I'm trying to resize an image using Sharp module and then render it on GET request path.

    fs.readFile(`${imageDir}${filename}.jpg`, (err, img) => {
      if (err) { // File name doesn't match existing images
        res.send('Error: No image found');
      }
      // Resizing image and saving it on file system
      sharp(img)
      .resize(Number(width), Number(height))
      .toFile(`${thumbDir}${filename}-${width}-${height}.jpg`) // ---> THIS HERE DOES res.end() or res.send()
      .then(info => {
        // Rendering image on page
        fs.readFile(`${thumbDir}${filename}-${width}-${height}.jpg`,(err, img) => {
          if (err) throw err;
          res.end(img); // -----> THIS ONE DOESN'T WORK
        });
      });
    });

I want to stop sharp().resize().toFile() from "send" or "end" the response so I can "end" with resized image.

I can't remember what I did but something made res.end(img) line work and I got an error that I can't set header after response is sent.

P.S. I'm so sorry for any badly explained sections, please feel free to ask for any clarification.

CodePudding user response：

Even without knowing all of the context, I would recommend switching to the fs/promises APIs so you don't need to mix fs's callback-style asynchronicity with Sharp's promises. Then you can make your request handler async:

const fsp = require("fs/promises");

app.get("...", async (req, res) => {
  // (... read width, height, filename here...)
  try {
    const img = await fsp.readFile(`${imageDir}${filename}.jpg`);
    const thumbName = `${thumbDir}${filename}-${width}-${height}.jpg`;
    await sharp(img).resize(Number(width), Number(height)).toFile(thumbName);
    const thumb = await fsp.readFile(thumbName);
    // TODO: add correct content-type, etc. headers
    res.end(thumb);
  } catch (err) {
    // TODO: improve error handling
    console.error(err);
    res.status(400).end("Error processing file");
  }
});

PS: be sure to sanitize filename, width and height if they're user inputs; the above code is currently wide open to various file system traversal vulnerabilities.