Vendor dependencies

Let's see how I like this workflow.

vendor/hex/src/serde.rs

@@ -0,0 +1,102 @@
+//! Hex encoding with `serde`.
+#[cfg_attr(
+    all(feature = "alloc", feature = "serde"),
+    doc = r##"
+# Example
+
+```
+use serde::{Serialize, Deserialize};
+
+#[derive(Serialize, Deserialize)]
+struct Foo {
+    #[serde(with = "hex")]
+    bar: Vec<u8>,
+}
+```
+"##
+)]
+use serde::de::{Error, Visitor};
+use serde::Deserializer;
+#[cfg(feature = "alloc")]
+use serde::Serializer;
+
+#[cfg(feature = "alloc")]
+use alloc::string::String;
+
+use core::fmt;
+use core::marker::PhantomData;
+
+use crate::FromHex;
+
+#[cfg(feature = "alloc")]
+use crate::ToHex;
+
+/// Serializes `data` as hex string using uppercase characters.
+///
+/// Apart from the characters' casing, this works exactly like `serialize()`.
+#[cfg(feature = "alloc")]
+pub fn serialize_upper<S, T>(data: T, serializer: S) -> Result<S::Ok, S::Error>
+where
+    S: Serializer,
+    T: ToHex,
+{
+    let s = data.encode_hex_upper::<String>();
+    serializer.serialize_str(&s)
+}
+
+/// Serializes `data` as hex string using lowercase characters.
+///
+/// Lowercase characters are used (e.g. `f9b4ca`). The resulting string's length
+/// is always even, each byte in data is always encoded using two hex digits.
+/// Thus, the resulting string contains exactly twice as many bytes as the input
+/// data.
+#[cfg(feature = "alloc")]
+pub fn serialize<S, T>(data: T, serializer: S) -> Result<S::Ok, S::Error>
+where
+    S: Serializer,
+    T: ToHex,
+{
+    let s = data.encode_hex::<String>();
+    serializer.serialize_str(&s)
+}
+
+/// Deserializes a hex string into raw bytes.
+///
+/// Both, upper and lower case characters are valid in the input string and can
+/// even be mixed (e.g. `f9b4ca`, `F9B4CA` and `f9B4Ca` are all valid strings).
+pub fn deserialize<'de, D, T>(deserializer: D) -> Result<T, D::Error>
+where
+    D: Deserializer<'de>,
+    T: FromHex,
+    <T as FromHex>::Error: fmt::Display,
+{
+    struct HexStrVisitor<T>(PhantomData<T>);
+
+    impl<'de, T> Visitor<'de> for HexStrVisitor<T>
+    where
+        T: FromHex,
+        <T as FromHex>::Error: fmt::Display,
+    {
+        type Value = T;
+
+        fn expecting(&self, f: &mut fmt::Formatter) -> fmt::Result {
+            write!(f, "a hex encoded string")
+        }
+
+        fn visit_str<E>(self, data: &str) -> Result<Self::Value, E>
+        where
+            E: Error,
+        {
+            FromHex::from_hex(data).map_err(Error::custom)
+        }
+
+        fn visit_borrowed_str<E>(self, data: &'de str) -> Result<Self::Value, E>
+        where
+            E: Error,
+        {
+            FromHex::from_hex(data).map_err(Error::custom)
+        }
+    }
+
+    deserializer.deserialize_str(HexStrVisitor(PhantomData))
+}