pangolin_exporter

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// Copyright 2023 The Prometheus Authors
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package collector
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import (
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	"database/sql"
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	"fmt"
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	"regexp"
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	"github.com/blang/semver/v4"
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)
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type instance struct {
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	dsn     string
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	db      *sql.DB
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	version semver.Version
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}
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func newInstance(dsn string) (*instance, error) {
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	i := &instance{
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		dsn: dsn,
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	}
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	// "Create" a database handle to verify the DSN provided is valid.
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	// Open is not guaranteed to create a connection.
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	db, err := sql.Open("postgres", dsn)
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	if err != nil {
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		return nil, err
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	}
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	db.Close()
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	return i, nil
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}
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// copy returns a copy of the instance.
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func (i *instance) copy() *instance {
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	return &instance{
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		dsn: i.dsn,
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	}
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}
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func (i *instance) setup() error {
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	db, err := sql.Open("postgres", i.dsn)
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	if err != nil {
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		return err
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	}
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	db.SetMaxOpenConns(1)
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	db.SetMaxIdleConns(1)
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	i.db = db
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	version, err := queryVersion(i.db)
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	if err != nil {
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		return fmt.Errorf("error querying postgresql version: %w", err)
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	} else {
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		i.version = version
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	}
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	return nil
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}
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func (i *instance) getDB() *sql.DB {
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	return i.db
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}
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func (i *instance) Close() error {
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	return i.db.Close()
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}
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// Regex used to get the "short-version" from the postgres version field.
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// The result of SELECT version() is something like "PostgreSQL 9.6.2 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 6.2.1 20160830, 64-bit"
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var versionRegex = regexp.MustCompile(`^\w+ ((\d+)(\.\d+)?(\.\d+)?)`)
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var serverVersionRegex = regexp.MustCompile(`^((\d+)(\.\d+)?(\.\d+)?)`)
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func queryVersion(db *sql.DB) (semver.Version, error) {
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	var version string
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	err := db.QueryRow("SELECT version();").Scan(&version)
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	if err != nil {
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		return semver.Version{}, err
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	}
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	submatches := versionRegex.FindStringSubmatch(version)
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	if len(submatches) > 1 {
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		return semver.ParseTolerant(submatches[1])
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	}
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	// We could also try to parse the version from the server_version field.
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	// This is of the format 13.3 (Debian 13.3-1.pgdg100+1)
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	err = db.QueryRow("SHOW server_version;").Scan(&version)
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	if err != nil {
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		return semver.Version{}, err
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	}
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	submatches = serverVersionRegex.FindStringSubmatch(version)
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	if len(submatches) > 1 {
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		return semver.ParseTolerant(submatches[1])
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	}
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	return semver.Version{}, fmt.Errorf("could not parse version from %q", version)
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}
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