'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R',
+        'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j',
+        'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1',
+        '2', '3', '4', '5', '6', '7', '8', '9', '+', '/',
     ],
     pad: '=',
 };
@@ -33,9 +32,9 @@ impl B64Alphabet {
     pub fn idx(&self, c: char) -> Option<usize> {
         for (idx, x) in self.items.iter().enumerate() {
             if *x == c {
-                return Some(idx)
+                return Some(idx);
             }
-        };
+        }
         None
     }