weldr/compose/ostree: introduce URL parameter

For now this is simply used to resolve the parent commit, in case
one is not provided. In the future it will be used by new image
types to actually pull content from.

This extends the weldr API, so that future work does not have to
modify that.

The logic we now implement for the ostree commit image types is:
If the URL is provided, but the parent commit is not. The parent
commit is taken to be the current HEAD of the ostree repo at the
given url, with the given (or default) ref.

This only provides a small optional convenience, but we will
soon introduce image types where the URL of the repository is
required.

This commit still needs testing.

Signed-off-by: Tom Gundersen <teg@jklm.no>

internal/weldr/api.go

@@ -4,6 +4,7 @@ import (
 	"archive/tar"
 	"bytes"
 	"crypto/rand"
+	"encoding/hex"
 	"encoding/json"
 	errors_package "errors"
 	"fmt"
@@ -1798,6 +1799,36 @@ func (api *API) blueprintsTagHandler(writer http.ResponseWriter, request *http.R
 	statusResponseOK(writer)
 }
 
+func ostreeResolveRef(location, ref string) (string, error) {
+	u, err := url.Parse(location)
+	if err != nil {
+		return "", err
+	}
+	u, err = u.Parse("refs/heads/")
+	if err != nil {
+		return "", err
+	}
+	u, err = u.Parse(ref)
+	if err != nil {
+		return "", err
+	}
+	resp, err := http.Get(u.String())
+	if err != nil {
+		return "", err
+	}
+	body, err := ioutil.ReadAll(resp.Body)
+	if err != nil {
+		return "", err
+	}
+	parent := strings.TrimSpace(string(body))
+	// Check that this is at least a hex string.
+	_, err = hex.DecodeString(parent)
+	if err != nil {
+		return "", err
+	}
+	return parent, nil
+}
+
 // Schedule new compose by first translating the appropriate blueprint into a pipeline and then
 // pushing it into the channel for waiting builds.
 func (api *API) composeHandler(writer http.ResponseWriter, request *http.Request, params httprouter.Params) {
@@ -1806,6 +1837,7 @@ func (api *API) composeHandler(writer http.ResponseWriter, request *http.Request
 	}
 
 	type OSTreeRequest struct {
+		URL    string `json:"url"`
 		Ref    string `json:"ref"`
 		Parent string `json:"parent"`
 	}
@@ -1883,6 +1915,31 @@ func (api *API) composeHandler(writer http.ResponseWriter, request *http.Request
 		return
 	}
 
+	// Fetch parent ostree commit from ref + url if commit is not
+	// provided. The parameter name "parent" is perhaps slightly misleading
+	// as it represent whatever commit sha the image type requires, not
+	// strictly speaking just the parent commit.
+	if cr.OSTree.Ref != "" && cr.OSTree.URL != "" {
+		if cr.OSTree.Parent != "" {
+			errors := responseError{
+				ID:  "OSTreeOptionsError",
+				Msg: "Supply at most one of Parent and URL",
+			}
+			statusResponseError(writer, http.StatusBadRequest, errors)
+			return
+		}
+		parent, err := ostreeResolveRef(cr.OSTree.URL, cr.OSTree.Ref)
+		if err != nil {
+			errors := responseError{
+				ID:  "OSTreeCommitError",
+				Msg: err.Error(),
+			}
+			statusResponseError(writer, http.StatusBadRequest, errors)
+			return
+		}
+		cr.OSTree.Parent = parent
+	}
+
 	packages, buildPackages, err := api.depsolveBlueprint(bp, imageType)
 	if err != nil {
 		errors := responseError{