Bug: BasicLogger Panics When len(keyvals) is 1

[vicluq]

Context

When calling kgo.BasicLogger .Log() with only one extra argument (len(keyvals) = 1), it panics because len(keyvals) / 2 will be 0 for int variables, the second parameter of strings.Repeat. Since the result is 0, the length of the format variable will be 0, which will cause an out of slice bound access. Therefore that single value should be an EXTRA attribute such as when passing an even number of keyvals.

Refer to PR #857

Error Reproduction

package main

import (
	"os"
	"time"

	"github.com/twmb/franz-go/pkg/kgo"
)

func main() {
	logger := kgo.BasicLogger(os.Stderr, kgo.LogLevelInfo, func() string {
		return time.Now().Format("[2006-01-02 15:04:05.999] ")
	})

	logger.Log(kgo.LogLevelDebug, "main message", "key1")
	// Error: Key1 should be an EXTRA, but it panics
}

Output:

panic: runtime error: slice bounds out of range [:-2]

goroutine 1 [running]:
github.com/twmb/franz-go/pkg/kgo.(*basicLogger).Log(0x14000153f18, 0x4, {0x104168e66, 0xc}, {0x14000153f08, 0x1, 0x1})
	/Users/victorialuquet/go/pkg/mod/github.com/twmb/[email protected]/pkg/kgo/logger.go:92 +0x26c
main.main()
	/Users/victorialuquet/documents/go_tests/kgo_logger_debug.go:16 +0x98
exit status 2

But, when passing an even number of keyvals greater than 1, it is treated as an EXTRA attribute and we have the following behavior:

	logger.Log(kgo.LogLevelDebug, "main message", "key1", "val1") // Normal key value
	logger.Log(kgo.LogLevelDebug, "main message", "key1", "val1", "key2")
	logger.Log(kgo.LogLevelDebug, "main message", "key1", "val1", "key2", "val2")

Output:

[2024-11-06 19:29:49.425] [DEBUG] main message; key1: val1
[2024-11-06 19:29:49.425] [DEBUG] main message; key1: val1%!(EXTRA string=key2)
[2024-11-06 19:29:49.425] [DEBUG] main message; key1: val1, key2: val2

Expected Behavior

If keyvals length is equal to 1, it should be treated as an EXTRA as follows:

[2024-11-06 19:32:06.375] [DEBUG] main message; %!(EXTRA string=key1)