no_std support

Based on the original work by Justin Moon.

*MSRV unchanged from 1.29.0.*

When `std` is off, `no-std` must be on, and we use the [`alloc`](https://doc.rust-lang.org/alloc/) and core2 crates. The `alloc` crate requires the user define a global allocator.

* Import from `core` and `alloc` instead of `std`
* `alloc` only used if `no-std` is on
* Create `std` feature
* Create `no-std` feature which adds a core2 dependency to polyfill `std::io` features. This is an experimental feature and should be
used with caution.
* CI runs tests `no-std`
* MSRV for `no-std` is 1.51 or so

.github/workflows/rust.yml

@@ -13,14 +13,17 @@ jobs:
             env:
               DO_COV: true
               AS_DEPENDENCY: true
+              DO_NO_STD: true
           - rust: beta
             env:
               AS_DEPENDENCY: true
+              DO_NO_STD: true
           - rust: nightly
             env:
               DO_FUZZ: true
               DO_BENCH: true
               AS_DEPENDENCY: true
+              DO_NO_STD: true
           - rust: 1.29.0
             env:
               AS_DEPENDENCY: true

Cargo.toml

@@ -12,7 +12,7 @@ readme = "README.md"
 
 
 [features]
-default = [ "secp-recovery" ]
+default = [ "std", "secp-recovery" ]
 base64 = [ "base64-compat" ]
 fuzztarget = []
 unstable = []
@@ -21,14 +21,24 @@ use-serde = ["serde", "bitcoin_hashes/serde", "secp256k1/serde"]
 secp-lowmemory = ["secp256k1/lowmemory"]
 secp-recovery = ["secp256k1/recovery"]
 
+# At least one of std, no-std must be enabled.
+#
+# The no-std feature doesn't disable std - you need to turn off the std feature for that by disabling default.
+# Instead no-std enables additional features required for this crate to be usable without std.
+# As a result, both can be enabled without conflict.
+std = ["secp256k1/std", "bitcoin_hashes/std", "bech32/std"]
+no-std = ["hashbrown", "core2/alloc", "bitcoin_hashes/alloc"]
+
 [dependencies]
-bech32 = "0.8.0"
+bech32 = { version = "0.8.1", default-features = false }
-bitcoin_hashes = "0.9.6"
+bitcoin_hashes = { version = "0.10.0", default-features = false }
-secp256k1 = "0.20.2"
+secp256k1 = { version = "0.20.2", default-features = false }
+core2 = { version = "0.3.0", optional = true, default-features = false }
 
 base64-compat = { version = "1.0.0", optional = true }
 bitcoinconsensus = { version = "0.19.0-3", optional = true }
 serde = { version = "1", features = [ "derive" ], optional = true }
+hashbrown = { version = "0.8", optional = true }
 
 [dev-dependencies]
 serde_json = "<1.0.45"
@@ -37,3 +47,10 @@ secp256k1 = { version = "0.20.0", features = [ "recovery", "rand-std" ] }
 bincode = "1.3.1"
 # We need to pin ryu (transitive dep from serde_json) to stay compatible with Rust 1.22.0
 ryu = "<1.0.5"
+
+[[example]]
+name = "bip32"
+
+[[example]]
+name = "handshake"
+required-features = ["std"]

contrib/test.sh

@@ -1,6 +1,12 @@
 #!/bin/sh -ex
 
-FEATURES="base64 bitcoinconsensus use-serde rand"
+FEATURES="base64 bitcoinconsensus use-serde rand secp-recovery"
+
+# Use toolchain if explicitly specified
+if [ -n "$TOOLCHAIN" ]
+then
+    alias cargo="cargo +$TOOLCHAIN"
+fi
 
 pin_common_verions() {
     cargo generate-lockfile --verbose
@@ -10,7 +16,7 @@ pin_common_verions() {
 }
 
 # Pin `cc` for Rust 1.29
-if [ -n "$PIN_VERSIONS" ]; then
+if [ "$PIN_VERSIONS" = true ]; then
     pin_common_verions
     cargo update -p byteorder --precise "1.3.4"
 fi
@@ -21,20 +27,43 @@ then
 fi
 
 
-# Use toolchain if explicitly specified
+echo "********* Testing std *************"
-if [ -n "$TOOLCHAIN" ]
+# Test without any features other than std first
-then
+cargo test --verbose --no-default-features --features="std"
-    alias cargo="cargo +$TOOLCHAIN"
-fi
 
-# Test without any features first
+echo "********* Testing default *************"
-cargo test --verbose --no-default-features
 # Then test with the default features
 cargo test --verbose
 
+if [ "$DO_NO_STD" = true ]
+then
+echo "********* Testing no-std build *************"
+  # Build no_std, to make sure that cfg(test) doesn't hide any issues
+  cargo build --verbose --features="no-std" --no-default-features
+
+  # Build std + no_std, to make sure they are not incompatible
+  cargo build --verbose --features="no-std"
+
+  # Test no_std
+  cargo test --verbose --features="no-std" --no-default-features
+
+  # Build all features
+  cargo build --verbose --features="no-std $FEATURES" --no-default-features
+
+  # Build specific features
+  for feature in ${FEATURES}
+  do
+      cargo build --verbose --features="no-std $feature"
+  done
+
+  cargo run --example bip32 L1HKVVLHXiUhecWnwFYF6L3shkf1E12HUmuZTESvBXUdx3yqVP1D
+  cargo run --no-default-features --features no-std --example bip32 L1HKVVLHXiUhecWnwFYF6L3shkf1E12HUmuZTESvBXUdx3yqVP1D
+fi
+
 # Test each feature
 for feature in ${FEATURES}
 do
+    echo "********* Testing "$feature" *************"
     cargo test --verbose --features="$feature"
 done
 
@@ -55,7 +84,7 @@ then
 fi
 
 # Use as dependency if told to
-if [ -n "$AS_DEPENDENCY" ]
+if [ "$AS_DEPENDENCY" = true ]
 then
     cargo new dep_test
     cd dep_test

examples/bip32.rs

@@ -10,6 +10,7 @@ use bitcoin::util::bip32::ExtendedPubKey;
 use bitcoin::util::bip32::DerivationPath;
 use bitcoin::util::bip32::ChildNumber;
 use bitcoin::util::address::Address;
+use bitcoin::secp256k1::ffi::types::AlignedType;
 
 fn main() {
     // This example derives root xprv
@@ -36,7 +37,9 @@ fn main() {
     let seed = wif.to_bytes();
 
     // we need secp256k1 context for key derivation
-    let secp = Secp256k1::new();
+    let mut buf: Vec<AlignedType> = Vec::new();
+    buf.resize(Secp256k1::preallocate_size(), AlignedType::zeroed());
+    let secp = Secp256k1::preallocated_new(buf.as_mut_slice()).unwrap();
 
     // calculate root key from seed
     let root = ExtendedPrivKey::new_master(network, &seed).unwrap();

src/blockdata/block.rs

@@ -20,6 +20,8 @@
 //! these blocks and the blockchain.
 //!
 
+use prelude::*;
+
 use core::fmt;
 
 use util;
@@ -308,6 +310,7 @@ impl fmt::Display for Bip34Error {
     }
 }
 
+#[cfg(feature = "std")]
 impl ::std::error::Error for Bip34Error {}
 
 #[cfg(test)]

src/blockdata/constants.rs

@@ -19,9 +19,11 @@
 //! single transaction
 //!
 
+use prelude::*;
+
 use core::default::Default;
 
-use hashes::hex::FromHex;
+use hashes::hex::{HexIterator, Error as HexError};
 use hashes::sha256d;
 use blockdata::opcodes;
 use blockdata::script;
@@ -84,8 +86,11 @@ fn bitcoin_genesis_tx() -> Transaction {
     });
 
     // Outputs
+    let script_bytes: Result<Vec<u8>, HexError> =
+        HexIterator::new("04678afdb0fe5548271967f1a67130b7105cd6a828e03909a67962e0ea1f61deb649f6bc3f4cef38c4f35504e51ec112de5c384df7ba0b8d578a4c702b6bf11d5f").unwrap()
+            .collect();
     let out_script = script::Builder::new()
-        .push_slice(&Vec::from_hex("04678afdb0fe5548271967f1a67130b7105cd6a828e03909a67962e0ea1f61deb649f6bc3f4cef38c4f35504e51ec112de5c384df7ba0b8d578a4c702b6bf11d5f").unwrap())
+        .push_slice(script_bytes.unwrap().as_slice())
         .push_opcode(opcodes::all::OP_CHECKSIG)
         .into_script();
     ret.output.push(TxOut {

src/blockdata/opcodes.rs

@@ -22,6 +22,8 @@
 
 #[cfg(feature = "serde")] use serde;
 
+#[cfg(feature = "serde")] use prelude::*;
+
 use core::{fmt, convert::From};
 
 // Note: I am deliberately not implementing PartialOrd or Ord on the

src/blockdata/script.rs

@@ -24,8 +24,9 @@
 //! This module provides the structures and functions needed to support scripts.
 //!
 
-use io;
+use prelude::*;
 
+use io;
 use core::{fmt, default::Default};
 
 #[cfg(feature = "serde")] use serde;
@@ -36,7 +37,7 @@ use consensus::{encode, Decodable, Encodable};
 use hashes::{Hash, hex};
 use policy::DUST_RELAY_TX_FEE;
 #[cfg(feature="bitcoinconsensus")] use bitcoinconsensus;
-#[cfg(feature="bitcoinconsensus")] use std::convert;
+#[cfg(feature="bitcoinconsensus")] use core::convert::From;
 #[cfg(feature="bitcoinconsensus")] use OutPoint;
 
 use util::ecdsa::PublicKey;
@@ -145,11 +146,12 @@ impl fmt::Display for Error {
     }
 }
 
+#[cfg(feature = "std")]
 impl ::std::error::Error for Error {}
 
 #[cfg(feature="bitcoinconsensus")]
 #[doc(hidden)]
-impl convert::From<bitcoinconsensus::Error> for Error {
+impl From<bitcoinconsensus::Error> for Error {
     fn from(err: bitcoinconsensus::Error) -> Error {
         match err {
             _ => Error::BitcoinConsensus(err)
@@ -421,11 +423,11 @@ impl Script {
         } else if self.is_witness_program() {
             32 + 4 + 1 + (107 / 4) + 4 + // The spend cost copied from Core
             8 + // The serialized size of the TxOut's amount field
-            self.consensus_encode(&mut ::std::io::sink()).unwrap() as u64 // The serialized size of this script_pubkey
+            self.consensus_encode(&mut sink()).unwrap() as u64 // The serialized size of this script_pubkey
         } else {
             32 + 4 + 1 + 107 + 4 + // The spend cost copied from Core
             8 + // The serialized size of the TxOut's amount field
-            self.consensus_encode(&mut ::std::io::sink()).unwrap() as u64 // The serialized size of this script_pubkey
+            self.consensus_encode(&mut sink()).unwrap() as u64 // The serialized size of this script_pubkey
         };
 
         ::Amount::from_sat(sats)

src/blockdata/transaction.rs

@@ -23,9 +23,11 @@
 //! This module provides the structures and functions needed to support transactions.
 //!
 
+use prelude::*;
+
 use io;
 use core::{fmt, str, default::Default};
-use std::error;
+#[cfg(feature = "std")] use std::error;
 
 use hashes::{self, Hash, sha256d};
 use hashes::hex::FromHex;
@@ -130,8 +132,9 @@ impl fmt::Display for ParseOutPointError {
     }
 }
 
-impl error::Error for ParseOutPointError {
+#[cfg(feature = "std")]
-    fn cause(&self) -> Option<&dyn error::Error> {
+impl  error::Error for ParseOutPointError {
+    fn cause(&self) -> Option<&dyn  error::Error> {
         match *self {
             ParseOutPointError::Txid(ref e) => Some(e),
             ParseOutPointError::Vout(ref e) => Some(e),
@@ -630,6 +633,7 @@ impl fmt::Display for NonStandardSigHashType {
     }
 }
 
+#[cfg(feature = "std")]
 impl error::Error for NonStandardSigHashType {}
 
 /// Hashtype of an input's signature, encoded in the last byte of the signature
@@ -1360,6 +1364,7 @@ mod tests {
         use hashes::hex::FromHex;
         use std::collections::HashMap;
         use blockdata::script;
+
         // a random recent segwit transaction from blockchain using both old and segwit inputs
         let mut spending: Transaction = deserialize(Vec::from_hex("020000000001031cfbc8f54fbfa4a33a30068841371f80dbfe166211242213188428f437445c91000000006a47304402206fbcec8d2d2e740d824d3d36cc345b37d9f65d665a99f5bd5c9e8d42270a03a8022013959632492332200c2908459547bf8dbf97c65ab1a28dec377d6f1d41d3d63e012103d7279dfb90ce17fe139ba60a7c41ddf605b25e1c07a4ddcb9dfef4e7d6710f48feffffff476222484f5e35b3f0e43f65fc76e21d8be7818dd6a989c160b1e5039b7835fc00000000171600140914414d3c94af70ac7e25407b0689e0baa10c77feffffffa83d954a62568bbc99cc644c62eb7383d7c2a2563041a0aeb891a6a4055895570000000017160014795d04cc2d4f31480d9a3710993fbd80d04301dffeffffff06fef72f000000000017a91476fd7035cd26f1a32a5ab979e056713aac25796887a5000f00000000001976a914b8332d502a529571c6af4be66399cd33379071c588ac3fda0500000000001976a914fc1d692f8de10ae33295f090bea5fe49527d975c88ac522e1b00000000001976a914808406b54d1044c429ac54c0e189b0d8061667e088ac6eb68501000000001976a914dfab6085f3a8fb3e6710206a5a959313c5618f4d88acbba20000000000001976a914eb3026552d7e3f3073457d0bee5d4757de48160d88ac0002483045022100bee24b63212939d33d513e767bc79300051f7a0d433c3fcf1e0e3bf03b9eb1d70220588dc45a9ce3a939103b4459ce47500b64e23ab118dfc03c9caa7d6bfc32b9c601210354fd80328da0f9ae6eef2b3a81f74f9a6f66761fadf96f1d1d22b1fd6845876402483045022100e29c7e3a5efc10da6269e5fc20b6a1cb8beb92130cc52c67e46ef40aaa5cac5f0220644dd1b049727d991aece98a105563416e10a5ac4221abac7d16931842d5c322012103960b87412d6e169f30e12106bdf70122aabb9eb61f455518322a18b920a4dfa887d30700")
             .unwrap().as_slice()).unwrap();

src/consensus/encode.rs

@@ -29,22 +29,23 @@
 //! big-endian decimals, etc.)
 //!
 
+use prelude::*;
+
 use core::{fmt, mem, u32, convert::From};
-use std::borrow::Cow;
+#[cfg(feature = "std")] use std::error;
-use std::error;
-use hashes::hex::ToHex;
 
 use hashes::{sha256d, Hash};
 use hash_types::{BlockHash, FilterHash, TxMerkleNode, FilterHeader};
 
-use io::{self, Cursor, Read, Write};
+use io::{self, Cursor, Read};
 
 use util::endian;
 use util::psbt;
+use hashes::hex::ToHex;
 
 use blockdata::transaction::{TxOut, Transaction, TxIn};
-use network::message_blockdata::Inventory;
+#[cfg(feature = "std")]
-use network::address::{Address, AddrV2Message};
+use network::{message_blockdata::Inventory, address::{Address, AddrV2Message}};
 
 /// Encoding error
 #[derive(Debug)]
@@ -104,8 +105,9 @@ impl fmt::Display for Error {
     }
 }
 
-impl error::Error for Error {
+#[cfg(feature = "std")]
-    fn cause(&self) -> Option<&dyn error::Error> {
+impl ::std::error::Error for Error {
+    fn cause(&self) -> Option<&dyn  error::Error> {
         match *self {
             Error::Io(ref e) => Some(e),
             Error::Psbt(ref e) => Some(e),
@@ -240,7 +242,7 @@ macro_rules! decoder_fn {
     ($name:ident, $val_type:ty, $readfn:ident, $byte_len: expr) => {
         #[inline]
         fn $name(&mut self) -> Result<$val_type, Error> {
-            debug_assert_eq!(::std::mem::size_of::<$val_type>(), $byte_len); // size_of isn't a constfn in 1.22
+            debug_assert_eq!(::core::mem::size_of::<$val_type>(), $byte_len); // size_of isn't a constfn in 1.22
             let mut val = [0; $byte_len];
             self.read_exact(&mut val[..]).map_err(Error::Io)?;
             Ok(endian::$readfn(&val))
@@ -248,7 +250,7 @@ macro_rules! decoder_fn {
     }
 }
 
-impl<W: Write> WriteExt for W {
+impl<W: io::Write> WriteExt for W {
     encoder_fn!(emit_u64, u64, u64_to_array_le);
     encoder_fn!(emit_u32, u32, u32_to_array_le);
     encoder_fn!(emit_u16, u16, u16_to_array_le);
@@ -591,11 +593,12 @@ impl_vec!(TxMerkleNode);
 impl_vec!(Transaction);
 impl_vec!(TxOut);
 impl_vec!(TxIn);
-impl_vec!(Inventory);
 impl_vec!(Vec<u8>);
-impl_vec!((u32, Address));
 impl_vec!(u64);
-impl_vec!(AddrV2Message);
+
+#[cfg(feature = "std")] impl_vec!(Inventory);
+#[cfg(feature = "std")] impl_vec!((u32, Address));
+#[cfg(feature = "std")] impl_vec!(AddrV2Message);
 
 fn consensus_encode_with_size<S: io::Write>(data: &[u8], mut s: S) -> Result<usize, io::Error> {
     let vi_len = VarInt(data.len() as u64).consensus_encode(&mut s)?;
@@ -694,13 +697,13 @@ impl<'a, T: Encodable> Encodable for &'a mut T {
     }
 }
 
-impl<T: Encodable> Encodable for ::std::rc::Rc<T> {
+impl<T: Encodable> Encodable for rc::Rc<T> {
     fn consensus_encode<S: io::Write>(&self, s: S) -> Result<usize, io::Error> {
         (&**self).consensus_encode(s)
     }
 }
 
-impl<T: Encodable> Encodable for ::std::sync::Arc<T> {
+impl<T: Encodable> Encodable for sync::Arc<T> {
     fn consensus_encode<S: io::Write>(&self, s: S) -> Result<usize, io::Error> {
         (&**self).consensus_encode(s)
     }
@@ -763,8 +766,8 @@ mod tests {
     use consensus::{Encodable, deserialize_partial, Decodable};
     use util::endian::{u64_to_array_le, u32_to_array_le, u16_to_array_le};
     use secp256k1::rand::{thread_rng, Rng};
-    use network::message_blockdata::Inventory;
+    #[cfg(feature = "std")]
-    use network::Address;
+    use network::{Address, message_blockdata::Inventory};
 
     #[test]
     fn serialize_int_test() {
@@ -839,7 +842,7 @@ mod tests {
     }
 
     fn test_varint_len(varint: VarInt, expected: usize) {
-        let mut encoder = io::Cursor::new(vec![]);
+        let mut encoder = vec![];
         assert_eq!(varint.consensus_encode(&mut encoder).unwrap(), expected);
         assert_eq!(varint.len(), expected);
     }
@@ -970,10 +973,12 @@ mod tests {
         test_len_is_max_vec::<Transaction>();
         test_len_is_max_vec::<TxOut>();
         test_len_is_max_vec::<TxIn>();
-        test_len_is_max_vec::<Inventory>();
         test_len_is_max_vec::<Vec<u8>>();
-        test_len_is_max_vec::<(u32, Address)>();
         test_len_is_max_vec::<u64>();
+        #[cfg(feature = "std")]
+        test_len_is_max_vec::<(u32, Address)>();
+        #[cfg(feature = "std")]
+        test_len_is_max_vec::<Inventory>();
     }
 
     fn test_len_is_max_vec<T>() where Vec<T>: Decodable, T: fmt::Debug {
@@ -988,7 +993,7 @@ mod tests {
         assert_eq!(deserialize(&[6u8, 0x41, 0x6e, 0x64, 0x72, 0x65, 0x77]).ok(), Some("Andrew".to_string()));
         assert_eq!(
             deserialize(&[6u8, 0x41, 0x6e, 0x64, 0x72, 0x65, 0x77]).ok(),
-            Some(::std::borrow::Cow::Borrowed("Andrew"))
+            Some(Cow::Borrowed("Andrew"))
         );
     }
 

src/internal_macros.rs

@@ -162,7 +162,7 @@ macro_rules! display_from_debug {
 macro_rules! hex_script (($s:expr) => (<$crate::Script as ::core::str::FromStr>::from_str($s).unwrap()));
 
 #[cfg(test)]
-macro_rules! hex_hash (($h:ident, $s:expr) => ($h::from_slice(&<Vec<u8> as $crate::hashes::hex::FromHex>::from_hex($s).unwrap()).unwrap()));
+macro_rules! hex_hash (($h:ident, $s:expr) => ($h::from_slice(&<$crate::prelude::Vec<u8> as $crate::hashes::hex::FromHex>::from_hex($s).unwrap()).unwrap()));
 
 macro_rules! serde_string_impl {
     ($name:ident, $expecting:expr) => {
@@ -563,10 +563,14 @@ macro_rules! user_enum {
             fn from_str(s: &str) -> Result<Self, Self::Err> {
                 match s {
                     $($txt => Ok($name::$elem)),*,
-                    _ => Err($crate::io::Error::new(
+                    _ => {
-                        $crate::io::ErrorKind::InvalidInput,
+                        #[cfg(not(feature = "std"))] let message = "Unknown network";
-                        format!("Unknown network (type {})", s),
+                        #[cfg(feature = "std")] let message = format!("Unknown network (type {})", s);
-                    )),
+                        Err($crate::io::Error::new(
+                            $crate::io::ErrorKind::InvalidInput,
+                            message,
+                        ))
+                    }
                 }
             }
         }
@@ -607,7 +611,7 @@ macro_rules! user_enum {
                         self.visit_str(v)
                     }
 
-                    fn visit_string<E>(self, v: String) -> Result<Self::Value, E>
+                    fn visit_string<E>(self, v: $crate::prelude::String) -> Result<Self::Value, E>
                     where
                         E: $crate::serde::de::Error,
                     {

src/lib.rs

@@ -23,6 +23,8 @@
 //! software.
 //!
 
+#![cfg_attr(all(not(feature = "std"), not(test)), no_std)]
+
 // Experimental features we need
 #![cfg_attr(all(test, feature = "unstable"), feature(test))]
 
@@ -38,12 +40,26 @@
 #![deny(unused_must_use)]
 #![deny(broken_intra_doc_links)]
 
-extern crate core;
+#[cfg(not(any(feature = "std", feature = "no-std")))]
+compile_error!("at least one of the `std` or `no-std` features must be enabled");
+
+#[cfg(feature = "no-std")]
+#[macro_use]
+extern crate alloc;
+#[cfg(feature = "no-std")]
+extern crate core2;
+
+#[cfg(any(feature = "std", test))]
+extern crate core; // for Rust 1.29 and no-std tests
 
 // Re-exported dependencies.
 #[macro_use] pub extern crate bitcoin_hashes as hashes;
 pub extern crate secp256k1;
 pub extern crate bech32;
+
+#[cfg(feature = "no-std")]
+extern crate hashbrown;
+
 #[cfg(feature = "base64")] pub extern crate base64;
 
 #[cfg(feature="bitcoinconsensus")] extern crate bitcoinconsensus;
@@ -98,14 +114,68 @@ pub use util::ecdsa::PrivateKey;
 #[deprecated(since = "0.26.1", note = "Please use `ecdsa::PublicKey` instead")]
 pub use util::ecdsa::PublicKey;
 
+#[cfg(feature = "std")]
 use std::io;
+#[cfg(not(feature = "std"))]
+use core2::io;
+
+#[cfg(not(feature = "std"))]
+mod io_extras {
+    /// A writer which will move data into the void.
+    pub struct Sink {
+        _priv: (),
+    }
+
+    /// Creates an instance of a writer which will successfully consume all data.
+    pub const fn sink() -> Sink {
+        Sink { _priv: () }
+    }
+
+    impl core2::io::Write for Sink {
+        #[inline]
+        fn write(&mut self, buf: &[u8]) -> core2::io::Result<usize> {
+            Ok(buf.len())
+        }
+
+        #[inline]
+        fn flush(&mut self) -> core2::io::Result<()> {
+            Ok(())
+        }
+    }
+}
+
+mod prelude {
+    #[cfg(all(not(feature = "std"), not(test)))]
+    pub use alloc::{string::{String, ToString}, vec::Vec, boxed::Box, borrow::{Cow, ToOwned}, slice, rc, sync};
+
+    #[cfg(any(feature = "std", test))]
+    pub use std::{string::{String, ToString}, vec::Vec, boxed::Box, borrow::{Cow, ToOwned}, slice, rc, sync};
+
+    #[cfg(all(not(feature = "std"), not(test)))]
+    pub use alloc::collections::{BTreeMap, btree_map};
+
+    #[cfg(any(feature = "std", test))]
+    pub use std::collections::{BTreeMap, btree_map};
+
+    #[cfg(feature = "std")]
+    pub use std::io::sink;
+
+    #[cfg(not(feature = "std"))]
+    pub use io_extras::sink;
+
+    #[cfg(feature = "hashbrown")]
+    pub use hashbrown::HashSet;
+
+    #[cfg(not(feature = "hashbrown"))]
+    pub use std::collections::HashSet;
+}
 
 #[cfg(all(test, feature = "unstable"))] use tests::EmptyWrite;
 
 #[cfg(all(test, feature = "unstable"))]
 mod tests {
-    use std::io::{IoSlice, Result, Write};
+    use core::fmt::Arguments;
-    use std::fmt::Arguments;
+    use io::{IoSlice, Result, Write};
 
     #[derive(Default, Clone, Debug, PartialEq, Eq)]
     pub struct EmptyWrite;

src/network/address.rs

@@ -17,6 +17,7 @@
 //! This module defines the structures and functions needed to encode
 //! network addresses in Bitcoin messages.
 //!
+use prelude::*;
 
 use core::{fmt, iter};
 use std::net::{SocketAddr, Ipv6Addr, SocketAddrV4, SocketAddrV6, Ipv4Addr, ToSocketAddrs};

src/network/message.rs

@@ -19,8 +19,9 @@
 //! also defines (de)serialization routines for many primitives.
 //!
 
+use prelude::*;
+
 use core::{mem, fmt, iter};
-use std::borrow::Cow;
 
 use io;
 use blockdata::block;

src/network/message_blockdata.rs

@@ -18,6 +18,8 @@
 //! Bitcoin data (blocks and transactions) around.
 //!
 
+use prelude::*;
+
 use io;
 
 use hashes::sha256d;
@@ -149,7 +151,7 @@ impl_consensus_encoding!(GetHeadersMessage, version, locator_hashes, stop_hash);
 
 #[cfg(test)]
 mod tests {
-    use super::{GetHeadersMessage, GetBlocksMessage};
+    use super::{Vec, GetHeadersMessage, GetBlocksMessage};
 
     use hashes::hex::FromHex;
 

src/network/message_network.rs

@@ -18,8 +18,9 @@
 //! capabilities
 //!
 
+use prelude::*;
+
 use io;
-use std::borrow::Cow;
 
 use network::address::Address;
 use network::constants::{self, ServiceFlags};

src/network/mod.rs

@@ -20,17 +20,17 @@
 
 use io;
 use core::fmt;
-use std::error;
+#[cfg(feature = "std")] use std::error;
 
 pub mod constants;
 
-pub mod address;
+#[cfg(feature = "std")] pub mod address;
-pub use self::address::Address;
+#[cfg(feature = "std")] pub use self::address::Address;
-pub mod message;
+#[cfg(feature = "std")] pub mod message;
-pub mod message_blockdata;
+#[cfg(feature = "std")] pub mod message_blockdata;
-pub mod message_network;
+#[cfg(feature = "std")] pub mod message_network;
-pub mod message_filter;
+#[cfg(feature = "std")] pub mod message_filter;
-pub mod stream_reader;
+#[cfg(feature = "std")] pub mod stream_reader;
 
 /// Network error
 #[derive(Debug)]
@@ -60,8 +60,8 @@ impl From<io::Error> for Error {
     }
 }
 
+#[cfg(feature = "std")]
 impl error::Error for Error {
-
     fn cause(&self) -> Option<&dyn error::Error> {
         match *self {
             Error::Io(ref e) => Some(e),

src/network/stream_reader.rs

@@ -20,6 +20,8 @@
 //! (like can happen with reading from TCP socket)
 //!
 
+use prelude::*;
+
 use core::fmt;
 use io::{self, Read};
 

src/serde_utils.rs

@@ -7,14 +7,14 @@ pub mod btreemap_byte_values {
 
     // NOTE: This module can be exactly copied to use with HashMap.
 
-    use ::std::collections::BTreeMap;
+    use prelude::*;
     use hashes::hex::{FromHex, ToHex};
     use serde;
 
     pub fn serialize<S, T>(v: &BTreeMap<T, Vec<u8>>, s: S)
         -> Result<S::Ok, S::Error> where
         S: serde::Serializer,
-        T: serde::Serialize + ::std::hash::Hash + Eq + Ord,
+        T: serde::Serialize + ::core::hash::Hash + Eq + Ord,
     {
         use serde::ser::SerializeMap;
 
@@ -33,17 +33,17 @@ pub mod btreemap_byte_values {
     pub fn deserialize<'de, D, T>(d: D)
         -> Result<BTreeMap<T, Vec<u8>>, D::Error> where
         D: serde::Deserializer<'de>,
-        T: serde::Deserialize<'de> + ::std::hash::Hash + Eq + Ord,
+        T: serde::Deserialize<'de> + ::core::hash::Hash + Eq + Ord,
     {
-        use ::std::marker::PhantomData;
+        use ::core::marker::PhantomData;
 
         struct Visitor<T>(PhantomData<T>);
         impl<'de, T> serde::de::Visitor<'de> for Visitor<T> where
-            T: serde::Deserialize<'de> + ::std::hash::Hash + Eq + Ord,
+            T: serde::Deserialize<'de> + ::core::hash::Hash + Eq + Ord,
         {
             type Value = BTreeMap<T, Vec<u8>>;
 
-            fn expecting(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
+            fn expecting(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
                 write!(f, "a map with hexadecimal values")
             }
 
@@ -74,13 +74,13 @@ pub mod btreemap_as_seq {
 
     // NOTE: This module can be exactly copied to use with HashMap.
 
-    use ::std::collections::BTreeMap;
+    use prelude::*;
     use serde;
 
     pub fn serialize<S, T, U>(v: &BTreeMap<T, U>, s: S)
         -> Result<S::Ok, S::Error> where
         S: serde::Serializer,
-        T: serde::Serialize + ::std::hash::Hash + Eq + Ord,
+        T: serde::Serialize + ::core::hash::Hash + Eq + Ord,
         U: serde::Serialize,
     {
         use serde::ser::SerializeSeq;
@@ -100,19 +100,19 @@ pub mod btreemap_as_seq {
     pub fn deserialize<'de, D, T, U>(d: D)
         -> Result<BTreeMap<T, U>, D::Error> where
         D: serde::Deserializer<'de>,
-        T: serde::Deserialize<'de> + ::std::hash::Hash + Eq + Ord,
+        T: serde::Deserialize<'de> + ::core::hash::Hash + Eq + Ord,
         U: serde::Deserialize<'de>,
     {
-        use ::std::marker::PhantomData;
+        use ::core::marker::PhantomData;
 
         struct Visitor<T, U>(PhantomData<(T, U)>);
         impl<'de, T, U> serde::de::Visitor<'de> for Visitor<T, U> where
-            T: serde::Deserialize<'de> + ::std::hash::Hash + Eq + Ord,
+            T: serde::Deserialize<'de> + ::core::hash::Hash + Eq + Ord,
             U: serde::Deserialize<'de>,
         {
             type Value = BTreeMap<T, U>;
 
-            fn expecting(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
+            fn expecting(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
                 write!(f, "a sequence of pairs")
             }
 
@@ -143,7 +143,7 @@ pub mod btreemap_as_seq_byte_values {
 
     // NOTE: This module can be exactly copied to use with HashMap.
 
-    use ::std::collections::BTreeMap;
+    use prelude::*;
     use serde;
 
     /// A custom key-value pair type that serialized the bytes as hex.
@@ -165,7 +165,7 @@ pub mod btreemap_as_seq_byte_values {
     pub fn serialize<S, T>(v: &BTreeMap<T, Vec<u8>>, s: S)
         -> Result<S::Ok, S::Error> where
         S: serde::Serializer,
-        T: serde::Serialize + ::std::hash::Hash + Eq + Ord + 'static,
+        T: serde::Serialize + ::core::hash::Hash + Eq + Ord + 'static,
     {
         use serde::ser::SerializeSeq;
 
@@ -184,17 +184,17 @@ pub mod btreemap_as_seq_byte_values {
     pub fn deserialize<'de, D, T>(d: D)
         -> Result<BTreeMap<T, Vec<u8>>, D::Error> where
         D: serde::Deserializer<'de>,
-        T: serde::Deserialize<'de> + ::std::hash::Hash + Eq + Ord,
+        T: serde::Deserialize<'de> + ::core::hash::Hash + Eq + Ord,
     {
-        use ::std::marker::PhantomData;
+        use ::core::marker::PhantomData;
 
         struct Visitor<T>(PhantomData<T>);
         impl<'de, T> serde::de::Visitor<'de> for Visitor<T> where
-            T: serde::Deserialize<'de> + ::std::hash::Hash + Eq + Ord,
+            T: serde::Deserialize<'de> + ::core::hash::Hash + Eq + Ord,
         {
             type Value = BTreeMap<T, Vec<u8>>;
 
-            fn expecting(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
+            fn expecting(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
                 write!(f, "a sequence of pairs")
             }
 
@@ -239,19 +239,19 @@ pub mod hex_bytes {
     pub fn deserialize<'de, D, B>(d: D) -> Result<B, D::Error>
         where D: serde::Deserializer<'de>, B: serde::Deserialize<'de> + FromHex,
     {
-        struct Visitor<B>(::std::marker::PhantomData<B>);
+        struct Visitor<B>(::core::marker::PhantomData<B>);
 
         impl<'de, B: FromHex> serde::de::Visitor<'de> for Visitor<B> {
             type Value = B;
 
-            fn expecting(&self, formatter: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
+            fn expecting(&self, formatter: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
                 formatter.write_str("an ASCII hex string")
             }
 
             fn visit_bytes<E>(self, v: &[u8]) -> Result<Self::Value, E>
                 where E: serde::de::Error,
             {
-                if let Ok(hex) = ::std::str::from_utf8(v) {
+                if let Ok(hex) = ::core::str::from_utf8(v) {
                     FromHex::from_hex(hex).map_err(E::custom)
                 } else {
                     return Err(E::invalid_value(serde::de::Unexpected::Bytes(v), &self));
@@ -269,7 +269,7 @@ pub mod hex_bytes {
         if !d.is_human_readable() {
             serde::Deserialize::deserialize(d)
         } else {
-            d.deserialize_str(Visitor(::std::marker::PhantomData))
+            d.deserialize_str(Visitor(::core::marker::PhantomData))
         }
     }
 }

src/util/address.rs

@@ -33,9 +33,11 @@
 //! let address = Address::p2pkh(&public_key, Network::Bitcoin);
 //! ```
 
+use prelude::*;
+
 use core::fmt;
 use core::str::FromStr;
-use std::error;
+#[cfg(feature = "std")] use std::error;
 
 use bech32;
 use hashes::Hash;
@@ -84,8 +86,9 @@ impl fmt::Display for Error {
     }
 }
 
-impl error::Error for Error {
+#[cfg(feature = "std")]
-    fn cause(&self) -> Option<&dyn error::Error> {
+impl ::std::error::Error for Error {
+    fn cause(&self) -> Option<&dyn  error::Error> {
         match *self {
             Error::Base58(ref e) => Some(e),
             Error::Bech32(ref e) => Some(e),
@@ -524,8 +527,8 @@ impl FromStr for Address {
     }
 }
 
-impl ::std::fmt::Debug for Address {
+impl fmt::Debug for Address {
-    fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         write!(f, "{}", self.to_string())
     }
 }

src/util/amount.rs

@@ -14,6 +14,8 @@
 //! We refer to the documentation on the types for more information.
 //!
 
+use prelude::*;
+
 use core::{ops, default, str::FromStr, cmp::Ordering};
 use core::fmt::{self, Write};
 
@@ -111,6 +113,7 @@ impl fmt::Display for ParseAmountError {
     }
 }
 
+#[cfg(feature = "std")]
 impl ::std::error::Error for ParseAmountError {}
 
 fn is_too_precise(s: &str, precision: usize) -> bool {
@@ -972,8 +975,8 @@ pub mod serde {
 
             use serde::{Deserializer, Serializer, de};
             use util::amount::serde::SerdeAmountForOpt;
-            use std::fmt;
+            use core::fmt;
-            use std::marker::PhantomData;
+            use core::marker::PhantomData;
 
             pub fn serialize<A: SerdeAmountForOpt, S: Serializer>(
                 a: &Option<A>,
@@ -1035,8 +1038,8 @@ pub mod serde {
 
             use serde::{Deserializer, Serializer, de};
             use util::amount::serde::SerdeAmountForOpt;
-            use std::fmt;
+            use core::fmt;
-            use std::marker::PhantomData;
+            use core::marker::PhantomData;
 
             pub fn serialize<A: SerdeAmountForOpt, S: Serializer>(
                 a: &Option<A>,
@@ -1081,6 +1084,7 @@ pub mod serde {
 #[cfg(test)]
 mod tests {
     use super::*;
+    #[cfg(feature = "std")]
     use std::panic;
     use core::str::FromStr;
 
@@ -1113,7 +1117,11 @@ mod tests {
         assert_eq!(b, ssat(10));
         b %= 3;
         assert_eq!(b, ssat(1));
+    }
 
+    #[cfg(feature = "std")]
+    #[test]
+    fn test_overflows() {
         // panic on overflow
         let result = panic::catch_unwind(|| Amount::max_value() + Amount::from_sat(1));
         assert!(result.is_err());

src/util/base58.rs

@@ -14,7 +14,8 @@
 
 //! Base58 encoder and decoder
 
-use std::error;
+use prelude::*;
+
 use core::{fmt, str, iter, slice};
 
 use hashes::{sha256d, Hash};
@@ -57,7 +58,8 @@ impl fmt::Display for Error {
     }
 }
 
-impl error::Error for Error {}
+#[cfg(feature = "std")]
+impl ::std::error::Error for Error {}
 
 /// Vector-like object that holds the first 100 elements on the stack. If more space is needed it
 /// will be allocated on the heap.

src/util/bip143.rs

@@ -25,6 +25,8 @@ use blockdata::script::Script;
 use blockdata::transaction::{Transaction, TxIn, SigHashType};
 use consensus::{encode, Encodable};
 
+use prelude::*;
+
 use io;
 use core::ops::{Deref, DerefMut};
 

src/util/bip158.rs

@@ -45,7 +45,8 @@
 //!  ```
 //!  
 
-use std::collections::HashSet;
+use prelude::*;
+
 use io::{self as io, Cursor};
 use core::fmt::{self, Display, Formatter};
 use core::cmp::{self, Ordering};
@@ -73,6 +74,7 @@ pub enum Error {
     Io(io::Error),
 }
 
+#[cfg(feature = "std")]
 impl ::std::error::Error for Error {}
 
 impl Display for Error {
@@ -123,14 +125,14 @@ impl BlockFilter {
     /// Compute a SCRIPT_FILTER that contains spent and output scripts
     pub fn new_script_filter<M>(block: &Block, script_for_coin: M) -> Result<BlockFilter, Error>
         where M: Fn(&OutPoint) -> Result<Script, Error> {
-        let mut out = Cursor::new(Vec::new());
+        let mut out = Vec::new();
         {
             let mut writer = BlockFilterWriter::new(&mut out, block);
             writer.add_output_scripts();
             writer.add_input_scripts(script_for_coin)?;
             writer.finish()?;
         }
-        Ok(BlockFilter { content: out.into_inner() })
+        Ok(BlockFilter { content: out })
     }
 
     /// match any query pattern
@@ -361,9 +363,9 @@ impl<'a> GCSFilterWriter<'a> {
         mapped.sort();
 
         // write number of elements as varint
-        let mut encoder = io::Cursor::new(Vec::new());
+        let mut encoder = Vec::new();
         VarInt(mapped.len() as u64).consensus_encode(&mut encoder).unwrap();
-        let mut wrote = self.writer.write(encoder.into_inner().as_slice())?;
+        let mut wrote = self.writer.write(encoder.as_slice())?;
 
         // write out deltas of sorted values into a Golonb-Rice coded bit stream
         let mut writer = BitStreamWriter::new(self.writer);
@@ -508,8 +510,7 @@ impl<'a> BitStreamWriter<'a> {
 
 #[cfg(test)]
 mod test {
-    use std::collections::{HashSet, HashMap};
+    use io::Cursor;
-    use std::io::Cursor;
 
     use hash_types::BlockHash;
     use hashes::hex::FromHex;
@@ -520,6 +521,7 @@ mod test {
     use self::serde_json::{Value};
 
     use consensus::encode::deserialize;
+    use std::collections::HashMap;
 
     #[test]
     fn test_blockfilters() {
@@ -607,7 +609,7 @@ mod test {
         patterns.insert(Vec::from_hex("eeeeee").unwrap());
         patterns.insert(Vec::from_hex("ffffff").unwrap());
 
-        let mut out = Cursor::new(Vec::new());
+        let mut out = Vec::new();
         {
             let mut writer = GCSFilterWriter::new(&mut out, 0, 0, M, P);
             for p in &patterns {
@@ -616,7 +618,7 @@ mod test {
             writer.finish().unwrap();
         }
 
-        let bytes = out.into_inner();
+        let bytes = out;
 
         {
             let mut query = Vec::new();
@@ -659,7 +661,7 @@ mod test {
 
     #[test]
     fn test_bit_stream() {
-        let mut out = Cursor::new(Vec::new());
+        let mut out = Vec::new();
         {
             let mut writer = BitStreamWriter::new(&mut out);
             writer.write(0, 1).unwrap(); // 0
@@ -671,7 +673,7 @@ mod test {
             writer.write(7, 7).unwrap(); // 0000111
             writer.flush().unwrap();
         }
-        let bytes = out.into_inner();
+        let bytes = out;
         assert_eq!("01011010110000110000000001110000", format!("{:08b}{:08b}{:08b}{:08b}", bytes[0], bytes[1], bytes[2], bytes[3]));
         {
             let mut input = Cursor::new(bytes);

src/util/bip32.rs

@@ -16,8 +16,10 @@
 //! Implementation of BIP32 hierarchical deterministic wallets, as defined
 //! at <https://github.com/bitcoin/bips/blob/master/bip-0032.mediawiki>
 
+use prelude::*;
+
 use core::{fmt, str::FromStr, default::Default};
-use std::error;
+#[cfg(feature = "std")] use std::error;
 #[cfg(feature = "serde")] use serde;
 
 use hash_types::XpubIdentifier;
@@ -274,7 +276,7 @@ impl ::core::iter::FromIterator<ChildNumber> for DerivationPath {
 
 impl<'a> ::core::iter::IntoIterator for &'a DerivationPath {
     type Item = &'a ChildNumber;
-    type IntoIter = ::std::slice::Iter<'a, ChildNumber>;
+    type IntoIter = slice::Iter<'a, ChildNumber>;
     fn into_iter(self) -> Self::IntoIter {
         self.0.iter()
     }
@@ -457,6 +459,7 @@ impl fmt::Display for Error {
     }
 }
 
+#[cfg(feature = "std")]
 impl error::Error for Error {
     fn cause(&self) -> Option<&dyn error::Error> {
        if let Error::Ecdsa(ref e) = *self {

src/util/contracthash.rs

@@ -20,8 +20,10 @@
 
 #![cfg_attr(not(test), deprecated)]
 
+use prelude::*;
+
 use core::fmt;
-use std::error;
+#[cfg(feature = "std")] use std::error;
 
 use secp256k1::{self, Secp256k1};
 use PrivateKey;
@@ -72,6 +74,7 @@ impl fmt::Display for Error {
     }
 }
 
+#[cfg(feature = "std")]
 impl ::std::error::Error for Error {
     fn cause(&self) -> Option<&dyn error::Error> {
         match *self {

src/util/ecdsa.rs

@@ -16,6 +16,8 @@
 //! ECDSA keys used in Bitcoin that can be roundtrip (de)serialized.
 //!
 
+use prelude::*;
+
 use core::{ops, str::FromStr};
 use core::fmt::{self, Write as _fmtWrite};
 use io;
@@ -100,7 +102,17 @@ impl PublicKey {
         };
 
         reader.read_exact(&mut bytes[1..])?;
-        Self::from_slice(bytes).map_err(|e| io::Error::new(io::ErrorKind::InvalidData, e))
+        Self::from_slice(bytes).map_err(|e|{
+            // Need a static string for core2
+            #[cfg(feature = "std")]
+            let reason = e;
+            #[cfg(not(feature = "std"))]
+            let reason = match e {
+                Error::Base58(_) => "base58 error",
+                Error::Secp256k1(_) => "secp256k1 error",
+            };
+            io::Error::new(io::ErrorKind::InvalidData, reason)
+        })
     }
 
     /// Serialize the public key to bytes
@@ -299,7 +311,7 @@ impl<'de> ::serde::Deserialize<'de> for PrivateKey {
         impl<'de> ::serde::de::Visitor<'de> for WifVisitor {
             type Value = PrivateKey;
 
-            fn expecting(&self, formatter: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
+            fn expecting(&self, formatter: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
                 formatter.write_str("an ASCII WIF string")
             }
 
@@ -307,7 +319,7 @@ impl<'de> ::serde::Deserialize<'de> for PrivateKey {
             where
                 E: ::serde::de::Error,
             {
-                if let Ok(s) = ::std::str::from_utf8(v) {
+                if let Ok(s) = ::core::str::from_utf8(v) {
                     PrivateKey::from_str(s).map_err(E::custom)
                 } else {
                     Err(E::invalid_value(::serde::de::Unexpected::Bytes(v), &self))
@@ -350,7 +362,7 @@ impl<'de> ::serde::Deserialize<'de> for PublicKey {
             impl<'de> ::serde::de::Visitor<'de> for HexVisitor {
                 type Value = PublicKey;
 
-                fn expecting(&self, formatter: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
+                fn expecting(&self, formatter: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
                     formatter.write_str("an ASCII hex string")
                 }
 
@@ -358,7 +370,7 @@ impl<'de> ::serde::Deserialize<'de> for PublicKey {
                 where
                     E: ::serde::de::Error,
                 {
-                    if let Ok(hex) = ::std::str::from_utf8(v) {
+                    if let Ok(hex) = ::core::str::from_utf8(v) {
                         PublicKey::from_str(hex).map_err(E::custom)
                     } else {
                         Err(E::invalid_value(::serde::de::Unexpected::Bytes(v), &self))
@@ -379,7 +391,7 @@ impl<'de> ::serde::Deserialize<'de> for PublicKey {
             impl<'de> ::serde::de::Visitor<'de> for BytesVisitor {
                 type Value = PublicKey;
 
-                fn expecting(&self, formatter: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
+                fn expecting(&self, formatter: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
                     formatter.write_str("a bytestring")
                 }
 

src/util/hash.rs

@@ -15,6 +15,8 @@
 //!
 //! Utility functions related to hashing data, including merkleization
 
+use prelude::*;
+
 use io;
 use core::cmp::min;
 

src/util/key.rs

@@ -20,7 +20,7 @@
 pub use util::ecdsa::{PrivateKey, PublicKey};
 
 use core::fmt;
-use std::error;
+#[cfg(feature = "std")] use std::error;
 
 use secp256k1;
 use util::base58;
@@ -44,7 +44,8 @@ impl fmt::Display for Error {
     }
 }
 
-impl error::Error for Error {
+#[cfg(feature = "std")]
+impl ::std::error::Error for Error {
     fn cause(&self) -> Option<&dyn error::Error> {
         match *self {
             Error::Base58(ref e) => Some(e),

src/util/merkleblock.rs

@@ -51,7 +51,8 @@
 //! assert_eq!(1, index.len());
 //! assert_eq!(1, index[0]);
 //! ```
-use std::collections::HashSet;
+use prelude::*;
+
 use io;
 
 use hashes::Hash;
@@ -392,10 +393,10 @@ pub struct MerkleBlock {
 }
 
 impl MerkleBlock {
-    /// Create a MerkleBlock from a block, that should contain proofs for the txids.
+    /// Create a MerkleBlock from a block, that contains proofs for specific txids.
     ///
     /// The `block` is a full block containing the header and transactions and `match_txids` is a
-    /// set containing the transaction ids that should be included in the partial merkle tree.
+    /// function that returns true for the ids that should be included in the partial merkle tree.
     ///
     /// # Examples
     ///
@@ -420,8 +421,8 @@ impl MerkleBlock {
     /// // Create a merkle block containing a single transaction
     /// let txid = Txid::from_hex(
     ///     "5a4ebf66822b0b2d56bd9dc64ece0bc38ee7844a23ff1d7320a88c5fdb2ad3e2").unwrap();
-    /// let match_txids = vec![txid].into_iter().collect();
+    /// let match_txids: Vec<Txid> = vec![txid].into_iter().collect();
-    /// let mb = MerkleBlock::from_block(&block, &match_txids);
+    /// let mb = MerkleBlock::from_block_with_predicate(&block, |t| match_txids.contains(t));
     ///
     /// // Authenticate and extract matched transaction ids
     /// let mut matches: Vec<Txid> = vec![];
@@ -429,23 +430,31 @@ impl MerkleBlock {
     /// assert!(mb.extract_matches(&mut matches, &mut index).is_ok());
     /// assert_eq!(txid, matches[0]);
     /// ```
-    pub fn from_block(block: &Block, match_txids: &HashSet<Txid>) -> Self {
+    pub fn from_block_with_predicate<F>(block: &Block, match_txids: F) -> Self
+        where F: Fn(&Txid) -> bool {
         let block_txids: Vec<_> = block.txdata.iter().map(Transaction::txid).collect();
-        Self::from_header_txids(&block.header, &block_txids, match_txids)
+        Self::from_header_txids_with_predicate(&block.header, &block_txids, match_txids)
     }
 
-    /// Create a MerkleBlock from the block's header and txids, that should contain proofs for match_txids.
+    /// Create a MerkleBlock from a block, that contains proofs for specific txids.
+    #[cfg(feature = "std")]
+    #[deprecated(since="0.26.2", note="use from_block_with_predicate")]
+    pub fn from_block(block: &Block, match_txids: &::std::collections::HashSet<Txid>) -> Self {
+        Self::from_block_with_predicate(block, |t| match_txids.contains(t))
+    }
+
+    /// Create a MerkleBlock from the block's header and txids, that contain proofs for specific txids.
     ///
     /// The `header` is the block header, `block_txids` is the full list of txids included in the block and
-    /// `match_txids` is a set containing the transaction ids that should be included in the partial merkle tree.
+    /// `match_txids` is a function that returns true for the ids that should be included in the partial merkle tree.
-    pub fn from_header_txids(
+    pub fn from_header_txids_with_predicate<F>(
         header: &BlockHeader,
         block_txids: &[Txid],
-        match_txids: &HashSet<Txid>,
+        match_txids: F,
-    ) -> Self {
+    ) -> Self where F: Fn(&Txid) -> bool {
         let matches: Vec<bool> = block_txids
             .iter()
-            .map(|txid| match_txids.contains(txid))
+            .map(match_txids)
             .collect();
 
         let pmt = PartialMerkleTree::from_txids(&block_txids, &matches);
@@ -455,6 +464,17 @@ impl MerkleBlock {
         }
     }
 
+    /// Create a MerkleBlock from the block's header and txids, that should contain proofs for match_txids.
+    #[cfg(feature = "std")]
+    #[deprecated(since="0.26.2", note="use from_header_txids_with_predicate")]
+    pub fn from_header_txids(
+        header: &BlockHeader,
+        block_txids: &[Txid],
+        match_txids: &::std::collections::HashSet<Txid>,
+    ) -> Self {
+        Self::from_header_txids_with_predicate(header, block_txids, |t| match_txids.contains(t))
+    }
+
     /// Extract the matching txid's represented by this partial merkle tree
     /// and their respective indices within the partial tree.
     /// returns Ok(()) on success, or error in case of failure
@@ -642,9 +662,9 @@ mod tests {
 
         let txid1 = txids[0];
         let txid2 = txids[1];
-        let txids = txids.into_iter().collect();
+        let txids = vec![txid1, txid2];
 
-        let merkle_block = MerkleBlock::from_block(&block, &txids);
+        let merkle_block = MerkleBlock::from_block_with_predicate(&block, |t| txids.contains(t));
 
         assert_eq!(merkle_block.header.block_hash(), block.block_hash());
 
@@ -672,12 +692,12 @@ mod tests {
     #[test]
     fn merkleblock_construct_from_txids_not_found() {
         let block = get_block_13b8a();
-        let txids = ["c0ffee00003bafa802c8aa084379aa98d9fcd632ddc2ed9782b586ec87451f20"]
+        let txids: Vec<Txid> = ["c0ffee00003bafa802c8aa084379aa98d9fcd632ddc2ed9782b586ec87451f20"]
             .iter()
             .map(|hex| Txid::from_hex(hex).unwrap())
             .collect();
 
-        let merkle_block = MerkleBlock::from_block(&block, &txids);
+        let merkle_block = MerkleBlock::from_block_with_predicate(&block, |t| txids.contains(t));
 
         assert_eq!(merkle_block.header.block_hash(), block.block_hash());
 

src/util/misc.rs

@@ -16,6 +16,8 @@
 //!
 //! Various utility functions
 
+use prelude::*;
+
 use hashes::{sha256d, Hash, HashEngine};
 
 use blockdata::opcodes;
@@ -29,8 +31,9 @@ pub const BITCOIN_SIGNED_MSG_PREFIX: &[u8] = b"\x18Bitcoin Signed Message:\n";
 
 #[cfg(feature = "secp-recovery")]
 mod message_signing {
+    #[cfg(feature = "base64")] use prelude::*;
     use core::fmt;
-    use std::error;
+    #[cfg(feature = "std")] use std::error;
 
     use hashes::sha256d;
     use secp256k1;
@@ -60,6 +63,7 @@ mod message_signing {
         }
     }
 
+    #[cfg(feature = "std")]
     impl error::Error for MessageSignatureError {
         fn cause(&self) -> Option<&dyn error::Error> {
             match *self {

src/util/mod.rs

@@ -35,8 +35,10 @@ pub mod bip158;
 
 pub(crate) mod endian;
 
+use prelude::*;
+use io;
 use core::fmt;
-use std::error;
+#[cfg(feature = "std")] use std::error;
 
 use network;
 use consensus::encode;
@@ -87,8 +89,9 @@ impl fmt::Display for Error {
     }
 }
 
-impl error::Error for Error {
+#[cfg(feature = "std")]
-    fn cause(&self) -> Option<&dyn error::Error> {
+impl ::std::error::Error for Error {
+    fn cause(&self) -> Option<&dyn  error::Error> {
         match *self {
             Error::Encode(ref e) => Some(e),
             Error::Network(ref e) => Some(e),
@@ -110,3 +113,18 @@ impl From<network::Error> for Error {
         Error::Network(e)
     }
 }
+
+// core2 doesn't have read_to_end
+pub(crate) fn read_to_end<D: io::Read>(mut d: D) -> Result<Vec<u8>, io::Error> {
+    let mut result = vec![];
+    let mut buf = [0u8; 64];
+    loop {
+        match d.read(&mut buf) {
+            Ok(0) => break,
+            Ok(n) => result.extend_from_slice(&buf[0..n]),
+            Err(ref e) if e.kind() == io::ErrorKind::Interrupted => {},
+            Err(e) => return Err(e.into()),
+        };
+    }
+    Ok(result)
+}

src/util/psbt/error.rs

@@ -12,7 +12,8 @@
 // If not, see <http://creativecommons.org/publicdomain/zero/1.0/>.
 //
 
-use std::error;
+use prelude::*;
+
 use core::fmt;
 
 use blockdata::transaction::Transaction;
@@ -105,7 +106,8 @@ impl fmt::Display for Error {
     }
 }
 
-impl error::Error for Error {}
+#[cfg(feature = "std")]
+impl ::std::error::Error for Error {}
 
 #[doc(hidden)]
 impl From<hashes::Error> for Error {

src/util/psbt/macros.rs

@@ -14,7 +14,7 @@
 
 #[allow(unused_macros)]
 macro_rules! hex_psbt {
-    ($s:expr) => { $crate::consensus::deserialize::<$crate::util::psbt::PartiallySignedTransaction>(&<Vec<u8> as $crate::hashes::hex::FromHex>::from_hex($s).unwrap()) };
+    ($s:expr) => { $crate::consensus::deserialize::<$crate::util::psbt::PartiallySignedTransaction>(&<$crate::prelude::Vec<u8> as $crate::hashes::hex::FromHex>::from_hex($s).unwrap()) };
 }
 
 macro_rules! merge {
@@ -45,7 +45,7 @@ macro_rules! impl_psbt_deserialize {
 macro_rules! impl_psbt_serialize {
     ($thing:ty) => {
         impl $crate::util::psbt::serialize::Serialize for $thing {
-            fn serialize(&self) -> Vec<u8> {
+            fn serialize(&self) -> $crate::prelude::Vec<u8> {
                 $crate::consensus::serialize(self)
             }
         }
@@ -118,11 +118,11 @@ macro_rules! impl_psbt_insert_pair {
         if !$raw_key.key.is_empty() {
             let key_val: $keyed_key_type = $crate::util::psbt::serialize::Deserialize::deserialize(&$raw_key.key)?;
             match $slf.$keyed_name.entry(key_val) {
-                ::std::collections::btree_map::Entry::Vacant(empty_key) => {
+                $crate::prelude::btree_map::Entry::Vacant(empty_key) => {
                     let val: $keyed_value_type = $crate::util::psbt::serialize::Deserialize::deserialize(&$raw_value)?;
                     empty_key.insert(val);
                 }
-                ::std::collections::btree_map::Entry::Occupied(_) => return Err($crate::util::psbt::Error::DuplicateKey($raw_key).into()),
+                $crate::prelude::btree_map::Entry::Occupied(_) => return Err($crate::util::psbt::Error::DuplicateKey($raw_key).into()),
             }
         } else {
             return Err($crate::util::psbt::Error::InvalidKey($raw_key).into());
@@ -180,7 +180,7 @@ macro_rules! impl_psbt_hash_deserialize {
 macro_rules! impl_psbt_hash_serialize {
     ($hash_type:ty) => {
         impl $crate::util::psbt::serialize::Serialize for $hash_type {
-            fn serialize(&self) -> Vec<u8> {
+            fn serialize(&self) -> $crate::prelude::Vec<u8> {
                 self.into_inner().to_vec()
             }
         }

src/util/psbt/map/global.rs

@@ -12,8 +12,8 @@
 // If not, see <http://creativecommons.org/publicdomain/zero/1.0/>.
 //
 
-use std::collections::BTreeMap;
+use prelude::*;
-use std::collections::btree_map::Entry;
+
 use io::{self, Cursor, Read};
 use core::cmp;
 
@@ -89,12 +89,12 @@ impl Map for Global {
         match raw_key.type_value {
             PSBT_GLOBAL_UNSIGNED_TX => return Err(Error::DuplicateKey(raw_key).into()),
             PSBT_GLOBAL_PROPRIETARY => match self.proprietary.entry(raw::ProprietaryKey::from_key(raw_key.clone())?) {
-                Entry::Vacant(empty_key) => {empty_key.insert(raw_value);},
+                btree_map::Entry::Vacant(empty_key) => {empty_key.insert(raw_value);},
-                Entry::Occupied(_) => return Err(Error::DuplicateKey(raw_key).into()),
+                btree_map::Entry::Occupied(_) => return Err(Error::DuplicateKey(raw_key).into()),
             }
             _ => match self.unknown.entry(raw_key) {
-                Entry::Vacant(empty_key) => {empty_key.insert(raw_value);},
+                btree_map::Entry::Vacant(empty_key) => {empty_key.insert(raw_value);},
-                Entry::Occupied(k) => return Err(Error::DuplicateKey(k.key().clone()).into()),
+                btree_map::Entry::Occupied(k) => return Err(Error::DuplicateKey(k.key().clone()).into()),
             }
         }
 
@@ -183,10 +183,10 @@ impl Map for Global {
         // Merging xpubs
         for (xpub, (fingerprint1, derivation1)) in other.xpub {
             match self.xpub.entry(xpub) {
-                Entry::Vacant(entry) => {
+                btree_map::Entry::Vacant(entry) => {
                     entry.insert((fingerprint1, derivation1));
                 },
-                Entry::Occupied(mut entry) => {
+                btree_map::Entry::Occupied(mut entry) => {
                     // Here in case of the conflict we select the version with algorithm:
                     // 1) if everything is equal we do nothing
                     // 2) report an error if
@@ -215,7 +215,7 @@ impl Map for Global {
                     }
                     return Err(psbt::Error::MergeConflict(format!(
                         "global xpub {} has inconsistent key sources", xpub
-                    ).to_owned()));
+                    )));
                 }
             }
         }
@@ -321,12 +321,12 @@ impl Decodable for Global {
                             }
                         }
                         PSBT_GLOBAL_PROPRIETARY => match proprietary.entry(raw::ProprietaryKey::from_key(pair.key.clone())?) {
-                            Entry::Vacant(empty_key) => {empty_key.insert(pair.value);},
+                            btree_map::Entry::Vacant(empty_key) => {empty_key.insert(pair.value);},
-                            Entry::Occupied(_) => return Err(Error::DuplicateKey(pair.key).into()),
+                            btree_map::Entry::Occupied(_) => return Err(Error::DuplicateKey(pair.key).into()),
                         }
                         _ => match unknowns.entry(pair.key) {
-                            Entry::Vacant(empty_key) => {empty_key.insert(pair.value);},
+                            btree_map::Entry::Vacant(empty_key) => {empty_key.insert(pair.value);},
-                            Entry::Occupied(k) => return Err(Error::DuplicateKey(k.key().clone()).into()),
+                            btree_map::Entry::Occupied(k) => return Err(Error::DuplicateKey(k.key().clone()).into()),
                         }
                     }
                 }

src/util/psbt/map/input.rs

@@ -12,8 +12,9 @@
 // If not, see <http://creativecommons.org/publicdomain/zero/1.0/>.
 //
 
+use prelude::*;
+
 use io;
-use std::collections::btree_map::{BTreeMap, Entry};
 
 use blockdata::script::Script;
 use blockdata::transaction::{SigHashType, Transaction, TxOut};
@@ -177,14 +178,14 @@ impl Map for Input {
                 psbt_insert_hash_pair(&mut self.hash256_preimages, raw_key, raw_value, error::PsbtHash::Hash256)?;
             }
             PSBT_IN_PROPRIETARY => match self.proprietary.entry(raw::ProprietaryKey::from_key(raw_key.clone())?) {
-                ::std::collections::btree_map::Entry::Vacant(empty_key) => {empty_key.insert(raw_value);},
+                btree_map::Entry::Vacant(empty_key) => {empty_key.insert(raw_value);},
-                ::std::collections::btree_map::Entry::Occupied(_) => return Err(Error::DuplicateKey(raw_key).into()),
+                btree_map::Entry::Occupied(_) => return Err(Error::DuplicateKey(raw_key).into()),
             }
             _ => match self.unknown.entry(raw_key) {
-                Entry::Vacant(empty_key) => {
+                btree_map::Entry::Vacant(empty_key) => {
                     empty_key.insert(raw_value);
                 }
-                Entry::Occupied(k) => {
+                btree_map::Entry::Occupied(k) => {
                     return Err(Error::DuplicateKey(k.key().clone()).into())
                 }
             },
@@ -307,7 +308,7 @@ where
     }
     let key_val: H = Deserialize::deserialize(&raw_key.key)?;
     match map.entry(key_val) {
-        Entry::Vacant(empty_key) => {
+        btree_map::Entry::Vacant(empty_key) => {
             let val: Vec<u8> = Deserialize::deserialize(&raw_value)?;
             if <H as hashes::Hash>::hash(&val) != key_val {
                 return Err(psbt::Error::InvalidPreimageHashPair {
@@ -320,6 +321,6 @@ where
             empty_key.insert(val);
             Ok(())
         }
-        Entry::Occupied(_) => return Err(psbt::Error::DuplicateKey(raw_key).into()),
+        btree_map::Entry::Occupied(_) => return Err(psbt::Error::DuplicateKey(raw_key).into()),
     }
 }

src/util/psbt/map/mod.rs

@@ -12,6 +12,8 @@
 // If not, see <http://creativecommons.org/publicdomain/zero/1.0/>.
 //
 
+use prelude::*;
+
 use io;
 
 use consensus::encode;

src/util/psbt/map/output.rs

@@ -12,9 +12,9 @@
 // If not, see <http://creativecommons.org/publicdomain/zero/1.0/>.
 //
 
+use prelude::*;
+
 use io;
-use std::collections::BTreeMap;
-use std::collections::btree_map::Entry;
 
 use blockdata::script::Script;
 use consensus::encode;
@@ -79,12 +79,12 @@ impl Map for Output {
                 }
             }
             PSBT_OUT_PROPRIETARY => match self.proprietary.entry(raw::ProprietaryKey::from_key(raw_key.clone())?) {
-                Entry::Vacant(empty_key) => {empty_key.insert(raw_value);},
+                btree_map::Entry::Vacant(empty_key) => {empty_key.insert(raw_value);},
-                Entry::Occupied(_) => return Err(Error::DuplicateKey(raw_key.clone()).into()),
+                btree_map::Entry::Occupied(_) => return Err(Error::DuplicateKey(raw_key.clone()).into()),
             }
             _ => match self.unknown.entry(raw_key) {
-                    Entry::Vacant(empty_key) => {empty_key.insert(raw_value);},
+                btree_map::Entry::Vacant(empty_key) => {empty_key.insert(raw_value);},
-                    Entry::Occupied(k) => return Err(Error::DuplicateKey(k.key().clone()).into()),
+                btree_map::Entry::Occupied(k) => return Err(Error::DuplicateKey(k.key().clone()).into()),
             }
         }
 

src/util/psbt/mod.rs

@@ -23,6 +23,8 @@ use blockdata::transaction::Transaction;
 use consensus::{encode, Encodable, Decodable};
 use consensus::encode::MAX_VEC_SIZE;
 
+use prelude::*;
+
 use io;
 
 mod error;
@@ -95,8 +97,8 @@ impl PartiallySignedTransaction {
 #[cfg(feature = "base64")]
 mod display_from_str {
     use super::PartiallySignedTransaction;
-    use std::fmt::{Display, Formatter, self};
+    use core::fmt::{Display, Formatter, self};
-    use std::str::FromStr;
+    use core::str::FromStr;
     use consensus::encode::{Error, self};
     use ::base64::display::Base64Display;
 
@@ -118,6 +120,7 @@ mod display_from_str {
         }
     }
 
+    #[cfg(feature = "std")]
     impl ::std::error::Error for PsbtParseError { }
 
     impl Display for PartiallySignedTransaction {
@@ -215,7 +218,6 @@ mod tests {
     use hashes::{sha256, hash160, Hash, ripemd160};
     use hash_types::Txid;
 
-    use std::collections::BTreeMap;
 
     use secp256k1::Secp256k1;
 
@@ -230,6 +232,7 @@ mod tests {
 
     use super::PartiallySignedTransaction;
     use util::psbt::raw::ProprietaryKey;
+    use std::collections::BTreeMap;
 
     #[test]
     fn trivial_psbt() {
@@ -464,7 +467,6 @@ mod tests {
     }
 
     mod bip_vectors {
-        use std::collections::BTreeMap;
         #[cfg(feature = "base64")]
         use std::str::FromStr;
 
@@ -477,6 +479,7 @@ mod tests {
         use util::psbt::map::{Map, Global, Input, Output};
         use util::psbt::raw;
         use util::psbt::{PartiallySignedTransaction, Error};
+        use std::collections::BTreeMap;
 
         #[test]
         #[should_panic(expected = "InvalidMagic")]

src/util/psbt/raw.rs

@@ -17,12 +17,14 @@
 //! Raw PSBT key-value pairs as defined at
 //! <https://github.com/bitcoin/bips/blob/master/bip-0174.mediawiki>.
 
+use prelude::*;
 use core::fmt;
-use io;
 
+use io;
 use consensus::encode::{self, ReadExt, WriteExt, Decodable, Encodable, VarInt, serialize, deserialize, MAX_VEC_SIZE};
 use hashes::hex;
 use util::psbt::Error;
+use util::read_to_end;
 
 /// A PSBT key in its raw byte form.
 #[derive(Debug, PartialEq, Hash, Eq, Clone, Ord, PartialOrd)]
@@ -152,9 +154,8 @@ impl<Subtype> Encodable for ProprietaryKey<Subtype> where Subtype: Copy + From<u
 impl<Subtype> Decodable for ProprietaryKey<Subtype> where Subtype: Copy + From<u8> + Into<u8> {
     fn consensus_decode<D: io::Read>(mut d: D) -> Result<Self, encode::Error> {
         let prefix = Vec::<u8>::consensus_decode(&mut d)?;
-        let mut key = vec![];
         let subtype = Subtype::from(d.read_u8()?);
-        d.read_to_end(&mut key)?;
+        let key = read_to_end(d)?;
 
         Ok(ProprietaryKey {
             prefix,

src/util/psbt/serialize.rs

@@ -17,6 +17,8 @@
 //! Defines traits used for (de)serializing PSBT values into/from raw
 //! bytes in PSBT key-value pairs.
 
+use prelude::*;
+
 use io;
 
 use blockdata::script::Script;

src/util/uint.rs

@@ -450,7 +450,7 @@ macro_rules! construct_uint {
             fn deserialize<D: $crate::serde::Deserializer<'de>>(
                 deserializer: D,
             ) -> Result<Self, D::Error> {
-                use ::std::fmt;
+                use ::core::fmt;
                 use $crate::hashes::hex::FromHex;
                 use $crate::serde::de;
                 struct Visitor;
@@ -465,7 +465,7 @@ macro_rules! construct_uint {
                     where
                         E: de::Error,
                     {
-                        let bytes = Vec::from_hex(s)
+                        let bytes = $crate::prelude::Vec::from_hex(s)
                             .map_err(|_| de::Error::invalid_value(de::Unexpected::Str(s), &self))?;
                         $name::from_be_slice(&bytes)
                             .map_err(|_| de::Error::invalid_length(bytes.len() * 2, &self))
@@ -509,6 +509,7 @@ impl ::core::fmt::Display for ParseLengthError {
     }
 }
 
+#[cfg(feature = "std")]
 impl ::std::error::Error for ParseLengthError {}
 
 impl Uint256 {