EXAMPLES.md

Examples

• Detect MIME type
• Test against a MIME type
• Whitelist
• Binary file vs text file

Detect MIME type Go Playground

Get the MIME type from a path to a file.

file := "testdata/pdf.pdf"
mime, err := mimetype.DetectFile(file)
fmt.Println(mime.String(), mime.Extension(), err)
// Output: application/pdf .pdf nil

Get the MIME type from a reader.

reader, _ := os.Open(file) // ignoring error for brevity's sake
mime, err := mimetype.DetectReader(reader)
fmt.Println(mime.String(), mime.Extension(), err)
// Output: application/pdf .pdf nil

Get the MIME type from a byte slice.

data, _ := ioutil.ReadFile(file) // ignoring error for brevity's sake
mime := mimetype.Detect(data)
fmt.Println(mime.String(), mime.Extension())
// Output: application/pdf .pdf

Test against a MIME type Go Playground

Test if a file has a specific MIME type. Different from the string comparison, e.g.: mime.String() == "application/zip", mime.Is("application/zip") method has the following advantages:

• handles MIME aliases,
• is case insensitive,
• ignores optional MIME parameters,
• ignores any leading and trailing whitespace.

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>

Whitelist Go Playground

Test if a MIME type is in a list of allowed MIME types.

allowed := []string{"text/plain", "text/html", "text/csv"}
mime, _ := mimetype.DetectFile("/etc/passwd")

if mimetype.EqualsAny(mime.String(), allowed...) {
    fmt.Printf("%s is allowed\n", mime)
} else {
    fmt.Printf("%s is now allowed\n", mime)
}
// Output: text/plain; charset=utf-8 is allowed

Binary file vs text file Go Playground

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

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>