Node. js solves the problem of obtaining the real image file type _ node. js

This article mainly introduces node. js solves the problem of obtaining the actual file type of an image. This article obtains the mime-type of the file type based on the binary stream and file header, then reads the binary header information of the file, and obtains its actual file type, if you need a file, you can refer to the following requirement: Assume that there is an image file of the actual type as jpg, and someone is lazy to copy a jpg file and save it as a png file of the same name, in this way, as3 will not encounter problems when reading files, but c ++ will encounter problems when reading files --!

Now you need to write a program to traverse all the files in the folder and find the file in an "abnormal" format. Our resources are mainly gif, png, and jpg. At first, I found an article on the Internet: get the file type mime-type based on the binary stream and file header, then, read the binary header of the file to obtain its actual file type, and compare it with the file type obtained by the suffix.

The Code 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 );
}

When searching information about node image, find this article: node. js module ranking> (images)

Then, the module "node-imageinfo" is filtered out, and an example is written for testing (intentionally changing the jpg file suffix to png ):

Its source code can be studied as follows:

The Code 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. Server Load balancer (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;
};