訂判斷及所需輸入
測試 PDF 把 SECRETALPHA 放黑色蓋層下，另有 VISIBLE。此檔案即使視覺蓋住，仍可抽到 SECRETALPHA；更正路徑要在生成新 PDF 前，從文件內容省略該字。
| 情況 | 輸入 JSON |
|---|---|
| 原例測試 | {"secret":"SECRETALPHA","remove":true} |
跑所附比較
兩個 PDF 都在記憶體生成，再用 PDF.js 抽字。只核本例指定字及仍須保留的可見字；未確認全部 metadata、註解、內嵌內容，亦不是通用安全刪改程序。
| 路徑 | 輸出 JSON |
|---|---|
| 錯誤路徑 | {"secretExtractable":true,"visibleExtractable":true,"pageCount":1} |
| 所需路徑 | {"secretExtractable":false,"visibleExtractable":true,"pageCount":1} |
import assert from 'node:assert/strict';
import {createRequire} from 'node:module';
import {pathToFileURL} from 'node:url';
const htmlEscape=s=>String(s).replace(/&/g,'&').replace(/</g,'<').replace(/>/g,'>').replace(/"/g,'"');
async function withPage(action,options={}){
const require=createRequire(import.meta.url);const {chromium}=require('playwright');
const browser=await chromium.launch({headless:true});
try{const context=await browser.newContext(options);const page=await context.newPage();
const requests=[];await page.route('**/*',route=>{requests.push(route.request().url());return route.abort();});
return await action(page,context,requests);
}finally{await browser.close();}
}
async function pdfObservation(html){
const bytes=await withPage(async page=>{await page.setContent(html);return page.pdf({preferCSSPageSize:true,printBackground:true});});
const require=createRequire(import.meta.url);
const {getDocument}=await import(pathToFileURL(require.resolve('pdfjs-dist/legacy/build/pdf.mjs')).href);
const loadingTask=getDocument({data:Uint8Array.from(bytes),useSystemFonts:true,disableFontFace:true});
try{const document=await loadingTask.promise;const pages=[];for(let n=1;n<=document.numPages;n++){
const page=await document.getPage(n);const content=await page.getTextContent();
pages.push(content.items.filter(x=>typeof x.str==='string'&&x.str).map(x=>({text:x.str,x:x.transform[4],y:x.transform[5]})));
}return {pageCount:document.numPages,pages};}finally{await loadingTask.destroy();}
}
const printStyle='<style>@page{size:100mm 100mm;margin:10mm}body{margin:0;font:10px Arial}p{margin:0}</style>';
const run=async function run(i,corrected=true){
if(typeof i.remove!=='boolean'||typeof i.secret!=='string'||!/^[A-Z]{1,20}$/.test(i.secret)||i.secret==='VISIBLE')return {held:true};
const secret=corrected&&i.remove?'':i.secret;
const observation=await pdfObservation(printStyle+'<div style="position:relative;height:10mm"><p>'+htmlEscape(secret)+'</p><div style="position:absolute;inset:0;background:black"></div></div><p>VISIBLE</p>');
const words=observation.pages.flat().map(x=>x.text);
return {secretExtractable:words.includes(i.secret),visibleExtractable:words.includes('VISIBLE'),pageCount:observation.pageCount};
};
const cases=[{"input":{"secret":"SECRETALPHA","remove":true},"corrected":false,"expected":{"secretExtractable":true,"visibleExtractable":true,"pageCount":1}},{"input":{"secret":"SECRETALPHA","remove":true},"corrected":true,"expected":{"secretExtractable":false,"visibleExtractable":true,"pageCount":1}},{"input":{"secret":"SECRETALPHA","remove":false},"corrected":true,"expected":{"secretExtractable":true,"visibleExtractable":true,"pageCount":1}},{"input":{"secret":"SECRETALPHA","remove":null},"corrected":true,"expected":{"held":true}}];
for(const test of cases){const actual=await run(test.input,test.corrected);assert.deepEqual(actual,test.expected);console.log(actual);}
按邊界依據作判斷
已訂保留就照留；移除決定未知便停，不能因有黑格就推已刪字。
- 訂明指定字怎樣處理
- 生成所需新檔案
- 抽字核指定內容
視覺蓋層不能證明儲存文字已移除。
| 條件 | 輸入 JSON | 預期輸出 JSON |
|---|---|---|
| 已訂保留該字 | {"secret":"SECRETALPHA","remove":false} | {"secretExtractable":true,"visibleExtractable":true,"pageCount":1} |
| 移除決定未知 | {"secret":"SECRETALPHA","remove":null} | {"held":true} |
原例更正後抽字，確立了甚麼？
查看參考答案
這份新 PDF 抽不到 SECRETALPHA，VISIBLE 仍在，共一頁。只屬該檔案的有限結果，不是通用安全保證。