feat(pgsql): implement application_name handling in connection

pkg/pgsql/connection.go

@@ -0,0 +1,85 @@
+package pgsql
+
+import (
+	"context"
+	"fmt"
+	"runtime/debug"
+	"strings"
+
+	"github.com/jackc/pgx/v5"
+)
+
+const (
+	defaultApplicationPrefix = "relspecgo"
+	postgresIdentifierMaxLen = 63
+)
+
+// BuildApplicationName returns a PostgreSQL application_name in the form:
+// relspecgo/<version>[:<component>]
+func BuildApplicationName(component string) string {
+	appName := fmt.Sprintf("%s/%s", defaultApplicationPrefix, relspecVersion())
+	component = strings.TrimSpace(component)
+	if component != "" {
+		appName = appName + ":" + component
+	}
+	if len(appName) > postgresIdentifierMaxLen {
+		appName = appName[:postgresIdentifierMaxLen]
+	}
+	return appName
+}
+
+// ParseConfigWithApplicationName parses a connection string and applies a default
+// application_name when one is not explicitly provided by the caller.
+func ParseConfigWithApplicationName(connString, component string) (*pgx.ConnConfig, error) {
+	cfg, err := pgx.ParseConfig(connString)
+	if err != nil {
+		return nil, err
+	}
+
+	if cfg.RuntimeParams == nil {
+		cfg.RuntimeParams = map[string]string{}
+	}
+
+	if strings.TrimSpace(cfg.RuntimeParams["application_name"]) == "" {
+		cfg.RuntimeParams["application_name"] = BuildApplicationName(component)
+	}
+
+	return cfg, nil
+}
+
+// Connect establishes a PostgreSQL connection with a default relspec
+// application_name when the caller does not provide one in the DSN.
+func Connect(ctx context.Context, connString, component string) (*pgx.Conn, error) {
+	cfg, err := ParseConfigWithApplicationName(connString, component)
+	if err != nil {
+		return nil, err
+	}
+
+	return pgx.ConnectConfig(ctx, cfg)
+}
+
+func relspecVersion() string {
+	info, ok := debug.ReadBuildInfo()
+	if !ok {
+		return "dev"
+	}
+
+	version := strings.TrimSpace(info.Main.Version)
+	if version != "" && version != "(devel)" {
+		return version
+	}
+
+	for _, setting := range info.Settings {
+		if setting.Key == "vcs.revision" {
+			revision := strings.TrimSpace(setting.Value)
+			if len(revision) >= 7 {
+				return revision[:7]
+			}
+			if revision != "" {
+				return revision
+			}
+		}
+	}
+
+	return "dev"
+}