Introduce alloc to generate C string allocated by sqlite3

Safe to send to SQLite for deallocation.

src/inner_connection.rs

@@ -372,25 +372,19 @@ rusqlite was built against SQLite {} but the runtime SQLite version is {}. To fi
     });
 }
 
-#[cfg(not(any(
-    target_arch = "wasm32"
-)))]
+#[cfg(not(any(target_arch = "wasm32")))]
 static SQLITE_INIT: std::sync::Once = std::sync::Once::new();
 
 pub static BYPASS_SQLITE_INIT: AtomicBool = AtomicBool::new(false);
 
 // threading mode checks are not necessary (and do not work) on target
 // platforms that do not have threading (such as webassembly)
-#[cfg(any(
-    target_arch = "wasm32"
-))]
+#[cfg(any(target_arch = "wasm32"))]
 fn ensure_safe_sqlite_threading_mode() -> Result<()> {
     Ok(())
 }
 
-#[cfg(not(any(
-    target_arch = "wasm32"
-)))]
+#[cfg(not(any(target_arch = "wasm32")))]
 fn ensure_safe_sqlite_threading_mode() -> Result<()> {
     // Ensure SQLite was compiled in thredsafe mode.
     if unsafe { ffi::sqlite3_threadsafe() == 0 } {

src/vtab/mod.rs

@@ -10,7 +10,6 @@
 //!
 //! (See [SQLite doc](http://sqlite.org/vtab.html))
 use std::borrow::Cow::{self, Borrowed, Owned};
-use std::ffi::CString;
 use std::marker::PhantomData;
 use std::marker::Sync;
 use std::os::raw::{c_char, c_int, c_void};
@@ -705,23 +704,23 @@ where
                     ffi::SQLITE_OK
                 } else {
                     let err = error_from_sqlite_code(rc, None);
-                    *err_msg = mprintf(&err.to_string());
+                    *err_msg = alloc(&err.to_string());
                     rc
                 }
             }
             Err(err) => {
-                *err_msg = mprintf(&err.to_string());
+                *err_msg = alloc(&err.to_string());
                 ffi::SQLITE_ERROR
             }
         },
         Err(Error::SqliteFailure(err, s)) => {
             if let Some(s) = s {
-                *err_msg = mprintf(&s);
+                *err_msg = alloc(&s);
             }
             err.extended_code
         }
         Err(err) => {
-            *err_msg = mprintf(&err.to_string());
+            *err_msg = alloc(&err.to_string());
             ffi::SQLITE_ERROR
         }
     }
@@ -757,23 +756,23 @@ where
                     ffi::SQLITE_OK
                 } else {
                     let err = error_from_sqlite_code(rc, None);
-                    *err_msg = mprintf(&err.to_string());
+                    *err_msg = alloc(&err.to_string());
                     rc
                 }
             }
             Err(err) => {
-                *err_msg = mprintf(&err.to_string());
+                *err_msg = alloc(&err.to_string());
                 ffi::SQLITE_ERROR
             }
         },
         Err(Error::SqliteFailure(err, s)) => {
             if let Some(s) = s {
-                *err_msg = mprintf(&s);
+                *err_msg = alloc(&s);
             }
             err.extended_code
         }
         Err(err) => {
-            *err_msg = mprintf(&err.to_string());
+            *err_msg = alloc(&err.to_string());
             ffi::SQLITE_ERROR
         }
     }
@@ -971,7 +970,7 @@ unsafe fn set_err_msg(vtab: *mut ffi::sqlite3_vtab, err_msg: &str) {
     if !(*vtab).zErrMsg.is_null() {
         ffi::sqlite3_free((*vtab).zErrMsg as *mut c_void);
     }
-    (*vtab).zErrMsg = mprintf(err_msg);
+    (*vtab).zErrMsg = alloc(err_msg);
 }
 
 /// To raise an error, the `column` method should use this method to set the
@@ -1006,12 +1005,25 @@ unsafe fn result_error<T>(ctx: *mut ffi::sqlite3_context, result: Result<T>) ->
     }
 }
 
-// Space to hold this error message string must be obtained
-// from an SQLite memory allocation function.
-fn mprintf(err_msg: &str) -> *mut c_char {
-    let c_format = CString::new("%s").unwrap();
-    let c_err = CString::new(err_msg).unwrap();
-    unsafe { ffi::sqlite3_mprintf(c_format.as_ptr(), c_err.as_ptr()) }
+// Space to hold this string must be obtained
+// from an SQLite memory allocation function
+unsafe fn alloc<S: AsRef<[u8]>>(s: S) -> *mut c_char {
+    use std::convert::TryInto;
+    let s = s.as_ref();
+    if memchr::memchr(0, s).is_some() {
+        panic!("Null character found")
+    }
+    let len = s.len();
+    let total_len = len.checked_add(1).unwrap();
+
+    let dst = ffi::sqlite3_malloc(total_len.try_into().unwrap()) as *mut c_char;
+    if dst.is_null() {
+        panic!("Out of memory")
+    }
+    ptr::copy_nonoverlapping(s.as_ptr() as *const c_char, dst, len);
+    // null terminator
+    *dst.offset(len.try_into().unwrap()) = 0;
+    dst
 }
 
 #[cfg(feature = "array")]