blob: 12f34c7b609a94d5c9340f312ccb59265914affe [file] [log] [blame]
package builder
import (
// When downloading remote contexts, limit the amount (in bytes)
// to be read from the response body in order to detect its Content-Type
const maxPreambleLength = 100
const acceptableRemoteMIME = `(?:application/(?:(?:x\-)?tar|octet\-stream|((?:x\-)?(?:gzip|bzip2?|xz)))|(?:text/plain))`
var mimeRe = regexp.MustCompile(acceptableRemoteMIME)
// MakeRemoteContext downloads a context from remoteURL and returns it.
// If contentTypeHandlers is non-nil, then the Content-Type header is read along with a maximum of
// maxPreambleLength bytes from the body to help detecting the MIME type.
// Look at acceptableRemoteMIME for more details.
// If a match is found, then the body is sent to the contentType handler and a (potentially compressed) tar stream is expected
// to be returned. If no match is found, it is assumed the body is a tar stream (compressed or not).
// In either case, an (assumed) tar stream is passed to MakeTarSumContext whose result is returned.
func MakeRemoteContext(remoteURL string, contentTypeHandlers map[string]func(io.ReadCloser) (io.ReadCloser, error)) (ModifiableContext, error) {
f, err := httputils.Download(remoteURL)
if err != nil {
return nil, fmt.Errorf("Error downloading remote context %s: %v", remoteURL, err)
defer f.Body.Close()
var contextReader io.ReadCloser
if contentTypeHandlers != nil {
contentType := f.Header.Get("Content-Type")
clen := f.ContentLength
contentType, contextReader, err = inspectResponse(contentType, f.Body, clen)
if err != nil {
return nil, fmt.Errorf("Error detecting content type for remote %s: %v", remoteURL, err)
defer contextReader.Close()
// This loop tries to find a content-type handler for the detected content-type.
// If it could not find one from the caller-supplied map, it tries the empty content-type `""`
// which is interpreted as a fallback handler (usually used for raw tar contexts).
for _, ct := range []string{contentType, ""} {
if fn, ok := contentTypeHandlers[ct]; ok {
defer contextReader.Close()
if contextReader, err = fn(contextReader); err != nil {
return nil, err
// Pass through - this is a pre-packaged context, presumably
// with a Dockerfile with the right name inside it.
return MakeTarSumContext(contextReader)
// DetectContextFromRemoteURL returns a context and in certain cases the name of the dockerfile to be used
// irrespective of user input.
// progressReader is only used if remoteURL is actually a URL (not empty, and not a Git endpoint).
func DetectContextFromRemoteURL(r io.ReadCloser, remoteURL string, createProgressReader func(in io.ReadCloser) io.ReadCloser) (context ModifiableContext, dockerfileName string, err error) {
switch {
case remoteURL == "":
context, err = MakeTarSumContext(r)
case urlutil.IsGitURL(remoteURL):
context, err = MakeGitContext(remoteURL)
case urlutil.IsURL(remoteURL):
context, err = MakeRemoteContext(remoteURL, map[string]func(io.ReadCloser) (io.ReadCloser, error){
httputils.MimeTypes.TextPlain: func(rc io.ReadCloser) (io.ReadCloser, error) {
dockerfile, err := ioutil.ReadAll(rc)
if err != nil {
return nil, err
// dockerfileName is set to signal that the remote was interpreted as a single Dockerfile, in which case the caller
// should use dockerfileName as the new name for the Dockerfile, irrespective of any other user input.
dockerfileName = DefaultDockerfileName
// TODO: return a context without tarsum
return archive.Generate(dockerfileName, string(dockerfile))
// fallback handler (tar context)
"": func(rc io.ReadCloser) (io.ReadCloser, error) {
return createProgressReader(rc), nil
err = fmt.Errorf("remoteURL (%s) could not be recognized as URL", remoteURL)
// inspectResponse looks into the http response data at r to determine whether its
// content-type is on the list of acceptable content types for remote build contexts.
// This function returns:
// - a string representation of the detected content-type
// - an io.Reader for the response body
// - an error value which will be non-nil either when something goes wrong while
// reading bytes from r or when the detected content-type is not acceptable.
func inspectResponse(ct string, r io.ReadCloser, clen int64) (string, io.ReadCloser, error) {
plen := clen
if plen <= 0 || plen > maxPreambleLength {
plen = maxPreambleLength
preamble := make([]byte, plen, plen)
rlen, err := r.Read(preamble)
if rlen == 0 {
return ct, r, errors.New("Empty response")
if err != nil && err != io.EOF {
return ct, r, err
preambleR := bytes.NewReader(preamble)
bodyReader := ioutil.NopCloser(io.MultiReader(preambleR, r))
// Some web servers will use application/octet-stream as the default
// content type for files without an extension (e.g. 'Dockerfile')
// so if we receive this value we better check for text content
contentType := ct
if len(ct) == 0 || ct == httputils.MimeTypes.OctetStream {
contentType, _, err = httputils.DetectContentType(preamble)
if err != nil {
return contentType, bodyReader, err
contentType = selectAcceptableMIME(contentType)
var cterr error
if len(contentType) == 0 {
cterr = fmt.Errorf("unsupported Content-Type %q", ct)
contentType = ct
return contentType, bodyReader, cterr
func selectAcceptableMIME(ct string) string {
return mimeRe.FindString(ct)