From 4a7e83f0af8a1e7fab3faa7e348dcd62216409e5 Mon Sep 17 00:00:00 2001
From: gwenn <gtreguier@gmail.com>
Date: Sat, 1 Aug 2015 17:21:41 +0200
Subject: [PATCH 01/13] Feature sqlite3_{log,trace,profile}.

---
 Cargo.toml                |  1 +
 libsqlite3-sys/src/lib.rs |  2 +
 src/lib.rs                |  4 +-
 src/trace_extension.rs    | 98 +++++++++++++++++++++++++++++++++++++++
 4 files changed, 104 insertions(+), 1 deletion(-)
 create mode 100644 src/trace_extension.rs

diff --git a/Cargo.toml b/Cargo.toml
index 5d05ed5..772b4cc 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -14,6 +14,7 @@ name = "rusqlite"
 
 [features]
 load_extension = ["libsqlite3-sys/load_extension"]
+trace_extension = []
 
 [dependencies]
 time = "~0.1.0"
diff --git a/libsqlite3-sys/src/lib.rs b/libsqlite3-sys/src/lib.rs
index 5d37276..51f33c5 100644
--- a/libsqlite3-sys/src/lib.rs
+++ b/libsqlite3-sys/src/lib.rs
@@ -92,3 +92,5 @@ pub fn code_to_str(code: c_int) -> &'static str {
         _                => "Unknown error code",
     }
 }
+
+pub const SQLITE_CONFIG_LOG  : c_int = 16;
diff --git a/src/lib.rs b/src/lib.rs
index f98780b..d96fdfd 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -50,6 +50,7 @@
 //!     }
 //! }
 //! ```
+#![cfg_attr(test, feature(duration))]
 extern crate libc;
 extern crate libsqlite3_sys as ffi;
 #[macro_use] extern crate bitflags;
@@ -79,6 +80,7 @@ pub use transaction::{SqliteTransactionBehavior,
 pub mod types;
 mod transaction;
 #[cfg(feature = "load_extension")] mod load_extension_guard;
+#[cfg(feature = "trace_extension")] pub mod trace_extension;
 
 /// A typedef of the result returned by many methods.
 pub type SqliteResult<T> = Result<T, SqliteError>;
@@ -664,7 +666,7 @@ impl<'conn> SqliteStatement<'conn> {
     }
 
     /// Executes the prepared statement and maps a function over the resulting
-    /// rows. 
+    /// rows.
     ///
     /// Unlike the iterator produced by `query`, the returned iterator does not expose the possibility
     /// for accessing stale rows.
diff --git a/src/trace_extension.rs b/src/trace_extension.rs
new file mode 100644
index 0000000..cde1d75
--- /dev/null
+++ b/src/trace_extension.rs
@@ -0,0 +1,98 @@
+use libc::{c_char, c_int, c_void};
+use std::ffi::CString;
+use std::ptr;
+
+use super::ffi;
+use {SqliteError, SqliteResult, SqliteConnection};
+
+pub type LogCallback =
+    Option<extern "C" fn (udp: *mut c_void, err: c_int, msg: *const c_char)>;
+
+/// Set up the error logging callback
+///
+/// cf [The Error And Warning Log](http://sqlite.org/errlog.html).
+pub fn config_log(cb: LogCallback) -> SqliteResult<()> {
+    let rc = unsafe {
+        let p_arg: *mut c_void = ptr::null_mut();
+        ffi::sqlite3_config(ffi::SQLITE_CONFIG_LOG, cb, p_arg)
+    };
+    if rc != ffi::SQLITE_OK {
+        return Err(SqliteError{ code: rc, message: "sqlite3_config(SQLITE_CONFIG_LOG, ...)".to_string() });
+    }
+    Ok(())
+}
+
+/// Write a message into the error log established by `config_log`.
+pub fn log(err_code: c_int, msg: &str) {
+    let msg = CString::new(msg).unwrap();
+    unsafe {
+        ffi::sqlite3_log(err_code, msg.as_ptr());
+    }
+}
+
+pub type TraceCallback =
+    Option<extern "C" fn (p_arg: *mut c_void, z_sql: *const c_char)>;
+pub type ProfileCallback =
+    Option<extern "C" fn (p_arg: *mut c_void, z_sql: *const c_char, nanoseconds: u64)>;
+impl SqliteConnection {
+    /// Register or clear a callback function that can be used for tracing the execution of SQL statements.
+    /// Prepared statement placeholders are replaced/logged with their assigned values.
+    /// There can only be a single tracer defined for each database connection.
+    /// Setting a new tracer clears the old one.
+    pub fn trace(&mut self, x_trace: TraceCallback) {
+        let c = self.db.borrow_mut();
+        unsafe { ffi::sqlite3_trace(c.db(), x_trace, ptr::null_mut()); }
+    }
+    /// Register or clear a callback function that can be used for profiling the execution of SQL statements.
+    /// There can only be a single profiler defined for each database connection.
+    /// Setting a new profiler clears the old one.
+    pub fn profile(&mut self, x_profile: ProfileCallback) {
+        let c = self.db.borrow_mut();
+        unsafe { ffi::sqlite3_profile(c.db(), x_profile, ptr::null_mut()); }
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use libc::{c_char, c_int, c_void};
+    use std::ffi::CStr;
+    use std::io::Write;
+    use std::str;
+
+    use ffi;
+    use SqliteConnection;
+
+    extern "C" fn log_callback(_: *mut c_void, err: c_int, msg: *const c_char) {
+        unsafe {
+            let c_slice = CStr::from_ptr(msg).to_bytes();
+            let _ = writeln!(::std::io::stderr(), "{}: {:?}", err, str::from_utf8(c_slice));
+        }
+    }
+
+    #[test]
+    fn test_log() {
+        if true { // To avoid freezing tests
+            return
+        }
+        unsafe { ffi::sqlite3_shutdown() };
+        super::config_log(Some(log_callback)).unwrap();
+        //super::log(ffi::SQLITE_NOTICE, "message from rusqlite");
+        super::config_log(None).unwrap();
+    }
+
+    extern "C" fn profile_callback(_: *mut ::libc::c_void, sql: *const ::libc::c_char, nanoseconds: u64) {
+        use std::time::Duration;
+        unsafe {
+            let c_slice = ::std::ffi::CStr::from_ptr(sql).to_bytes();
+            let d = Duration::from_millis(nanoseconds / 1_000_000);
+            let _ = writeln!(::std::io::stderr(), "PROFILE: {:?} ({})", ::std::str::from_utf8(c_slice), d);
+        }
+    }
+
+    #[test]
+    fn test_profile() {
+        let mut db = SqliteConnection::open_in_memory().unwrap();
+        db.profile(Some(profile_callback));
+        db.execute_batch("PRAGMA application_id = 1").unwrap();
+    }
+}
\ No newline at end of file

From ef254fdca00d2fbf79830e0f1abb3e6dcef9f702 Mon Sep 17 00:00:00 2001
From: gwenn <gtreguier@gmail.com>
Date: Sat, 1 Aug 2015 18:58:04 +0200
Subject: [PATCH 02/13] Rename feature to 'trace'

---
 Cargo.toml                           | 2 +-
 src/lib.rs                           | 2 +-
 src/{trace_extension.rs => trace.rs} | 0
 3 files changed, 2 insertions(+), 2 deletions(-)
 rename src/{trace_extension.rs => trace.rs} (100%)

diff --git a/Cargo.toml b/Cargo.toml
index 772b4cc..777d50c 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -14,7 +14,7 @@ name = "rusqlite"
 
 [features]
 load_extension = ["libsqlite3-sys/load_extension"]
-trace_extension = []
+trace = []
 
 [dependencies]
 time = "~0.1.0"
diff --git a/src/lib.rs b/src/lib.rs
index d96fdfd..3c03fef 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -80,7 +80,7 @@ pub use transaction::{SqliteTransactionBehavior,
 pub mod types;
 mod transaction;
 #[cfg(feature = "load_extension")] mod load_extension_guard;
-#[cfg(feature = "trace_extension")] pub mod trace_extension;
+#[cfg(feature = "trace")] pub mod trace;
 
 /// A typedef of the result returned by many methods.
 pub type SqliteResult<T> = Result<T, SqliteError>;
diff --git a/src/trace_extension.rs b/src/trace.rs
similarity index 100%
rename from src/trace_extension.rs
rename to src/trace.rs

From 9c415f9c9e433101564767603e0be7aa341c7343 Mon Sep 17 00:00:00 2001
From: Gwenael Treguier <gwen@cas75-5-78-192-41-37.fbxo.proxad.net>
Date: Sun, 2 Aug 2015 12:16:01 +0200
Subject: [PATCH 03/13] Remove usage of unstable library feature 'duration'

---
 src/lib.rs   |  1 -
 src/trace.rs | 10 ++++------
 2 files changed, 4 insertions(+), 7 deletions(-)

diff --git a/src/lib.rs b/src/lib.rs
index 3c03fef..4dfd068 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -50,7 +50,6 @@
 //!     }
 //! }
 //! ```
-#![cfg_attr(test, feature(duration))]
 extern crate libc;
 extern crate libsqlite3_sys as ffi;
 #[macro_use] extern crate bitflags;
diff --git a/src/trace.rs b/src/trace.rs
index cde1d75..de03742 100644
--- a/src/trace.rs
+++ b/src/trace.rs
@@ -80,19 +80,17 @@ mod test {
         super::config_log(None).unwrap();
     }
 
-    extern "C" fn profile_callback(_: *mut ::libc::c_void, sql: *const ::libc::c_char, nanoseconds: u64) {
-        use std::time::Duration;
+    extern "C" fn trace_callback(_: *mut ::libc::c_void, sql: *const ::libc::c_char) {
         unsafe {
             let c_slice = ::std::ffi::CStr::from_ptr(sql).to_bytes();
-            let d = Duration::from_millis(nanoseconds / 1_000_000);
-            let _ = writeln!(::std::io::stderr(), "PROFILE: {:?} ({})", ::std::str::from_utf8(c_slice), d);
+            let _ = writeln!(::std::io::stderr(), "TRACE: {:?}", ::std::str::from_utf8(c_slice));
         }
     }
 
     #[test]
-    fn test_profile() {
+    fn test_trace() {
         let mut db = SqliteConnection::open_in_memory().unwrap();
-        db.profile(Some(profile_callback));
+        db.trace(Some(trace_callback));
         db.execute_batch("PRAGMA application_id = 1").unwrap();
     }
 }
\ No newline at end of file

From 59a4c5593a92c61058bff40ed64edd2a07f5423f Mon Sep 17 00:00:00 2001
From: Gwenael Treguier <gwen@cas75-5-78-192-41-37.fbxo.proxad.net>
Date: Sat, 8 Aug 2015 09:57:07 +0200
Subject: [PATCH 04/13] Improve documentation.

---
 src/trace.rs | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/trace.rs b/src/trace.rs
index de03742..b3c9939 100644
--- a/src/trace.rs
+++ b/src/trace.rs
@@ -1,3 +1,4 @@
+//! Tracing and profiling functions. Error and warning log.
 use libc::{c_char, c_int, c_void};
 use std::ffi::CString;
 use std::ptr;
@@ -30,12 +31,16 @@ pub fn log(err_code: c_int, msg: &str) {
     }
 }
 
+/// The trace callback function signature.
 pub type TraceCallback =
     Option<extern "C" fn (p_arg: *mut c_void, z_sql: *const c_char)>;
+/// The profile callback function signature.
 pub type ProfileCallback =
     Option<extern "C" fn (p_arg: *mut c_void, z_sql: *const c_char, nanoseconds: u64)>;
+
 impl SqliteConnection {
     /// Register or clear a callback function that can be used for tracing the execution of SQL statements.
+    ///
     /// Prepared statement placeholders are replaced/logged with their assigned values.
     /// There can only be a single tracer defined for each database connection.
     /// Setting a new tracer clears the old one.
@@ -44,6 +49,7 @@ impl SqliteConnection {
         unsafe { ffi::sqlite3_trace(c.db(), x_trace, ptr::null_mut()); }
     }
     /// Register or clear a callback function that can be used for profiling the execution of SQL statements.
+    ///
     /// There can only be a single profiler defined for each database connection.
     /// Setting a new profiler clears the old one.
     pub fn profile(&mut self, x_profile: ProfileCallback) {

From 50bfba1e1d5192aa78069bf88fdc57236f2afb38 Mon Sep 17 00:00:00 2001
From: Gwenael Treguier <gwen@cas75-5-78-192-41-37.fbxo.proxad.net>
Date: Wed, 11 Nov 2015 14:29:40 +0100
Subject: [PATCH 05/13] Ignore test_log.

---
 src/trace.rs | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/src/trace.rs b/src/trace.rs
index b3c9939..29473a2 100644
--- a/src/trace.rs
+++ b/src/trace.rs
@@ -75,11 +75,8 @@ mod test {
         }
     }
 
-    #[test]
+    #[test] #[ignore] // To avoid freezing tests
     fn test_log() {
-        if true { // To avoid freezing tests
-            return
-        }
         unsafe { ffi::sqlite3_shutdown() };
         super::config_log(Some(log_callback)).unwrap();
         //super::log(ffi::SQLITE_NOTICE, "message from rusqlite");
@@ -99,4 +96,4 @@ mod test {
         db.trace(Some(trace_callback));
         db.execute_batch("PRAGMA application_id = 1").unwrap();
     }
-}
\ No newline at end of file
+}

From a2327fb048c96297ecad41243b4b4d04dfb7367b Mon Sep 17 00:00:00 2001
From: Gwenael Treguier <gwen@cas75-5-78-192-41-37.fbxo.proxad.net>
Date: Wed, 11 Nov 2015 15:00:39 +0100
Subject: [PATCH 06/13] Revert "Remove usage of unstable library feature
 'duration'"

This reverts commit 9c415f9c9e433101564767603e0be7aa341c7343.
---
 src/lib.rs   |  1 +
 src/trace.rs | 10 ++++++----
 2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/src/lib.rs b/src/lib.rs
index c639831..c6f82ce 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -50,6 +50,7 @@
 //!     }
 //! }
 //! ```
+#![cfg_attr(test, feature(duration))]
 extern crate libc;
 extern crate libsqlite3_sys as ffi;
 #[macro_use] extern crate bitflags;
diff --git a/src/trace.rs b/src/trace.rs
index 29473a2..b024f13 100644
--- a/src/trace.rs
+++ b/src/trace.rs
@@ -83,17 +83,19 @@ mod test {
         super::config_log(None).unwrap();
     }
 
-    extern "C" fn trace_callback(_: *mut ::libc::c_void, sql: *const ::libc::c_char) {
+    extern "C" fn profile_callback(_: *mut ::libc::c_void, sql: *const ::libc::c_char, nanoseconds: u64) {
+        use std::time::Duration;
         unsafe {
             let c_slice = ::std::ffi::CStr::from_ptr(sql).to_bytes();
-            let _ = writeln!(::std::io::stderr(), "TRACE: {:?}", ::std::str::from_utf8(c_slice));
+            let d = Duration::from_millis(nanoseconds / 1_000_000);
+            let _ = writeln!(::std::io::stderr(), "PROFILE: {:?} ({})", ::std::str::from_utf8(c_slice), d);
         }
     }
 
     #[test]
-    fn test_trace() {
+    fn test_profile() {
         let mut db = SqliteConnection::open_in_memory().unwrap();
-        db.trace(Some(trace_callback));
+        db.profile(Some(profile_callback));
         db.execute_batch("PRAGMA application_id = 1").unwrap();
     }
 }

From 20c1213482ddd1bf5c19ebc4994b103f76d991f9 Mon Sep 17 00:00:00 2001
From: Gwenael Treguier <gwen@cas75-5-78-192-41-37.fbxo.proxad.net>
Date: Wed, 11 Nov 2015 15:03:07 +0100
Subject: [PATCH 07/13] Remove feature duration.

---
 src/lib.rs | 1 -
 1 file changed, 1 deletion(-)

diff --git a/src/lib.rs b/src/lib.rs
index c6f82ce..c639831 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -50,7 +50,6 @@
 //!     }
 //! }
 //! ```
-#![cfg_attr(test, feature(duration))]
 extern crate libc;
 extern crate libsqlite3_sys as ffi;
 #[macro_use] extern crate bitflags;

From dbfa6ca31f0c839dcc3afd33861d909265fd6f59 Mon Sep 17 00:00:00 2001
From: John Gallagher <jgallagher@bignerdranch.com>
Date: Mon, 30 Nov 2015 15:29:50 -0500
Subject: [PATCH 08/13] Change config_log to take a Rust fn instead of an
 extern "C" fn.

Moves the unit test for config_log out of #[ignore] and into its own
test file since it affects the entire process.
---
 Cargo.toml          |  5 ++++
 src/trace.rs        | 65 ++++++++++++++++++++++++---------------------
 tests/config_log.rs | 36 +++++++++++++++++++++++++
 3 files changed, 76 insertions(+), 30 deletions(-)
 create mode 100644 tests/config_log.rs

diff --git a/Cargo.toml b/Cargo.toml
index 673044c..0078216 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -23,7 +23,12 @@ libc = "~0.1"
 
 [dev-dependencies]
 tempdir = "~0.3.4"
+lazy_static = "~0.1"
 
 [dependencies.libsqlite3-sys]
 path = "libsqlite3-sys"
 version = "0.2.0"
+
+[[test]]
+name = "config_log"
+harness = false
diff --git a/src/trace.rs b/src/trace.rs
index b024f13..33b5997 100644
--- a/src/trace.rs
+++ b/src/trace.rs
@@ -1,31 +1,55 @@
 //! Tracing and profiling functions. Error and warning log.
+
 use libc::{c_char, c_int, c_void};
-use std::ffi::CString;
+use std::ffi::{CStr, CString};
 use std::ptr;
+use std::str;
 
 use super::ffi;
 use {SqliteError, SqliteResult, SqliteConnection};
 
-pub type LogCallback =
-    Option<extern "C" fn (udp: *mut c_void, err: c_int, msg: *const c_char)>;
-
-/// Set up the error logging callback
+/// Set up the process-wide SQLite error logging callback.
+/// This function is marked unsafe for two reasons:
+///
+/// * The function is not threadsafe. No other SQLite calls may be made while
+///   `config_log` is running, and multiple threads may not call `config_log`
+///   simultaneously.
+/// * The provided `callback` itself function has two requirements:
+///     * It must not invoke any SQLite calls.
+///     * It must be threadsafe if SQLite is used in a multithreaded way.
 ///
 /// cf [The Error And Warning Log](http://sqlite.org/errlog.html).
-pub fn config_log(cb: LogCallback) -> SqliteResult<()> {
-    let rc = unsafe {
-        let p_arg: *mut c_void = ptr::null_mut();
-        ffi::sqlite3_config(ffi::SQLITE_CONFIG_LOG, cb, p_arg)
+pub unsafe fn config_log(callback: Option<fn(c_int, &str)>) -> SqliteResult<()> {
+    extern "C" fn log_callback(p_arg: *mut c_void, err: c_int, msg: *const c_char) {
+        let c_slice = unsafe { CStr::from_ptr(msg).to_bytes() };
+        let callback: fn(c_int, &str) = unsafe { mem::transmute(p_arg) };
+
+        if let Ok(s) = str::from_utf8(c_slice) {
+            callback(err, s);
+        }
+    }
+
+    let rc = match callback {
+        Some(f) => {
+            let p_arg: *mut c_void = mem::transmute(f);
+            ffi::sqlite3_config(ffi::SQLITE_CONFIG_LOG, Some(log_callback), p_arg)
+        },
+        None => {
+            let nullptr: *mut c_void = ptr::null_mut();
+            ffi::sqlite3_config(ffi::SQLITE_CONFIG_LOG, nullptr, nullptr)
+        }
     };
+
     if rc != ffi::SQLITE_OK {
         return Err(SqliteError{ code: rc, message: "sqlite3_config(SQLITE_CONFIG_LOG, ...)".to_string() });
     }
+
     Ok(())
 }
 
 /// Write a message into the error log established by `config_log`.
 pub fn log(err_code: c_int, msg: &str) {
-    let msg = CString::new(msg).unwrap();
+    let msg = CString::new(msg).expect("SQLite log messages cannot contain embedded zeroes");
     unsafe {
         ffi::sqlite3_log(err_code, msg.as_ptr());
     }
@@ -60,35 +84,16 @@ impl SqliteConnection {
 
 #[cfg(test)]
 mod test {
-    use libc::{c_char, c_int, c_void};
-    use std::ffi::CStr;
     use std::io::Write;
-    use std::str;
 
-    use ffi;
     use SqliteConnection;
 
-    extern "C" fn log_callback(_: *mut c_void, err: c_int, msg: *const c_char) {
-        unsafe {
-            let c_slice = CStr::from_ptr(msg).to_bytes();
-            let _ = writeln!(::std::io::stderr(), "{}: {:?}", err, str::from_utf8(c_slice));
-        }
-    }
-
-    #[test] #[ignore] // To avoid freezing tests
-    fn test_log() {
-        unsafe { ffi::sqlite3_shutdown() };
-        super::config_log(Some(log_callback)).unwrap();
-        //super::log(ffi::SQLITE_NOTICE, "message from rusqlite");
-        super::config_log(None).unwrap();
-    }
-
     extern "C" fn profile_callback(_: *mut ::libc::c_void, sql: *const ::libc::c_char, nanoseconds: u64) {
         use std::time::Duration;
         unsafe {
             let c_slice = ::std::ffi::CStr::from_ptr(sql).to_bytes();
             let d = Duration::from_millis(nanoseconds / 1_000_000);
-            let _ = writeln!(::std::io::stderr(), "PROFILE: {:?} ({})", ::std::str::from_utf8(c_slice), d);
+            let _ = writeln!(::std::io::stderr(), "PROFILE: {:?} ({:?})", ::std::str::from_utf8(c_slice), d);
         }
     }
 
diff --git a/tests/config_log.rs b/tests/config_log.rs
new file mode 100644
index 0000000..e0167bd
--- /dev/null
+++ b/tests/config_log.rs
@@ -0,0 +1,36 @@
+//! This file contains unit tests for rusqlite::trace::config_log. This function affects
+//! SQLite process-wide and so is not safe to run as a normal #[test] in the library.
+
+#[macro_use] extern crate lazy_static;
+extern crate libc;
+extern crate rusqlite;
+
+#[cfg(feature = "trace")]
+fn main() {
+    use libc::c_int;
+    use std::sync::Mutex;
+
+    lazy_static! {
+        static ref LOGS_RECEIVED: Mutex<Vec<(c_int, String)>> = Mutex::new(Vec::new());
+    }
+
+    fn log_handler(err: c_int, message: &str) {
+        let mut logs_received = LOGS_RECEIVED.lock().unwrap();
+        logs_received.push((err, message.to_owned()));
+    }
+
+    use rusqlite::trace;
+
+    unsafe { trace::config_log(Some(log_handler)) }.unwrap();
+    trace::log(10, "First message from rusqlite");
+    unsafe { trace::config_log(None) }.unwrap();
+    trace::log(11, "Second message from rusqlite");
+
+    let logs_received = LOGS_RECEIVED.lock().unwrap();
+    assert_eq!(logs_received.len(), 1);
+    assert_eq!(logs_received[0].0, 10);
+    assert_eq!(logs_received[0].1, "First message from rusqlite");
+}
+
+#[cfg(not(feature = "trace"))]
+fn main() {}

From ace5b1ebdc2e9d31cda1a7bbd928fc09b12f8722 Mon Sep 17 00:00:00 2001
From: John Gallagher <jgallagher@bignerdranch.com>
Date: Mon, 30 Nov 2015 16:33:47 -0500
Subject: [PATCH 09/13] Change trace() to take a Rust fn instead of an extern
 "C" fn.

---
 src/lib.rs   | 10 +---------
 src/trace.rs | 49 ++++++++++++++++++++++++++++++++++++++++++++-----
 2 files changed, 45 insertions(+), 14 deletions(-)

diff --git a/src/lib.rs b/src/lib.rs
index d11b98a..cd24ad9 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -53,6 +53,7 @@
 extern crate libc;
 extern crate libsqlite3_sys as ffi;
 #[macro_use] extern crate bitflags;
+#[cfg(test)] #[macro_use] extern crate lazy_static;
 
 use std::default::Default;
 use std::convert;
@@ -142,15 +143,6 @@ fn path_to_cstring(p: &Path) -> SqliteResult<CString> {
 }
 
 /// A connection to a SQLite database.
-///
-/// ## Warning
-///
-/// Note that despite the fact that most `SqliteConnection` methods take an immutable reference to
-/// `self`, `SqliteConnection` is NOT threadsafe, and using it from multiple threads may result in
-/// runtime panics or data races. The SQLite connection handle has at least two pieces of internal
-/// state (the last insertion ID and the last error message) that rusqlite uses, but wrapping these
-/// APIs in a safe way from Rust would be too restrictive (for example, you would not be able to
-/// prepare multiple statements at the same time).
 pub struct SqliteConnection {
     db: RefCell<InnerSqliteConnection>,
     path: Option<PathBuf>,
diff --git a/src/trace.rs b/src/trace.rs
index 33b5997..1777057 100644
--- a/src/trace.rs
+++ b/src/trace.rs
@@ -2,6 +2,7 @@
 
 use libc::{c_char, c_int, c_void};
 use std::ffi::{CStr, CString};
+use std::mem;
 use std::ptr;
 use std::str;
 
@@ -55,9 +56,6 @@ pub fn log(err_code: c_int, msg: &str) {
     }
 }
 
-/// The trace callback function signature.
-pub type TraceCallback =
-    Option<extern "C" fn (p_arg: *mut c_void, z_sql: *const c_char)>;
 /// The profile callback function signature.
 pub type ProfileCallback =
     Option<extern "C" fn (p_arg: *mut c_void, z_sql: *const c_char, nanoseconds: u64)>;
@@ -68,10 +66,22 @@ impl SqliteConnection {
     /// Prepared statement placeholders are replaced/logged with their assigned values.
     /// There can only be a single tracer defined for each database connection.
     /// Setting a new tracer clears the old one.
-    pub fn trace(&mut self, x_trace: TraceCallback) {
+    pub fn trace(&mut self, trace_fn: Option<fn(&str)>) {
+        extern "C" fn trace_callback (p_arg: *mut c_void, z_sql: *const c_char) {
+            let trace_fn: fn(&str) = unsafe { mem::transmute(p_arg) };
+            let c_slice = unsafe { CStr::from_ptr(z_sql).to_bytes() };
+            if let Ok(s) = str::from_utf8(c_slice) {
+                trace_fn(s);
+            }
+        }
+
         let c = self.db.borrow_mut();
-        unsafe { ffi::sqlite3_trace(c.db(), x_trace, ptr::null_mut()); }
+        match trace_fn {
+            Some(f) => unsafe { ffi::sqlite3_trace(c.db(), Some(trace_callback), mem::transmute(f)); },
+            None    => unsafe { ffi::sqlite3_trace(c.db(), None, ptr::null_mut()); },
+        }
     }
+
     /// Register or clear a callback function that can be used for profiling the execution of SQL statements.
     ///
     /// There can only be a single profiler defined for each database connection.
@@ -85,9 +95,38 @@ impl SqliteConnection {
 #[cfg(test)]
 mod test {
     use std::io::Write;
+    use std::sync::Mutex;
 
     use SqliteConnection;
 
+    #[test]
+    fn test_trace() {
+        lazy_static! {
+            static ref TRACED_STMTS: Mutex<Vec<String>> = Mutex::new(Vec::new());
+        }
+        fn tracer(s: &str) {
+            let mut traced_stmts = TRACED_STMTS.lock().unwrap();
+            traced_stmts.push(s.to_owned());
+        }
+
+        let mut db = SqliteConnection::open_in_memory().unwrap();
+        db.trace(Some(tracer));
+        {
+            let _ = db.query_row("SELECT ?", &[&1i32], |_| {});
+            let _ = db.query_row("SELECT ?", &[&"hello"], |_| {});
+        }
+        db.trace(None);
+        {
+            let _ = db.query_row("SELECT ?", &[&2i32], |_| {});
+            let _ = db.query_row("SELECT ?", &[&"goodbye"], |_| {});
+        }
+
+        let traced_stmts = TRACED_STMTS.lock().unwrap();
+        assert_eq!(traced_stmts.len(), 2);
+        assert_eq!(traced_stmts[0], "SELECT 1");
+        assert_eq!(traced_stmts[1], "SELECT 'hello'");
+    }
+
     extern "C" fn profile_callback(_: *mut ::libc::c_void, sql: *const ::libc::c_char, nanoseconds: u64) {
         use std::time::Duration;
         unsafe {

From e6fef5107dd599bb4dd8dcec12fbb1889bf3334f Mon Sep 17 00:00:00 2001
From: John Gallagher <jgallagher@bignerdranch.com>
Date: Tue, 1 Dec 2015 10:34:18 -0500
Subject: [PATCH 10/13] Change profile() to take a Rust fn instead of an extern
 "C" fn.

---
 src/trace.rs | 51 ++++++++++++++++++++++++++++++++++-----------------
 1 file changed, 34 insertions(+), 17 deletions(-)

diff --git a/src/trace.rs b/src/trace.rs
index 1777057..4296ddc 100644
--- a/src/trace.rs
+++ b/src/trace.rs
@@ -5,6 +5,7 @@ use std::ffi::{CStr, CString};
 use std::mem;
 use std::ptr;
 use std::str;
+use std::time::Duration;
 
 use super::ffi;
 use {SqliteError, SqliteResult, SqliteConnection};
@@ -56,10 +57,6 @@ pub fn log(err_code: c_int, msg: &str) {
     }
 }
 
-/// The profile callback function signature.
-pub type ProfileCallback =
-    Option<extern "C" fn (p_arg: *mut c_void, z_sql: *const c_char, nanoseconds: u64)>;
-
 impl SqliteConnection {
     /// Register or clear a callback function that can be used for tracing the execution of SQL statements.
     ///
@@ -86,16 +83,31 @@ impl SqliteConnection {
     ///
     /// There can only be a single profiler defined for each database connection.
     /// Setting a new profiler clears the old one.
-    pub fn profile(&mut self, x_profile: ProfileCallback) {
+    pub fn profile(&mut self, profile_fn: Option<fn(&str, Duration)>) {
+        extern "C" fn profile_callback(p_arg: *mut c_void, z_sql: *const c_char, nanoseconds: u64) {
+            let profile_fn: fn(&str, Duration) = unsafe { mem::transmute(p_arg) };
+            let c_slice = unsafe { CStr::from_ptr(z_sql).to_bytes() };
+            if let Ok(s) = str::from_utf8(c_slice) {
+                const NANOS_PER_SEC: u64 = 1_000_000_000;
+
+                let duration = Duration::new(nanoseconds / NANOS_PER_SEC,
+                                             (nanoseconds % NANOS_PER_SEC) as u32);
+                profile_fn(s, duration);
+            }
+        }
+
         let c = self.db.borrow_mut();
-        unsafe { ffi::sqlite3_profile(c.db(), x_profile, ptr::null_mut()); }
+        match profile_fn {
+            Some(f) => unsafe { ffi::sqlite3_profile(c.db(), Some(profile_callback), mem::transmute(f)) },
+            None    => unsafe { ffi::sqlite3_profile(c.db(), None, ptr::null_mut()) },
+        };
     }
 }
 
 #[cfg(test)]
 mod test {
-    use std::io::Write;
     use std::sync::Mutex;
+    use std::time::Duration;
 
     use SqliteConnection;
 
@@ -127,19 +139,24 @@ mod test {
         assert_eq!(traced_stmts[1], "SELECT 'hello'");
     }
 
-    extern "C" fn profile_callback(_: *mut ::libc::c_void, sql: *const ::libc::c_char, nanoseconds: u64) {
-        use std::time::Duration;
-        unsafe {
-            let c_slice = ::std::ffi::CStr::from_ptr(sql).to_bytes();
-            let d = Duration::from_millis(nanoseconds / 1_000_000);
-            let _ = writeln!(::std::io::stderr(), "PROFILE: {:?} ({:?})", ::std::str::from_utf8(c_slice), d);
-        }
-    }
-
     #[test]
     fn test_profile() {
+        lazy_static! {
+            static ref PROFILED: Mutex<Vec<(String, Duration)>> = Mutex::new(Vec::new());
+        }
+        fn profiler(s: &str, d: Duration) {
+            let mut profiled = PROFILED.lock().unwrap();
+            profiled.push((s.to_owned(), d));
+        }
+
         let mut db = SqliteConnection::open_in_memory().unwrap();
-        db.profile(Some(profile_callback));
+        db.profile(Some(profiler));
         db.execute_batch("PRAGMA application_id = 1").unwrap();
+        db.profile(None);
+        db.execute_batch("PRAGMA application_id = 2").unwrap();
+
+        let profiled = PROFILED.lock().unwrap();
+        assert_eq!(profiled.len(), 1);
+        assert_eq!(profiled[0].0, "PRAGMA application_id = 1");
     }
 }

From cba64a7deee3a372612410b3634dc9e822b91e85 Mon Sep 17 00:00:00 2001
From: John Gallagher <jgallagher@bignerdranch.com>
Date: Tue, 1 Dec 2015 10:37:01 -0500
Subject: [PATCH 11/13] Add trace feature to Changelog

---
 Changelog.md | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/Changelog.md b/Changelog.md
index 2987801..5a1eaec 100644
--- a/Changelog.md
+++ b/Changelog.md
@@ -1,3 +1,7 @@
+# Version UPCOMING (TBD)
+
+* Adds `trace` feature that allows the use of SQLite's logging, tracing, and profiling hooks.
+
 # Version 0.4.0 (2015-11-03)
 
 * Adds `Sized` bound to `FromSql` trait as required by RFC 1214.

From 1af3fcd0539a7699ae13d7707d62d6d2f5585491 Mon Sep 17 00:00:00 2001
From: John Gallagher <jgallagher@bignerdranch.com>
Date: Tue, 1 Dec 2015 11:47:55 -0500
Subject: [PATCH 12/13] Fix error messages when failing to convert paths and
 strings to C-compatible versions

---
 src/lib.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/lib.rs b/src/lib.rs
index cae3c59..364d6d9 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -128,14 +128,14 @@ impl SqliteError {
 fn str_to_cstring(s: &str) -> SqliteResult<CString> {
     CString::new(s).map_err(|_| SqliteError{
         code: ffi::SQLITE_MISUSE,
-        message: "Could not convert path to C-combatible string".to_string()
+        message: format!("Could not convert string {} to C-combatible string", s),
     })
 }
 
 fn path_to_cstring(p: &Path) -> SqliteResult<CString> {
     let s = try!(p.to_str().ok_or(SqliteError{
         code: ffi::SQLITE_MISUSE,
-        message: "Could not convert path to UTF-8 string".to_string()
+        message: format!("Could not convert path {} to UTF-8 string", p.to_string_lossy()),
     }));
     str_to_cstring(s)
 }

From 3d654aeed17c22c084764bef48a3d5ad7cd35730 Mon Sep 17 00:00:00 2001
From: John Gallagher <jgallagher@bignerdranch.com>
Date: Tue, 1 Dec 2015 12:05:29 -0500
Subject: [PATCH 13/13] Add more documentation for failure modes of functions
 that return s

---
 CONTRIBUTORS.md |  1 +
 Changelog.md    |  1 +
 src/lib.rs      | 88 +++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 90 insertions(+)

diff --git a/CONTRIBUTORS.md b/CONTRIBUTORS.md
index eca404b..61121a5 100644
--- a/CONTRIBUTORS.md
+++ b/CONTRIBUTORS.md
@@ -9,3 +9,4 @@ rusqlite contributors (sorted alphabetically)
 * [Patrick Fernie](https://github.com/pfernie)
 * [Steve Klabnik](https://github.com/steveklabnik)
 * [krdln](https://github.com/krdln)
+* [Ben Striegel](https://github.com/bstrie)
diff --git a/Changelog.md b/Changelog.md
index 0af134a..f5e1775 100644
--- a/Changelog.md
+++ b/Changelog.md
@@ -3,6 +3,7 @@
 * Slight change to the closure types passed to `query_map` and `query_and_then`:
     * Remove the `'static` requirement on the closure's output type.
     * Give the closure a `&SqliteRow` instead of a `SqliteRow`.
+* Add more documentation for failure modes of functions that return `SqliteResult`s.
 
 # Version 0.4.0 (2015-11-03)
 
diff --git a/src/lib.rs b/src/lib.rs
index 364d6d9..1e77854 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -162,12 +162,21 @@ impl SqliteConnection {
     ///
     /// `SqliteConnection::open(path)` is equivalent to `SqliteConnection::open_with_flags(path,
     /// SQLITE_OPEN_READ_WRITE | SQLITE_OPEN_CREATE)`.
+    ///
+    /// # Failure
+    ///
+    /// Will return `Err` if `path` cannot be converted to a C-compatible string or if the
+    /// underlying SQLite open call fails.
     pub fn open<P: AsRef<Path>>(path: P) -> SqliteResult<SqliteConnection> {
         let flags = Default::default();
         SqliteConnection::open_with_flags(path, flags)
     }
 
     /// Open a new connection to an in-memory SQLite database.
+    ///
+    /// # Failure
+    ///
+    /// Will return `Err` if the underlying SQLite open call fails.
     pub fn open_in_memory() -> SqliteResult<SqliteConnection> {
         let flags = Default::default();
         SqliteConnection::open_in_memory_with_flags(flags)
@@ -177,6 +186,11 @@ impl SqliteConnection {
     ///
     /// Database Connection](http://www.sqlite.org/c3ref/open.html) for a description of valid
     /// flag combinations.
+    ///
+    /// # Failure
+    ///
+    /// Will return `Err` if `path` cannot be converted to a C-compatible string or if the
+    /// underlying SQLite open call fails.
     pub fn open_with_flags<P: AsRef<Path>>(path: P, flags: SqliteOpenFlags)
             -> SqliteResult<SqliteConnection> {
         let c_path = try!(path_to_cstring(path.as_ref()));
@@ -189,6 +203,10 @@ impl SqliteConnection {
     ///
     /// Database Connection](http://www.sqlite.org/c3ref/open.html) for a description of valid
     /// flag combinations.
+    ///
+    /// # Failure
+    ///
+    /// Will return `Err` if the underlying SQLite open call fails.
     pub fn open_in_memory_with_flags(flags: SqliteOpenFlags) -> SqliteResult<SqliteConnection> {
         let c_memory = try!(str_to_cstring(":memory:"));
         InnerSqliteConnection::open_with_flags(&c_memory, flags).map(|db| {
@@ -216,6 +234,10 @@ impl SqliteConnection {
     ///     tx.commit()
     /// }
     /// ```
+    ///
+    /// # Failure
+    ///
+    /// Will return `Err` if the underlying SQLite call fails.
     pub fn transaction<'a>(&'a self) -> SqliteResult<SqliteTransaction<'a>> {
         SqliteTransaction::new(self, SqliteTransactionDeferred)
     }
@@ -223,6 +245,10 @@ impl SqliteConnection {
     /// Begin a new transaction with a specified behavior.
     ///
     /// See `transaction`.
+    ///
+    /// # Failure
+    ///
+    /// Will return `Err` if the underlying SQLite call fails.
     pub fn transaction_with_behavior<'a>(&'a self, behavior: SqliteTransactionBehavior)
             -> SqliteResult<SqliteTransaction<'a>> {
         SqliteTransaction::new(self, behavior)
@@ -243,6 +269,11 @@ impl SqliteConnection {
     ///                         COMMIT;")
     /// }
     /// ```
+    ///
+    /// # Failure
+    ///
+    /// Will return `Err` if `sql` cannot be converted to a C-compatible string or if the
+    /// underlying SQLite call fails.
     pub fn execute_batch(&self, sql: &str) -> SqliteResult<()> {
         self.db.borrow_mut().execute_batch(sql)
     }
@@ -263,6 +294,11 @@ impl SqliteConnection {
     ///     }
     /// }
     /// ```
+    ///
+    /// # Failure
+    ///
+    /// Will return `Err` if `sql` cannot be converted to a C-compatible string or if the
+    /// underlying SQLite call fails.
     pub fn execute(&self, sql: &str, params: &[&ToSql]) -> SqliteResult<c_int> {
         self.prepare(sql).and_then(|mut stmt| stmt.execute(params))
     }
@@ -289,6 +325,11 @@ impl SqliteConnection {
     /// ```
     ///
     /// If the query returns more than one row, all rows except the first are ignored.
+    ///
+    /// # Failure
+    ///
+    /// Will return `Err` if `sql` cannot be converted to a C-compatible string or if the
+    /// underlying SQLite call fails.
     pub fn query_row<T, F>(&self, sql: &str, params: &[&ToSql], f: F) -> SqliteResult<T>
                            where F: FnOnce(SqliteRow) -> T {
         let mut stmt = try!(self.prepare(sql));
@@ -319,6 +360,11 @@ impl SqliteConnection {
     /// ```
     ///
     /// If the query returns more than one row, all rows except the first are ignored.
+    ///
+    /// # Failure
+    ///
+    /// Will return `Err` if `sql` cannot be converted to a C-compatible string or if the
+    /// underlying SQLite call fails.
     pub fn query_row_and_then<T, E, F>(&self, sql: &str, params: &[&ToSql], f: F) -> Result<T, E>
                            where F: FnOnce(SqliteRow) -> Result<T, E>,
                                  E: convert::From<SqliteError> {
@@ -371,6 +417,11 @@ impl SqliteConnection {
     ///     Ok(())
     /// }
     /// ```
+    ///
+    /// # Failure
+    ///
+    /// Will return `Err` if `sql` cannot be converted to a C-compatible string or if the
+    /// underlying SQLite call fails.
     pub fn prepare<'a>(&'a self, sql: &str) -> SqliteResult<SqliteStatement<'a>> {
         self.db.borrow_mut().prepare(self, sql)
     }
@@ -379,6 +430,10 @@ impl SqliteConnection {
     ///
     /// This is functionally equivalent to the `Drop` implementation for `SqliteConnection` except
     /// that it returns any error encountered to the caller.
+    ///
+    /// # Failure
+    ///
+    /// Will return `Err` if the underlying SQLite call fails.
     pub fn close(self) -> SqliteResult<()> {
         let mut db = self.db.borrow_mut();
         db.close()
@@ -398,6 +453,10 @@ impl SqliteConnection {
     ///     conn.load_extension_disable()
     /// }
     /// ```
+    ///
+    /// # Failure
+    ///
+    /// Will return `Err` if the underlying SQLite call fails.
     #[cfg(feature = "load_extension")]
     pub fn load_extension_enable(&self) -> SqliteResult<()> {
         self.db.borrow_mut().enable_load_extension(1)
@@ -406,6 +465,10 @@ impl SqliteConnection {
     /// Disable loading of SQLite extensions.
     ///
     /// See `load_extension_enable` for an example.
+    ///
+    /// # Failure
+    ///
+    /// Will return `Err` if the underlying SQLite call fails.
     #[cfg(feature = "load_extension")]
     pub fn load_extension_disable(&self) -> SqliteResult<()> {
         self.db.borrow_mut().enable_load_extension(0)
@@ -428,6 +491,10 @@ impl SqliteConnection {
     ///
     ///     conn.load_extension("my_sqlite_extension", None)
     /// }
+    ///
+    /// # Failure
+    ///
+    /// Will return `Err` if the underlying SQLite call fails.
     #[cfg(feature = "load_extension")]
     pub fn load_extension<P: AsRef<Path>>(&self, dylib_path: P, entry_point: Option<&str>) -> SqliteResult<()> {
         self.db.borrow_mut().load_extension(dylib_path, entry_point)
@@ -653,6 +720,11 @@ impl<'conn> SqliteStatement<'conn> {
     ///     Ok(())
     /// }
     /// ```
+    ///
+    /// # Failure
+    ///
+    /// Will return `Err` if binding parameters fails, the executed statement returns rows (in
+    /// which case `query` should be used instead), or the underling SQLite call fails.
     pub fn execute(&mut self, params: &[&ToSql]) -> SqliteResult<c_int> {
         unsafe {
             try!(self.bind_parameters(params));
@@ -694,6 +766,10 @@ impl<'conn> SqliteStatement<'conn> {
     ///     Ok(names)
     /// }
     /// ```
+    ///
+    /// # Failure
+    ///
+    /// Will return `Err` if binding parameters fails.
     pub fn query<'a>(&'a mut self, params: &[&ToSql]) -> SqliteResult<SqliteRows<'a>> {
         self.reset_if_needed();
 
@@ -710,6 +786,10 @@ impl<'conn> SqliteStatement<'conn> {
     ///
     /// Unlike the iterator produced by `query`, the returned iterator does not expose the possibility
     /// for accessing stale rows.
+    ///
+    /// # Failure
+    ///
+    /// Will return `Err` if binding parameters fails.
     pub fn query_map<'a, T, F>(&'a mut self, params: &[&ToSql], f: F)
                                      -> SqliteResult<MappedRows<'a, F>>
                                      where F: FnMut(&SqliteRow) -> T {
@@ -727,6 +807,10 @@ impl<'conn> SqliteStatement<'conn> {
     ///
     /// Unlike the iterator produced by `query`, the returned iterator does not expose the possibility
     /// for accessing stale rows.
+    ///
+    /// # Failure
+    ///
+    /// Will return `Err` if binding parameters fails.
     pub fn query_and_then<'a, T, E, F>(&'a mut self, params: &[&ToSql], f: F)
                                      -> SqliteResult<AndThenRows<'a, F>>
                                      where E: convert::From<SqliteError>,
@@ -743,6 +827,10 @@ impl<'conn> SqliteStatement<'conn> {
     ///
     /// Functionally equivalent to the `Drop` implementation, but allows callers to see any errors
     /// that occur.
+    ///
+    /// # Failure
+    ///
+    /// Will return `Err` if the underlying SQLite call fails.
     pub fn finalize(mut self) -> SqliteResult<()> {
         self.finalize_()
     }