Add SetErrorLog function

This function sets a callback that SQLite invokes when it detects an
anomaly. See https://sqlite.org/errlog.html.

callback.go

@@ -16,6 +16,7 @@ package sqlite3
 #else
 #include <sqlite3.h>
 #endif
+#include <stdint.h>
 #include <stdlib.h>
 
 void _sqlite3_result_text(sqlite3_context* ctx, const char* s);
@@ -29,9 +30,17 @@ import (
 	"math"
 	"reflect"
 	"sync"
+	"sync/atomic"
 	"unsafe"
 )
 
+var errorLogCallback atomic.Value
+
+//export errorLogTrampoline
+func errorLogTrampoline(_ C.uintptr_t, errCode C.int, msg *C.char) {
+	errorLogCallback.Load().(func(Error, string))(errorFromCode(errCode), C.GoString(msg))
+}
+
 //export callbackTrampoline
 func callbackTrampoline(ctx *C.sqlite3_context, argc int, argv **C.sqlite3_value) {
 	args := (*[(math.MaxInt32 - 1) / unsafe.Sizeof((*C.sqlite3_value)(nil))]*C.sqlite3_value)(unsafe.Pointer(argv))[:argc:argc]

sqlite3.go

@@ -59,6 +59,13 @@ package sqlite3
 # define USE_PWRITE64 1
 #endif
 
+void errorLogTrampoline(void *userPtr, int errCode, const char *msg);
+
+static int
+_sqlite3_config_log() {
+  return sqlite3_config(SQLITE_CONFIG_LOG, &errorLogTrampoline, NULL);
+}
+
 static int
 _sqlite3_open_v2(const char *filename, sqlite3 **ppDb, int flags, const char *zVfs) {
 #ifdef SQLITE_OPEN_URI
@@ -263,14 +270,35 @@ func Version() (libVersion string, libVersionNumber int, sourceID string) {
 	return libVersion, libVersionNumber, sourceID
 }
 
+// SetErrorLog registers the given callback to be invoked with a message whenever SQLite detects an
+// anomaly. It is good practice to redirect such messages to the application log. See
+// https://sqlite.org/errlog.html.
+// The provided callback function receives an SQLite error object, denoting the broad category of
+// error, and a message string. It must not call any SQLite functions; in fact, the SQLite docs
+// recommend treating the callback function like a signal handler, minimizing the work done in it.
+// SetErrorLog must not be called while any other goroutine is running that might be calling into
+// the SQLite library.
+func SetErrorLog(callback func(err Error, msg string)) error {
+	errorLogCallback.Store(callback)
+	if rc := C._sqlite3_config_log(); rc == 0 {
+		return nil
+	} else {
+		return errorFromCode(rc)
+	}
+}
+
 const (
+	// some common return codes
+	SQLITE_OK      = C.SQLITE_OK
+	SQLITE_NOTICE  = C.SQLITE_NOTICE
+	SQLITE_WARNING = C.SQLITE_WARNING
+
 	// used by authorizer and pre_update_hook
 	SQLITE_DELETE = C.SQLITE_DELETE
 	SQLITE_INSERT = C.SQLITE_INSERT
 	SQLITE_UPDATE = C.SQLITE_UPDATE
 
-	// used by authorzier - as return value
-	SQLITE_OK     = C.SQLITE_OK
+	// used by authorizer as return value, in addition to SQLITE_OK
 	SQLITE_IGNORE = C.SQLITE_IGNORE
 	SQLITE_DENY   = C.SQLITE_DENY
 
@@ -845,6 +873,13 @@ func lastError(db *C.sqlite3) error {
 	}
 }
 
+func errorFromCode(rc C.int) Error {
+	return Error{
+		Code:         ErrNo(rc & ErrNoMask),
+		ExtendedCode: ErrNoExtended(rc),
+	}
+}
+
 // Exec implements Execer.
 func (c *SQLiteConn) Exec(query string, args []driver.Value) (driver.Result, error) {
 	list := make([]driver.NamedValue, len(args))

sqlite3_test.go

@@ -1248,6 +1248,40 @@ func TestVersion(t *testing.T) {
 	}
 }
 
+func TestErrorLog(t *testing.T) {
+	var errorLogged bool
+	var capturedErr Error
+	var capturedMsg string
+	err := SetErrorLog(func(err Error, msg string) {
+		errorLogged = true
+		capturedErr = err
+		capturedMsg = msg
+	})
+	if err != nil {
+		t.Fatal("Failed to set error logger:", err)
+	}
+
+	db, err := sql.Open("sqlite3", ":memory:")
+	if err != nil {
+		t.Fatal("Failed to open database:", err)
+	}
+	defer db.Close()
+
+	if _, err := db.Exec(`SELECT "foo"`); err != nil {
+		t.Fatal("SELECT failed:", err)
+	}
+
+	if !errorLogged {
+		t.Fatal("No error was logged")
+	}
+	if capturedErr.Code != SQLITE_WARNING {
+		t.Errorf("Unexpected error log code: %d", capturedErr.Code)
+	}
+	if !strings.Contains(capturedMsg, "double-quoted string literal") {
+		t.Errorf("Unexpected error log message: '%s'", capturedMsg)
+	}
+}
+
 func TestStringContainingZero(t *testing.T) {
 	tempFilename := TempFilename(t)
 	defer os.Remove(tempFilename)