Added a simple client library and main file

client/client.go

@@ -0,0 +1,98 @@
+// Copyright 2023 Google LLC. All Rights Reserved.
+//
+// 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 client contains a simple RESTful client that retrieves information from
+// a distributor at a known URL.
+package client
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"strconv"
+
+	"github.com/transparency-dev/distributor/api"
+)
+
+// LogID is the globally unique name for a log.
+type LogID string
+
+// NewRestDistributor constructs a new client.
+func NewRestDistributor(baseURL string, client *http.Client) *RestDistributor {
+	return &RestDistributor{
+		baseURL: baseURL,
+		client:  client,
+	}
+}
+
+// RestDistributor is a client that fetches data via RESTful HTTP calls.
+type RestDistributor struct {
+	baseURL string
+	client  *http.Client
+}
+
+// GetLogs returns all logs that the distributor knows about.
+func (d *RestDistributor) GetLogs() ([]LogID, error) {
+	u, err := url.Parse(d.baseURL + api.HTTPGetLogs)
+	if err != nil {
+		return nil, err
+	}
+	r := make([]LogID, 0)
+	bs, err := d.fetchData(u)
+	if err != nil {
+		return nil, err
+	}
+	if err := json.Unmarshal(bs, &r); err != nil {
+		return nil, err
+	}
+	return r, nil
+}
+
+// GetCheckpointN returns the freshest checkpoint for the log that at least N witnesses
+// have provided signatures for.
+func (d *RestDistributor) GetCheckpointN(l LogID, n uint) ([]byte, error) {
+	u, err := url.Parse(d.baseURL + fmt.Sprintf(api.HTTPGetCheckpointN, l, strconv.Itoa(int(n))))
+	if err != nil {
+		return nil, err
+	}
+	return d.fetchData(u)
+}
+
+// GetCheckpointWitness returns the latest checkpoint that a named witness has provided
+// for the given log.
+func (d *RestDistributor) GetCheckpointWitness(l LogID, w string) ([]byte, error) {
+	u, err := url.Parse(d.baseURL + fmt.Sprintf(api.HTTPCheckpointByWitness, l, w))
+	if err != nil {
+		return nil, err
+	}
+	return d.fetchData(u)
+}
+
+func (d *RestDistributor) fetchData(u *url.URL) ([]byte, error) {
+	resp, err := d.client.Get(u.String())
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return nil, fmt.Errorf("failed to read body: %v", err)
+	}
+	if resp.StatusCode != 200 {
+		return nil, fmt.Errorf("bad status response (%s): %q", resp.Status, body)
+	}
+	return body, nil
+}

cmd/client/client.go

@@ -0,0 +1,49 @@
+// Copyright 2023 Google LLC. All Rights Reserved.
+//
+// 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.
+
+// client is a simple client that demonstrates fetching data from a distributor.
+package main
+
+import (
+	"flag"
+	"fmt"
+	"net/http"
+
+	"github.com/golang/glog"
+	"github.com/transparency-dev/distributor/client"
+)
+
+var (
+	baseURL = flag.String("base_url", "https://api.transparency.dev", "The base URL of the distributor")
+	n       = flag.Uint("n", 2, "The desired number of witness signatures for each log")
+)
+
+func main() {
+	flag.Parse()
+
+	d := client.NewRestDistributor(*baseURL, http.DefaultClient)
+
+	logs, err := d.GetLogs()
+	if err != nil {
+		glog.Exitf("Failed to enumerate logs: %v", err)
+	}
+	for _, l := range logs {
+		cp, err := d.GetCheckpointN(l, *n)
+		if err != nil {
+			glog.Warningf("Could not get checkpoint.%d for log %s: %v", *n, l, err)
+			continue
+		}
+		fmt.Printf("Checkpoint.%d for log %s:\n'''\n%s\n'''\n\n", *n, l, cp)
+	}
+}