mimetype

README

mimetype

A package for detecting MIME types and extensions based on magic numbers

No C bindings, zero dependencies and thread safe

Install

go get github.com/gabriel-vasile/mimetype

Usage

There are quick examples and GoDoc for full reference.

Supported MIME types

See supported mimes for the list of detected MIME types. If support is needed for a specific file format, please open an issue.

Structure

mimetype uses an hierarchical structure to keep the MIME type detection logic. This reduces the number of calls needed for detecting the file type. The reason behind this choice is that there are file formats used as containers for other file formats. For example, Microsoft Office files are just zip archives, containing specific metadata files. Once a file a file has been identified as a zip, there is no need to check if it is a text file, but it is worth checking if it is an Microsoft Office file.

To prevent loading entire files into memory, when detecting from a reader or from a file mimetype limits itself to reading only the first 3072 bytes from the input.

Contributing

See CONTRIBUTING.md.

Documentation

Overview

Package mimetype uses magic number signatures to detect the MIME type of a file.

mimetype stores the list of MIME types in a tree structure with "application/octet-stream" at the root of the hierarchy. The hierarchy approach minimizes the number of checks that need to be done on the input and allows for more precise results once the base type of file has been identified.

Example (Check)

To check if some bytes/reader/file has a specific MIME type, first perform a detect on the input and then test against the MIME.

Different from the string comparison, e.g.: mime.String() == "application/zip", mime.Is("application/zip") method has the following advantages: it handles MIME aliases, is case insensitive, ignores optional MIME parameters, and ignores any leading and trailing whitespace.

package main

import (
	"fmt"

	"github.com/gabriel-vasile/mimetype"
)

func main() {
	mime, err := mimetype.DetectFile("testdata/zip.zip")
	// application/x-zip is an alias of application/zip,
	// therefore Is returns true both times.
	fmt.Println(mime.Is("application/zip"), mime.Is("application/x-zip"), err)

}

Output:

true true <nil>

Example (Detect)

To find the MIME type of some input, perform a detect. In addition to the basic Detect,

mimetype.Detect([]byte) *MIME

there are shortcuts for detecting from a reader:

mimetype.DetectReader(io.Reader) (*MIME, error)

or from a file:

mimetype.DetectFile(string) (*MIME, error)

package main

import (
	"fmt"
	"io/ioutil"
	"os"

	"github.com/gabriel-vasile/mimetype"
)

func main() {
	file := "testdata/pdf.pdf"

	// Detect the MIME type of a file stored as a byte slice.
	data, _ := ioutil.ReadFile(file) // ignoring error for brevity's sake
	mime := mimetype.Detect(data)
	fmt.Println(mime.String(), mime.Extension())

	// Detect the MIME type of a reader.
	reader, _ := os.Open(file) // ignoring error for brevity's sake
	mime, rerr := mimetype.DetectReader(reader)
	fmt.Println(mime.String(), mime.Extension(), rerr)

	// Detect the MIME type of a file.
	mime, ferr := mimetype.DetectFile(file)
	fmt.Println(mime.String(), mime.Extension(), ferr)

}

Output:

application/pdf .pdf
application/pdf .pdf <nil>
application/pdf .pdf <nil>

Example (Parent)

It may happen that the returned MIME type is more accurate than needed.

Suppose we have a text file containing HTML code. Detection performed on this file will retrieve the `text/html` MIME. If you are interested in telling if the input can be used as a text file, you can walk up the MIME hierarchy until `text/plain` is found.

Remember to always check for nil before using the result of the Parent() method.

          .Parent()              .Parent()
text/html ----------> text/plain ----------> application/octet-stream

package main

import (
	"fmt"

	"github.com/gabriel-vasile/mimetype"
)

func main() {
	detectedMIME, err := mimetype.DetectFile("testdata/html.html")

	isText := false
	for mime := detectedMIME; mime != nil; mime = mime.Parent() {
		if mime.Is("text/plain") {
			isText = true
		}
	}

	// isText is true, even if the detected MIME was text/html.
	fmt.Println(isText, detectedMIME, err)

}

Output:

true text/html; charset=utf-8 <nil>

Example (TextVsBinary)

Considering the definition of a binary file as "a computer file that is not a text file", they can differentiated by searching for the text/plain MIME in it's MIME hierarchy.

package main

import (
	"fmt"

	"github.com/gabriel-vasile/mimetype"
)

func main() {
	detectedMIME, err := mimetype.DetectFile("testdata/xml.xml")

	isBinary := true
	for mime := detectedMIME; mime != nil; mime = mime.Parent() {
		if mime.Is("text/plain") {
			isBinary = false
		}
	}

	fmt.Println(isBinary, detectedMIME, err)

}

Output:

false text/xml; charset=utf-8 <nil>

Index

• type MIME
  • func Detect(in []byte) (mime *MIME)
  • func DetectFile(file string) (mime *MIME, err error)
  • func DetectReader(r io.Reader) (mime *MIME, err error)
  • func (n *MIME) Extension() string
  • func (n *MIME) Is(expectedMIME string) bool
  • func (n *MIME) Parent() *MIME
  • func (n *MIME) String() string

Examples

• Package (Check)
• Package (Detect)
• Package (Parent)
• Package (TextVsBinary)
• Detect
• DetectFile
• DetectReader
• MIME.Is

Types

type MIME

type MIME struct {
	// contains filtered or unexported fields
}

MIME struct holds information about a file format: the string representation of the MIME type, the extension and the parent file format.

func Detect

func Detect(in []byte) (mime *MIME)

Detect returns the MIME type found from the provided byte slice.

The result is always a valid MIME type, with application/octet-stream returned when identification failed.

Example

package main

import (
	"fmt"
	"io/ioutil"

	"github.com/gabriel-vasile/mimetype"
)

func main() {
	data, err := ioutil.ReadFile("testdata/zip.zip")
	mime := mimetype.Detect(data)

	fmt.Println(mime.String(), err)

}

Output:

application/zip <nil>

func DetectFile

func DetectFile(file string) (mime *MIME, err error)

DetectFile returns the MIME type of the provided file.

The result is always a valid MIME type, with application/octet-stream returned when identification failed with or without an error. Any error returned is related to the opening and reading from the input file.

To prevent loading entire files into memory, DetectFile reads at most matchers.ReadLimit bytes from the input file.

Example

package main

import (
	"fmt"

	"github.com/gabriel-vasile/mimetype"
)

func main() {
	mime, err := mimetype.DetectFile("testdata/zip.zip")

	fmt.Println(mime.String(), err)

}

Output:

application/zip <nil>

func DetectReader

func DetectReader(r io.Reader) (mime *MIME, err error)

DetectReader returns the MIME type of the provided reader.

The result is always a valid MIME type, with application/octet-stream returned when identification failed with or without an error. Any error returned is related to the reading from the input reader.

DetectReader assumes the reader offset is at the start. If the input is a ReadSeeker you read from before, it should be rewinded before detection:

reader.Seek(0, io.SeekStart)

To prevent loading entire files into memory, DetectReader reads at most matchers.ReadLimit bytes from the reader.

Example

package main

import (
	"fmt"
	"os"

	"github.com/gabriel-vasile/mimetype"
)

func main() {
	data, oerr := os.Open("testdata/zip.zip")
	mime, merr := mimetype.DetectReader(data)

	fmt.Println(mime.String(), oerr, merr)

}

Output:

application/zip <nil> <nil>

func (*MIME) Extension

func (n *MIME) Extension() string

Extension returns the file extension associated with the MIME type. It includes the leading dot, as in ".html". When the file format does not have an extension, the empty string is returned.

func (*MIME) Is

func (n *MIME) Is(expectedMIME string) bool

Is checks whether this MIME type, or any of its aliases, is equal to the expected MIME type. MIME type equality test is done on the "type/subtype" sections, ignores any optional MIME parameters, ignores any leading and trailing whitespace, and is case insensitive.

Example

package main

import (
	"fmt"

	"github.com/gabriel-vasile/mimetype"
)

func main() {
	mime, err := mimetype.DetectFile("testdata/pdf.pdf")

	pdf := mime.Is("application/pdf")
	xpdf := mime.Is("application/x-pdf")
	txt := mime.Is("text/plain")
	fmt.Println(pdf, xpdf, txt, err)

}

Output:

true true false <nil>

func (*MIME) Parent

func (n *MIME) Parent() *MIME

Parent returns the parent MIME type from the hierarchy. Each MIME type has a non-nil parent, except for the root MIME type.

For example, the application/json and text/html MIME types have text/plain as their parent because they are text files who happen to contain JSON or HTML. Another example is the ZIP format, which is used as container for Microsoft Office files, EPUB files, JAR files and others.

func (*MIME) String

func (n *MIME) String() string

String returns the string representation of the MIME type, e.g., "application/zip".