tools: Add gitiles package

Wraps the luci package to make it a bit friendlier.

Bug: dawn:1342
Change-Id: I70bf01b7ef5fcf210a2ff7ccafa49ea0720ae125
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/86526
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Ben Clayton <bclayton@chromium.org>

tools/src/gitiles/gitiles.go

@@ -0,0 +1,72 @@
+// Copyright 2022 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package gitiles provides helpers for interfacing with gitiles
+package gitiles
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+
+	"go.chromium.org/luci/common/api/gitiles"
+	gpb "go.chromium.org/luci/common/proto/gitiles"
+)
+
+// Gitiles is the client to communicate with Gitiles.
+type Gitiles struct {
+	client  gpb.GitilesClient
+	project string
+}
+
+// New creates a client to communicate with Gitiles, for the given host and
+// project.
+func New(ctx context.Context, host, project string) (*Gitiles, error) {
+	client, err := gitiles.NewRESTClient(http.DefaultClient, host, false)
+	if err != nil {
+		return nil, err
+	}
+	return &Gitiles{client, project}, nil
+}
+
+// Hash returns the git hash of the object with the given 'committish' reference.
+func (g *Gitiles) Hash(ctx context.Context, ref string) (string, error) {
+	res, err := g.client.Log(ctx, &gpb.LogRequest{
+		Project:    g.project,
+		Committish: ref,
+		PageSize:   1,
+	})
+	if err != nil {
+		return "", err
+	}
+	log := res.GetLog()
+	if len(log) == 0 {
+		return "", fmt.Errorf("gitiles returned log was empty")
+	}
+	return log[0].Id, nil
+}
+
+// DownloadFile downloads a single file with the given project-relative path at
+// the given reference.
+func (g *Gitiles) DownloadFile(ctx context.Context, ref, path string) (string, error) {
+	res, err := g.client.DownloadFile(ctx, &gpb.DownloadFileRequest{
+		Project:    g.project,
+		Committish: ref,
+		Path:       path,
+	})
+	if err != nil {
+		return "", err
+	}
+	return res.GetContents(), nil
+}