Drover's back, baby!

go/src/infra/tools/drover/disambiguate.go

Index: go/src/infra/tools/drover/disambiguate.go
diff --git a/go/src/infra/tools/drover/disambiguate.go b/go/src/infra/tools/drover/disambiguate.go
new file mode 100644
index 0000000000000000000000000000000000000000..c0f96b3553144d991dae9645b08fef5dce517624
--- /dev/null
+++ b/go/src/infra/tools/drover/disambiguate.go
@@ -0,0 +1,167 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+package main
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"net/http"
+	"reflect"
+	"sort"
+	"strings"
+
+	"infra/libs/gitiles"
+)
+
+const crRevAPI = "https://cr-rev.appspot.com/_ah/api/crrev/v1/"
+
+/* Takes a user-suppiled commit specifier, and resolves it to a commit hash and
+repo url.
+
+Possible input formats:
+  "deadbeefdeadbeefdeadbeefdeadbeefdeadbeef"
+  "29345"   # Cr-Commit-Position assuming refs/heads/master and src.git
+
+The disambiguation is done by crrev.com, and so this function may return an
+error if the service is not available.
+
+Additionally, this function may return an error if the commit specifier is
+not unambiguous.
+*/
+func disambiguateCommit(commitSpec string) (commit, url string, err error) {
+	commit = commitSpec
+	url = ""
+
+	resp, err := http.Get(crRevAPI + "redirect/" + commitSpec)
+	if err != nil {
+		return
+	}
+	defer resp.Body.Close()
+
+	// TODO(iannucci,stip): generate this from endpoints source code
+	jsonData := make(map[string]string)
+	if err = json.NewDecoder(resp.Body).Decode(&jsonData); err != nil {
+		return
+	}
+	commit, ok := jsonData["git_sha"]
+	if !ok {
+		err = errors.New("disambiguateCommit: expected 'git_sha' key")
+		return
+	}
+
+	rawURL, ok := jsonData["redirect_url"]
+	if !ok {
+		err = errors.New("disambiguateCommit: expected 'redirect_url' key")
+		return
+	}
+
+	url = strings.Split(rawURL, "+")[0]
+	return
+}
+
+type sortKey struct {
+	inexactMatch bool
+	partialMatch bool
+	nonHead      bool
+	refLength    int
+}
+
+// Sorts refCandidate's so that the least one is the best one.
+func (s *sortKey) less(other sortKey) bool {
+	return ((!s.inexactMatch && other.inexactMatch) ||
+		(!s.partialMatch && other.partialMatch) ||
+		(!s.nonHead && other.nonHead) ||
+		(s.refLength < other.refLength))
+}
+
+type refCandidate struct {
+	Ref       string
+	Confident bool
+	SortKey   sortKey
+}
+
+type sortableRefCandidates []refCandidate
+
+func (r sortableRefCandidates) Len() int      { return len(r) }
+func (r sortableRefCandidates) Swap(i, j int) { r[i], r[j] = r[j], r[i] }
+func (r sortableRefCandidates) Less(i, j int) bool {
+	return r[i].SortKey.less(r[j].SortKey)
+}
+
+func disambiguateRef(gitiles *gitiles.Gitiles, commit, refFragment string) (ref string, err error) {
+	result, err := gitiles.JSON(map[string]map[string]string{}, "+refs")
+	if err != nil {
+		return
+	}
+	refs := *result.(*map[string]map[string]string)
+
+	reverse := func(s []string) (ret []string) {
+		ret = make([]string, len(s))
+		for idx, el := range s {
+			ret[len(ret)-idx-1] = el
+		}
+		return
+	}
+
+	targetParts := reverse(strings.Split(refFragment, "/"))
+
+	// guess that we'll have about 10
+	candidates := make(sortableRefCandidates, 0, 10)
+
+	for ref := range refs {
+		if strings.HasSuffix(ref, refFragment) {
+			refParts := reverse(strings.Split(ref, "/"))
+
+			exactMatch := reflect.DeepEqual(refParts, targetParts)
+			wholeMatch := true
+			shortest := -1
+			if len(refParts) < len(targetParts) {
+				shortest = len(refParts)
+			} else {
+				shortest = len(targetParts)
+			}
+			for i := 0; i < shortest; i++ {
+				if refParts[i] != targetParts[i] {
+					wholeMatch = false
+					break
+				}
+			}
+			hasHeads := strings.Contains(ref, "heads")
+
+			confident := exactMatch || (wholeMatch && hasHeads)
+
+			candidates = append(candidates, refCandidate{
+				Ref:       ref,
+				Confident: confident,
+				SortKey: sortKey{
+					inexactMatch: !exactMatch,
+					partialMatch: !wholeMatch,
+					nonHead:      !hasHeads,
+					refLength:    len(ref),
+				},
+			})
+		}
+	}
+
+	if len(candidates) == 0 {
+		err = fmt.Errorf("disambiguateRef: no matching ref for %s", refFragment)
+		return
+	}
+
+	sort.Sort(candidates)
+	// TODO(iannucci): if we have logging, it would be good to dump all
+	// candidates in debug mode.
+	if !candidates[0].Confident {
+		fmt.Printf("No confident matches for refs given '%s'. Candidates:\n",
+			refFragment)
+		for _, c := range candidates {
+			fmt.Printf("  %s\n", c.Ref)
+		}
+		err = errors.New("disambiguateRef: no confident refs")
+	}
+
+	ref = candidates[0].Ref
+	return
+}