detect-file-type-lite
v3.0.4
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Detect file type by signature
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detect-file-type
Detect file type by signatures. Fork of detect-file-type.
- Removed dependency on node's
fs
module to enable this package to be used on browsers - Increase performance by removing usage of text recoding
- Typescript type definition file included
Supported types
jpg, png, gif, webp, flif, cr2, tif, bmp, jxr, psd, zip, epub, xpi, tar, rar, gz, bz2, 7z, dmg, mov, mp4, m4v, m4a, 3g2, 3gp, avi, wav, qcp, mid, mkv, webm, wasm, asf, wmv, wma, mpg, mp3, opus, ogg, ogv, oga, ogm, ogx, spx, flac, ape, wv, amr, pdf, exe, swf, rtf, woff, woff2, eot, ttf, otf, ico, cur, flv, ps, xz, sqlite, nes, dex, crx, elf, cab, deb, ar, rpm, Z, lz, msi, mxf, mts, blend, bpg, jp2, jpx, jpm, mj2, aif, xml, svg, mobi, heic, ktx, dcm, mpc, ics, glb, pcap, html, dll, xlsx, xlsm, xlsb, xlam, docx, docm, dotm, dotx, pptx, pptm, ppsm, ppsx
Installation
npm i --save detect-file-type-lite
Usage
import { readFile } from 'fs/promises'
import FileTypeDetector from 'detect-file-type-lite'
const fileTypeDetector = new FileTypeDetector()
const buffer = await readFile('img.jpg')
const result = await fileTypeDetector.fromBuffer(buffer);
console.log(result.ext) // jpg
API
fromBuffer(buffer) => Promise<FileTypeResult | null>
Detect file type from buffer
buffer
- uint8array/Buffer
addSignature(signature) => void
Add new signature for file type detecting
signature
- a signature. See section about it below
addCustomFunction(fn) => void
Add custom function which receive buffer and trying to detect file type.
fn
- function which receive buffer
This method needed for more complicated cases like DLL for example. A DLL file will be detected as a normal EXE file, unless you perform deeper checks on its headers.
import { readFile } from 'fs/promises'
import FileTypeDetector from 'detect-file-type-lite'
const fileTypeDetector = new FileTypeDetector()
fileTypeDetector.addCustomFunction((buffer: Buffer) => {
if(buffer.length < 2) return false
const mzHeader = Buffer.from([0x4D, 0x5A])
if(buffer.compare(mzHeader, 0, mzHeader.length, 0, mzHeader.length) != 0) return false
const PE_HEADER_OFFSET = buffer.readUInt32LE(0x3c)
const CHARACTERISTICS_OFFSET = PE_HEADER_OFFSET + 0x16
const characteristics = buffer.readUInt16LE(CHARACTERISTICS_OFFSET)
// IMAGE_FILE_DLL == 0x2000
if((characteristics & 0x2000) === 0x2000) {
return {
ext: 'dll',
mime: 'application/octet-stream'
}
}
return false
})
const buf = await readFile('winrsmgr.dll')
const res = await fileTypeDetector.fromBuffer(buf)
console.log(res) // { ext: 'dll', mime: 'application/octet-stream' }
Some custom functions, including the above example on DLL file type detection, are already declared during object instantiation. See custom-functions.ts for more details.
Custom functions can be async.
Signature and creating your own signatures
Detecting of file type work via signatures. The simplest signature in JSON format looks like:
{
"type": "jpg",
"ext": "jpg",
"mime": "image/jpeg",
"rules": [
{ "type": "equal", "start": 0, "end": 2, "bytes": "ffd8" }
]
}
params:
type
- signature type, mostly it's the same as param 'ext'ext
- file extensioniana
- optional iana registered mime type - will be added when actual used mime differs from iana, or when the old mime type we used was wrongmime
- mime type of filerules
- list of rules for detecting
More details about param rules
:
This param have to be array of objects
type
- a rule type. There are available a few types:equal
,notEqual
,contains
,notContains
,or
,and
,default
search
- a searching rule, that keeps the offset of the searched bytes in a special id.search_ref
- a reference to a previously performed search,start
andend
will be offset by it.
More details about: equal, notEqual, contains & notContains.
equal
- here is required fieldbytes
. We get a dump of buffer fromstart
(equals 0 by default) toend
(equals buffer.length by default). After that we compare the dump with value in parambytes
. If values are equal then this rule is correct.notEqual
- here is required fieldbytes
. We get a dump of buffer fromstart
(equals 0 by default) toend
(equals buffer.length by default). After that we compare the dump with value in parambytes
. If values aren't equal then this rule is correct.contains
- here is required fieldbytes
. We get a dump of buffer fromstart
(equals 0 by default) toend
(equals buffer.length by default). After that we try to find the sequence frombytes
in this dump. If the dump containsbytes
then rules is correct.notContains
- here is required fieldbytes
. We get a dump of buffer fromstart
(equals 0 by default) toend
(equals buffer.length by default). After that we try to find the sequence frombytes
in this dump. If the dump containsbytes
then rules is incorrect.
More details about the rule types or
and and
Actually, these types are necessary when you work with complicated signatures. For example, when file contains few sequences of bytes in different parts of file. Here is required field 'rules', where you should define set of another rules. See example:
{
"type": "tif",
"ext": "tif",
"mime": "image/tiff",
"rules": [
{ "type": "and", "rules":
[
{ "type": "notEqual", "start": 8, "end": 10, "bytes": "4352" },
{ "type": "or", "rules":
[
{ "type": "equal", "start": 0, "end": 4, "bytes": "49492a00" },
{ "type": "equal", "start": 0, "end": 4, "bytes": "4d4d002a" }
]
}
]
}
]
}
Explanation: If dump starts from 8th byte and ends to 10th byte isn't equal "4352", and dump starts from 0 and ends to 4th byte is equal "49492a00" or is equal "4d4d002a" then data looks like file with 'tif' format.
or
- means that any rules fromrules
should be correct. If at least 1 rule is correct then list are correct too.and
- means that each rule fromrules
should be correct. If all rules are correct then list is correct. When at least 1 rule fail then all list is incorrect.
The rules or
and and
can be nested without restrictions.
The default
type is special and is used as a fallback when a set of or
rules did not match, inside a larger tree with multiple mime detections.
More details about the search
object
id
- id to assign to the result (reference later withsearch_ref
)start
/end
- range to search inbytes
- bytes to search for
License
WTFPL © Dmitry Pavlovsky