Changes to sidecar to fix some issues

cmd/mixtool/server.go

@@ -16,14 +16,14 @@ package main
 
 import (
 	"bufio"
-	"bytes"
 	"context"
 	"errors"
 	"fmt"
 	"io"
 	"io/ioutil"
 	"net/http"
 	"os"
+	"path/filepath"
 
 	"github.com/urfave/cli"
 )
@@ -99,39 +99,56 @@ type ruleProvisioner struct {
 // to existing, does not provision them. It returns whether Prometheus should
 // be reloaded and if an error has occurred.
 func (p *ruleProvisioner) provision(r io.Reader) (bool, error) {
-	b := bytes.NewBuffer(nil)
-	tr := io.TeeReader(r, b)
+	newData, err := ioutil.ReadAll(r)
+	if err != nil {
+		return false, fmt.Errorf("unable to read new rules: %w", err)
+	}
 
-	f, err := os.Open(p.ruleFile)
-	if err != nil && !os.IsNotExist(err) {
-		return false, fmt.Errorf("open rule file: %w", err)
+	tempfile, err := ioutil.TempFile(filepath.Dir(p.ruleFile), "temp-mixtool")
+	if err != nil {
+		return false, fmt.Errorf("unable to create temp file: %w", err)
 	}
-	if os.IsNotExist(err) {
-		f, err = os.Create(p.ruleFile)
-		if err != nil {
-			return false, fmt.Errorf("create rule file: %w", err)
-		}
+
+	n, err := tempfile.Write(newData)
+	if err != nil {
+		return false, fmt.Errorf("error when writing new rules: %w", err)
 	}
 
-	equal, err := readersEqual(tr, f)
+	if n != len(newData) {
+		return false, fmt.Errorf("writing error, wrote %d bytes, expected %d", n, len(newData))
+	}
+
+	tempfile.Sync()
+
+	ruleFileReader, err := os.OpenFile(p.ruleFile, os.O_RDWR, 0644)
 	if err != nil {
-		return false, fmt.Errorf("compare existing rules with provisioned intention: %w", err)
+		return false, fmt.Errorf("unable to read existing rules: %w", err)
 	}
-	if equal {
-		return false, nil
+
+	newFileReader, err := os.OpenFile(tempfile.Name(), os.O_RDWR, 0644)
+	if err != nil {
+		return false, fmt.Errorf("unable to open new rules file: %w", err)
 	}
 
-	if err := f.Truncate(0); err != nil {
-		return false, fmt.Errorf("truncate file: %w", err)
+	equal, err := readersEqual(newFileReader, ruleFileReader)
+	if err != nil {
+		return false, fmt.Errorf("error from readersEqual: %w", err)
 	}
 
-	if _, err := io.Copy(f, b); err != nil {
-		return false, fmt.Errorf("provision rule to file: %w", err)
+	if equal {
+		return false, nil
 	}
 
+	if err = os.Rename(tempfile.Name(), p.ruleFile); err != nil {
+		return false, fmt.Errorf("cannot rename rules file: %w", err)
+	}
 	return true, nil
 }
 
+type prometheusReloader struct {
+	prometheusReloadURL string
+}
+
 func readersEqual(r1, r2 io.Reader) (bool, error) {
 	buf1 := bufio.NewReader(r1)
 	buf2 := bufio.NewReader(r2)
@@ -153,10 +170,6 @@ func readersEqual(r1, r2 io.Reader) (bool, error) {
 	}
 }
 
-type prometheusReloader struct {
-	prometheusReloadURL string
-}
-
 func (r *prometheusReloader) triggerReload(ctx context.Context) error {
 	req, err := http.NewRequest("POST", r.prometheusReloadURL, nil)
 	if err != nil {

go.mod

@@ -11,7 +11,7 @@ require (
 	github.com/go-macaron/inject v0.0.0-20160627170012-d8a0b8677191 // indirect
 	github.com/go-macaron/session v0.0.0-20170320172209-b8e286a0dba8 // indirect
 	github.com/gobuffalo/packr v1.30.1
-	github.com/gobuffalo/packr/v2 v2.8.0
+	github.com/gobuffalo/packr/v2 v2.8.1
 	github.com/google/go-jsonnet v0.16.1-0.20200908152747-b70cbd441a39
 	github.com/gosimple/slug v1.2.0 // indirect
 	github.com/grafana/grafana v5.2.4+incompatible

go.sum

@@ -313,6 +313,8 @@ github.com/gobuffalo/packr/v2 v2.5.1 h1:TFOeY2VoGamPjQLiNDT3mn//ytzk236VMO2j7iHx
 github.com/gobuffalo/packr/v2 v2.5.1/go.mod h1:8f9c96ITobJlPzI44jj+4tHnEKNt0xXWSVlXRN9X1Iw=
 github.com/gobuffalo/packr/v2 v2.8.0 h1:IULGd15bQL59ijXLxEvA5wlMxsmx/ZkQv9T282zNVIY=
 github.com/gobuffalo/packr/v2 v2.8.0/go.mod h1:PDk2k3vGevNE3SwVyVRgQCCXETC9SaONCNSXT1Q8M1g=
+github.com/gobuffalo/packr/v2 v2.8.1 h1:tkQpju6i3EtMXJ9uoF5GT6kB+LMTimDWD8Xvbz6zDVA=
+github.com/gobuffalo/packr/v2 v2.8.1/go.mod h1:c/PLlOuTU+p3SybaJATW3H6lX/iK7xEz5OeMf+NnJpg=
 github.com/gobuffalo/syncx v0.0.0-20190224160051-33c29581e754/go.mod h1:HhnNqWY95UYwwW3uSASeV7vtgYkT2t16hJgV3AEPUpw=
 github.com/gobwas/glob v0.2.3/go.mod h1:d3Ez4x06l9bZtSvzIay5+Yzi0fmZzPgnTbPcKjJAkT8=
 github.com/gogo/googleapis v1.1.0/go.mod h1:gf4bu3Q80BeJ6H1S1vYPm8/ELATdvryBaNFGgqEef3s=
@@ -491,6 +493,8 @@ github.com/karrick/godirwalk v1.10.12/go.mod h1:RoGL9dQei4vP9ilrpETWE8CLOZ1kiN0L
 github.com/karrick/godirwalk v1.15.3/go.mod h1:j4mkqPuvaLI8mp1DroR3P6ad7cyYd4c1qeJ3RV7ULlk=
 github.com/karrick/godirwalk v1.15.5 h1:ErdAEFW/cKxQ5+9Gm/hopxB8ki21/di+vyNb9mHnHrA=
 github.com/karrick/godirwalk v1.15.5/go.mod h1:j4mkqPuvaLI8mp1DroR3P6ad7cyYd4c1qeJ3RV7ULlk=
+github.com/karrick/godirwalk v1.15.8 h1:7+rWAZPn9zuRxaIqqT8Ohs2Q2Ac0msBqwRdxNCr2VVs=
+github.com/karrick/godirwalk v1.15.8/go.mod h1:j4mkqPuvaLI8mp1DroR3P6ad7cyYd4c1qeJ3RV7ULlk=
 github.com/kisielk/errcheck v1.1.0/go.mod h1:EZBBE59ingxPouuu3KfxchcWSUPOHkagtvWXihfKN4Q=
 github.com/kisielk/errcheck v1.2.0/go.mod h1:/BMXB+zMLi60iA8Vv6Ksmxu/1UDYcXs4uQLJ+jE2L00=
 github.com/kisielk/gotool v1.0.0/go.mod h1:XhKaO+MFFWcvkIS/tQcRk01m1F5IRFswLeQ+oQHNcck=