Logger

v1.8.1

Logger.Formatter View Source

Conveniences for formatting data for logs.

This module allows developers to specify a string that serves as template for log messages, for example:

$time $metadata[$level] $message\n

Will print error messages as:

18:43:12.439 user_id=13 [error] Hello\n

The valid parameters you can use are:

  • $time - the time the log message was sent
  • $date - the date the log message was sent
  • $message - the log message
  • $level - the log level
  • $node - the node that prints the message
  • $metadata - user controlled data presented in "key=val key2=val2 " format
  • $levelpad - sets to a single space if level is 4 characters long, otherwise set to the empty space. Used to align the message after level.

Backends typically allow developers to supply such control strings via configuration files. This module provides compile/1, which compiles the string into a format for fast operations at runtime and format/5 to format the compiled pattern into an actual IO data.

Metadata

Metadata to be sent to the logger can be read and written with the Logger.metadata/0 and Logger.metadata/1 functions. For example, you can set Logger.metadata([user_id: 13]) to add user_id metadata to the current process. The user can configure the backend to choose which metadata it wants to print and it will replace the $metadata value.

Link to this section Summary

Types

pattern()
time()

Functions

compile(pattern)

Compiles a format string into a data structure that format/5 can handle

format(config, level, msg, timestamp, metadata)

Takes a compiled format and injects the level, timestamp, message, and metadata keyword list and returns a properly formatted string

format_date(arg)

Formats date as chardata

format_time(arg)

Formats time as chardata

prune(binary)

Prunes non-valid UTF-8 codepoints

Link to this section Types

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pattern() View Source 
pattern() :: :date | :level | :levelpad | :message | :metadata | :node | :time

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time() View Source 
time() :: {{1970..10000, 1..12, 1..31}, {0..23, 0..59, 0..59, 0..999}}

Link to this section Functions

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compile(pattern) View Source 
compile(binary() | nil) :: [pattern() | binary()]
compile(pattern) :: pattern when pattern: {module(), function :: atom()}

Compiles a format string into a data structure that format/5 can handle.

Check the module doc for documentation on the valid parameters that will be interpolated in the pattern. If you pass nil as the pattern, the pattern defaults to:

"\n$time $metadata[$level] $levelpad$message\n"

If you want to customize formatting through a custom formatter, you can pass a {module, function} tuple as the pattern.

iex> Logger.Formatter.compile("$time $metadata [$level] $message\n")
[:time, " ", :metadata, " [", :level, "] ", :message, "\n"]

iex> Logger.Formatter.compile({MyLoggerFormatter, :format})
{MyLoggerFormatter, :format}
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format(config, level, msg, timestamp, metadata) View Source 
format(
  {atom(), atom()} | [pattern() | binary()],
  Logger.level(),
  Logger.message(),
  time(),
  keyword()
) :: IO.chardata()

Takes a compiled format and injects the level, timestamp, message, and metadata keyword list and returns a properly formatted string.

Examples 

iex> pattern = Logger.Formatter.compile("[$level] $message")
iex> timestamp = {{1977, 01, 28}, {13, 29, 00, 000}}
iex> formatted = Logger.Formatter.format(pattern, :info, "hello", timestamp, [])
iex> IO.chardata_to_string(formatted)
"[info] hello"
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format_date(arg) View Source 
format_date({1970..10000, 1..12, 1..31}) :: IO.chardata()

Formats date as chardata.

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format_time(arg) View Source 
format_time({0..23, 0..59, 0..59, 0..999}) :: IO.chardata()

Formats time as chardata.

Prunes non-valid UTF-8 codepoints.

Typically called after formatting when the data cannot be printed.