From a366460157f600c81814eba0c184bd4cc6bce764 Mon Sep 17 00:00:00 2001
From: Jack Grigg <jack@z.cash>
Date: Mon, 8 Mar 2021 04:46:19 +0000
Subject: [PATCH] zcash_address: ZcashAddress::convert() -> T: FromAddress

This enables easy conversion of an encoded Zcash address to a target
type, with automatic handling of Zcash address types that are not
supported by the target.
---
 components/zcash_address/src/convert.rs | 86 +++++++++++++++++++++++++
 components/zcash_address/src/lib.rs     |  4 +-
 2 files changed, 89 insertions(+), 1 deletion(-)
 create mode 100644 components/zcash_address/src/convert.rs

diff --git a/components/zcash_address/src/convert.rs b/components/zcash_address/src/convert.rs
new file mode 100644
index 000000000..50a500ad4
--- /dev/null
+++ b/components/zcash_address/src/convert.rs
@@ -0,0 +1,86 @@
+use std::{error::Error, fmt};
+
+use crate::{kind::*, AddressKind, Network, ZcashAddress};
+
+/// An address type is not supported for conversion.
+#[derive(Debug)]
+pub struct UnsupportedAddress(&'static str);
+
+impl fmt::Display for UnsupportedAddress {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "Zcash {} addresses are not supported", self.0)
+    }
+}
+
+impl Error for UnsupportedAddress {}
+
+impl ZcashAddress {
+    pub fn convert<T: FromAddress>(self) -> Result<T, UnsupportedAddress> {
+        match self.kind {
+            AddressKind::Sprout(data) => T::from_sprout(self.net, data),
+            AddressKind::Sapling(data) => T::from_sapling(self.net, data),
+            AddressKind::Orchard(data) => T::from_orchard(self.net, data),
+            AddressKind::P2pkh(data) => T::from_transparent_p2pkh(self.net, data),
+            AddressKind::P2sh(data) => T::from_transparent_p2sh(self.net, data),
+        }
+    }
+}
+
+/// A helper trait for converting a [`ZcashAddress`] into another type.
+///
+/// # Examples
+///
+/// ```
+/// use zcash_address::{FromAddress, Network, UnsupportedAddress, ZcashAddress};
+///
+/// #[derive(Debug)]
+/// struct MySapling([u8; 43]);
+///
+/// // Implement the FromAddress trait, overriding whichever conversion methods match your
+/// // requirements for the resulting type.
+/// impl FromAddress for MySapling {
+///     fn from_sapling(net: Network, data: [u8; 43]) -> Result<Self, UnsupportedAddress> {
+///         Ok(MySapling(data))
+///     }
+/// }
+///
+/// // For a supported address type, the conversion works.
+/// let addr: ZcashAddress =
+///     "zs1qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqpq6d8g"
+///         .parse()
+///         .unwrap();
+/// assert!(addr.convert::<MySapling>().is_ok());
+///
+/// // For an unsupported address type, we get an error.
+/// let addr: ZcashAddress = "t1Hsc1LR8yKnbbe3twRp88p6vFfC5t7DLbs".parse().unwrap();
+/// assert_eq!(
+///     addr.convert::<MySapling>().unwrap_err().to_string(),
+///     "Zcash transparent P2PKH addresses are not supported",
+/// );
+/// ```
+pub trait FromAddress: Sized {
+    fn from_sprout(net: Network, data: sprout::Data) -> Result<Self, UnsupportedAddress> {
+        let _ = (net, data);
+        Err(UnsupportedAddress("Sprout"))
+    }
+
+    fn from_sapling(net: Network, data: sapling::Data) -> Result<Self, UnsupportedAddress> {
+        let _ = (net, data);
+        Err(UnsupportedAddress("Sapling"))
+    }
+
+    fn from_orchard(net: Network, data: orchard::Data) -> Result<Self, UnsupportedAddress> {
+        let _ = (net, data);
+        Err(UnsupportedAddress("Orchard"))
+    }
+
+    fn from_transparent_p2pkh(net: Network, data: p2pkh::Data) -> Result<Self, UnsupportedAddress> {
+        let _ = (net, data);
+        Err(UnsupportedAddress("transparent P2PKH"))
+    }
+
+    fn from_transparent_p2sh(net: Network, data: p2sh::Data) -> Result<Self, UnsupportedAddress> {
+        let _ = (net, data);
+        Err(UnsupportedAddress("transparent P2SH"))
+    }
+}
diff --git a/components/zcash_address/src/lib.rs b/components/zcash_address/src/lib.rs
index 3a01029e7..76139aca1 100644
--- a/components/zcash_address/src/lib.rs
+++ b/components/zcash_address/src/lib.rs
@@ -1,6 +1,8 @@
+mod convert;
 mod encoding;
 mod kind;
 
+pub use convert::{FromAddress, UnsupportedAddress};
 pub use encoding::ParseError;
 
 /// A Zcash address.
@@ -12,7 +14,7 @@ pub struct ZcashAddress {
 
 /// The Zcash network for which an address is encoded.
 #[derive(Debug, PartialEq)]
-enum Network {
+pub enum Network {
     /// Zcash Mainnet.
     Main,
     /// Zcash Testnet.