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67 lines
2.1 KiB
Go
67 lines
2.1 KiB
Go
/*
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Copyright 2025 Docker Compose CLI 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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http://www.apache.org/licenses/LICENSE-2.0
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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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*/
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// Package pidfile provides helper functions to create and remove PID files.
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// A PID file is usually a file used to store the process ID of a running
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// process.
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//
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// This is a temporary copy of github.com/moby/moby/v2/pkg/pidfile, and
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// should be replaced once pidfile is available as a standalone module.
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package pidfile
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import (
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"bytes"
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"fmt"
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"os"
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"strconv"
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)
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// Read reads the "PID file" at path, and returns the PID if it contains a
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// valid PID of a running process, or 0 otherwise. It returns an error when
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// failing to read the file, or if the file doesn't exist, but malformed content
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// is ignored. Consumers should therefore check if the returned PID is a non-zero
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// value before use.
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func Read(path string) (pid int, _ error) {
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pidByte, err := os.ReadFile(path)
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if err != nil {
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return 0, err
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}
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pid, err = strconv.Atoi(string(bytes.TrimSpace(pidByte)))
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if err != nil {
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return 0, nil
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}
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if pid != 0 && alive(pid) {
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return pid, nil
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}
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return 0, nil
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}
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// Write writes a "PID file" at the specified path. It returns an error if the
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// file exists and contains a valid PID of a running process, or when failing
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// to write the file.
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func Write(path string, pid int) error {
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if pid < 1 {
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return fmt.Errorf("invalid PID (%d): only positive PIDs are allowed", pid)
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}
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oldPID, err := Read(path)
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if err != nil && !os.IsNotExist(err) {
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return err
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}
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if oldPID != 0 {
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return fmt.Errorf("process with PID %d is still running", oldPID)
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}
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return os.WriteFile(path, []byte(strconv.Itoa(pid)), 0o644)
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}
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