dotcloud/docker

package remotecontext // import "github.com/docker/docker/builder/remotecontext"

import (
    "bytes"
    "fmt"
    "io"
    "net"
    "net/http"
    "net/url"
    "regexp"

    "github.com/docker/docker/errdefs"
    "github.com/docker/docker/pkg/ioutils"
    "github.com/pkg/errors"
)

// 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)

// downloadRemote context from a url and returns it, along with the parsed content type
func downloadRemote(remoteURL string) (string, io.ReadCloser, error) {
    response, err := GetWithStatusError(remoteURL)
    if err != nil {
        return "", nil, errors.Wrapf(err, "error downloading remote context %s", remoteURL)
    }

    contentType, contextReader, err := inspectResponse(
        response.Header.Get("Content-Type"),
        response.Body,
        response.ContentLength)
    if err != nil {
        response.Body.Close()
        return "", nil, errors.Wrapf(err, "error detecting content type for remote %s", remoteURL)
    }

    return contentType, ioutils.NewReadCloserWrapper(contextReader, response.Body.Close), nil
}

// GetWithStatusError does an http.Get() and returns an error if the
// status code is 4xx or 5xx.
func GetWithStatusError(address string) (resp *http.Response, err error) {
    resp, err = http.Get(address) // #nosec G107 -- ignore G107: Potential HTTP request made with variable url
    if err != nil {
        if uerr, ok := err.(*url.Error); ok {
            if derr, ok := uerr.Err.(*net.DNSError); ok && !derr.IsTimeout {
                return nil, errdefs.NotFound(err)
            }
        }
        return nil, errdefs.System(err)
    }
    if resp.StatusCode < 400 {
        return resp, nil
    }
    msg := fmt.Sprintf("failed to GET %s with status %s", address, resp.Status)
    body, err := io.ReadAll(resp.Body)
    resp.Body.Close()
    if err != nil {
        return nil, errdefs.System(errors.New(msg + ": error reading body"))
    }

    msg += ": " + string(bytes.TrimSpace(body))
    switch resp.StatusCode {
    case http.StatusNotFound:
        return nil, errdefs.NotFound(errors.New(msg))
    case http.StatusBadRequest:
        return nil, errdefs.InvalidParameter(errors.New(msg))
    case http.StatusUnauthorized:
        return nil, errdefs.Unauthorized(errors.New(msg))
    case http.StatusForbidden:
        return nil, errdefs.Forbidden(errors.New(msg))
    }
    return nil, errdefs.Unknown(errors.New(msg))
}

// 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.Reader, clen int64) (string, io.Reader, error) {
    plen := clen
    if plen <= 0 || plen > maxPreambleLength {
        plen = maxPreambleLength
    }

    preamble := make([]byte, 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[:rlen])
    bodyReader := 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 == mimeTypeOctetStream {
        contentType, err = 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)
}