Add collector interface

Uses node_exporter style collector registration

Signed-off-by: Joe Adams <github@joeadams.io>

collector/server.go

@@ -0,0 +1,100 @@
+// Copyright 2022 The Prometheus 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 collector
+
+import (
+	"database/sql"
+	"fmt"
+	"strings"
+
+	"github.com/lib/pq"
+)
+
+type server struct {
+	dsn  string
+	name string
+	db   *sql.DB
+}
+
+func makeServer(dsn string) (*server, error) {
+	name, err := parseServerName(dsn)
+	if err != nil {
+		return nil, err
+	}
+	return &server{
+		dsn:  dsn,
+		name: name,
+	}, nil
+}
+
+func (s *server) GetDB() (*sql.DB, error) {
+	if s.db != nil {
+		return s.db, nil
+	}
+
+	db, err := sql.Open("postgres", s.dsn)
+	if err != nil {
+		return nil, err
+	}
+	db.SetMaxOpenConns(1)
+	db.SetMaxIdleConns(1)
+
+	s.db = db
+
+	return s.db, nil
+}
+
+func (s *server) GetName() string {
+	return s.name
+}
+
+func (s *server) String() string {
+	return s.name
+}
+
+func parseServerName(url string) (string, error) {
+	dsn, err := pq.ParseURL(url)
+	if err != nil {
+		dsn = url
+	}
+
+	pairs := strings.Split(dsn, " ")
+	kv := make(map[string]string, len(pairs))
+	for _, pair := range pairs {
+		splitted := strings.SplitN(pair, "=", 2)
+		if len(splitted) != 2 {
+			return "", fmt.Errorf("malformed dsn %q", dsn)
+		}
+		// Newer versions of pq.ParseURL quote values so trim them off if they exist
+		key := strings.Trim(splitted[0], "'\"")
+		value := strings.Trim(splitted[1], "'\"")
+		kv[key] = value
+	}
+
+	var fingerprint string
+
+	if host, ok := kv["host"]; ok {
+		fingerprint += host
+	} else {
+		fingerprint += "localhost"
+	}
+
+	if port, ok := kv["port"]; ok {
+		fingerprint += ":" + port
+	} else {
+		fingerprint += ":5432"
+	}
+
+	return fingerprint, nil
+}