feat: structured logging improvements

This change adds a child logger with request information to the
http request context. Also improved the log format for clarity.

- Unescaped the query string
- Use JSON log format when not in dev mode.
- Added request ip to the request child logger.
- The child logger is passed to the converter so we can associate
  any errors with a specific request / file.
- Add book file name as a logger attribute
- Add user agent header as a logger attribute
- Log the "X-Forwarded-For" header, falling back to RemoteAddr

convert/convert.go

@@ -1,9 +1,11 @@
 package convert
 
+import "log/slog"
+
 type Converter interface {
 	// Whether or not the converter is available
 	// Usually based on the availability of the underlying tool
 	Available() bool
 	// Convert the input file to the output file
-	Convert(input string) (string, error)
+	Convert(log *slog.Logger, input string) (string, error)
 }

convert/kepub.go

@@ -1,6 +1,7 @@
 package convert
 
 import (
+	"log/slog"
 	"os/exec"
 	"strings"
 	"sync"
@@ -21,7 +22,7 @@ func (kc *KepubConverter) Available() bool {
 	return kc.available
 }
 
-func (kc *KepubConverter) Convert(input string) (string, error) {
+func (kc *KepubConverter) Convert(_ *slog.Logger, input string) (string, error) {
 	kc.mutex.Lock()
 	defer kc.mutex.Unlock()
 

convert/mobi.go

@@ -23,7 +23,7 @@ func (mc *MobiConverter) Available() bool {
 	return mc.available
 }
 
-func (mc *MobiConverter) Convert(input string) (string, error) {
+func (mc *MobiConverter) Convert(log *slog.Logger, input string) (string, error) {
 	mc.mutex.Lock()
 	defer mc.mutex.Unlock()
 
@@ -49,14 +49,14 @@ func (mc *MobiConverter) Convert(input string) (string, error) {
 		isError := true
 		if exiterr, ok := err.(*exec.ExitError); ok {
 			// Sometimes warnings cause a 1 exit-code, but the file is still created
-			slog.Info("Exit code", slog.Any("code", exiterr.ExitCode()))
+			log.Info("Exit code", slog.Any("code", exiterr.ExitCode()))
 			if exiterr.ExitCode() == 1 {
 				isError = false
 			}
 		}
 
 		if isError {
-			slog.Error("Error converting file",
+			log.Error("Error converting file",
 				slog.Any("error", err),
 				slog.String("stdout", out.String()),
 				slog.String("stderr", stderr.String()),