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// Copyright 2021 The Gitea Authors. All rights reserved.
// SPDX-License-Identifier: MIT
package typesniffer
import (
"bytes"
"fmt"
"io"
"net/http"
"regexp"
"strings"
"code.gitea.io/gitea/modules/util"
)
// Use at most this many bytes to determine Content Type.
const sniffLen = 1024
const (
// SvgMimeType MIME type of SVG images.
SvgMimeType = "image/svg+xml"
// ApplicationOctetStream MIME type of binary files.
ApplicationOctetStream = "application/octet-stream"
)
var (
svgComment = regexp.MustCompile(`(?s)<!--.*?-->`)
svgTagRegex = regexp.MustCompile(`(?si)\A\s*(?:(<!DOCTYPE\s+svg([\s:]+.*?>|>))\s*)*<svg\b`)
svgTagInXMLRegex = regexp.MustCompile(`(?si)\A<\?xml\b.*?\?>\s*(?:(<!DOCTYPE\s+svg([\s:]+.*?>|>))\s*)*<svg\b`)
)
// SniffedType contains information about a blobs type.
type SniffedType struct {
contentType string
}
// IsText etects if content format is plain text.
func (ct SniffedType) IsText() bool {
return strings.Contains(ct.contentType, "text/")
}
// 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, SvgMimeType)
}
// 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 an video format
func (ct SniffedType) IsVideo() bool {
return strings.Contains(ct.contentType, "video/")
}
// IsAudio detects if data is an 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]
}
// DetectContentType extends http.DetectContentType with more content types. Defaults to text/unknown if input is empty.
func DetectContentType(data []byte) SniffedType {
if len(data) == 0 {
return SniffedType{"text/unknown"}
}
ct := http.DetectContentType(data)
if len(data) > sniffLen {
data = data[:sniffLen]
}
// 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 := svgComment.ReplaceAll(data, nil)
dataProcessed = bytes.TrimSpace(dataProcessed)
if detectByHTML && svgTagRegex.Match(dataProcessed) ||
detectByXML && svgTagInXMLRegex.Match(dataProcessed) {
ct = SvgMimeType
}
}
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, if result is text, then 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
}
}
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}
}
// DetectContentTypeFromReader guesses the content type contained in the reader.
func DetectContentTypeFromReader(r io.Reader) (SniffedType, error) {
buf := make([]byte, sniffLen)
n, err := util.ReadAtMost(r, buf)
if err != nil {
return SniffedType{}, fmt.Errorf("DetectContentTypeFromReader io error: %w", err)
}
buf = buf[:n]
return DetectContentType(buf), nil
}
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