Package kv provides support for working with collections of key/value pairs.
The List type represents a sequence of alternating key/value pairs. Lists
can render themselves as text in logfmt format,
so if you like logging messages with key value pairs but are not ready to move
away from the standard library log package you can use something like:
log.Println("this is a log message", kv.With(
"key1", "value 1",
"key2", 2,
))
// Output:
// this is a log message key1="value 1" key2=2The output from the previous example can be easily read by humans, and easily parsed by machines. This makes it an excellent format for structured logging.
The Error type implements the builtin error interface and renders its error message as a
free text message followed by key/value pairs:
cannot open file: permission denied file="/etc/passwd" user=alice
Errors are constructed with message text and key/value pairs.
// create an error
err := kv.NewError("permission denied").With("user", user)
log.Println(err)
// Output:
// permission denied user=aliceErrors can wrap other errors:
err = kv.Wrap(err, "cannot open file").With("file", filename)
log.Println(err)
// Output:
// cannot open file: permission denied file="/etc/passwd" user=aliceKey/value pairs can be stored in the context:
ctx := context.Background()
// associate some key/value pairs with the context
ctx = kv.From(ctx).With("url", "/api/widgets", "method", "get")
// ... later on ...
log.Println("access denied", kv.From(ctx).With("file", filename))
// Output:
// access denied file="/etc/passwd" url="/api/widgets" method=getOne of the key points of structured logging is that logs are machine
readable. The Parse function provides an easy way to read messages.
// read one line
line := []byte(`cannot open file: access denied file="/etc/passwd" user=alice`)
text, list := kv.Parse(line)
log.Println("text:", string(text))
log.Println("list:", list)
// Output:
// text: cannot open file: access denied
// list: file="/etc/passwd" user=aliceThe kvlog subdirectory contains a package that works well with the log package
in the Go standard library. Its usage is as simple as:
func main() {
kvlog.Attach() // attach to the standard logger
log.Println("program started", kv.With("args", os.Args))
}See the GoDoc for more details.
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