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