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124 lines
3.6 KiB
Markdown
124 lines
3.6 KiB
Markdown
# go-hclog
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[![Go Documentation](http://img.shields.io/badge/go-documentation-blue.svg?style=flat-square)][godocs]
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[godocs]: https://godoc.org/github.com/hashicorp/go-hclog
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`go-hclog` is a package for Go that provides a simple key/value logging
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interface for use in development and production environments.
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It provides logging levels that provide decreased output based upon the
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desired amount of output, unlike the standard library `log` package.
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It does not provide `Printf` style logging, only key/value logging that is
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exposed as arguments to the logging functions for simplicity.
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It provides a human readable output mode for use in development as well as
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JSON output mode for production.
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## Stability Note
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While this library is fully open source and HashiCorp will be maintaining it
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(since we are and will be making extensive use of it), the API and output
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format is subject to minor changes as we fully bake and vet it in our projects.
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This notice will be removed once it's fully integrated into our major projects
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and no further changes are anticipated.
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## Installation and Docs
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Install using `go get github.com/hashicorp/go-hclog`.
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Full documentation is available at
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http://godoc.org/github.com/hashicorp/go-hclog
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## Usage
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### Use the global logger
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```go
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hclog.Default().Info("hello world")
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```
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```text
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2017-07-05T16:15:55.167-0700 [INFO ] hello world
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```
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(Note timestamps are removed in future examples for brevity.)
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### Create a new logger
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```go
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appLogger := hclog.New(&hclog.LoggerOptions{
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Name: "my-app",
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Level: hclog.LevelFromString("DEBUG"),
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})
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```
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### Emit an Info level message with 2 key/value pairs
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```go
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input := "5.5"
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_, err := strconv.ParseInt(input, 10, 32)
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if err != nil {
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appLogger.Info("Invalid input for ParseInt", "input", input, "error", err)
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}
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```
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```text
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... [INFO ] my-app: Invalid input for ParseInt: input=5.5 error="strconv.ParseInt: parsing "5.5": invalid syntax"
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```
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### Create a new Logger for a major subsystem
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```go
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subsystemLogger := appLogger.Named("transport")
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subsystemLogger.Info("we are transporting something")
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```
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```text
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... [INFO ] my-app.transport: we are transporting something
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```
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Notice that logs emitted by `subsystemLogger` contain `my-app.transport`,
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reflecting both the application and subsystem names.
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### Create a new Logger with fixed key/value pairs
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Using `With()` will include a specific key-value pair in all messages emitted
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by that logger.
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```go
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requestID := "5fb446b6-6eba-821d-df1b-cd7501b6a363"
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requestLogger := subsystemLogger.With("request", requestID)
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requestLogger.Info("we are transporting a request")
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```
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```text
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... [INFO ] my-app.transport: we are transporting a request: request=5fb446b6-6eba-821d-df1b-cd7501b6a363
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```
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This allows sub Loggers to be context specific without having to thread that
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into all the callers.
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### Use this with code that uses the standard library logger
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If you want to use the standard library's `log.Logger` interface you can wrap
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`hclog.Logger` by calling the `StandardLogger()` method. This allows you to use
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it with the familiar `Println()`, `Printf()`, etc. For example:
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```go
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stdLogger := appLogger.StandardLogger(&hclog.StandardLoggerOptions{
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InferLevels: true,
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})
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// Printf() is provided by stdlib log.Logger interface, not hclog.Logger
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stdLogger.Printf("[DEBUG] %+v", stdLogger)
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```
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```text
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... [DEBUG] my-app: &{mu:{state:0 sema:0} prefix: flag:0 out:0xc42000a0a0 buf:[]}
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```
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Notice that if `appLogger` is initialized with the `INFO` log level _and_ you
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specify `InferLevels: true`, you will not see any output here. You must change
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`appLogger` to `DEBUG` to see output. See the docs for more information.
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