Pull out initialization code so that `PublicKey::from_secret_key` can be used safely

src/key.rs

@@ -7,6 +7,7 @@ use constants;
 use ffi;
 
 use super::{Result, InvalidNonce, InvalidPublicKey, InvalidSecretKey};
+use super::init;
 
 /// Secret 256-bit nonce used as `k` in an ECDSA signature
 pub struct Nonce([u8, ..constants::NONCE_SIZE]);
@@ -124,20 +125,22 @@ impl PublicKey {
         )
     }
 
-    /// Creates a new public key from a secret key
+    /// Creates a new public key from a secret key. Marked `unsafe` since you must
+    /// call `init()` (or construct a `Secp256k1`, which does this for you) before
+    /// using this function
     #[inline]
-    pub fn from_secret_key(sk: &SecretKey, compressed: bool) -> PublicKey {
+    pub unsafe fn from_secret_key(sk: &SecretKey, compressed: bool) -> PublicKey {
         let mut pk = PublicKey::new(compressed);
         let compressed = if compressed {1} else {0};
-        unsafe {
         let mut len = 0;
+
         while ffi::secp256k1_ecdsa_pubkey_create(
             pk.as_mut_ptr(), &mut len,
             sk.as_ptr(), compressed) != 1 {
             // loop
         }
         assert_eq!(len as uint, pk.len()); 
-        };
+
         pk
     }
 

src/secp256k1.rs

@@ -25,7 +25,7 @@
 extern crate libc;
 extern crate sync;
 
-use std::io::IoError;
+use std::io::{IoError, IoResult};
 use std::rand::OsRng;
 use libc::c_int;
 use sync::one::{Once, ONCE_INIT};
@@ -84,28 +84,40 @@ pub struct Secp256k1 {
     rng: OsRng
 }
 
-impl Secp256k1 {
+/// Does one-time initialization of the secp256k1 engine. Can be called
-    /// Constructs a new secp256k1 engine.
+/// multiple times, and is called by the `Secp256k1` constructor. This
-    pub fn new() -> Result<Secp256k1> {
+/// only needs to be called directly if you are using the library without
+/// a `Secp256k1` object, e.g. batch key generation through
+/// `key::PublicKey::from_secret_key`.
+pub fn init() {
     unsafe {
         Secp256k1_init.doit(|| {
             ffi::secp256k1_start();
         });
     }
+}
+
+impl Secp256k1 {
+    /// Constructs a new secp256k1 engine.
+    pub fn new() -> Result<Secp256k1> {
+        init();
         match OsRng::new() {
             Ok(rng) => Ok(Secp256k1 { rng: rng }),
             Err(e) => Err(RngError(e))
         }
     }
 
-    /// Generates a randam keypair
+    /// Generates a random keypair. Convenience function for `key::SecretKey::new`
+    /// and `key::PublicKey::from_secret_key`; call those functions directly for
+    /// batch key generation.
     pub fn generate_keypair(&mut self, compressed: bool)
                             -> (key::SecretKey, key::PublicKey) {
         let sk = key::SecretKey::new(&mut self.rng);
-        (sk, key::PublicKey::from_secret_key(&sk, compressed))
+        unsafe { (sk, key::PublicKey::from_secret_key(&sk, compressed)) }
     }
 
-    /// Generates a random nonce
+    /// Generates a random nonce. Convenience function for `key::Nonce::new`; call
+    /// that function directly for batch nonce generation
     pub fn generate_nonce(&mut self) -> key::Nonce {
         key::Nonce::new(&mut self.rng)
     }