feat: support no_std

Cargo.toml

@@ -7,8 +7,13 @@ license = "MIT"
 description = "A generalized merkle mountain range implementation"
 repository = "https://github.com/nervosnetwork/merkle-mountain-range"
 
+[features]
+default = ["std"]
+std = []
+
 [dependencies]
 failure = "0.1.5"
+cfg-if = "0.1"
 
 [dev-dependencies]
 faster-hex = "0.3"

Makefile

@@ -1,6 +1,6 @@
 default: ci
 
-ci: fmt clippy test bench-test
+ci: fmt check-no-std clippy test bench-test
 
 test:
 	cargo test --all --all-features
@@ -13,3 +13,6 @@ clippy:
 
 fmt:
 	cargo fmt --all -- --check
+
+check-no-std:
+	cargo check --all --no-default-features

src/error.rs

@@ -1,5 +1,5 @@
 pub use failure::Fail;
-pub type Result<T> = ::std::result::Result<T, Error>;
+pub type Result<T> = core::result::Result<T, Error>;
 
 #[derive(Fail, Debug, PartialEq, Eq, Clone)]
 pub enum Error {
@@ -8,5 +8,5 @@ pub enum Error {
     #[fail(display = "Inconsistent store")]
     InconsistentStore,
     #[fail(display = "Store error {}", _0)]
-    StoreError(String),
+    StoreError(crate::string::String),
 }

src/helper.rs

@@ -1,3 +1,5 @@
+use crate::vec::Vec;
+
 pub fn leaf_index_to_pos(index: u64) -> u64 {
     if index == 0 {
         return 0;

src/lib.rs

@@ -1,3 +1,5 @@
+#![cfg_attr(not(feature = "std"), no_std)]
+
 mod error;
 mod helper;
 mod merge;
@@ -12,3 +14,18 @@ pub use helper::{leaf_index_to_mmr_size, leaf_index_to_pos};
 pub use merge::Merge;
 pub use mmr::{MerkleProof, MMR};
 pub use mmr_store::MMRStore;
+
+cfg_if::cfg_if! {
+    if #[cfg(feature = "std")] {
+        use std::borrow;
+        use std::collections;
+        use std::vec;
+        use std::string;
+    } else {
+        extern crate alloc;
+        use alloc::borrow;
+        use alloc::collections;
+        use alloc::vec;
+        use alloc::string;
+    }
+}

src/mmr.rs

@@ -4,12 +4,13 @@
 //! https://github.com/mimblewimble/grin/blob/master/doc/mmr.md#structure
 //! https://github.com/mimblewimble/grin/blob/0ff6763ee64e5a14e70ddd4642b99789a1648a32/core/src/core/pmmr.rs#L606
 
+use crate::borrow::Cow;
 use crate::helper::{get_peaks, parent_offset, pos_height_in_tree, sibling_offset};
 use crate::mmr_store::{MMRBatch, MMRStore};
+use crate::vec::Vec;
 use crate::{Error, Merge, Result};
-use std::borrow::Cow;
-use std::fmt::Debug;
-use std::marker::PhantomData;
+use core::fmt::Debug;
+use core::marker::PhantomData;
 
 pub struct MMR<T, M, S: MMRStore<T>> {
     mmr_size: u64,

src/mmr_store.rs

@@ -1,4 +1,4 @@
-use crate::Result;
+use crate::{vec::Vec, Result};
 
 #[derive(Default)]
 pub struct MMRBatch<Elem, Store: MMRStore<Elem>> {
@@ -45,7 +45,7 @@ impl<Elem: Clone, Store: MMRStore<Elem>> MMRBatch<Elem, Store> {
 
 impl<Elem, Store: MMRStore<Elem>> IntoIterator for MMRBatch<Elem, Store> {
     type Item = (u64, Vec<Elem>);
-    type IntoIter = ::std::vec::IntoIter<Self::Item>;
+    type IntoIter = crate::vec::IntoIter<Self::Item>;
 
     fn into_iter(self) -> Self::IntoIter {
         self.memory_batch.into_iter()

src/util.rs

@@ -1,11 +1,11 @@
-use crate::{MMRStore, Merge, MerkleProof, Result, MMR};
-use std::cell::RefCell;
-use std::collections::HashMap;
-use std::fmt::Debug;
-use std::marker::PhantomData;
+use crate::collections::BTreeMap;
+use crate::{vec::Vec, MMRStore, Merge, MerkleProof, Result, MMR};
+use core::cell::RefCell;
+use core::fmt::Debug;
+use core::marker::PhantomData;
 
 #[derive(Clone)]
-pub struct MemStore<T>(RefCell<HashMap<u64, T>>);
+pub struct MemStore<T>(RefCell<BTreeMap<u64, T>>);
 
 impl<T> Default for MemStore<T> {
     fn default() -> Self {
@@ -15,7 +15,7 @@ impl<T> Default for MemStore<T> {
 
 impl<T> MemStore<T> {
     fn new() -> Self {
-        MemStore(RefCell::new(HashMap::new()))
+        MemStore(RefCell::new(Default::default()))
     }
 }