client: introduce the HTTP client (#7304)

ref #7300

Introduce the HTTP client.

Signed-off-by: JmPotato <ghzpotato@gmail.com>

Co-authored-by: ti-chi-bot[bot] <108142056+ti-chi-bot[bot]@users.noreply.github.com>

client/client.go

@@ -74,7 +74,7 @@ type GlobalConfigItem struct {
 	PayLoad   []byte
 }
 
-// Client is a PD (Placement Driver) client.
+// Client is a PD (Placement Driver) RPC client.
 // It should not be used after calling Close().
 type Client interface {
 	// GetClusterID gets the cluster ID from PD.
@@ -1062,7 +1062,7 @@ func (c *client) ScanRegions(ctx context.Context, key, endKey []byte, limit int)
 		defer span.Finish()
 	}
 	start := time.Now()
-	defer cmdDurationScanRegions.Observe(time.Since(start).Seconds())
+	defer func() { cmdDurationScanRegions.Observe(time.Since(start).Seconds()) }()
 
 	var cancel context.CancelFunc
 	scanCtx := ctx

client/http/api.go

@@ -0,0 +1,54 @@
+// Copyright 2023 TiKV Project 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 http
+
+import (
+	"fmt"
+	"net/url"
+)
+
+// The following constants are the paths of PD HTTP APIs.
+const (
+	HotRead             = "/pd/api/v1/hotspot/regions/read"
+	HotWrite            = "/pd/api/v1/hotspot/regions/write"
+	Regions             = "/pd/api/v1/regions"
+	regionByID          = "/pd/api/v1/region/id"
+	regionByKey         = "/pd/api/v1/region/key"
+	regionsByKey        = "/pd/api/v1/regions/key"
+	regionsByStoreID    = "/pd/api/v1/regions/store"
+	Stores              = "/pd/api/v1/stores"
+	MinResolvedTSPrefix = "/pd/api/v1/min-resolved-ts"
+)
+
+// RegionByID returns the path of PD HTTP API to get region by ID.
+func RegionByID(regionID uint64) string {
+	return fmt.Sprintf("%s/%d", regionByID, regionID)
+}
+
+// RegionByKey returns the path of PD HTTP API to get region by key.
+func RegionByKey(key []byte) string {
+	return fmt.Sprintf("%s/%s", regionByKey, url.QueryEscape(string(key)))
+}
+
+// RegionsByKey returns the path of PD HTTP API to scan regions with given start key, end key and limit parameters.
+func RegionsByKey(startKey, endKey []byte, limit int) string {
+	return fmt.Sprintf("%s?start_key=%s&end_key=%s&limit=%d",
+		regionsByKey, url.QueryEscape(string(startKey)), url.QueryEscape(string(endKey)), limit)
+}
+
+// RegionsByStoreID returns the path of PD HTTP API to get regions by store ID.
+func RegionsByStoreID(storeID uint64) string {
+	return fmt.Sprintf("%s/%d", regionsByStoreID, storeID)
+}