allow disabling the checksum with alternate Display

src/descriptor/bare.rs

@@ -23,7 +23,7 @@ use core::fmt;
 use bitcoin::blockdata::script;
 use bitcoin::{Address, Network, Script};
 
-use super::checksum::{desc_checksum, verify_checksum};
+use super::checksum::{self, verify_checksum};
 use crate::expression::{self, FromTree};
 use crate::miniscript::context::ScriptContext;
 use crate::policy::{semantic, Liftable};
@@ -132,9 +132,10 @@ impl<Pk: MiniscriptKey> fmt::Debug for Bare<Pk> {
 
 impl<Pk: MiniscriptKey> fmt::Display for Bare<Pk> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        let desc = format!("{}", self.ms);
-        let checksum = desc_checksum(&desc).map_err(|_| fmt::Error)?;
-        write!(f, "{}#{}", &desc, &checksum)
+        use fmt::Write;
+        let mut wrapped_f = checksum::Formatter::new(f);
+        write!(wrapped_f, "{}", self.ms)?;
+        wrapped_f.write_checksum_if_not_alt()
     }
 }
 
@@ -285,9 +286,10 @@ impl<Pk: MiniscriptKey> fmt::Debug for Pkh<Pk> {
 
 impl<Pk: MiniscriptKey> fmt::Display for Pkh<Pk> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        let desc = format!("pkh({})", self.pk);
-        let checksum = desc_checksum(&desc).map_err(|_| fmt::Error)?;
-        write!(f, "{}#{}", &desc, &checksum)
+        use fmt::Write;
+        let mut wrapped_f = checksum::Formatter::new(f);
+        write!(wrapped_f, "pkh({})", self.pk)?;
+        wrapped_f.write_checksum_if_not_alt()
     }
 }
 

src/descriptor/checksum.rs

@@ -3,13 +3,14 @@
 //! This module contains a re-implementation of the function used by Bitcoin Core to calculate the
 //! checksum of a descriptor
 
+use core::fmt;
 use core::iter::FromIterator;
 
 use crate::prelude::*;
 use crate::Error;
 
 const INPUT_CHARSET: &str =  "0123456789()[],'/*abcdefgh@:$%{}IJKLMNOPQRSTUVWXYZ&+-.;<=>?!^_|~ijklmnopqrstuvwxyzABCDEFGH`#\"\\ ";
-const CHECKSUM_CHARSET: &str = "qpzry9x8gf2tvdw0s3jn54khce6mua7l";
+const CHECKSUM_CHARSET: &[u8] = b"qpzry9x8gf2tvdw0s3jn54khce6mua7l";
 
 fn poly_mod(mut c: u64, val: u64) -> u64 {
     let c0 = c >> 35;
@@ -39,40 +40,9 @@ fn poly_mod(mut c: u64, val: u64) -> u64 {
 /// descriptor string is syntactically correct or not.
 /// This only computes the checksum
 pub fn desc_checksum(desc: &str) -> Result<String, Error> {
-    let mut c = 1;
-    let mut cls = 0;
-    let mut clscount = 0;
-
-    for ch in desc.chars() {
-        let pos = INPUT_CHARSET.find(ch).ok_or_else(|| {
-            Error::BadDescriptor(format!("Invalid character in checksum: '{}'", ch))
-        })? as u64;
-        c = poly_mod(c, pos & 31);
-        cls = cls * 3 + (pos >> 5);
-        clscount += 1;
-        if clscount == 3 {
-            c = poly_mod(c, cls);
-            cls = 0;
-            clscount = 0;
-        }
-    }
-    if clscount > 0 {
-        c = poly_mod(c, cls);
-    }
-    (0..8).for_each(|_| c = poly_mod(c, 0));
-    c ^= 1;
-
-    let mut chars = Vec::with_capacity(8);
-    for j in 0..8 {
-        chars.push(
-            CHECKSUM_CHARSET
-                .chars()
-                .nth(((c >> (5 * (7 - j))) & 31) as usize)
-                .unwrap(),
-        );
-    }
-
-    Ok(String::from_iter(chars))
+    let mut eng = Engine::new();
+    eng.input(desc)?;
+    Ok(eng.checksum())
 }
 
 /// Helper function for FromStr for various
@@ -99,6 +69,111 @@ pub(super) fn verify_checksum(s: &str) -> Result<&str, Error> {
     }
     Ok(desc_str)
 }
+
+/// An engine to compute a checksum from a string
+pub struct Engine {
+    c: u64,
+    cls: u64,
+    clscount: u64,
+}
+
+impl Engine {
+    /// Construct an engine with no input
+    pub fn new() -> Self {
+        Engine {
+            c: 1,
+            cls: 0,
+            clscount: 0,
+        }
+    }
+
+    /// Checksum some data
+    ///
+    /// If this function returns an error, the `Engine` will be left in an indeterminate
+    /// state! It is safe to continue feeding it data but the result will not be meaningful.
+    pub fn input(&mut self, s: &str) -> Result<(), Error> {
+        for ch in s.chars() {
+            let pos = INPUT_CHARSET.find(ch).ok_or_else(|| {
+                Error::BadDescriptor(format!("Invalid character in checksum: '{}'", ch))
+            })? as u64;
+            self.c = poly_mod(self.c, pos & 31);
+            self.cls = self.cls * 3 + (pos >> 5);
+            self.clscount += 1;
+            if self.clscount == 3 {
+                self.c = poly_mod(self.c, self.cls);
+                self.cls = 0;
+                self.clscount = 0;
+            }
+        }
+        Ok(())
+    }
+
+    /// Obtain the checksum of all the data thus-far fed to the engine
+    pub fn checksum_chars(&mut self) -> [char; 8] {
+        if self.clscount > 0 {
+            self.c = poly_mod(self.c, self.cls);
+        }
+        (0..8).for_each(|_| self.c = poly_mod(self.c, 0));
+        self.c ^= 1;
+
+        let mut chars = [0 as char; 8];
+        for j in 0..8 {
+            chars[j] = CHECKSUM_CHARSET[((self.c >> (5 * (7 - j))) & 31) as usize] as char;
+        }
+        chars
+    }
+
+    /// Obtain the checksum of all the data thus-far fed to the engine
+    pub fn checksum(&mut self) -> String {
+        String::from_iter(self.checksum_chars().iter().copied())
+    }
+}
+
+/// A wrapper around a `fmt::Formatter` which provides checksumming ability
+pub struct Formatter<'f, 'a> {
+    fmt: &'f mut fmt::Formatter<'a>,
+    eng: Engine,
+}
+
+impl<'f, 'a> Formatter<'f, 'a> {
+    /// Contruct a new `Formatter`, wrapping a given `fmt::Formatter`
+    pub fn new(f: &'f mut fmt::Formatter<'a>) -> Self {
+        Formatter {
+            fmt: f,
+            eng: Engine::new(),
+        }
+    }
+
+    /// Writes the checksum into the underlying `fmt::Formatter`
+    pub fn write_checksum(&mut self) -> fmt::Result {
+        use fmt::Write;
+        self.fmt.write_char('#')?;
+        for ch in self.eng.checksum_chars().iter().copied() {
+            self.fmt.write_char(ch)?;
+        }
+        Ok(())
+    }
+
+    /// Writes the checksum into the underlying `fmt::Formatter`, unless it has "alternate" display on
+    pub fn write_checksum_if_not_alt(&mut self) -> fmt::Result {
+        if !self.fmt.alternate() {
+            self.write_checksum()?;
+        }
+        Ok(())
+    }
+}
+
+impl<'f, 'a> fmt::Write for Formatter<'f, 'a> {
+    fn write_str(&mut self, s: &str) -> fmt::Result {
+        self.fmt.write_str(s)?;
+        if self.eng.input(s).is_ok() {
+            Ok(())
+        } else {
+            Err(fmt::Error)
+        }
+    }
+}
+
 #[cfg(test)]
 mod test {
     use core::str;

src/descriptor/mod.rs

@@ -808,25 +808,25 @@ impl_from_str!(
 impl<Pk: MiniscriptKey> fmt::Debug for Descriptor<Pk> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match *self {
-            Descriptor::Bare(ref sub) => write!(f, "{:?}", sub),
-            Descriptor::Pkh(ref pkh) => write!(f, "{:?}", pkh),
-            Descriptor::Wpkh(ref wpkh) => write!(f, "{:?}", wpkh),
-            Descriptor::Sh(ref sub) => write!(f, "{:?}", sub),
-            Descriptor::Wsh(ref sub) => write!(f, "{:?}", sub),
-            Descriptor::Tr(ref tr) => write!(f, "{:?}", tr),
+            Descriptor::Bare(ref sub) => fmt::Debug::fmt(sub, f),
+            Descriptor::Pkh(ref pkh) => fmt::Debug::fmt(pkh, f),
+            Descriptor::Wpkh(ref wpkh) => fmt::Debug::fmt(wpkh, f),
+            Descriptor::Sh(ref sub) => fmt::Debug::fmt(sub, f),
+            Descriptor::Wsh(ref sub) => fmt::Debug::fmt(sub, f),
+            Descriptor::Tr(ref tr) => fmt::Debug::fmt(tr, f),
         }
     }
 }
 
 impl<Pk: MiniscriptKey> fmt::Display for Descriptor<Pk> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match *self {
-            Descriptor::Bare(ref sub) => write!(f, "{}", sub),
-            Descriptor::Pkh(ref pkh) => write!(f, "{}", pkh),
-            Descriptor::Wpkh(ref wpkh) => write!(f, "{}", wpkh),
-            Descriptor::Sh(ref sub) => write!(f, "{}", sub),
-            Descriptor::Wsh(ref sub) => write!(f, "{}", sub),
-            Descriptor::Tr(ref tr) => write!(f, "{}", tr),
+            Descriptor::Bare(ref sub) => fmt::Display::fmt(sub, f),
+            Descriptor::Pkh(ref pkh) => fmt::Display::fmt(pkh, f),
+            Descriptor::Wpkh(ref wpkh) => fmt::Display::fmt(wpkh, f),
+            Descriptor::Sh(ref sub) => fmt::Display::fmt(sub, f),
+            Descriptor::Wsh(ref sub) => fmt::Display::fmt(sub, f),
+            Descriptor::Tr(ref tr) => fmt::Display::fmt(tr, f),
         }
     }
 }
@@ -1757,4 +1757,84 @@ pk(03f28773c2d975288bc7d1d205c3748651b075fbc6610e58cddeeddf8f19405aa8))";
             Ok(Some((1, expected_concrete)))
         );
     }
+
+    #[test]
+    fn display_alternate() {
+        let bare = StdDescriptor::from_str(
+            "pk(020000000000000000000000000000000000000000000000000000000000000002)",
+        )
+        .unwrap();
+        assert_eq!(
+            format!("{}", bare),
+            "pk(020000000000000000000000000000000000000000000000000000000000000002)#7yxkn84h",
+        );
+        assert_eq!(
+            format!("{:#}", bare),
+            "pk(020000000000000000000000000000000000000000000000000000000000000002)",
+        );
+
+        let pkh = StdDescriptor::from_str(
+            "pkh(020000000000000000000000000000000000000000000000000000000000000002)",
+        )
+        .unwrap();
+        assert_eq!(
+            format!("{}", pkh),
+            "pkh(020000000000000000000000000000000000000000000000000000000000000002)#ma7nspkf",
+        );
+        assert_eq!(
+            format!("{:#}", pkh),
+            "pkh(020000000000000000000000000000000000000000000000000000000000000002)",
+        );
+
+        let wpkh = StdDescriptor::from_str(
+            "wpkh(020000000000000000000000000000000000000000000000000000000000000002)",
+        )
+        .unwrap();
+        assert_eq!(
+            format!("{}", wpkh),
+            "wpkh(020000000000000000000000000000000000000000000000000000000000000002)#d3xz2xye",
+        );
+        assert_eq!(
+            format!("{:#}", wpkh),
+            "wpkh(020000000000000000000000000000000000000000000000000000000000000002)",
+        );
+
+        let shwpkh = StdDescriptor::from_str(
+            "sh(wpkh(020000000000000000000000000000000000000000000000000000000000000002))",
+        )
+        .unwrap();
+        assert_eq!(
+            format!("{}", shwpkh),
+            "sh(wpkh(020000000000000000000000000000000000000000000000000000000000000002))#45zpjtet",
+        );
+        assert_eq!(
+            format!("{:#}", shwpkh),
+            "sh(wpkh(020000000000000000000000000000000000000000000000000000000000000002))",
+        );
+
+        let wsh = StdDescriptor::from_str("wsh(1)").unwrap();
+        assert_eq!(format!("{}", wsh), "wsh(1)#mrg7xj7p");
+        assert_eq!(format!("{:#}", wsh), "wsh(1)");
+
+        let sh = StdDescriptor::from_str("sh(1)").unwrap();
+        assert_eq!(format!("{}", sh), "sh(1)#l8r75ggs");
+        assert_eq!(format!("{:#}", sh), "sh(1)");
+
+        let shwsh = StdDescriptor::from_str("sh(wsh(1))").unwrap();
+        assert_eq!(format!("{}", shwsh), "sh(wsh(1))#hcyfl07f");
+        assert_eq!(format!("{:#}", shwsh), "sh(wsh(1))");
+
+        let tr = StdDescriptor::from_str(
+            "tr(020000000000000000000000000000000000000000000000000000000000000002)",
+        )
+        .unwrap();
+        assert_eq!(
+            format!("{}", tr),
+            "tr(020000000000000000000000000000000000000000000000000000000000000002)#8hc7wq5h",
+        );
+        assert_eq!(
+            format!("{:#}", tr),
+            "tr(020000000000000000000000000000000000000000000000000000000000000002)",
+        );
+    }
 }

src/descriptor/segwitv0.rs

@@ -20,7 +20,7 @@ use core::fmt;
 
 use bitcoin::{self, Address, Network, Script};
 
-use super::checksum::{desc_checksum, verify_checksum};
+use super::checksum::{self, verify_checksum};
 use super::SortedMultiVec;
 use crate::expression::{self, FromTree};
 use crate::miniscript::context::{ScriptContext, ScriptContextError};
@@ -68,11 +68,9 @@ impl<Pk: MiniscriptKey> Wsh<Pk> {
     }
 
     /// Get the descriptor without the checksum
+    #[deprecated(since = "8.0.0", note = "use format!(\"{:#}\") instead")]
     pub fn to_string_no_checksum(&self) -> String {
-        match self.inner {
-            WshInner::SortedMulti(ref smv) => format!("wsh({})", smv),
-            WshInner::Ms(ref ms) => format!("wsh({})", ms),
-        }
+        format!("{:#}", self)
     }
 
     /// Checks whether the descriptor is safe.
@@ -229,9 +227,13 @@ impl<Pk: MiniscriptKey> fmt::Debug for Wsh<Pk> {
 
 impl<Pk: MiniscriptKey> fmt::Display for Wsh<Pk> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        let desc = self.to_string_no_checksum();
-        let checksum = desc_checksum(&desc).map_err(|_| fmt::Error)?;
-        write!(f, "{}#{}", &desc, &checksum)
+        use fmt::Write;
+        let mut wrapped_f = checksum::Formatter::new(f);
+        match self.inner {
+            WshInner::SortedMulti(ref smv) => write!(wrapped_f, "wsh({})", smv)?,
+            WshInner::Ms(ref ms) => write!(wrapped_f, "wsh({})", ms)?,
+        }
+        wrapped_f.write_checksum_if_not_alt()
     }
 }
 
@@ -307,8 +309,9 @@ impl<Pk: MiniscriptKey> Wpkh<Pk> {
     }
 
     /// Get the descriptor without the checksum
+    #[deprecated(since = "8.0.0", note = "use format!(\"{:#}\") instead")]
     pub fn to_string_no_checksum(&self) -> String {
-        format!("wpkh({})", self.pk)
+        format!("{:#}", self)
     }
 
     /// Checks whether the descriptor is safe.
@@ -398,9 +401,10 @@ impl<Pk: MiniscriptKey> fmt::Debug for Wpkh<Pk> {
 
 impl<Pk: MiniscriptKey> fmt::Display for Wpkh<Pk> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        let desc = self.to_string_no_checksum();
-        let checksum = desc_checksum(&desc).map_err(|_| fmt::Error)?;
-        write!(f, "{}#{}", &desc, &checksum)
+        use fmt::Write;
+        let mut wrapped_f = checksum::Formatter::new(f);
+        write!(wrapped_f, "wpkh({})", self.pk)?;
+        wrapped_f.write_checksum_if_not_alt()
     }
 }