Add serde and encode features, gate the code

Cargo.toml

@@ -16,19 +16,21 @@ name = "silentpayments"
 crate-type = ["lib"]
 
 [features]
-default = ["sending", "receiving"]
-sending = []
-receiving = []
+default = ["encode", "sending", "receiving"]
+encode = ["dep:bech32"]
+serde = ["dep:serde"]
+sending = ["dep:bitcoin_hashes", "dep:hex", "encode"]
+receiving = ["dep:bitcoin_hashes", "dep:hex", "dep:bimap", "serde", "encode"]
 
 [dependencies]
 secp256k1 = {version = "0.28.1", features = ["rand"] }
-hex = "0.4"
-bech32 = "0.9"
-bimap = "0.6"
-serde = { version = "1.0", features = ["derive"] }
-serde_json = "1.0"
-bitcoin_hashes = "0.13.0"
+hex = { version = "0.4", optional = true }
+bech32 = { version = "0.9", optional = true }
+bimap = { version = "0.6", optional = true }
+serde = { version = "1.0", features = ["derive"], optional = true }
+bitcoin_hashes = { version = "0.13.0", optional = true }
 
 [dev-dependencies]
 rust-bip39 = { version = "1.0.0", features = ["rand"] }
 bitcoin ={ version = "0.31.1", features = ["serde"] }
+serde_json = "1.0"

README.md

@@ -14,6 +14,47 @@ In the future, the library will probably be expanded to rely on structs from rus
 
 The library is split up in two parts: sending and receiving.
 
+## Feature Flags
+
+This library offers granular feature flags to minimize dependencies for different use cases:
+
+- **default**: Enables all features (`encode`, `sending`, `receiving`)
+- **encode**: Enables string encoding/decoding for `SilentPaymentAddress` (adds `bech32` dependency)
+- **serde**: Enables serde serialization/deserialization for types (adds `serde` dependency)
+- **sending**: Enables sending functionality (adds `bitcoin_hashes`, `hex` dependencies)
+- **receiving**: Enables receiving functionality (adds `bitcoin_hashes`, `hex`, `bimap`, `serde` dependencies)
+
+### Minimal Usage
+
+If you only need the type definitions (`Network` and `SilentPaymentAddress`) without any protocol functionality:
+
+```toml
+[dependencies]
+silentpayments = { version = "0.4", default-features = false }
+```
+
+This configuration only pulls in `secp256k1` as a dependency, significantly reducing the dependency tree for applications that only need to work with silent payment addresses without implementing the full protocol.
+
+**Bring Your Own Parser**: Even without the `encode` feature, you can construct a `SilentPaymentAddress` using `SilentPaymentAddress::new()` if you parse the bech32 yourself. This is useful if your application already has a bech32 parser and you want to avoid duplicate dependencies. The constructor documentation includes the complete bech32 format specification.
+
+### Custom Feature Combinations
+
+You can enable only the features you need:
+
+```toml
+# Just types and string encoding (no protocol implementation)
+silentpayments = { version = "0.4", default-features = false, features = ["encode"] }
+
+# Types with serde support (no protocol or encoding)
+silentpayments = { version = "0.4", default-features = false, features = ["serde"] }
+
+# Only sending capability
+silentpayments = { version = "0.4", default-features = false, features = ["sending"] }
+
+# Only receiving capability
+silentpayments = { version = "0.4", default-features = false, features = ["receiving"] }
+```
+
 ## Sending
 
 For sending to a silent payment address, you can call the `sender::generate_recipient_pubkeys` function.

examples/custom_parser.rs

@@ -0,0 +1,49 @@
+/// Example showing how to construct a SilentPaymentAddress without the `encode` feature.
+///
+/// This is useful if your application already has a bech32 parser and you want to
+/// avoid duplicate dependencies. You can parse the address yourself and then
+/// construct the type using the public constructor.
+///
+/// To run this example:
+/// ```bash
+/// cargo run --example custom_parser --no-default-features
+/// ```
+
+fn main() {
+    use secp256k1::{PublicKey, Secp256k1, SecretKey};
+    use silentpayments::{Network, SilentPaymentAddress};
+
+    // Example: Simulating what you'd get after parsing bech32 yourself
+    // In a real application, you would:
+    // 1. Parse the bech32m string (e.g., "sp1...")
+    // 2. Extract the HRP to determine the network
+    // 3. Decode the data part to get version + 33-byte scan key + 33-byte spend key
+    // 4. Deserialize the pubkeys from those bytes
+    // 5. Construct the SilentPaymentAddress using the constructor
+
+    // For this example, we'll generate valid pubkeys
+    let secp = Secp256k1::new();
+    let scan_secret = SecretKey::from_slice(&[0x01; 32]).expect("valid key");
+    let spend_secret = SecretKey::from_slice(&[0x02; 32]).expect("valid key");
+
+    let scan_pubkey = PublicKey::from_secret_key(&secp, &scan_secret);
+    let spend_pubkey = PublicKey::from_secret_key(&secp, &spend_secret);
+
+    // Construct the SilentPaymentAddress without needing the `encode` feature
+    let address = SilentPaymentAddress::new(
+        scan_pubkey,
+        spend_pubkey,
+        Network::Mainnet,
+        0, // version
+    )
+    .expect("Failed to create address");
+
+    println!("Successfully created SilentPaymentAddress without encode feature!");
+    println!("Network: {:?}", address.get_network());
+    println!("Version: {}", address.get_version());
+    println!("Scan key: {:?}", address.get_scan_key());
+    println!("Spend key: {:?}", address.get_spend_key());
+
+    println!("\n✅ This example compiled and ran with ZERO features enabled!");
+    println!("   Only dependencies: secp256k1, rand, rand_core, secp256k1-sys");
+}

src/error.rs

@@ -31,12 +31,14 @@ impl fmt::Display for Error {
 
 impl std::error::Error for Error {}
 
+#[cfg(any(feature = "sending", feature = "receiving"))]
 impl From<hex::FromHexError> for Error {
     fn from(e: hex::FromHexError) -> Self {
         Error::InvalidLabel(e.to_string())
     }
 }
 
+#[cfg(feature = "encode")]
 impl From<bech32::Error> for Error {
     fn from(e: bech32::Error) -> Self {
         Error::InvalidAddress(e.to_string())

src/lib.rs

@@ -1,9 +1,33 @@
 //! A rust implementation of BIP352: Silent Payments. This library
 //! can be used to add silent payment support to wallets.
 //!
-//! This library is split up in two parts: sending and receiving.
-//! Either of these can be implemented independently using
-//! the `sending` or `receiving` features.
+//! ## Feature Flags
+//!
+//! This library offers granular feature flags to minimize dependencies:
+//!
+//! - **default**: Enables `encode`, `sending`, and `receiving` features
+//! - **encode**: Enables string encoding/decoding for `SilentPaymentAddress` (requires `bech32`)
+//! - **serde**: Enables serde serialization/deserialization for types
+//! - **sending**: Enables sending functionality (requires `bitcoin_hashes`, `hex`, and `encode`)
+//! - **receiving**: Enables receiving functionality (requires `bitcoin_hashes`, `hex`, `bimap`, `serde`, and `encode`)
+//!
+//! ### Minimal Usage
+//!
+//! If you only need the type definitions (`Network` and `SilentPaymentAddress`) without
+//! any additional functionality, you can disable all default features:
+//!
+//! ```toml
+//! [dependencies]
+//! silentpayments = { version = "0.4", default-features = false }
+//! ```
+//!
+//! This will only pull in `secp256k1` as a dependency, giving you access to the core types
+//! without any encoding, serialization, or protocol functionality.
+//!
+//! **Note**: Even without the `encode` feature, you can still construct a `SilentPaymentAddress`
+//! from its components using `SilentPaymentAddress::new()`. This allows you to use your own
+//! bech32 parser (if your application already has one) and avoid duplicate dependencies.
+//! See the `SilentPaymentAddress::new()` documentation for the bech32 format specification.
 //!
 //! ## Examples
 //!
@@ -22,6 +46,7 @@ pub mod receiving;
 pub mod sending;
 pub mod utils;
 
+#[cfg(any(feature = "sending", feature = "receiving"))]
 pub use bitcoin_hashes;
 pub use secp256k1;
 

src/receiving.rs

@@ -148,7 +148,7 @@ impl Serialize for SerializablePubkey {
         S: serde::Serializer,
     {
         let mut seq = serializer.serialize_tuple(self.0.len())?;
-        for element in self.0.as_ref() {
+        for element in &self.0[..] {
             seq.serialize_element(element)?;
         }
         seq.end()

src/utils.rs

@@ -2,6 +2,7 @@
 //!
 //! This module contains functions that are more 'high-level'
 //! than the basic sending and receiving logic.
+#[cfg(any(feature = "sending", feature = "receiving"))]
 pub(crate) mod hash;
 #[cfg(feature = "receiving")]
 pub mod receiving;

src/utils/common.rs

@@ -1,22 +1,33 @@
+#[cfg(feature = "encode")]
 use core::fmt;
 
+#[cfg(any(feature = "sending", feature = "receiving"))]
 use crate::utils::hash::SharedSecretHash;
 use crate::Error;
 use crate::Result;
+#[cfg(feature = "encode")]
 use bech32::{FromBase32, ToBase32};
+#[cfg(any(feature = "sending", feature = "receiving"))]
 use bitcoin_hashes::Hash;
-use secp256k1::{PublicKey, Scalar, Secp256k1, SecretKey};
+use secp256k1::PublicKey;
+#[cfg(any(feature = "sending", feature = "receiving"))]
+use secp256k1::{Scalar, Secp256k1, SecretKey};
+#[cfg(all(feature = "serde", feature = "encode"))]
 use serde::ser::Serializer;
+#[cfg(all(feature = "serde", feature = "encode"))]
 use serde::Deserializer;
+#[cfg(feature = "serde")]
 use serde::{Deserialize, Serialize};
 
+#[cfg(any(feature = "sending", feature = "receiving"))]
 pub(crate) fn calculate_t_n(ecdh_shared_secret: &PublicKey, k: u32) -> Result<SecretKey> {
     let hash = SharedSecretHash::from_ecdh_and_k(ecdh_shared_secret, k).to_byte_array();
     let sk = SecretKey::from_slice(&hash)?;
 
     Ok(sk)
 }
 
+#[cfg(any(feature = "sending", feature = "receiving"))]
 pub(crate) fn calculate_P_n(B_spend: &PublicKey, t_n: Scalar) -> Result<PublicKey> {
     let secp = Secp256k1::new();
 
@@ -29,7 +40,8 @@ pub(crate) fn calculate_P_n(B_spend: &PublicKey, t_n: Scalar) -> Result<PublicKe
 ///
 /// There are three network types: Mainnet (`sp1..`), Testnet (`tsp1..`), and Regtest (`sprt1..`).
 /// Signet uses the same network type as Testnet.
-#[derive(Clone, Copy, Debug, Hash, PartialEq, Eq, Deserialize, Serialize)]
+#[derive(Clone, Copy, Debug, Hash, PartialEq, Eq)]
+#[cfg_attr(feature = "serde", derive(Deserialize, Serialize))]
 pub enum Network {
     Mainnet,
     Testnet,
@@ -69,6 +81,7 @@ pub struct SilentPaymentAddress {
     network: Network,
 }
 
+#[cfg(all(feature = "serde", feature = "encode"))]
 impl Serialize for SilentPaymentAddress {
     fn serialize<S>(&self, serializer: S) -> std::result::Result<S::Ok, S::Error>
     where
@@ -79,6 +92,7 @@ impl Serialize for SilentPaymentAddress {
     }
 }
 
+#[cfg(all(feature = "serde", feature = "encode"))]
 impl<'de> Deserialize<'de> for SilentPaymentAddress {
     fn deserialize<D>(deserializer: D) -> std::result::Result<Self, D::Error>
     where
@@ -91,6 +105,38 @@ impl<'de> Deserialize<'de> for SilentPaymentAddress {
 }
 
 impl SilentPaymentAddress {
+    /// Construct a `SilentPaymentAddress` from its component parts.
+    ///
+    /// This constructor is always available, even without the `encode` feature.
+    /// If you have your own bech32 parser, you can use it to extract the components
+    /// and then construct the address using this method.
+    ///
+    /// # Bech32 Format (for external parsers)
+    ///
+    /// Silent payment addresses use bech32m encoding with the following structure:
+    /// - **HRP (Human Readable Part)**:
+    ///   - Mainnet: `"sp"`
+    ///   - Testnet/Signet: `"tsp"`
+    ///   - Regtest: `"sprt"`
+    /// - **Data**: version (1 byte) + scan_pubkey (33 bytes) + spend_pubkey (33 bytes)
+    ///
+    /// # Example
+    ///
+    /// ```ignore
+    /// use secp256k1::PublicKey;
+    /// use silentpayments::{SilentPaymentAddress, Network};
+    ///
+    /// // After parsing bech32 yourself and extracting the pubkeys:
+    /// let scan_pubkey = PublicKey::from_slice(&scan_bytes)?;
+    /// let spend_pubkey = PublicKey::from_slice(&spend_bytes)?;
+    ///
+    /// let address = SilentPaymentAddress::new(
+    ///     scan_pubkey,
+    ///     spend_pubkey,
+    ///     Network::Mainnet,
+    ///     0  // version
+    /// )?;
+    /// ```
     pub fn new(
         scan_pubkey: PublicKey,
         m_pubkey: PublicKey,
@@ -111,25 +157,35 @@ impl SilentPaymentAddress {
         })
     }
 
+    /// Get the scan public key.
     pub fn get_scan_key(&self) -> PublicKey {
         self.scan_pubkey
     }
 
+    /// Get the spend public key.
     pub fn get_spend_key(&self) -> PublicKey {
         self.m_pubkey
     }
 
+    /// Get the network.
     pub fn get_network(&self) -> Network {
         self.network
     }
+
+    /// Get the version byte.
+    pub fn get_version(&self) -> u8 {
+        self.version
+    }
 }
 
+#[cfg(feature = "encode")]
 impl fmt::Display for SilentPaymentAddress {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         write!(f, "{}", <SilentPaymentAddress as Into<String>>::into(*self))
     }
 }
 
+#[cfg(feature = "encode")]
 impl TryFrom<&str> for SilentPaymentAddress {
     type Error = Error;
 
@@ -163,6 +219,7 @@ impl TryFrom<&str> for SilentPaymentAddress {
     }
 }
 
+#[cfg(feature = "encode")]
 impl TryFrom<String> for SilentPaymentAddress {
     type Error = Error;
 
@@ -171,6 +228,7 @@ impl TryFrom<String> for SilentPaymentAddress {
     }
 }
 
+#[cfg(feature = "encode")]
 impl From<SilentPaymentAddress> for String {
     fn from(val: SilentPaymentAddress) -> Self {
         let hrp = match val.network {