Safe load_or_generate_self_public_key

The function is made safe and now returns Result.  Functionally it now
fails when it can not write the newly generated key to the database
whereas before it still returned the key but logged a warning.  There
is no reason this shouldn't be able to store the key and silently not
storing the key may result in later operations assuming the key is
available, so failing seems like a better choice.

The function now also uses a proper mutex to guard against multiple
threads generating keys.  And this mutex is Context-scoped rather than
fully global (static).

src/dc_e2ee.rs

@@ -1,3 +1,5 @@
+//! End-to-end encryption support.
+
 use std::collections::HashSet;
 use std::ffi::CStr;
 use std::str::FromStr;
@@ -98,9 +100,11 @@ pub unsafe fn dc_e2ee_encrypt(
         let addr = context.sql.get_config(context, "configured_addr");
 
         if let Some(addr) = addr {
-            if let Some(public_key) =
-                load_or_generate_self_public_key(context, &addr, in_out_message)
-            {
+            let pubkey_ret = load_or_generate_self_public_key(context, &addr).map_err(|err| {
+                error!(context, 0, "Failed to load public key: {}", err);
+                err
+            });
+            if let Ok(public_key) = pubkey_ret {
                 /*only for random-seed*/
                 if prefer_encrypt == EncryptPreference::Mutual || 0 != e2ee_guaranteed {
                     do_encrypt = 1i32;
@@ -475,65 +479,52 @@ unsafe fn new_data_part(
     return 0 as *mut mailmime;
 }
 
-/*******************************************************************************
- * Generate Keypairs
- ******************************************************************************/
-unsafe fn load_or_generate_self_public_key(
-    context: &Context,
-    self_addr: impl AsRef<str>,
-    _random_data_mime: *mut mailmime,
-) -> Option<Key> {
-    /* avoid double creation (we unlock the database during creation) */
-    static mut S_IN_KEY_CREATION: libc::c_int = 0;
+/// Load public key from database or generate a new one.
+///
+/// This will load a public key from the database, generating and
+/// storing a new one when one doesn't exist yet.  Care is taken to
+/// only generate one key per context even when multiple threads call
+/// this function concurrently.
+fn load_or_generate_self_public_key(context: &Context, self_addr: impl AsRef<str>) -> Result<Key> {
+    if let Some(key) = Key::from_self_public(context, &self_addr, &context.sql) {
+        return Ok(key);
+    }
+    let _guard = context.generating_key_mutex.lock().unwrap();
 
-    let mut key = Key::from_self_public(context, &self_addr, &context.sql);
-    if key.is_some() {
-        return key;
+    // Check again in case the key was generated while we were waiting for the lock.
+    if let Some(key) = Key::from_self_public(context, &self_addr, &context.sql) {
+        return Ok(key);
     }
 
-    /* create the keypair - this may take a moment, however, as this is in a thread, this is no big deal */
-    if 0 != S_IN_KEY_CREATION {
-        return None;
-    }
-    let key_creation_here = 1;
-    S_IN_KEY_CREATION = 1;
-
-    let start = clock();
+    let start = std::time::Instant::now();
     info!(
         context,
         0, "Generating keypair with {} bits, e={} ...", 2048, 65537,
     );
-
-    if let Some((public_key, private_key)) = dc_pgp_create_keypair(&self_addr) {
-        if !dc_key_save_self_keypair(
-            context,
-            &public_key,
-            &private_key,
-            &self_addr,
-            1i32,
-            &context.sql,
-        ) {
-            /*set default*/
-            warn!(context, 0, "Cannot save keypair.",);
-        } else {
-            info!(
+    match dc_pgp_create_keypair(&self_addr) {
+        Some((public_key, private_key)) => {
+            match dc_key_save_self_keypair(
                 context,
-                0,
-                "Keypair generated in {:.3}s.",
-                clock().wrapping_sub(start) as libc::c_double / 1000000 as libc::c_double,
-            );
+                &public_key,
+                &private_key,
+                &self_addr,
+                1,
+                &context.sql,
+            ) {
+                true => {
+                    info!(
+                        context,
+                        0,
+                        "Keypair generated in {:.3}s.",
+                        start.elapsed().as_secs()
+                    );
+                    Ok(public_key)
+                }
+                false => Err(format_err!("Failed to save keypair")),
+            }
         }
-
-        key = Some(public_key);
-    } else {
-        warn!(context, 0, "Cannot create keypair.");
+        None => Err(format_err!("Failed to generate keypair")),
     }
-
-    if 0 != key_creation_here {
-        S_IN_KEY_CREATION = 0;
-    }
-
-    key
 }
 
 /* returns 1 if sth. was decrypted, 0 in other cases */
@@ -1050,8 +1041,7 @@ pub unsafe fn dc_e2ee_thanks(helper: &mut dc_e2ee_helper_t) {
 /// Ensures a private key exists for the configured user.
 ///
 /// Normally the private key is generated when the first message is
-/// sent (allowing the use of some extra random seed from the message
-/// content) but in a few locations there are no such guarantees,
+/// sent but in a few locations there are no such guarantees,
 /// e.g. when exporting keys, and calling this function ensures a
 /// private key will be present.
 ///
@@ -1064,10 +1054,7 @@ pub fn dc_ensure_secret_key_exists(context: &Context) -> Result<String> {
             "Failed to get self address, ",
             "cannot ensure secret key if not configured."
         )))?;
-    unsafe {
-        load_or_generate_self_public_key(context, &self_addr, 0 as *mut mailmime)
-            .ok_or(format_err!("Failed to generate private key."))?;
-    }
+    load_or_generate_self_public_key(context, &self_addr)?;
     Ok(self_addr)
 }
 
@@ -1154,4 +1141,47 @@ Sent with my Delta Chat Messenger: https://delta.chat";
 
         unsafe { free(decrypted_mime as *mut _) };
     }
+
+    mod load_or_generate_self_public_key {
+        use super::*;
+
+        #[test]
+        fn test_existing() {
+            let t = dummy_context();
+            let addr = configure_alice_keypair(&t.ctx);
+            let key = load_or_generate_self_public_key(&t.ctx, addr);
+            assert!(key.is_ok());
+        }
+
+        #[test]
+        #[ignore] // generating keys is expensive
+        fn test_generate() {
+            let t = dummy_context();
+            let addr = "alice@example.org";
+            let key0 = load_or_generate_self_public_key(&t.ctx, addr);
+            assert!(key0.is_ok());
+            let key1 = load_or_generate_self_public_key(&t.ctx, addr);
+            assert!(key1.is_ok());
+            assert_eq!(key0.unwrap(), key1.unwrap());
+        }
+
+        #[test]
+        #[ignore]
+        fn test_generate_concurrent() {
+            use std::sync::Arc;
+            use std::thread;
+
+            let t = dummy_context();
+            let ctx = Arc::new(t.ctx);
+            let ctx0 = Arc::clone(&ctx);
+            let thr0 =
+                thread::spawn(move || load_or_generate_self_public_key(&ctx0, "alice@example.org"));
+            let ctx1 = Arc::clone(&ctx);
+            let thr1 =
+                thread::spawn(move || load_or_generate_self_public_key(&ctx1, "alice@example.org"));
+            let res0 = thr0.join().unwrap();
+            let res1 = thr1.join().unwrap();
+            assert_eq!(res0.unwrap(), res1.unwrap());
+        }
+    }
 }