insert a watermark to any jpeg image pushed to an S3 bucket

ImageWatermark.js

// dependencies
const AWS = require("aws-sdk");
const util = require("util");
const sharp = require("sharp");

// get reference to S3 client
const s3 = new AWS.S3();

exports.compressImage = async (event, context) => {
  // Read options from the event parameter.
  console.log(
    "Reading options from event:\n",
    util.inspect(event, { depth: 5 })
  );
  const srcBucket = event.Records[0].s3.bucket.name;
  // Object key may have spaces or unicode non-ASCII characters.
  const srcKey = decodeURIComponent(
    event.Records[0].s3.object.key.replace(/\+/g, " ")
  );

  //this lambda function will rename the image file by adding
  //a custom prefix "resized" to avoid triggering a "loop" of events
  //when it saved into the same bucket!
  if(srcKey.indexOf("resized") > -1) return;

  const dstKey = "resized-" + srcKey; // concatinate the prefix "resized"

  // Infer the image type from the file suffix.
  const typeMatch = srcKey.match(/\.([^.]*)$/);
  if (!typeMatch) {
    console.log("Could not determine the image type.");
    return;
  }

  // Check that the image type is supported
  const imageType = typeMatch[1].toLowerCase();
  if (imageType != "jpeg" && imageType != "jpg") {
    console.log(`Unsupported image type: ${imageType}`);
    return;
  }

  // Download the image from the S3 source bucket.

  try {
    const params = {
      Bucket: srcBucket,
      Key: srcKey,
    };
    var origimage = await s3.getObject(params).promise();
  } catch (error) {
    console.log(error);
    return;
  }

  // set thumbnail width. Resize will set the height automatically to maintain aspect ratio.
  const width = 480;

  
  try {
    
    //using SVG as a text Watermark
    //you can define an envirenment variable called WATERMARK_TEXT
    //the font-familly files must be added to the lambda function fonts by
    //defining another env variable contains the font dir path like "FONTCONFIG_PATH":"./MyFont"
    const textedSVG = Buffer.from(`<svg
    xmlns="http://www.w3.org/2000/svg" 
    xml:lang="en"
    height="40"
    width="200">
    <text
    font-family="MyFont"
    font-style="italic"
    x="0" y="20" font-size="16" fill="#fff">
    ${process.env.WATERMARK_TEXT}
    </text></svg>`);

   
    let imgDst = sharp(origimage.Body);

    var buffer = await imgDst
     
      .composite([
        {
          input: textedSVG,
          gravity: "southeast",
        },
      ])
      // Use the Sharp module to resize the image and save in a buffer.
      .resize(width)
      .jpeg({ quality: 70 }) //decrease the image quality
      .toBuffer();

  } catch (error) {
    console.log("add watermark to the resized image!", error);
    return;
  }

  // Upload the thumbnail image to the destination bucket
  try {
    const destparams = {
      Bucket: srcBucket,
      Key: dstKey,
      Body: buffer,
      ContentType: "image/jpeg",
    };

    const putResult = await s3.putObject(destparams).promise();
  } catch (error) {
    console.log("putObject",error);
    return;
  }

  //finally!
  console.log(
    "Successfully resized " +
      srcBucket +
      "/" +
      srcKey +
      " and uploaded with" +
      dstKey
  );
};

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