Logging in the peer application and in the shim interface to chaincodes is programmed using facilities provided by the github.com/op/go-logging package. This package supports
- Logging control based on the severity of the message
- Logging control based on the software module generating the message
- Different pretty-printing options based on the severity of the message
All logs are currently directed to stderr, and the pretty-printing is currently fixed. However global and module-level control of logging by severity is provided for both users and developers. There are currently no formalized rules for the types of information provided at each severity level, however when submitting bug reports the developers may want to see full logs down to the DEBUG level.
In pretty-printed logs the logging level is indicated both by color and by a 4-character code, e.g, "ERRO" for ERROR, "DEBU" for DEBUG, etc. In the logging context a module is an arbitrary name (string) given by developers to groups of related messages. In the pretty-printed example below, the logging modules "peer", "rest" and "main" are generating logs.
16:47:09.634 [peer] GetLocalAddress -> INFO 033 Auto detected peer address: 9.3.158.178:7051
16:47:09.635 [rest] StartOpenchainRESTServer -> INFO 035 Initializing the REST service...
16:47:09.635 [main] serve -> INFO 036 Starting peer with id=name:"vp1" , network id=dev, address=9.3.158.178:7051, discovery.rootnode=, validator=true
An arbitrary number of logging modules can be created at runtime, therefore there is no "master list" of modules, and logging control constructs can not check whether logging modules actually do or will exist. Also note that the logging module system does not understand hierarchy or wildcarding: You may see module names like "foo/bar" in the code, but the logging system only sees a flat string. It doesn't understand that "foo/bar" is related to "foo" in any way, or that "foo/*" might indicate all "submodules" of foo.
The logging level of the peer command can be controlled from the command line for each invocation using the --logging-level flag, for example
peer node start --logging-level=debug
The default logging level for each individual peer subcommand can also be
set in the
core.yaml
file. For example the key logging.node sets the default level for the node
subcommmand. Comments in the file also explain how the logging level can be
overridden in various ways by using environment varaibles.
Logging severity levels are specified using case-insensitive strings chosen from
CRITICAL | ERROR | WARNING | NOTICE | INFO | DEBUG
The full logging level specification for the peer is of the form
[<module>[,<module>...]=]<level>[:[<module>[,<module>...]=]<level>...]
A logging level by itself is taken as the overall default. Otherwise, overrides for individual or groups of modules can be specified using the
<module>[,<module>...]=<level>
syntax. Examples of specifications (valid for all of
--logging-level, environment variable and
core.yaml
settings):
info - Set default to INFO
warning:main,db=debug:chaincode=info - Default WARNING; Override for main,db,chaincode
chaincode=info:main=debug:db=debug:warning - Same as above
As independently executed programs, user-provided chaincodes can use any appropriate technique to create their private logs - from simple print statements to fully-annotated and level-controlled logs. The chaincode shim package provides APIs that allow a chaincode to create and manage logging objects whose logs will be formatted and interleaved consistently with the shim logs.
NewLogger(name string) *ChaincodeLogger - Create a logging object for use by a chaincode
(c *ChaincodeLogger) SetLevel(level LoggingLevel) - Set the logging level of the logger
(c *ChaincodeLogger) IsEnabledFor(level LoggingLevel) bool - Return true if logs will be generated at the given level
LogLevel(levelString string) (LoggingLevel, error) - Convert a string to a LoggingLevel
A LoggingLevel is a member of the enumeration
LogDebug, LogInfo, LogNotice, LogWarning, LogError, LogCritical
which can be used directly, or generated by passing a case-insensitive version of the strings
DEBUG, INFO, NOTICE, WARNING, ERROR, CRITICAL
to the LogLevel API.
Formatted logging at various severity levels is provided by the functions
(c *ChaincodeLogger) Debug(args ...interface{})
(c *ChaincodeLogger) Info(args ...interface{})
(c *ChaincodeLogger) Notice(args ...interface{})
(c *ChaincodeLogger) Warning(args ...interface{})
(c *ChaincodeLogger) Error(args ...interface{})
(c *ChaincodeLogger) Critical(args ...interface{})
(c *ChaincodeLogger) Debugf(format string, args ...interface{})
(c *ChaincodeLogger) Infof(format string, args ...interface{})
(c *ChaincodeLogger) Noticef(format string, args ...interface{})
(c *ChaincodeLogger) Warningf(format string, args ...interface{})
(c *ChaincodeLogger) Errorf(format string, args ...interface{})
(c *ChaincodeLogger) Criticalf(format string, args ...interface{})
The f forms of the logging APIs provide for precise control over the formatting of the logs. The non-f forms of the APIs currently insert a space between the printed representations of the arguments, and arbitrarily choose the formats to use.
In the current implementation, the logs produced by the shim and a ChaincodeLogger are timestamped, marked with the logger name and severity level, and written to stderr. Note that logging level control is currently based on the name provided when the ChaincodeLogger is created. To avoid ambiguities, all ChaincodeLogger should be given unique names other than "shim". The logger name will appear in all log messages created by the logger. The shim logs as "shim".
Go language chaincodes can also control the logging level of the chaincode shim interface through the SetLoggingLevel API.
SetLoggingLevel(LoggingLevel level) - Control the logging level of the shim
The default logging level for the shim is LogDebug.
Below is a simple example of how a chaincode might create a private logging object logging at the LogInfo level, and also control the amount of logging provided by the shim based on an environment variable.
var logger = shim.NewLogger("myChaincode")
func main() {
logger.SetLevel(shim.LogInfo)
logLevel, _ := shim.LogLevel(os.Getenv("SHIM_LOGGING_LEVEL"))
shim.SetLoggingLevel(logLevel)
...
}