refactor(native-player): share player helpers

shared/cpp/sanitize_utf8.h

@@ -0,0 +1,48 @@
+#ifndef SANITIZE_UTF8_H_
+#define SANITIZE_UTF8_H_
+
+#include <cstring>
+#include <string>
+#include <simdutf.h>
+
+// Sanitize a C string that may contain invalid UTF-8 sequences.
+// Uses simdutf for SIMD-accelerated validation (fast path for valid strings),
+// then falls back to iterative replacement with U+FFFD on the rare invalid case.
+// mpv does not guarantee UTF-8 for log messages, error strings, or
+// system-encoded paths — sending these unsanitized through Flutter's
+// StandardMessageCodec causes FormatException crashes.
+static inline std::string SanitizeUtf8(const char* input) {
+  if (!input) return std::string();
+  size_t len = strlen(input);
+  if (len == 0) return std::string();
+
+  // Fast path: SIMD-accelerated validation — almost all strings pass this
+  if (simdutf::validate_utf8(input, len)) {
+    return std::string(input, len);
+  }
+
+  // Slow path: find each invalid position, copy valid prefix, insert U+FFFD,
+  // skip the bad byte, and repeat.
+  std::string result;
+  result.reserve(len);
+  size_t pos = 0;
+
+  while (pos < len) {
+    auto r = simdutf::validate_utf8_with_errors(input + pos, len - pos);
+    // Copy the valid prefix up to the error
+    if (r.count > 0) {
+      result.append(input + pos, r.count);
+    }
+    pos += r.count;
+    if (r.error == simdutf::error_code::SUCCESS) {
+      break;  // remaining tail is valid
+    }
+    // Replace the invalid byte with U+FFFD and skip it
+    result.append("\xEF\xBF\xBD");
+    pos++;
+  }
+
+  return result;
+}
+
+#endif  // SANITIZE_UTF8_H_