add the NewPidFileFn to helper

Signed-off-by: sbookworm <lisong.cruise@gmail.com>

prometheus/helper.go

@@ -0,0 +1,38 @@
+// Copyright 2020 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 prometheus
+
+import (
+	"fmt"
+	"io/ioutil"
+	"strconv"
+	"strings"
+)
+
+// NewPidFileFn returns a function that retrieves a pid from the specified file.
+// It is meant to be used for the PidFn field in ProcessCollectorOpts.
+func NewPidFileFn(pidFilePath string) func() (int, error) {
+	return func() (int, error) {
+		content, err := ioutil.ReadFile(pidFilePath)
+		if err != nil {
+			return 0, fmt.Errorf("can't read pid file %q: %+v", pidFilePath, err)
+		}
+		pid, err := strconv.Atoi(strings.TrimSpace(string(content)))
+		if err != nil {
+			return 0, fmt.Errorf("can't parse pid file %q: %+v", pidFilePath, err)
+		}
+
+		return pid, nil
+	}
+}

prometheus/helper_test.go

@@ -0,0 +1,84 @@
+// Copyright 2020 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 prometheus
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+// TestNewPidFileFn ...
+func TestNewPidFileFn(t *testing.T) {
+	folderPath, err := os.Getwd()
+	if err != nil {
+		t.Error("failed to get current path")
+	}
+	mockPidFilePath := filepath.Join(folderPath, "mockPidFile")
+	defer os.Remove(mockPidFilePath)
+
+	testCases := []struct {
+		mockPidFile       func()
+		expectedErrPrefix string
+		expectedPid       int
+		desc              string
+	}{
+		{
+			mockPidFile: func() {
+				os.Remove(mockPidFilePath)
+			},
+			expectedErrPrefix: "can't read pid file",
+			expectedPid:       0,
+			desc:              "no existed pid file",
+		},
+		{
+			mockPidFile: func() {
+				os.Remove(mockPidFilePath)
+				f, _ := os.Create(mockPidFilePath)
+				f.Write([]byte("abc"))
+				f.Close()
+			},
+			expectedErrPrefix: "can't parse pid file",
+			expectedPid:       0,
+			desc:              "existed pid file, error pid number",
+		},
+		{
+			mockPidFile: func() {
+				os.Remove(mockPidFilePath)
+				f, _ := os.Create(mockPidFilePath)
+				f.Write([]byte("123"))
+				f.Close()
+			},
+			expectedErrPrefix: "",
+			expectedPid:       123,
+			desc:              "existed pid file, correct pid number",
+		},
+	}
+
+	for _, tc := range testCases {
+		fn := NewPidFileFn(mockPidFilePath)
+		if fn == nil {
+			t.Error("Should not get nil PidFileFn")
+		}
+
+		tc.mockPidFile()
+
+		if pid, err := fn(); pid != tc.expectedPid || (err != nil && !strings.HasPrefix(err.Error(), tc.expectedErrPrefix)) {
+			fmt.Println(err.Error())
+			t.Error(tc.desc)
+		}
+	}
+}