octet stream header 분석

``` import java.io.File; import java.io.FileInputStream; import java.io.IOException; import lombok.extern.slf4j.Slf4j;

@Slf4j public class OctetStream {

public String changeFileNameForExtension(File originFile) throws IOException { byte[] buf = new byte[32]; try (FileInputStream fis = new FileInputStream(originFile)) {

fis.read(buf); } catch (Exception e) { throw new IOException(" file read Error : " + originFile); } String extractedExt = getExtFromFileHeaderFormat(buf); if (extractedExt == null) { throw new IOException( "Unknown Image format found.. Cannot infer file type! " + originFile.getName()); } log.info("Infer success : file format was {} so start renaming", extractedExt); String onlyFileNameWithoutExtension = com.google.common.io.Files.getNameWithoutExtension(originFile.getName()); File renamedFile = new File(originFile.getParent() + "/" + onlyFileNameWithoutExtension + "." + extractedExt); if (originFile.renameTo(renamedFile)) { log.debug("new file name from {} to {}", originFile.getName(), renamedFile.getName()); } return renamedFile.getName(); }

private String getExtFromFileHeaderFormat(byte[] targets) {

final byte[][][] checksum = new byte[][][]{ { /* GIF CASE 1*/ {(byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0x00, (byte) 0xFF}, {(byte) 0x47, (byte) 0x49, (byte) 0x46, (byte) 0x38, (byte) 0x00, (byte) 0x61} }, { /* GIF CASE 2*/ {(byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0x00, (byte) 0xFF}, {(byte) 0x47, (byte) 0x49, (byte) 0x46, (byte) 0x38, (byte) 0x00, (byte) 0x61} }, { /* PNG CASE */ {(byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0xFF}, {(byte) 0x89, (byte) 0x50, (byte) 0x4e, (byte) 0x47, (byte) 0x0d, (byte) 0x0a, (byte) 0x1a, (byte) 0x0a} }, { /* JPG CASE 1 */ {(byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0x00, (byte) 0x00, (byte) 0xFF, (byte) 0xFF}, {(byte) 0xFF, (byte) 0xD8, (byte) 0xFF, (byte) 0xE0, (byte) 0x00, (byte) 0x00, (byte) 0x4A, (byte) 0x46} }, { /* JPG CASE 2 */ {(byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0x00, (byte) 0x00, (byte) 0xFF, (byte) 0xFF}, {(byte) 0xFF, (byte) 0xD8, (byte) 0xFF, (byte) 0xE1, (byte) 0x00, (byte) 0x00, (byte) 0x45, (byte) 0x78} }, { /* JPG CASE 3 */ {(byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0x00, (byte) 0x00, (byte) 0xFF, (byte) 0xFF}, {(byte) 0xFF, (byte) 0xD8, (byte) 0xFF, (byte) 0xE8, (byte) 0x00, (byte) 0x00, (byte) 0x53, (byte) 0x50} }, { /* WEBP CASE 3 */ {(byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00}, {(byte) 0x52, (byte) 0x49, (byte) 0x46, (byte) 0x46, (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00}, {(byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00}, {(byte) 0x57, (byte) 0x45, (byte) 0x42, (byte) 0x50, (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00} } }; final String[] returnValues = new String[]{ "GIF", "GIF", "PNG", "JPG", "JPG", "JPG", "WEBP" }; boolean isAllZero = false; for (int i = 0; i mime-type octet stream일 경우 파일 헤더 분석을 통해 확장자 매칭 코드