hashes: Make hex dependency optional

The only reason we need `hex-conservative` is to parse strings and
format them as hex. For users that do not require this functionality we
can make the `hex-conservative` crate an optional dependency.

The `serde` feature requires `Display` so we enable `hex` from the
`serde` feature.

If `hex` feature is not enabled we still need to be able to debug so
provide `fmt::Debug` functionality by way of macros.

Close: #2654

.github/workflows/rust.yml

@@ -253,8 +253,10 @@ jobs:
         run: cd bitcoin/embedded && cargo run --target thumbv7m-none-eabi
       - name: "Run hashes/embedded no alloc"
         run: cd hashes/embedded && cargo run --target thumbv7m-none-eabi
-      - name: "Run hashes/embedded with alloc"
+      - name: "Run hashes/embedded with alloc and no hex"
         run: cd hashes/embedded && cargo run --target thumbv7m-none-eabi --features=alloc
+      - name: "Run hashes/embedded with alloc and hex"
+        run: cd hashes/embedded && cargo run --target thumbv7m-none-eabi --features=alloc,hex
 
   ASAN:                         # hashes crate only.
     name: ASAN - nightly toolchain

bitcoin/Cargo.toml

@@ -27,7 +27,7 @@ arbitrary = ["dep:arbitrary", "units/arbitrary", "primitives/arbitrary"]
 [dependencies]
 base58 = { package = "base58ck", version = "0.1.0", default-features = false, features = ["alloc"] }
 bech32 = { version = "0.11.0", default-features = false, features = ["alloc"] }
-hashes = { package = "bitcoin_hashes", version = "0.15.0", default-features = false, features = ["alloc", "bitcoin-io"] }
+hashes = { package = "bitcoin_hashes", version = "0.15.0", default-features = false, features = ["alloc", "bitcoin-io", "hex"] }
 hex = { package = "hex-conservative", version = "0.3.0", default-features = false, features = ["alloc"] }
 internals = { package = "bitcoin-internals", version = "0.4.0", features = ["alloc"] }
 io = { package = "bitcoin-io", version = "0.2.0", default-features = false, features = ["alloc"] }

hashes/Cargo.toml

@@ -17,12 +17,13 @@ exclude = ["tests", "contrib"]
 default = ["std"]
 std = ["alloc", "bitcoin-io?/std", "hex/std"]
 alloc = ["bitcoin-io?/alloc", "hex/alloc"]
+serde = ["dep:serde", "hex"]
 # Smaller (but slower) implementation of sha256, sha512 and ripemd160
 small-hash = []
 
 [dependencies]
-hex = { package = "hex-conservative", version = "0.3.0", default-features = false }
 
+hex = { package = "hex-conservative", version = "0.3.0", default-features = false, optional = true }
 bitcoin-io = { version = "0.2.0", default-features = false, optional = true }
 serde = { version = "1.0", default-features = false, optional = true }
 

hashes/embedded/Cargo.toml

@@ -11,6 +11,7 @@ members = ["."]
 
 [features]
 alloc = ["alloc-cortex-m", "bitcoin_hashes/alloc"]
+hex = ["bitcoin_hashes/hex"]
 
 [dependencies]
 cortex-m = "0.6.0"

hashes/embedded/src/main.rs

@@ -12,13 +12,20 @@ extern crate bitcoin_hashes;
 use bitcoin_hashes::{sha256, HashEngine};
 use bitcoin_io::Write;
 use cortex_m_rt::entry;
-use cortex_m_semihosting::{debug, hprintln};
+use cortex_m_semihosting::debug;
+#[cfg(feature = "hex")]
+use cortex_m_semihosting::hprintln;
 use panic_halt as _;
 
 hash_newtype! {
     struct TestType(sha256::Hash);
 }
 
+#[cfg(feature = "hex")]
+bitcoin_hashes::impl_hex_for_newtype!(TestType);
+#[cfg(not(feature = "hex"))]
+bitcoin_hashes::impl_debug_only_for_newtype!(TestType);
+
 // this is the allocator the application will use
 #[cfg(feature = "alloc")]
 #[global_allocator]
@@ -34,16 +41,19 @@ fn main() -> ! {
 
     let mut engine = sha256::Hash::engine();
     engine.write_all(b"abc").unwrap();
+    #[cfg(feature = "hex")]
     check_result(engine);
 
     let mut engine = sha256::Hash::engine();
     engine.input(b"abc");
+    #[cfg(feature = "hex")]
     check_result(engine);
 
     debug::exit(debug::EXIT_SUCCESS);
     loop {}
 }
 
+#[cfg(feature = "hex")]
 fn check_result(engine: sha256::HashEngine) {
     let hash = TestType(sha256::Hash::from_engine(engine));
 

hashes/src/internal_macros.rs

@@ -21,7 +21,10 @@
 macro_rules! hash_trait_impls {
     ($bits:expr, $reverse:expr $(, $gen:ident: $gent:ident)*) => {
         $crate::impl_bytelike_traits!(Hash, { $bits / 8 } $(, $gen: $gent)*);
+        #[cfg(feature = "hex")]
         $crate::impl_hex_string_traits!(Hash, { $bits / 8 }, $reverse $(, $gen: $gent)*);
+        #[cfg(not(feature = "hex"))]
+        $crate::impl_debug_only!(Hash, { $bits / 8 }, $reverse $(, $gen: $gent)*);
 
         impl<$($gen: $gent),*> $crate::GeneralHash for Hash<$($gen),*> {
             type Engine = HashEngine;

hashes/src/lib.rs

@@ -86,6 +86,7 @@ extern crate serde_test;
 extern crate test;
 
 /// Re-export the `hex-conservative` crate.
+#[cfg(feature = "hex")]
 pub extern crate hex;
 
 #[doc(hidden)]
@@ -126,6 +127,7 @@ pub mod serde_macros {
     }
 }
 
+use core::fmt::{self, Write as _};
 use core::{convert, hash};
 
 #[rustfmt::skip]                // Keep public re-exports separate.
@@ -312,6 +314,22 @@ fn incomplete_block_len<H: HashEngine>(eng: &H) -> usize {
     (eng.n_bytes_hashed() % block_size) as usize
 }
 
+/// Writes `bytes` as a `hex` string to the formatter.
+///
+/// For when we cannot rely on having the `hex` feature enabled. Ignores formatter options and just
+/// writes with plain old `f.write_char()`.
+pub fn debug_hex(bytes: &[u8], f: &mut fmt::Formatter) -> fmt::Result {
+    const HEX_TABLE: [u8; 16] = *b"0123456789abcdef";
+
+    for &b in bytes {
+        let lower = HEX_TABLE[usize::from(b >> 4)];
+        let upper = HEX_TABLE[usize::from(b & 0b00001111)];
+        f.write_char(char::from(lower))?;
+        f.write_char(char::from(upper))?;
+    }
+    Ok(())
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -325,7 +343,10 @@ mod tests {
         struct TestNewtype2(sha256d::Hash);
     }
 
+    #[cfg(feature = "hex")]
     crate::impl_hex_for_newtype!(TestNewtype, TestNewtype2);
+    #[cfg(not(feature = "hex"))]
+    crate::impl_debug_only_for_newtype!(TestNewtype, TestNewtype2);
 
     #[test]
     #[cfg(feature = "alloc")]

hashes/src/macros.rs

@@ -203,6 +203,7 @@ macro_rules! hash_newtype {
 /// * `fmt::{LowerHex, UpperHex}` using `hex-conservative`
 /// * `fmt::{Display, Debug}` by calling `LowerHex`
 #[macro_export]
+#[cfg(feature = "hex")]
 macro_rules! impl_hex_for_newtype {
     ($($newtype:ident),*) => {
         $(
@@ -211,6 +212,18 @@ macro_rules! impl_hex_for_newtype {
     }
 }
 
+/// Implements `fmt::Debug` using hex for a new type crated with [`crate::hash_newtype`] macro.
+///
+/// This is provided in case you do not want to use the `hex` feature.
+#[macro_export]
+macro_rules! impl_debug_only_for_newtype {
+    ($($newtype:ident),*) => {
+        $(
+            $crate::impl_debug_only!($newtype, { <$newtype as $crate::Hash>::LEN }, { <$newtype as $crate::Hash>::DISPLAY_BACKWARD });
+        )*
+    }
+}
+
 /// Adds trait impls to a bytelike type.
 ///
 /// Implements:
@@ -274,6 +287,7 @@ macro_rules! impl_bytelike_traits {
 /// [`hex-conservative`]: <https://crates.io/crates/hex-conservative>
 #[doc(hidden)]
 #[macro_export]
+#[cfg(feature = "hex")]
 macro_rules! impl_hex_string_traits {
     ($ty:ident, $len:expr, $reverse:expr $(, $gen:ident: $gent:ident)*) => {
         impl<$($gen: $gent),*> $crate::_export::_core::str::FromStr for $ty<$($gen),*> {
@@ -299,6 +313,20 @@ macro_rules! impl_hex_string_traits {
     }
 }
 
+/// Implements `fmt::Debug` using hex.
+#[doc(hidden)]
+#[macro_export]
+macro_rules! impl_debug_only {
+    ($ty:ident, $len:expr, $reverse:expr $(, $gen:ident: $gent:ident)*) => {
+        impl<$($gen: $gent),*> $crate::_export::_core::fmt::Debug for $ty<$($gen),*> {
+            #[inline]
+            fn fmt(&self, f: &mut $crate::_export::_core::fmt::Formatter) -> $crate::_export::_core::fmt::Result {
+                $crate::debug_hex(self.as_byte_array(), f)
+            }
+        }
+    }
+}
+
 // Generates the struct only (no impls)
 //
 // This is a separate macro to make it more readable and have a separate interface that allows for
@@ -542,14 +570,29 @@ mod test {
         /// Test hash.
         struct TestHash(crate::sha256d::Hash);
     }
+    #[cfg(feature = "hex")]
     crate::impl_hex_for_newtype!(TestHash);
+    #[cfg(not(feature = "hex"))]
+    crate::impl_debug_only_for_newtype!(TestHash);
 
     impl TestHash {
         fn all_zeros() -> Self { Self::from_byte_array([0; 32]) }
     }
 
+    // NB: This runs with and without `hex` feature enabled, testing different code paths for each.
     #[test]
     #[cfg(feature = "alloc")]
+    fn debug() {
+        use alloc::format;
+
+        let want = "0000000000000000000000000000000000000000000000000000000000000000";
+        let got = format!("{:?}", TestHash::all_zeros());
+        assert_eq!(got, want)
+    }
+
+    #[test]
+    #[cfg(feature = "alloc")]
+    #[cfg(feature = "hex")]
     fn display() {
         use alloc::format;
 
@@ -560,6 +603,7 @@ mod test {
 
     #[test]
     #[cfg(feature = "alloc")]
+    #[cfg(feature = "hex")]
     fn display_alternate() {
         use alloc::format;
 
@@ -570,6 +614,7 @@ mod test {
 
     #[test]
     #[cfg(feature = "alloc")]
+    #[cfg(feature = "hex")]
     fn lower_hex() {
         use alloc::format;
 
@@ -580,6 +625,7 @@ mod test {
 
     #[test]
     #[cfg(feature = "alloc")]
+    #[cfg(feature = "hex")]
     fn lower_hex_alternate() {
         use alloc::format;
 

hashes/src/sha256.rs

@@ -8,8 +8,6 @@ use core::arch::x86::*;
 use core::arch::x86_64::*;
 use core::{cmp, convert, fmt};
 
-use hex::DisplayHex;
-
 use crate::{incomplete_block_len, sha256d, HashEngine as _};
 #[cfg(doc)]
 use crate::{sha256t, sha256t_tag};
@@ -218,8 +216,15 @@ impl Midstate {
 
 impl fmt::Debug for Midstate {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        struct Encoder<'a> {
+            bytes: &'a [u8; 32],
+        }
+        impl fmt::Debug for Encoder<'_> {
+            fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { crate::debug_hex(self.bytes, f) }
+        }
+
         f.debug_struct("Midstate")
-            .field("bytes", &self.bytes.as_hex())
+            .field("bytes", &Encoder { bytes: &self.bytes })
             .field("length", &self.bytes_hashed)
             .finish()
     }

hashes/src/sha256t.rs

@@ -321,10 +321,14 @@ mod tests {
         #[hash_newtype(backward)]
         struct NewTypeHashBackward(sha256t::Hash<NewTypeTagBackward>);
     }
+    #[cfg(feature = "hex")]
     crate::impl_hex_for_newtype!(NewTypeHashBackward);
+    #[cfg(not(feature = "hex"))]
+    crate::impl_debug_only_for_newtype!(NewTypeHashBackward);
 
     #[test]
     #[cfg(feature = "alloc")]
+    #[cfg(feature = "hex")]
     fn macro_created_sha256t_hash_type_backward() {
         use alloc::string::ToString;
 
@@ -345,10 +349,14 @@ mod tests {
         #[hash_newtype(forward)]
         struct NewTypeHashForward(sha256t::Hash<NewTypeTagForward>);
     }
+    #[cfg(feature = "hex")]
     crate::impl_hex_for_newtype!(NewTypeHashForward);
+    #[cfg(not(feature = "hex"))]
+    crate::impl_debug_only_for_newtype!(NewTypeHashForward);
 
     #[test]
     #[cfg(feature = "alloc")]
+    #[cfg(feature = "hex")]
     fn macro_created_sha256t_hash_type_prints_forward() {
         use alloc::string::ToString;
 

hashes/tests/io.rs

@@ -3,6 +3,7 @@
 //! Test the `bitcoin-io` implementations.
 
 #![cfg(feature = "bitcoin-io")]
+#![cfg(feature = "hex")]
 
 use bitcoin_hashes::{
     hash160, hmac, ripemd160, sha1, sha256, sha256d, sha384, sha512, sha512_256, siphash24,

hashes/tests/regression.rs

@@ -2,6 +2,8 @@
 //!
 //! Note that if `bitcoin-io` is enabled then we get more regression-like testing from `./io.rs`.
 
+#![cfg(feature = "hex")]
+
 use bitcoin_hashes::{
     hash160, ripemd160, sha1, sha256, sha256d, sha256t, sha384, sha512, sha512_256, siphash24,
     GeneralHash as _, HashEngine as _, Hmac, HmacEngine,

primitives/Cargo.toml

@@ -22,7 +22,7 @@ serde = ["dep:serde", "hashes/serde", "internals/serde", "units/serde", "alloc"]
 arbitrary = ["dep:arbitrary", "units/arbitrary"]
 
 [dependencies]
-hashes = { package = "bitcoin_hashes", version = "0.15.0", default-features = false, features = ["bitcoin-io"] }
+hashes = { package = "bitcoin_hashes", version = "0.15.0", default-features = false, features = ["bitcoin-io", "hex"] }
 hex = { package = "hex-conservative", version = "0.3.0", default-features = false }
 internals = { package = "bitcoin-internals", version = "0.4.0" }
 io = { package = "bitcoin-io", version = "0.2.0", default-features = false }