chain: ensure impl Deserialize for Amount validates data.

This uses serde's try_from attribute to run deserialized values through the
TryFrom impl.  Also adds a test to make sure that validation actually does
happen.

Cargo.lock

@@ -152,6 +152,16 @@ version = "0.7.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "cdcf67bb7ba7797a081cd19009948ab533af7c355d5caf1d08c777582d351e9c"
 
+[[package]]
+name = "bincode"
+version = "1.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f30d3a39baa26f9651f17b375061f3233dde33424a8b72b0dbe93a68a0bc896d"
+dependencies = [
+ "byteorder",
+ "serde",
+]
+
 [[package]]
 name = "bit-set"
 version = "0.5.2"
@@ -2611,6 +2621,7 @@ name = "zebra-chain"
 version = "3.0.0-alpha.0"
 dependencies = [
  "bech32",
+ "bincode",
  "blake2b_simd",
  "blake2s_simd",
  "bs58",

zebra-chain/Cargo.toml

@@ -37,3 +37,4 @@ proptest = "0.10"
 proptest-derive = "0.2.0"
 zebra-test = { path = "../zebra-test/" }
 color-eyre = "0.5"
+bincode = "1"

zebra-chain/src/types/amount.rs

@@ -9,6 +9,8 @@ type Result<T, E = Error> = std::result::Result<T, E>;
 
 /// A runtime validated type for representing amounts of zatoshis
 #[derive(Debug, Eq, PartialEq, Clone, Copy, Serialize, Deserialize)]
+#[serde(try_from = "i64")]
+#[serde(bound = "C: AmountConstraint")]
 pub struct Amount<C = NegativeAllowed>(i64, PhantomData<C>);
 
 impl<C> Amount<C> {
@@ -384,4 +386,27 @@ mod test {
 
         Ok(())
     }
+
+    #[test]
+    fn deserialize_checks_bounds() -> Result<()> {
+        let big = MAX_MONEY * 2;
+        let neg = -10;
+
+        let big_bytes = bincode::serialize(&big)?;
+        let neg_bytes = bincode::serialize(&neg)?;
+
+        bincode::deserialize::<Amount<NonNegative>>(&big_bytes)
+            .expect_err("deserialization should reject too large values");
+        bincode::deserialize::<Amount<NegativeAllowed>>(&big_bytes)
+            .expect_err("deserialization should reject too large values");
+
+        bincode::deserialize::<Amount<NonNegative>>(&neg_bytes)
+            .expect_err("NonNegative deserialization should reject negative values");
+        let amount = bincode::deserialize::<Amount<NegativeAllowed>>(&neg_bytes)
+            .expect("NegativeAllowed deserialization should allow negative values");
+
+        assert_eq!(amount.0, neg);
+
+        Ok(())
+    }
 }