Creates okhttp3.Requests for uploading files to an Amazon S3 storage bucket. Implements https://docs.aws.amazon.com/AmazonS3/latest/API/sigv4-authentication-HTTPPOST.html

AmazonS3RequestFactory.java

import java.io.File;
import java.io.IOException;
import java.nio.charset.Charset;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Locale;
import java.util.TimeZone;
import okio.BufferedSource;
import okio.ByteString;
import okio.Okio;

public final class AmazonS3RequestFactory {
  private static final Charset UTF_8 = Charset.forName("UTF-8");
  private static final ThreadLocal<DateFormat> AWS_DATE_FORMAT = new ThreadLocal<DateFormat>() {
    @Override protected DateFormat initialValue() {
      SimpleDateFormat format =
          new SimpleDateFormat("EEE, d MMM yyyy HH:mm:ss 'GMT+00:00'", Locale.US);
      format.setTimeZone(TimeZone.getTimeZone("GMT"));
      return format;
    }
  };

  private final HttpUrl base;
  private final String accessKeyId;
  private final String secretKey;

  public AmazonS3RequestFactory(String bucket, String accessKeyId, String secretKey) {
    base = new HttpUrl.Builder().scheme("https")
        .host("s3.amazonaws.com")
        .addPathSegment(bucket)
        .build();
    this.accessKeyId = accessKeyId;
    this.secretKey = secretKey;
  }

  public Request request(String relativeUrlPath, File media) {
    if (media == null) {
      throw new NullPointerException("media == null");
    }
    if (!media.exists()) {
      throw new IllegalArgumentException(
          String.format(Locale.US, "File %1$s does not exist.", media));
    }
    if (relativeUrlPath == null) {
      throw new NullPointerException("relativeUrlPath == null");
    }
    HttpUrl url =
        base.newBuilder().addPathSegments(relativeUrlPath).addPathSegment(media.getName()).build();
    String extensionName;
    try {
      extensionName = fileExtensionName(media);
    } catch (IOException e) {
      extensionName = "jpeg";
    }
    String mime = "image/" + extensionName;
    String date = AWS_DATE_FORMAT.get().format(new Date());
    String stringToSign = "PUT\n\n" + mime + "\n" + date + "\n" + url.encodedPath();
    return new Request.Builder().url(url)
        .put(RequestBody.create(MediaType.parse(mime), media))
        .header("Date", date)
        .header("Host", "s3.amazonaws.com")
        .header("Authorization", "AWS " + accessKeyId + ":" + awsSignature(secretKey, stringToSign))
        .build();
  }

  // https://docs.aws.amazon.com/AmazonS3/latest/API/sigv4-authentication-HTTPPOST.html
  private static String awsSignature(String secret, String stringToSign) {
    return ByteString.of(stringToSign.getBytes(UTF_8))
        .hmacSha1(ByteString.of(secret.getBytes(UTF_8)))
        .base64();
  }

  private static final ByteString PNG_HEADER = ByteString.decodeHex("89504e470d0a1a0a");
  private static final ByteString JPEG_HEADER = ByteString.decodeHex("ffd8ff");
  private static final ByteString GIF_HEADER_87 = ByteString.decodeHex("474946383761");
  private static final ByteString GIF_HEADER_89 = ByteString.decodeHex("474946383961");
  private static final ByteString TIFF_HEADER_LITTLE_ENDIAN = ByteString.decodeHex("49492A00");
  private static final ByteString TIFF_HEADER_BIG_ENDIAN = ByteString.decodeHex("4D4D002A");

  private static String fileExtensionName(File media) throws IOException {
    BufferedSource mediaSource = Okio.buffer(Okio.source(media));
    try {
      if (mediaSource.rangeEquals(0, PNG_HEADER)) {
        return "png";
      }
      if (mediaSource.rangeEquals(0, JPEG_HEADER)) {
        return "jpeg";
      }
      if (mediaSource.rangeEquals(0, GIF_HEADER_87)) {
        return "gif";
      }
      if (mediaSource.rangeEquals(0, GIF_HEADER_89)) {
        return "gif";
      }
      if (mediaSource.rangeEquals(0, TIFF_HEADER_LITTLE_ENDIAN)) {
        return "tiff";
      }
      if (mediaSource.rangeEquals(0, TIFF_HEADER_BIG_ENDIAN)) {
        return "tiff";
      }
      throw new IOException(
          String.format(Locale.US, "Unsupported file type. File name: %1$s. Hex: %2$s.",
              media.getPath(), mediaSource.readByteString().hex()));
    } finally {
      try {
        mediaSource.close();
      } catch (IOException ignored) {
      }
    }
  }
}