PostHooks

You can customize the PostHooks of the Logger instance using the following methods:

// hooks.gofunc PostHooks(hooks Hooks) *Logger { ... }func RawPostHooks(hooks Hooks) *Logger { ... }

note

The returned Logger instance will be a copy of the previous one, sharing the same Configuration struct. The only difference will be the PostHooks.

More info at the Loggers clonage page.

As you may have seen, PostHooks will be executed at the Thirty phase of the life cycle, right after the AdHoc fields are applied.

info

PostHooks share the same characteristics as the PreHooks: just a function that receive a Log struct and returns the field value.

Read the introduction in the PreHooks page for details.

The advantage of PostHooks is that since they're being applied after the Base fields, PreHooks and AdHoc fields, you can query more fields using the Log.Field method from the hook argument:

someLogger := logger.New(logger.DefaultConfig()).  Fields(logger.LogFields{    "base-field": 10,  }).  PreHooks(logger.Hooks{    "preHook": func(l logger.Log) interface{} {      return l.Field("base-field").(int) + 10    },  }).  PostHooks(logger.Hooks{    "postHook": func(l logger.Log) interface{} {      // Querying the adHoc field that will be defined at log creation time      return l.Field("preHook").(int) + l.Field("adHoc-field").(int)    },  }).  Outputs(logger.OutputJsonToWriter(os.Stdout, nil))someLogger.Debug("some log", logger.LogFields{  "adHoc-field": 5,})/*  {    "msg": "some log",    "lvl": 2,    "base-field": 10,    "preHook": 20,    "adHoc-field": 5,    "postHook": 25,  }*/

PostHooks method

Similar to the PreHooks method, this method will return a new copy of the Logger instance with the given PostHooks applied, overriding previous PostHooks with the same key:

firstLogger := logger.New(logger.DefaultConfig()).  PostHooks(logger.Hooks{    "field-A": func(_ logger.Log) interface{} { return "dynamic value-A" },    "field-B": func(_ logger.Log) interface{} { return "dynamic value-B" },    "field-C": func(_ logger.Log) interface{} { return "dynamic value-C" },  }).  Outputs(logger.OutputJsonToWriter(os.Stdout, nil))firstLogger.Info("first log")/*  {    "msg": "first log",    "lvl": 4,    "field-A": "dynamic value-A",    "field-B": "dynamic value-B",    "field-C": "dynamic value-C"  }*/
secondLogger := firstLogger.  PostHooks(logger.Hooks{    "field-B": func(_ logger.Log) interface{} { return "new value" },  })secondLogger.Info("second log")/*  {    "msg": "second log",    "lvl": 4,    "field-A": "dynamic value-A",    "field-B": "new value",    "field-C": "dynamic value-C"  }*/

RawPostHooks method

If you want to reset the Logger PostHooks you can use the RawPostHooks method, that will set the Logger PostHooks right away, ignoring any previous values (returning a new copy of the Logger instance, just like PostHooks). Example:

firstLogger := logger.New(logger.DefaultConfig()).  PostHooks(logger.Hooks{    "field-A": func(_ logger.Log) interface{} { return "dynamic value-A" },    "field-B": func(_ logger.Log) interface{} { return "dynamic value-B" },    "field-C": func(_ logger.Log) interface{} { return "dynamic value-C" },  }).  Outputs(logger.OutputJsonToWriter(os.Stdout, nil))firstLogger.Info("first log")/*  {    "msg": "first log",    "lvl": 4,    "field-A": "dynamic value-A",    "field-B": "dynamic value-B",    "field-C": "dynamic value-C"  }*/
secondLogger := firstLogger.  RawPostHooks(logger.Hooks{    "field-B": func(_ logger.Log) interface{} { return "value" },  })secondLogger.Info("second log")/*  {    "msg": "second log",    "lvl": 4,    "field-B": "value",  }*/

PostHooks querying PostHooks

Note that if you try to use the Log.Field() method inside a PostHook to get query some PostHook field, you will fall into the same (possible) bug that was discussed when a PreHook query another PreHook field (here). Pay attention.