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219 lines
12 KiB
Markdown
219 lines
12 KiB
Markdown
flume [](https://godoc.org/github.com/gemalto/flume) [](https://goreportcard.com/report/gemalto/flume) [](https://github.com/gemalto/flume/actions?query=branch%3Amaster+workflow%3ABuild+)
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=====
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flume is a logging package, build on top of [zap](https://github.com/uber-go/zap). It's structured and leveled logs, like zap/logrus/etc.
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It adds a global registry of all loggers, allowing global re-configuration at runtime. Instantiating
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new loggers automatically registers them: even loggers created in init() functions, package variable
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initializers, or 3rd party code, can all be managed from the central registry.
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Features
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- Structured: Log entries have key/value attributes.
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- Leveled:
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- Error: Something that would be reported up to an error reporting service
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- Info: High priority, low volume messages. Appropriate for production runtime use. Used for coarse-grained
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feedback
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- Debug: Slow, verbose logging, not appropriate for long-term production use
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Flume is a little opinionated about having only a few logs levels. Warns should either be errors
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or infos, trace should just be debug, and a log package shouldn't be responsible for panics or exits.
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- Named: Loggers have a name. Levels can be configured for each named logger. For example, a common usage
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pattern is to create a unique logger for each go package, then selectively turn on debug logging for
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specific packages.
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- Built on top of zap, which is super fast.
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- Supports JSON, LTSV, and colorized console output formats.
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- Optional call site logging (file and line number of log call)
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- Output can be directed to any writer, defaults to stdout
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- Helpers for managing application logs during tests
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- Supports creating child loggers with pre-set context: `Logger.With()`
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- Levels can be configured via a single string, which is convenient for configuration via env var, see `LevelsString()`
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- All loggers can be reconfigured dynamically at runtime.
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- Thoughtful handling of multi-line log output: Multi-line output is collapsed to a single line, or encoded,
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depending on the encoder. The terminal encoders, which are optimized for human viewing, retain multi-line
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formatting.
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- By default, all logs are discarded. Flume is completely silent unless explicitly configured otherwise.
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This is ideal for logging inside libraries, where the log level and output will be managed by
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the code importing the library.
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This package does not offer package level log functions, so you need to create a logger instance first:
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A common pattern is to create a single, package-wide logger, named after the package:
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var log = flume.New("mypkg")
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Then, write some logs:
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log.Debug("created user", "username", "frank", "role", "admin")
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Logs have a message, then matched pairs of key/value properties. Child loggers can be created
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and pre-seeded with a set of properties:
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reqLogger := log.With("remoteAddr", req.RemoteAddr)
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Expensive log events can be avoid by explicitly checking level:
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if log.IsDebug() {
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log.Debug("created resource", "resource", resource.ExpensiveToString())
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}
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Loggers can be bound to context.Context, which is convenient for carrying
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per-transaction loggers (pre-seeded with transaction specific context) through layers of request
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processing code:
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ctx = flume.WithLogger(ctx, log.With("transactionID", tid))
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// ...later...
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flume.FromContext(ctx).Info("Request handled.")
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By default, all these messages will simply be discard. To enable output, flume needs to
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be configured. Only entry-point code, like main() or test setup, should configure flume.
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To configure logging settings from environment variables, call the configuration function from main():
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flume.ConfigFromEnv()
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Other configuration methods are available: see `ConfigString()`, `LevelString()`, and `Configure()`.
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This reads the log configuration from the environment variable "FLUME" (the default, which can be
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overridden). The value is JSON, e.g.:
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{"level":"INF","levels":"http=DBG","development"="true"}
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The properties of the config string:
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- "level": ERR, INF, or DBG. The default level for all loggers.
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- "levels": A string configuring log levels for specific loggers, overriding the default level.
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See note below for syntax.
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- "development": true or false. In development mode, the defaults for the other
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settings change to be more suitable for developers at a terminal (colorized, multiline, human
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readable, etc). See note below for exact defaults.
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- "addCaller": true or false. Adds call site information to log entries (file and line).
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- "encoding": json, ltsv, term, or term-color. Configures how log entries are encoded in the output.
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"term" and "term-color" are multi-line, human-friendly
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formats, intended for terminal output.
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- "encoderConfig": a JSON object which configures advanced encoding settings, like how timestamps
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are formatted. See docs for go.uber.org/zap/zapcore/EncoderConfig
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- "messageKey": the label of the message property of the log entry. If empty, message is omitted.
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- "levelKey": the label of the level property of the log entry. If empty, level is omitted.
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- "timeKey": the label of the timestamp of the log entry. If empty, timestamp is omitted.
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- "nameKey": the label of the logger name in the log entry. If empty, logger name is omitted.
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- "callerKey": the label of the logger name in the log entry. If empty, logger name is omitted.
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- "stacktraceKey": the label of the stacktrace in the log entry. If empty, stacktrace is omitted.
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- "lineEnding": the end of each log output line.
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- "levelEncoder": capital, capitalColor, color, lower, or abbr. Controls how the log entry level
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is rendered. "abbr" renders 3-letter abbreviations, like ERR and INF.
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- "timeEncoder": iso8601, millis, nanos, unix, or justtime. Controls how timestamps are rendered.
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"millis", "nanos", and "unix" are since UNIX epoch. "unix" is in floating point seconds.
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"justtime" omits the date, and just prints the time in the format "15:04:05.000".
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- "durationEncoder": string, nanos, or seconds. Controls how time.Duration values are rendered.
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- "callerEncoder": full or short. Controls how the call site is rendered.
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"full" includes the entire package path, "short" only includes the last folder of the package.
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Defaults:
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{
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"level":"INF",
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"levels":"",
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"development":false,
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"addCaller":false,
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"encoding":"term-color",
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"encoderConfig":nil
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}
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If "encoderConfig" is omitted, it defaults to:
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{
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"messageKey":"msg",
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"levelKey":"level",
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"timeKey":"time",
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"nameKey":"name",
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"callerKey":"caller",
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"stacktraceKey":"stacktrace",
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"lineEnding":"\n",
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"levelEncoder":"abbr",
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"timeEncoder":"iso8601",
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"durationEncoder":"seconds",
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"callerEncoder":"short",
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}
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These defaults are only applied if one of the configuration functions is called, like ConfigFromEnv(), ConfigString(),
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Configure(), or LevelsString(). Initially, all loggers are configured to discard everything, following
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flume's opinion that log packages should be silent unless spoken too. Ancillary to this: library packages
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should *not* call these functions, or configure logging levels or output in anyway. Only program entry points,
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like main() or test code, should configure logging. Libraries should just create loggers and log to them.
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Development mode: if "development"=true, the defaults for the rest of the settings change, equivalent to:
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{
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"addCaller":true,
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"encoding":"term-color",
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"encodingConfig": {
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"timeEncoder":"justtime",
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"durationEncoder":"string",
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}
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}
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The "levels" value is a list of key=value pairs, configuring the level of individual named loggers.
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If the key is "*", it sets the default level. If "level" and "levels" both configure the default
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level, "levels" wins.
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Examples:
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* // set the default level to ALL, equivalent to {"level"="ALL"}
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*=INF // same, but set default level to INF
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*,sql=WRN // set default to ALL, set "sql" logger to WRN
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*=INF,http=ALL // set default to INF, set "http" to ALL
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*=INF,http // same as above. If name has no level, level is set to ALL
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*=INF,-http // set default to INF, set "http" to OFF
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http=INF // leave default setting unchanged.
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Examples of log output:
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"term"
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11:42:08.126 INF | Hello World! @:root@flume.git/example_test.go:15
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11:42:08.127 INF | This entry has properties color:red @:root@flume.git/example_test.go:16
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11:42:08.127 DBG | This is a debug message @:root@flume.git/example_test.go:17
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11:42:08.127 ERR | This is an error message @:root@flume.git/example_test.go:18
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11:42:08.127 INF | This message has a multiline value essay:
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Four score and seven years ago
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our fathers brought forth on this continent, a new nation,
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conceived in Liberty, and dedicated to the proposition that all men are created equal.
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@:root@flume.git/example_test.go:19
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"term-color"
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"json"
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{"level":"INF","time":"15:06:28.422","name":"root","caller":"flume.git/example_test.go:15","msg":"Hello World!"}
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{"level":"INF","time":"15:06:28.423","name":"root","caller":"flume.git/example_test.go:16","msg":"This entry has properties","color":"red"}
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{"level":"DBG","time":"15:06:28.423","name":"root","caller":"flume.git/example_test.go:17","msg":"This is a debug message"}
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{"level":"ERR","time":"15:06:28.423","name":"root","caller":"flume.git/example_test.go:18","msg":"This is an error message"}
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{"level":"INF","time":"15:06:28.423","name":"root","caller":"flume.git/example_test.go:19","msg":"This message has a multiline value","essay":"Four score and seven years ago\nour fathers brought forth on this continent, a new nation, \nconceived in Liberty, and dedicated to the proposition that all men are created equal."}
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"ltsv"
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level:INF time:15:06:55.325 msg:Hello World! name:root caller:flume.git/example_test.go:15
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level:INF time:15:06:55.325 msg:This entry has properties name:root caller:flume.git/example_test.go:16 color:red
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level:DBG time:15:06:55.325 msg:This is a debug message name:root caller:flume.git/example_test.go:17
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level:ERR time:15:06:55.325 msg:This is an error message name:root caller:flume.git/example_test.go:18
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level:INF time:15:06:55.325 msg:This message has a multiline value name:root caller:flume.git/example_test.go:19 essay:Four score and seven years ago\nour fathers brought forth on this continent, a new nation, \nconceived in Liberty, and dedicated to the proposition that all men are created equal.
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tl;dr
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The implementation is a wrapper around zap. zap does levels, structured logs, and is very fast.
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zap doesn't do centralized, global configuration, so this package
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adds that by maintaining an internal registry of all loggers, and using the sync.atomic stuff to swap out
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levels and writers in a thread safe way.
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Contributing
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------------
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To build, be sure to have a recent go SDK, and make. Run `make tools` to install other dependencies. Then run `make`.
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There is also a dockerized build, which only requires make and docker-compose: `make docker`. You can also
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do `make fish` or `make bash` to shell into the docker build container.
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Merge requests are welcome! Before submitting, please run `make` and make sure all tests pass and there are
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no linter findings. |