promtool: support creating tsdb blocks from a pipe (#16011)

This is very useful when piping the input file to stdin and then using
/dev/stdin as the input file. e.g.

    xzcat dump.xz |
    	promtool tsdb create-blocks-from openmetrics /dev/stdin /tmp/data

Signed-off-by: Nicolas Peugnet <nicolas.peugnet@lip6.fr>

cmd/promtool/tsdb.go

@@ -826,17 +826,31 @@ func checkErr(err error) int {
 }
 
 func backfillOpenMetrics(path, outputDir string, humanReadable, quiet bool, maxBlockDuration time.Duration, customLabels map[string]string) int {
-	inputFile, err := fileutil.OpenMmapFile(path)
+	var buf []byte
+	info, err := os.Stat(path)
 	if err != nil {
 		return checkErr(err)
 	}
-	defer inputFile.Close()
+	if info.Mode()&(os.ModeNamedPipe|os.ModeCharDevice) != 0 {
+		// Read the pipe chunks by chunks as it cannot be mmap-ed
+		buf, err = os.ReadFile(path)
+		if err != nil {
+			return checkErr(err)
+		}
+	} else {
+		inputFile, err := fileutil.OpenMmapFile(path)
+		if err != nil {
+			return checkErr(err)
+		}
+		defer inputFile.Close()
+		buf = inputFile.Bytes()
+	}
 
 	if err := os.MkdirAll(outputDir, 0o777); err != nil {
 		return checkErr(fmt.Errorf("create output dir: %w", err))
 	}
 
-	return checkErr(backfill(5000, inputFile.Bytes(), outputDir, humanReadable, quiet, maxBlockDuration, customLabels))
+	return checkErr(backfill(5000, buf, outputDir, humanReadable, quiet, maxBlockDuration, customLabels))
 }
 
 func displayHistogram(dataType string, datas []int, total int) {

cmd/promtool/tsdb_posix_test.go

@@ -0,0 +1,69 @@
+// Copyright 2017 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.
+
+//go:build !windows
+
+package main
+
+import (
+	"bytes"
+	"io"
+	"math"
+	"os"
+	"path"
+	"syscall"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/prometheus/prometheus/tsdb"
+)
+
+func TestTSDBDumpOpenMetricsRoundTripPipe(t *testing.T) {
+	initialMetrics, err := os.ReadFile("testdata/dump-openmetrics-roundtrip-test.prom")
+	require.NoError(t, err)
+	initialMetrics = normalizeNewLine(initialMetrics)
+
+	pipeDir := t.TempDir()
+	dbDir := t.TempDir()
+
+	// create pipe
+	pipe := path.Join(pipeDir, "pipe")
+	err = syscall.Mkfifo(pipe, 0o666)
+	require.NoError(t, err)
+
+	go func() {
+		// open pipe to write
+		in, err := os.OpenFile(pipe, os.O_WRONLY, os.ModeNamedPipe)
+		require.NoError(t, err)
+		defer func() { require.NoError(t, in.Close()) }()
+		_, err = io.Copy(in, bytes.NewReader(initialMetrics))
+		require.NoError(t, err)
+	}()
+
+	// Import samples from OM format
+	code := backfillOpenMetrics(pipe, dbDir, false, false, 2*time.Hour, map[string]string{})
+	require.Equal(t, 0, code)
+	db, err := tsdb.Open(dbDir, nil, nil, tsdb.DefaultOptions(), nil)
+	require.NoError(t, err)
+	t.Cleanup(func() {
+		require.NoError(t, db.Close())
+	})
+
+	// Dump the blocks into OM format
+	dumpedMetrics := getDumpedSamples(t, dbDir, "", math.MinInt64, math.MaxInt64, []string{"{__name__=~'(?s:.*)'}"}, formatSeriesSetOpenMetrics)
+
+	// Should get back the initial metrics.
+	require.Equal(t, string(initialMetrics), dumpedMetrics)
+}