use std::ffi::{CStr, CString};use serde::Serialize; #[derive(Debug, Clone, Serialize)]#[serde(rename_all = "camelCase")]pub struct PDFMetadata {    num_pages: i32,     #[serde(skip_serializing_if = "Option::is_none")]    title: Option<String>,} fn _get_pdf_metadata(path: &str) -> Result<PDFMetadata, String> {    let doc = match lopdf::Document::load(path) {        Ok(x) => x,        Err(_) => {            return Err("Failed to load PDF".to_string());        }    };     let num_pages = doc.get_pages().len() as i32;    let title = doc.trailer.get(b"Info")        .and_then(|info| info.as_dict()            .and_then(|info| info.get(b"Title"))            .and_then(|title| title.as_str().map(|s| String::from_utf8_lossy(s).to_string()))        ).ok()        .or_else(|| doc.objects.iter()            .find_map(|(_i, obj)| obj.as_dict()                .and_then(|obj| obj.get(b"Title"))                .and_then(|title| title.as_str())                .map(|s| String::from_utf8_lossy(s).to_string())                .ok()            )        )        .map(|x| x.trim_matches(|x| char::is_whitespace(x) || x == '\0').to_string());        Ok(PDFMetadata { num_pages, title })} /// Returns the metadata of a PDF file/// /// # Safety/// Input path must be a C string of a path pointing to a PDF file. Output will be a JSON string of the PDF metadata.#[no_mangle]pub unsafe extern "C" fn get_pdf_metadata(path: *const libc::c_char) -> *const libc::c_char {    let path: String = match unsafe { CStr::from_ptr(path) }.to_str().map_err(|_| ()) {        Ok(x) => x.to_string(),        Err(_) => {            return CString::new("RUSTFC:ERROR:Failed to parse input path as C string").unwrap().into_raw();        }    };     let metadata = match _get_pdf_metadata(&path) {        Ok(x) => x,        Err(e) => {            return CString::new(format!("RUSTFC:ERROR:Failed to get PDF metadata: {}", e)).unwrap().into_raw();        }    };     let json = match serde_json::to_string(&metadata) {        Ok(x) => x,        Err(e) => {            return CString::new(format!("RUSTFC:ERROR:Serde failed to serialize metadata: {}", e)).unwrap().into_raw();        }    };     CString::new(json).unwrap().into_raw()}