Add contracts module

Author: stevenroose

Cargo.toml

@@ -9,6 +9,9 @@ repository = "https://github.com/ElementsProject/rust-elements/"
 documentation = "https://docs.rs/elements/"
 
 [features]
+default = [ "contracts" ]
+
+contracts = [ "serde", "serde_cbor", "serde_json" ]
 "serde-feature" = [
     "bitcoin/use-serde",
     "serde"
@@ -22,9 +25,11 @@ bitcoin = "0.23"
 # to avoid requiring two version of bitcoin_hashes.
 bitcoin_hashes = "0.7.6"
 
-[dependencies.serde]
-version = "1.0"
-optional = true
+serde = { version = "1.0", optional = true, features = ["derive"] }
+
+# Used for contracts module.
+serde_cbor = { version = "0.11.1", optional = true }
+serde_json = { version = "<=1.0.44", optional = true }
 
 [dev-dependencies]
 rand = "0.6.5"

src/contracts.rs

@@ -0,0 +1,192 @@
+//! Handling asset contracts.
+
+use std::collections::BTreeMap;
+use std::{error, fmt};
+
+use serde_cbor;
+use serde_json;
+use bitcoin::hashes::Hash;
+
+use ::ContractHash;
+
+/// The maximum precision of an asset.
+pub const MAX_PRECISION: u8 = 8;
+
+/// The maximum ticker string length.
+pub const MAX_TICKER_LENGTH: usize = 5;
+
+/// An asset contract error.
+#[derive(Debug)]
+pub enum Error {
+    /// The contract was empty.
+    Empty,
+    /// The CBOR format was invalid.
+    InvalidCbor(serde_cbor::Error),
+    /// the JSON format was invalid.
+    InvalidJson(serde_json::Error),
+    /// The contract's content are invalid.
+    InvalidContract(&'static str),
+    /// An unknown contract version was encountered.
+    UnknownVersion(u8),
+}
+
+impl fmt::Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match *self {
+            Error::Empty => write!(f, "the contract was empty"),
+            Error::InvalidCbor(ref e) => write!(f, "invalid CBOR format: {}", e),
+            Error::InvalidJson(ref e) => write!(f, "invalid JSON format: {}", e),
+            Error::InvalidContract(ref e) => write!(f, "invalid contract: {}", e),
+            Error::UnknownVersion(v) => write!(f, "unknown contract version: {}", v),
+        }
+    }
+}
+
+impl error::Error for Error {
+    fn cause(&self) -> Option<&error::Error> {
+        match *self {
+            Error::InvalidCbor(ref e) => Some(e),
+            Error::InvalidJson(ref e) => Some(e),
+            _ => None,
+        }
+    }
+
+    fn description(&self) -> &str {
+        "a contract error"
+    }
+}
+
+/// The structure of a legacy (JSON) contract.
+#[derive(Debug, Clone, Deserialize)]
+struct LegacyContract {
+    precision: u8,
+    ticker: String,
+    #[serde(flatten)]
+    other: BTreeMap<String, serde_json::Value>,
+}
+
+/// The contents of an asset contract.
+#[derive(Debug, Clone)]
+enum Content {
+    Legacy(LegacyContract),
+    Modern {
+        precision: u8,
+        ticker: String,
+        //TODO(stevenroose) consider requiring String keys
+        other: BTreeMap<serde_cbor::Value, serde_cbor::Value>,
+    },
+}
+
+impl Content {
+    fn from_bytes(contract: &[u8]) -> Result<Content, Error> {
+        if contract.len() < 1 {
+            return Err(Error::Empty);
+        }
+
+        if contract[0] == '{' as u8 {
+            let content: LegacyContract =
+                serde_json::from_slice(contract).map_err(Error::InvalidJson)?;
+            if content.precision > MAX_PRECISION {
+                return Err(Error::InvalidContract("invalid precision"));
+            }
+            if content.ticker.len() > MAX_TICKER_LENGTH {
+                return Err(Error::InvalidContract("ticker too long"));
+            }
+            Ok(Content::Legacy(content))
+        } else if contract[0] == 1 {
+            let content: Vec<serde_cbor::Value> =
+                serde_cbor::from_slice(contract).map_err(Error::InvalidCbor)?;
+            if content.len() != 3 {
+                return Err(Error::InvalidContract("CBOR value must be array of 3 elements"));
+            }
+            let mut iter = content.into_iter();
+            Ok(Content::Modern {
+                precision: if let serde_cbor::Value::Integer(i) = iter.next().unwrap() {
+                    if i < 0 || i > MAX_PRECISION as i128 {
+                        return Err(Error::InvalidContract("invalid precision"));
+                    }
+                    i as u8
+                } else {
+                    return Err(Error::InvalidContract("first CBOR value must be integer"));
+                },
+                ticker: if let serde_cbor::Value::Text(t) = iter.next().unwrap() {
+                    if t.len() > MAX_TICKER_LENGTH {
+                        return Err(Error::InvalidContract("ticker too long"));
+                    }
+                    t
+                } else {
+                    return Err(Error::InvalidContract("second CBOR value must be string"));
+                },
+                other: if let serde_cbor::Value::Map(m) = iter.next().unwrap() {
+                    m
+                } else {
+                    return Err(Error::InvalidContract("third CBOR value must be map"));
+                },
+            })
+        } else {
+            Err(Error::UnknownVersion(contract[0]))
+        }
+    }
+}
+
+/// An asset contract.
+#[derive(Clone, Hash, PartialEq, Eq, PartialOrd, Ord)]
+pub struct Contract(Vec<u8>);
+
+impl Contract {
+    /// Parse an asset contract from bytes.
+    pub fn from_bytes(contract: &[u8]) -> Result<Contract, Error> {
+        // Check for validity and then store raw contract.
+        let _ = Content::from_bytes(contract)?;
+        Ok(Contract(contract.to_vec()))
+    }
+
+    /// Get the binary representation of the asset contract.
+    pub fn as_bytes(&self) -> &[u8] {
+        &self.0
+    }
+
+    /// Get the contract hash of this asset contract.
+    pub fn contract_hash(&self) -> ContractHash {
+        ContractHash::hash(self.as_bytes())
+    }
+
+    /// Get the precision of the asset.
+    pub fn precision(&self) -> u8 {
+        match Content::from_bytes(&self.as_bytes()).expect("invariant") {
+            Content::Legacy(c) => c.precision,
+            Content::Modern { precision, .. } => precision,
+        }
+    }
+
+    /// Get the ticker of the asset.
+    pub fn ticker(&self) -> String {
+        match Content::from_bytes(&self.as_bytes()).expect("invariant") {
+            Content::Legacy(c) => c.ticker,
+            Content::Modern { ticker, .. } => ticker,
+        }
+    }
+    
+    /// Retrieve a property from the contract.
+    /// For precision and ticker, use the designated methods instead.
+    pub fn property<T: serde::de::DeserializeOwned>(&self, key: &str) -> Result<Option<T>, Error> {
+        match Content::from_bytes(&self.as_bytes()).expect("invariant") {
+            Content::Legacy(c) => {
+                let value = match c.other.get(key) {
+                    Some(v) => v,
+                    None => return Ok(None),
+                };
+                Ok(serde_json::from_value(value.clone()).map_err(Error::InvalidJson)?)
+            },
+            Content::Modern { other, .. } => {
+                let value = match other.get(&key.to_owned().into()) {
+                    Some(v) => v,
+                    None => return Ok(None),
+                };
+                //TODO(stevenroose) optimize this when serde_cbor implements from_value
+                let bytes = serde_cbor::to_vec(&value).map_err(Error::InvalidCbor)?;
+                Ok(serde_cbor::from_slice(&bytes).map_err(Error::InvalidCbor)?)
+            },
+        }
+    }
+}

src/lib.rs

@@ -28,16 +28,19 @@
 pub extern crate bitcoin;
 #[macro_use]
 pub extern crate bitcoin_hashes;
-#[cfg(feature = "serde")] extern crate serde;
+#[cfg(feature = "serde")] #[macro_use] extern crate serde;
+#[cfg(feature = "serde_cbor")] extern crate serde_cbor;
+#[cfg(feature = "serde_json")] extern crate serde_json;
 
 #[cfg(test)] extern crate rand;
-#[cfg(test)] extern crate serde_json;
 
 #[macro_use] mod internal_macros;
 pub mod address;
 pub mod blech32;
 mod block;
 pub mod confidential;
+#[cfg(feature = "contracts")]
+pub mod contracts;
 pub mod dynafed;
 pub mod encode;
 mod fast_merkle_root;