Helper for serializing CompactSize-prefixed vectors

Cargo.lock

@@ -703,6 +703,9 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 [[package]]
 name = "zcash_primitives"
 version = "0.0.0"
+dependencies = [
+ "byteorder 1.2.2 (registry+https://github.com/rust-lang/crates.io-index)",
+]
 
 [[package]]
 name = "zcash_proofs"

zcash_primitives/Cargo.toml

@@ -6,3 +6,4 @@ authors = [
 ]
 
 [dependencies]
+byteorder = "1"

zcash_primitives/src/lib.rs

@@ -1,7 +1,3 @@
-#[cfg(test)]
-mod tests {
-    #[test]
-    fn it_works() {
-        assert_eq!(2 + 2, 4);
-    }
-}
+extern crate byteorder;
+
+mod serialize;

zcash_primitives/src/serialize.rs

@@ -0,0 +1,154 @@
+use byteorder::{LittleEndian, ReadBytesExt, WriteBytesExt};
+use std::io::{self, Read, Write};
+
+struct CompactSize;
+
+impl CompactSize {
+    fn read<R: Read>(mut reader: R) -> io::Result<usize> {
+        let flag = reader.read_u8()?;
+        match if flag < 253 {
+            Ok(flag as usize)
+        } else if flag == 253 {
+            match reader.read_u16::<LittleEndian>()? {
+                n if n < 253 => Err(io::Error::new(
+                    io::ErrorKind::InvalidInput,
+                    "non-canonical CompactSize",
+                )),
+                n => Ok(n as usize),
+            }
+        } else if flag == 254 {
+            match reader.read_u32::<LittleEndian>()? {
+                n if n < 0x10000 => Err(io::Error::new(
+                    io::ErrorKind::InvalidInput,
+                    "non-canonical CompactSize",
+                )),
+                n => Ok(n as usize),
+            }
+        } else {
+            match reader.read_u64::<LittleEndian>()? {
+                n if n < 0x100000000 => Err(io::Error::new(
+                    io::ErrorKind::InvalidInput,
+                    "non-canonical CompactSize",
+                )),
+                n => Ok(n as usize),
+            }
+        }? {
+            s if s > 0x02000000 => Err(io::Error::new(
+                io::ErrorKind::InvalidInput,
+                "CompactSize too large",
+            )),
+            s => Ok(s),
+        }
+    }
+
+    fn write<W: Write>(mut writer: W, size: usize) -> io::Result<()> {
+        match size {
+            s if s < 253 => writer.write_u8(s as u8),
+            s if s <= 0xFFFF => {
+                writer.write_u8(253)?;
+                writer.write_u16::<LittleEndian>(s as u16)
+            }
+            s if s <= 0xFFFFFFFF => {
+                writer.write_u8(254)?;
+                writer.write_u32::<LittleEndian>(s as u32)
+            }
+            s => {
+                writer.write_u8(255)?;
+                writer.write_u64::<LittleEndian>(s as u64)
+            }
+        }
+    }
+}
+
+pub struct Vector;
+
+impl Vector {
+    pub fn read<R: Read, E, F>(mut reader: R, func: F) -> io::Result<Vec<E>>
+    where
+        F: Fn(&mut R) -> io::Result<E>,
+    {
+        let count = CompactSize::read(&mut reader)?;
+        (0..count).into_iter().map(|_| func(&mut reader)).collect()
+    }
+
+    pub fn write<W: Write, E, F>(mut writer: W, vec: &Vec<E>, func: F) -> io::Result<()>
+    where
+        F: Fn(&mut W, &E) -> io::Result<()>,
+    {
+        CompactSize::write(&mut writer, vec.len())?;
+        vec.iter().map(|e| func(&mut writer, e)).collect()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn compact_size() {
+        macro_rules! eval {
+            ($value:expr, $expected:expr) => {
+                let mut data = vec![];
+                CompactSize::write(&mut data, $value).unwrap();
+                assert_eq!(&data[..], &$expected[..]);
+                match CompactSize::read(&data[..]) {
+                    Ok(n) => assert_eq!(n, $value),
+                    Err(e) => panic!("Unexpected error: {:?}", e),
+                }
+            };
+        }
+
+        eval!(0, [0]);
+        eval!(1, [1]);
+        eval!(252, [252]);
+        eval!(253, [253, 253, 0]);
+        eval!(254, [253, 254, 0]);
+        eval!(255, [253, 255, 0]);
+        eval!(256, [253, 0, 1]);
+        eval!(256, [253, 0, 1]);
+        eval!(65535, [253, 255, 255]);
+        eval!(65536, [254, 0, 0, 1, 0]);
+        eval!(65537, [254, 1, 0, 1, 0]);
+
+        eval!(33554432, [254, 0, 0, 0, 2]);
+
+        {
+            let value = 33554433;
+            let encoded = &[254, 1, 0, 0, 2][..];
+            let mut data = vec![];
+            CompactSize::write(&mut data, value).unwrap();
+            assert_eq!(&data[..], encoded);
+            assert!(CompactSize::read(encoded).is_err());
+        }
+    }
+
+    #[test]
+    fn vector() {
+        macro_rules! eval {
+            ($value:expr, $expected:expr) => {
+                let mut data = vec![];
+                Vector::write(&mut data, &$value, |w, e| w.write_u8(*e)).unwrap();
+                assert_eq!(&data[..], &$expected[..]);
+                match Vector::read(&data[..], |r| r.read_u8()) {
+                    Ok(v) => assert_eq!(v, $value),
+                    Err(e) => panic!("Unexpected error: {:?}", e),
+                }
+            };
+        }
+
+        eval!(vec![], [0]);
+        eval!(vec![0], [1, 0]);
+        eval!(vec![1], [1, 1]);
+        eval!(vec![5; 8], [8, 5, 5, 5, 5, 5, 5, 5, 5]);
+
+        {
+            // expected = [253, 4, 1, 7, 7, 7, ...]
+            let mut expected = vec![7; 263];
+            expected[0] = 253;
+            expected[1] = 4;
+            expected[2] = 1;
+
+            eval!(vec![7; 260], expected);
+        }
+    }
+}