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// Copyright 2016 The Linux Foundation
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package main
import (
"encoding/json"
"io"
"io/ioutil"
"net/http"
"os"
"github.com/opencontainers/image-spec/schema"
"github.com/pkg/errors"
)
// supported autodetection types
const (
typeImageLayout = "imageLayout"
typeImage = "image"
typeManifest = "manifest"
typeManifestList = "manifestList"
typeConfig = "config"
)
// autodetect detects the validation type for the given path
// or an error if the validation type could not be resolved.
func autodetect(path string) (string, error) {
fi, err := os.Stat(path)
if err != nil {
return "", errors.Wrapf(err, "unable to access path") // err from os.Stat includes path name
}
if fi.IsDir() {
return typeImageLayout, nil
}
f, err := os.Open(path)
if err != nil {
return "", errors.Wrap(err, "unable to open file") // os.Open includes the filename
}
defer f.Close()
buf, err := ioutil.ReadAll(io.LimitReader(f, 512)) // read some initial bytes to detect content
if err != nil {
return "", errors.Wrap(err, "unable to read")
}
mimeType := http.DetectContentType(buf)
switch mimeType {
case "application/x-gzip":
return typeImage, nil
case "application/octet-stream":
return typeImage, nil
case "text/plain; charset=utf-8":
// might be a JSON file, will be handled below
default:
return "", errors.New("unknown file type")
}
if _, err := f.Seek(0, os.SEEK_SET); err != nil {
return "", errors.Wrap(err, "unable to seek")
}
header := struct {
SchemaVersion int `json:"schemaVersion"`
MediaType string `json:"mediaType"`
Config interface{} `json:"config"`
}{}
if err := json.NewDecoder(f).Decode(&header); err != nil {
if _, errSeek := f.Seek(0, os.SEEK_SET); errSeek != nil {
return "", errors.Wrap(err, "unable to seek")
}
e := errors.Wrap(
schema.WrapSyntaxError(f, err),
"unable to parse JSON",
)
return "", e
}
switch {
case header.MediaType == string(schema.MediaTypeManifest):
return typeManifest, nil
case header.MediaType == string(schema.MediaTypeManifestList):
return typeManifestList, nil
case header.MediaType == "" && header.SchemaVersion == 0 && header.Config != nil:
// config files don't have mediaType/schemaVersion header
return typeConfig, nil
}
return "", errors.New("unknown media type")
}
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