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artifact.go
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artifact.go
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// Copyright 2016 Amazon.com, Inc. or its affiliates. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License"). You may not
// use this file except in compliance with the License. A copy of the
// License is located at
//
// http://aws.amazon.com/apache2.0/
//
// or in the "license" file accompanying this file. This file 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 artifact contains utilities for working downloading files.
package artifact
import (
"crypto/md5"
"crypto/sha256"
"encoding/hex"
"fmt"
"io"
"net/http"
"net/url"
"os"
"path/filepath"
"strings"
"github.com/aws/amazon-ssm-agent/agent/appconfig"
"github.com/aws/amazon-ssm-agent/agent/fileutil"
"github.com/aws/amazon-ssm-agent/agent/log"
"github.com/aws/amazon-ssm-agent/agent/s3util"
"github.com/aws/aws-sdk-go/aws"
"github.com/aws/aws-sdk-go/aws/session"
"github.com/aws/aws-sdk-go/service/s3"
)
// DownloadOutput holds the result of file download operation.
type DownloadOutput struct {
LocalFilePath string
IsUpdated bool
IsHashMatched bool
}
// DownloadInput specifies the input to file download operation
type DownloadInput struct {
SourceURL string
DestinationDirectory string
SourceHashValue string
SourceHashType string
}
// httpDownload attempts to download a file via http/s call
func httpDownload(log log.T, fileURL string, destFile string) (output DownloadOutput, err error) {
log.Debugf("attempting to download as http/https download %v", destFile)
eTagFile := destFile + ".etag"
var check http.Client
var request *http.Request
request, err = http.NewRequest("GET", fileURL, nil)
if err != nil {
return
}
if fileutil.Exists(destFile) == true && fileutil.Exists(eTagFile) == true {
var existingETag string
existingETag, err = fileutil.ReadAllText(eTagFile)
request.Header.Add("If-None-Match", existingETag)
}
check = http.Client{
CheckRedirect: func(r *http.Request, via []*http.Request) error {
r.URL.Opaque = r.URL.Path
return nil
},
}
var resp *http.Response
resp, err = check.Do(request)
if err != nil {
log.Debug("failed to download from http/https, ", err)
fileutil.DeleteFile(destFile)
fileutil.DeleteFile(eTagFile)
return
}
if resp.StatusCode == http.StatusNotModified {
log.Debugf("Unchanged file.")
output.IsUpdated = false
output.LocalFilePath = destFile
return output, nil
} else if resp.StatusCode != http.StatusOK {
log.Debug("failed to download from http/https, ", err)
fileutil.DeleteFile(destFile)
fileutil.DeleteFile(eTagFile)
err = fmt.Errorf("http request failed. status:%v statuscode:%v", resp.Status, resp.StatusCode)
return
}
defer resp.Body.Close()
eTagValue := resp.Header.Get("Etag")
if eTagValue != "" {
log.Debug("file eTagValue is ", eTagValue)
err = fileutil.WriteAllText(eTagFile, eTagValue)
if err != nil {
log.Errorf("failed to write eTagfile %v, %v ", eTagFile, err)
return
}
}
_, err = FileCopy(log, destFile, resp.Body)
if err == nil {
output.LocalFilePath = destFile
output.IsUpdated = true
} else {
log.Errorf("failed to write destFile %v, %v ", destFile, err)
}
return
}
// s3Download attempts to download a file via the aws sdk.
func s3Download(log log.T, amazonS3URL s3util.AmazonS3URL, destFile string) (output DownloadOutput, err error) {
log.Debugf("attempting to download as s3 download %v", destFile)
eTagFile := destFile + ".etag"
config := &aws.Config{}
var appConfig appconfig.SsmagentConfig
appConfig, err = appconfig.Config(false)
if err != nil {
log.Error("failed to read appconfig.")
} else {
creds, err1 := appConfig.ProfileCredentials()
if err1 != nil {
config.Credentials = creds
}
}
config.S3ForcePathStyle = aws.Bool(amazonS3URL.IsPathStyle)
config.Region = aws.String(amazonS3URL.Region)
params := &s3.GetObjectInput{
Bucket: aws.String(amazonS3URL.Bucket),
Key: aws.String(amazonS3URL.Key),
}
if fileutil.Exists(destFile) == true && fileutil.Exists(eTagFile) == true {
var existingETag string
existingETag, err = fileutil.ReadAllText(eTagFile)
if err != nil {
log.Debugf("failed to read etag file %v, %v", eTagFile, err)
return
}
params.IfNoneMatch = aws.String(existingETag)
}
s3client := s3.New(session.New(config))
req, resp := s3client.GetObjectRequest(params)
err = req.Send()
if err != nil {
if req.HTTPResponse == nil || req.HTTPResponse.StatusCode != http.StatusNotModified {
log.Debug("failed to download from s3, ", err)
fileutil.DeleteFile(destFile)
fileutil.DeleteFile(eTagFile)
return
}
log.Debugf("Unchanged file.")
output.IsUpdated = false
output.LocalFilePath = destFile
return output, nil
}
if *resp.ETag != "" {
log.Debug("files etag is ", *resp.ETag)
err = fileutil.WriteAllText(eTagFile, *resp.ETag)
if err != nil {
log.Errorf("failed to write eTagfile %v, %v ", eTagFile, err)
return
}
}
defer resp.Body.Close()
_, err = FileCopy(log, destFile, resp.Body)
if err == nil {
output.LocalFilePath = destFile
output.IsUpdated = true
} else {
log.Errorf("failed to write destFile %v, %v ", destFile, err)
}
return
}
// FileCopy copies the content from reader to destinationPath file
func FileCopy(log log.T, destinationPath string, src io.Reader) (written int64, err error) {
var file *os.File
file, err = os.Create(destinationPath)
if err != nil {
log.Errorf("failed to create file. %v", err)
return
}
defer file.Close()
var size int64
size, err = io.Copy(file, src)
log.Infof("%s with %v bytes downloaded", destinationPath, size)
return
}
// Download is a generic utility which attempts to download smartly.
func Download(log log.T, input DownloadInput) (output DownloadOutput, err error) {
// parse the url
var fileURL *url.URL
fileURL, err = url.Parse(input.SourceURL)
if err != nil {
err = fmt.Errorf("url parsing failed. %v", err)
return
}
// create destination directory
var destinationDir = input.DestinationDirectory
if destinationDir == "" {
destinationDir = appconfig.DownloadRoot
}
// create directory where artifacts are downloaded.
err = fileutil.MakeDirs(destinationDir)
if err != nil {
err = fmt.Errorf("failed to create directory=%v, err=%v", destinationDir, err)
return
}
// process if the url is local file or it has already been downloaded.
var isLocalFile = false
isLocalFile, err = fileutil.LocalFileExist(input.SourceURL)
if err != nil {
err = fmt.Errorf("check for local file exists returned %v", err)
err = nil
}
if isLocalFile == true {
err = fmt.Errorf("source is a local file, skipping download. %v", input.SourceURL)
output.LocalFilePath = input.SourceURL
output.IsUpdated = false
output.IsHashMatched, err = VerifyHash(log, input, output)
} else {
err = fmt.Errorf("source file wasn't found locally, will attempt as web download. %v", input.SourceURL)
// compute the local filename which is hash of url_filename
// Generating a hash_filename will also help against attackers
// from specifying a directory and filename to overwrite any ami/built-in files.
urlHash := md5.Sum([]byte(fileURL.String()))
fileName := filepath.Base(fileURL.String())
output.LocalFilePath = filepath.Join(destinationDir, fmt.Sprintf("%x_%v", urlHash, fileName))
amazonS3URL := s3util.ParseAmazonS3URL(log, fileURL)
if amazonS3URL.IsBucketAndKeyPresent() {
// source is s3
output, err = s3Download(log, amazonS3URL, output.LocalFilePath)
} else {
// simple httphttps download
output, err = httpDownload(log, input.SourceURL, output.LocalFilePath)
}
if err != nil {
return
}
isLocalFile, err = fileutil.LocalFileExist(output.LocalFilePath)
if isLocalFile == true {
output.IsHashMatched, err = VerifyHash(log, input, output)
}
}
return
}
// VerifyHash verifies the hash of the url file as per specified hash algorithm type and its value
func VerifyHash(log log.T, input DownloadInput, output DownloadOutput) (match bool, err error) {
match = false
// if there is no hash specified, do not check
if input.SourceHashValue == "" {
match = true
return
}
// check and set default hashing algorithm
hashAlgorithm := input.SourceHashType
if hashAlgorithm == "" {
hashAlgorithm = "sha256"
}
computedHashValue := ""
if strings.EqualFold(hashAlgorithm, "sha256") {
computedHashValue, err = Sha256HashValue(log, output.LocalFilePath)
} else if strings.EqualFold(hashAlgorithm, "md5") {
computedHashValue, err = Md5HashValue(log, output.LocalFilePath)
}
if err != nil {
return
}
match = strings.EqualFold(input.SourceHashValue, computedHashValue)
if match == false {
err = fmt.Errorf("failed to verify hash of downloadinput %v", input)
}
return
}
// Sha256HashValue gets the sha256 hash value
func Sha256HashValue(log log.T, filePath string) (hash string, err error) {
var exists = false
exists, err = fileutil.LocalFileExist(filePath)
if err != nil || exists == false {
return
}
var f *os.File
f, err = os.Open(filePath)
if err != nil {
log.Error(err)
}
defer f.Close()
hasher := sha256.New()
if _, err = io.Copy(hasher, f); err != nil {
log.Error(err)
}
hash = hex.EncodeToString(hasher.Sum(nil))
log.Debugf("Hash=%v, FilePath=%v", hash, filePath)
return
}
// Md5HashValue gets the md5 hash value
func Md5HashValue(log log.T, filePath string) (hash string, err error) {
var exists = false
exists, err = fileutil.LocalFileExist(filePath)
if err != nil || exists == false {
return
}
var f *os.File
f, err = os.Open(filePath)
if err != nil {
log.Error(err)
}
defer f.Close()
hasher := md5.New()
if _, err = io.Copy(hasher, f); err != nil {
log.Error(err)
}
hash = hex.EncodeToString(hasher.Sum(nil))
log.Debugf("Hash=%v, FilePath=%v", hash, filePath)
return
}