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// Copyright 2021 The Gitea Authors. All rights reserved.
// SPDX-License-Identifier: MIT
package typesniffer
import (
"bytes"
"encoding/binary"
"net/http"
"regexp"
"slices"
"strings"
"sync"
)
const SniffContentSize = 1024
const (
MimeTypeImageSvg = "image/svg+xml"
MimeTypeImageAvif = "image/avif"
MimeTypeApplicationOctetStream = "application/octet-stream"
)
var globalVars = sync.OnceValue(func() (ret struct {
svgComment, svgTagRegex, svgTagInXMLRegex *regexp.Regexp
},
) {
ret.svgComment = regexp.MustCompile(`(?s)<!--.*?-->`)
ret.svgTagRegex = regexp.MustCompile(`(?si)\A\s*(?:(<!DOCTYPE\s+svg([\s:]+.*?>|>))\s*)*<svg\b`)
ret.svgTagInXMLRegex = regexp.MustCompile(`(?si)\A<\?xml\b.*?\?>\s*(?:(<!DOCTYPE\s+svg([\s:]+.*?>|>))\s*)*<svg\b`)
return ret
})
// SniffedType contains information about a blob's type.
type SniffedType struct {
contentType string
}
// IsText detects if the content format is text family, including text/plain, text/html, text/css, etc.
func (ct SniffedType) IsText() bool {
return strings.Contains(ct.contentType, "text/")
}
func (ct SniffedType) IsTextPlain() bool {
return strings.Contains(ct.contentType, "text/plain")
}
// IsImage detects if data is an image format
func (ct SniffedType) IsImage() bool {
return strings.Contains(ct.contentType, "image/")
}
// IsSvgImage detects if data is an SVG image format
func (ct SniffedType) IsSvgImage() bool {
return strings.Contains(ct.contentType, MimeTypeImageSvg)
}
// IsPDF detects if data is a PDF format
func (ct SniffedType) IsPDF() bool {
return strings.Contains(ct.contentType, "application/pdf")
}
// IsVideo detects if data is a video format
func (ct SniffedType) IsVideo() bool {
return strings.Contains(ct.contentType, "video/")
}
// IsAudio detects if data is a video format
func (ct SniffedType) IsAudio() bool {
return strings.Contains(ct.contentType, "audio/")
}
// IsRepresentableAsText returns true if file content can be represented as
// plain text or is empty.
func (ct SniffedType) IsRepresentableAsText() bool {
return ct.IsText() || ct.IsSvgImage()
}
// IsBrowsableBinaryType returns whether a non-text type can be displayed in a browser
func (ct SniffedType) IsBrowsableBinaryType() bool {
return ct.IsImage() || ct.IsSvgImage() || ct.IsPDF() || ct.IsVideo() || ct.IsAudio()
}
// GetMimeType returns the mime type
func (ct SniffedType) GetMimeType() string {
return strings.SplitN(ct.contentType, ";", 2)[0]
}
// https://en.wikipedia.org/wiki/ISO_base_media_file_format#File_type_box
func detectFileTypeBox(data []byte) (brands []string, found bool) {
if len(data) < 12 {
return nil, false
}
boxSize := int(binary.BigEndian.Uint32(data[:4]))
if boxSize < 12 || boxSize > len(data) {
return nil, false
}
tag := string(data[4:8])
if tag != "ftyp" {
return nil, false
}
brands = append(brands, string(data[8:12]))
for i := 16; i+4 <= boxSize; i += 4 {
brands = append(brands, string(data[i:i+4]))
}
return brands, true
}
// DetectContentType extends http.DetectContentType with more content types. Defaults to text/plain if input is empty.
func DetectContentType(data []byte) SniffedType {
if len(data) == 0 {
return SniffedType{"text/plain"}
}
ct := http.DetectContentType(data)
if len(data) > SniffContentSize {
data = data[:SniffContentSize]
}
vars := globalVars()
// SVG is unsupported by http.DetectContentType, https://github.com/golang/go/issues/15888
detectByHTML := strings.Contains(ct, "text/plain") || strings.Contains(ct, "text/html")
detectByXML := strings.Contains(ct, "text/xml")
if detectByHTML || detectByXML {
dataProcessed := vars.svgComment.ReplaceAll(data, nil)
dataProcessed = bytes.TrimSpace(dataProcessed)
if detectByHTML && vars.svgTagRegex.Match(dataProcessed) ||
detectByXML && vars.svgTagInXMLRegex.Match(dataProcessed) {
ct = MimeTypeImageSvg
}
}
if strings.HasPrefix(ct, "audio/") && bytes.HasPrefix(data, []byte("ID3")) {
// The MP3 detection is quite inaccurate, any content with "ID3" prefix will result in "audio/mpeg".
// So remove the "ID3" prefix and detect again, then if the result is "text", it must be text content.
// This works especially because audio files contain many unprintable/invalid characters like `0x00`
ct2 := http.DetectContentType(data[3:])
if strings.HasPrefix(ct2, "text/") {
ct = ct2
}
}
fileTypeBrands, found := detectFileTypeBox(data)
if found && slices.Contains(fileTypeBrands, "avif") {
ct = MimeTypeImageAvif
}
if ct == "application/ogg" {
dataHead := data
if len(dataHead) > 256 {
dataHead = dataHead[:256] // only need to do a quick check for the file header
}
if bytes.Contains(dataHead, []byte("theora")) || bytes.Contains(dataHead, []byte("dirac")) {
ct = "video/ogg" // ogg is only used for some video formats, and it's not popular
} else {
ct = "audio/ogg" // for most cases, it is used as an audio container
}
}
return SniffedType{ct}
}
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