build: move log level parse code and add new leveled sub logger interface

build/log.go

@@ -1,7 +1,9 @@
 package build
 
 import (
+	"fmt"
 	"io"
+	"strings"
 
 	"github.com/btcsuite/btclog"
 )
@@ -93,3 +95,106 @@ func NewSubLogger(subsystem string,
 	// For any other configurations, we'll disable logging.
 	return btclog.Disabled
 }
+
+// SubLoggers is a type that holds a map of subsystem loggers keyed by their
+// subsystem name.
+type SubLoggers map[string]btclog.Logger
+
+// LeveledSubLogger provides the ability to retrieve the subsystem loggers of
+// a logger and set their log levels individually or all at once.
+type LeveledSubLogger interface {
+	// SubLoggers returns the map of all registered subsystem loggers.
+	SubLoggers() SubLoggers
+
+	// SupportedSubsystems returns a slice of strings containing the names
+	// of the supported subsystems. Should ideally correspond to the keys
+	// of the subsystem logger map and be sorted.
+	SupportedSubsystems() []string
+
+	// SetLogLevel assigns an individual subsystem logger a new log level.
+	SetLogLevel(subsystemID string, logLevel string)
+
+	// SetLogLevels assigns all subsystem loggers the same new log level.
+	SetLogLevels(logLevel string)
+}
+
+// ParseAndSetDebugLevels attempts to parse the specified debug level and set
+// the levels accordingly on the given logger. An appropriate error is returned
+// if anything is invalid.
+func ParseAndSetDebugLevels(level string, logger LeveledSubLogger) error {
+	// When the specified string doesn't have any delimiters, treat it as
+	// the log level for all subsystems.
+	if !strings.Contains(level, ",") && !strings.Contains(level, "=") {
+		// Validate debug log level.
+		if !validLogLevel(level) {
+			str := "the specified debug level [%v] is invalid"
+			return fmt.Errorf(str, level)
+		}
+
+		// Change the logging level for all subsystems.
+		logger.SetLogLevels(level)
+
+		return nil
+	}
+
+	// Split the specified string into subsystem/level pairs while detecting
+	// issues and update the log levels accordingly.
+	for _, logLevelPair := range strings.Split(level, ",") {
+		if !strings.Contains(logLevelPair, "=") {
+			str := "the specified debug level contains an " +
+				"invalid subsystem/level pair [%v]"
+			return fmt.Errorf(str, logLevelPair)
+		}
+
+		// Extract the specified subsystem and log level.
+		fields := strings.Split(logLevelPair, "=")
+		if len(fields) != 2 {
+			str := "the specified debug level has an invalid " +
+				"format [%v] -- use format subsystem1=level1," +
+				"subsystem2=level2"
+			return fmt.Errorf(str, logLevelPair)
+		}
+		subsysID, logLevel := fields[0], fields[1]
+		subLoggers := logger.SubLoggers()
+
+		// Validate subsystem.
+		if _, exists := subLoggers[subsysID]; !exists {
+			str := "the specified subsystem [%v] is invalid -- " +
+				"supported subsystems are %v"
+			return fmt.Errorf(
+				str, subsysID, logger.SupportedSubsystems(),
+			)
+		}
+
+		// Validate log level.
+		if !validLogLevel(logLevel) {
+			str := "the specified debug level [%v] is invalid"
+			return fmt.Errorf(str, logLevel)
+		}
+
+		logger.SetLogLevel(subsysID, logLevel)
+	}
+
+	return nil
+}
+
+// validLogLevel returns whether or not logLevel is a valid debug log level.
+func validLogLevel(logLevel string) bool {
+	switch logLevel {
+	case "trace":
+		fallthrough
+	case "debug":
+		fallthrough
+	case "info":
+		fallthrough
+	case "warn":
+		fallthrough
+	case "error":
+		fallthrough
+	case "critical":
+		fallthrough
+	case "off":
+		return true
+	}
+	return false
+}