update cosmovisor README and set buffer size to ENV setting

cosmovisor/args.go

@@ -1,11 +1,13 @@
 package cosmovisor
 
 import (
+	"bufio"
 	"errors"
 	"fmt"
 	"net/url"
 	"os"
 	"path/filepath"
+	"strconv"
 )
 
 const (
@@ -21,6 +23,7 @@ type Config struct {
 	Name                  string
 	AllowDownloadBinaries bool
 	RestartAfterUpgrade   bool
+	LogBufferSize         int
 }
 
 // Root returns the root directory where all info lives
@@ -99,6 +102,17 @@ func GetConfigFromEnv() (*Config, error) {
 		cfg.RestartAfterUpgrade = true
 	}
 
+	logBufferSizeStr := os.Getenv("DAEMON_LOG_BUFFER_SIZE")
+	if logBufferSizeStr != "" {
+		logBufferSize, err := strconv.Atoi(logBufferSizeStr)
+		if err != nil {
+			return nil, err
+		}
+		cfg.LogBufferSize = logBufferSize * 1024
+	} else {
+		cfg.LogBufferSize = bufio.MaxScanTokenSize
+	}
+
 	if err := cfg.validate(); err != nil {
 		return nil, err
 	}

cosmovisor/process.go

@@ -38,6 +38,17 @@ func LaunchProcess(cfg *Config, args []string, stdout, stderr io.Writer) (bool,
 
 	scanOut := bufio.NewScanner(io.TeeReader(outpipe, stdout))
 	scanErr := bufio.NewScanner(io.TeeReader(errpipe, stderr))
+	// set scanner's buffer size to cfg.LogBufferSize, and ensure larger than bufio.MaxScanTokenSize otherwise fallback to bufio.MaxScanTokenSize
+	var maxCapacity int
+	if cfg.LogBufferSize < bufio.MaxScanTokenSize {
+		maxCapacity = bufio.MaxScanTokenSize
+	} else {
+		maxCapacity = cfg.LogBufferSize
+	}
+	bufOut := make([]byte, maxCapacity)
+	bufErr := make([]byte, maxCapacity)
+	scanOut.Buffer(bufOut, maxCapacity)
+	scanErr.Buffer(bufErr, maxCapacity)
 
 	if err := cmd.Start(); err != nil {
 		return false, fmt.Errorf("launching process %s %s: %w", bin, strings.Join(args, " "), err)

cosmovisor/scanner.go

@@ -27,10 +27,6 @@ type UpgradeInfo struct {
 // It returns (nil, err) if the input stream errored
 // It returns (nil, nil) if the input closed without ever matching the regexp
 func WaitForUpdate(scanner *bufio.Scanner) (*UpgradeInfo, error) {
-	// set larger buffer in case the line is too long, the default one is 64*1024
-	const maxCapacity = 512 * 1024
-	buf := make([]byte, maxCapacity)
-	scanner.Buffer(buf, maxCapacity)
 	for scanner.Scan() {
 		line := scanner.Text()
 		if upgradeRegex.MatchString(line) {

docs/run-node/cosmovisor.md

@@ -25,6 +25,7 @@ binary).
 command line arguments and flags (but new binary) after a successful upgrade. By default, `cosmovisor` dies
 afterwards and allows the supervisor to restart it if needed. Note that this will not auto-restart the child
 if there was an error.
+* `DAEMON_LOG_BUFFER_SIZE` (*optional*) is the buffer size for cosmovisor to scan log. If not set, it will use the default [64](https://github.com/golang/go/blob/2217e89ba326875470a856cd0da79f3ec9a896b8/src/bufio/scan.go#L80). (e.g. set to `256` or `512`) It is to avoid scanning stuck in case of long line of the log.
 
 ## Data Folder Layout