I encountered a requirement: Suppose there is an image file with the real type of jpg, and someone is lazy to copy jpg directly and save it as a png file of the same name. In this way, there will be no problems when reading the file as3, but mobile phone C++ encounters problems when reading the file - -!
Now you need to write a program to traverse all files in folders and find files with "unusual" file format. Our resources are mainly gif, png, and jpg. At the beginning, I found an article online: obtain the file type mime-type based on the binary stream and file header, and then read the header information of the file binary, obtain its real file type, and compare it with the file type obtained through the suffix name.
The code copy is as follows:
var fd = fs.openSync(new_file_path, 'r');
var buffer = new Buffer(8);
var mineType = mime.lookup(new_file_path);
var fileType = mime.extension(mineType);
fs.readSync(fd, buffer, 0, 8, 0);
var newBuf = buffer.slice(0, 4);
var head_1 = newBuf[0].toString(16);
var head_2 = newBuf[1].toString(16);
var head_3 = newBuf[2].toString(16);
var head_4 = newBuf[3].toString(16);
var head_iden = head_1 + head_2;
var tempFileType = FILE_TYPE_CONFIG[head_iden];
if (!tempFileType) {
head_iden += head_3;
tempFileType = FILE_TYPE_CONFIG[head_iden];
if (!tempFileType) {
var msg = "Unknow fileType " + new_file_path + '-' + fileType;
showLog(msg);
continue;
}
}
if (tempFileType != fileType) {
var msg = "Error fileType" + new_file_path + '-' + fileType + '|' + tempFileType + '--Correct image file format';
showLog(msg);
g_errorFileTypArr.push(msg);
}
Later, when searching for information related to node image, I found this article: node.js module ranking>> (images)
Then filter a module "node-imageinfo" and wrote an example for testing (deliberately modify the suffix name of the jpg file directly to png):
Its source code, if you are interested, you can study it:
The code copy is as follows:
function readUInt32(buffer, offset, bigEndian) {
if (buffer.readUInt32) {
return buffer.readUInt32(offset, bigEndian);
}
var value;
if (bigEndian) {
if (buffer.readUInt32BE) {
return buffer.readUInt32BE(offset);
}
value = (buffer[offset] << 24) + (buffer[offset+1] << 16) + (buffer[offset+2] << 8) + buffer[offset+3];
}
else {
if (buffer.readUInt32LE) {
return buffer.readUInt32LE(offset);
}
value = buffer[offset] + (buffer[offset+1] << 8) + (buffer[offset+2] << 16) + (buffer[offset+3] << 24);
}
return value;
}
function readUInt16(buffer, offset, bigEndian) {
if (buffer.readUInt16) {
return buffer.readUInt16(offset, bigEndian);
}
var value;
if (bigEndian) {
if (buffer.readUInt16BE) {
return buffer.readUInt16BE(offset);
}
value = (buffer[offset] << 8) + buffer[offset+1];
}
else {
if (buffer.readUInt16LE) {
return buffer.readUInt16LE(offset);
}
value = buffer[offset] + (buffer[offset+1] << 8);
}
return value;
}
function readBit(buffer, offset, bitOffset) {
if (bitOffset > 7) {
offset += Math.floor(bitOffset / 8);
bitOffset = bitOffset % 8;
}
var b = buffer[offset];
if (bitOffset < 7) {
b >>>= (7 - bitOffset);
}
var val = b & 0x01;
return val;
}
function readBits(buffer, offset, bitOffset, bitLen, signed) {
var val = 0;
var neg = false;
if (signed) {
if (readBit(buffer, offset, bitOffset) > 0) {
neg = true;
}
bitLen--;
bitOffset++;
}
var bytes = [];
for (var i = 0; i < bitLen; i++) {
var b = readBit(buffer, offset, bitOffset + i);
if (i>0 && (bitLen - i) % 8 == 0) {
bytes.push(val);
val = 0;
}
val <<= 1;
val |= b;
}
bytes.push(val);
val = new Buffer(bytes);
val.negative = neg?true:false;
return val;
}
function imageInfoPng(buffer) {
var imageHeader = [0x49, 0x48, 0x44, 0x52],
pos = 12;
if (!checkSig(buffer, pos, imageHeader)) {
return false;
}
pos += 4;
return {
type: 'image',
format: 'PNG',
mimeType: 'image/png',
width: readUInt32(buffer, pos, true),
height: readUInt32(buffer, pos+4, true),
};
}
function imageInfoJpg(buffer) {
var pos = 2,
len = buffer.length,
sizeSig = [0xff, [0xc0, 0xc2]];
while (pos < len) {
if (checkSig(buffer, pos, sizeSig)) {
pos += 5;
return {
type: 'image',
format: 'JPG',
mimeType: 'image/jpeg',
width: readUInt16(buffer, pos+2, true),
height: readUInt16(buffer, pos, true),
};
}
pos += 2;
var size = readUInt16(buffer, pos, true);
pos += size;
}
}
function imageInfoGif(buffer) {
var pos = 6;
return {
type: 'image',
format: 'GIF',
mimeType: 'image/gif',
width: readUInt16(buffer, pos, false),
height: readUInt16(buffer, pos+2, false),
};
}
function imageInfoSwf(buffer) {
var pos = 8,
bitPos = 0,
val;
if (buffer[0] === 0x43) {
try {
// If you have zlib available ( npm install zlib ) then we can read compressed flash files
buffer = require('zlib').inflate(buffer.slice(8, 100));
pos = 0;
}
catch (ex) {
// Can't get width/height of compressed flash files... yet (need zlib)
return {
type: 'flash',
format: 'SWF',
mimeType: 'application/x-shockwave-flash',
width: null,
height: null,
}
}
}
var numBits = readBits(buffer, pos, bitPos, 5)[0];
bitPos += 5;
val = readBits(buffer, pos, bitPos, numBits, true);
var xMin = (numBits > 9 ? readUInt16(val, 0, true) : val[0]) * (val.negative ? -1 : 1);
bitPos += numBits;
val = readBits(buffer, pos, bitPos, numBits, true);
var xMax = (numBits > 9 ? readUInt16(val, 0, true) : val[0]) * (val.negative ? -1 : 1);
bitPos += numBits;
val = readBits(buffer, pos, bitPos, numBits, true);
var yMin = (numBits > 9 ? readUInt16(val, 0, true) : val[0]) * (val.negative ? -1 : 1);
bitPos += numBits;
val = readBits(buffer, pos, bitPos, numBits, true);
var yMax = (numBits > 9 ? readUInt16(val, 0, true) : val[0]) * (val.negative ? -1 : 1);
return {
type: 'flash',
format: 'SWF',
mimeType: 'application/x-shockwave-flash',
width: Math.ceil((xMax - xMin) / 20),
height: Math.ceil((yMax - yMin) / 20),
};
}
function checkSig(buffer, offset, sig) {
var len = sig.length;
for (var i = 0; i < len; i++) {
var b = buffer[i+offset],
s = sig[i],
m = false;
if ('number' == typeof s) {
m = s === b;
}
else {
for (var k in s) {
var o = s[k];
if (o === b) {
m = true;
}
}
}
if (!m) {
return false;
}
}
return true;
}
module.exports = function imageInfo(buffer, path) {
var pngSig = [0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a];
var jpgSig = [0xff, 0xd8, 0xff];
var gifSig = [0x47, 0x49, 0x46, 0x38, [0x37, 0x39], 0x61];
var swfSig = [[0x46, 0x43], 0x57, 0x53];
if (checkSig(buffer, 0, pngSig)) return imageInfoPng(buffer);
if (checkSig(buffer, 0, jpgSig)) return imageInfoJpg(buffer);
if (checkSig(buffer, 0, gifSig)) return imageInfoGif(buffer);
if (checkSig(buffer, 0, swfSig)) return imageInfoSwf(buffer);
return false;
};