Add option for -debug-log. (#74)

* Add options for -disable-logging and -logfile.

Both of these options have to do with the logging surrounding issues
such as #39. Where in that issue the server was returning data after
the connection was closed. Therefore, I added two options one for
completely disabling all of the internal logging functionality aka
sending it to /dev/null. Another for writing the logging information
to a file so it can be retrieved later if need be.

* Changed to automatically disable internal logging.

Per the changes requested by @joohoi, changed to a single
flag `-debug-log` which will place all of the internal logging
into the specified file. If the file fails to be opened or is
not specified it will disable the logging.

* Update readme with the changes for -debug-log.

README.md

@@ -167,6 +167,8 @@ To define the test case for ffuf, use the keyword `FUZZ` anywhere in the URL (`-
     	Wordlist file path or - to read from standard input
   -x string
     	HTTP Proxy URL
+  -debug-log string
+      Write the debug logging information to the specified file.
 ```
 
 eg. `ffuf -u https://example.org/FUZZ -w /path/to/wordlist`
@@ -186,10 +188,13 @@ The only dependency of ffuf is Go 1.11. No dependencies outside of Go standard l
   - New
     - New CLI flag: -l, shows target location of redirect responses
     - New CLI flac: -acc, custom auto-calibration strings
+    - New CLI flag: -debug-log, writes the debug logging to the specified file.
+
   - Changed
     - New CLI flag: -i, dummy flag that does nothing. for compatibility with copy as curl.
     - New CLI flag: -b/--cookie, cookie data for compatibility with copy as curl.
     - Filtering and matching by status code, response size or word count now allow using ranges in addition to single values
+    - The internal logging information to be discarded, and can be written to a file with the new `-debug-log` flag.
 
 - v0.10
 

main.go

@@ -4,6 +4,8 @@ import (
 	"context"
 	"flag"
 	"fmt"
+	"io/ioutil"
+	"log"
 	"net/http"
 	"net/url"
 	"os"
@@ -34,6 +36,7 @@ type cliOptions struct {
 	cookies                multiStringFlag
 	AutoCalibrationStrings multiStringFlag
 	showVersion            bool
+	debugLog               string
 }
 
 type multiStringFlag []string
@@ -94,11 +97,24 @@ func main() {
 	flag.IntVar(&conf.Threads, "t", 40, "Number of concurrent threads.")
 	flag.IntVar(&conf.Timeout, "timeout", 10, "HTTP request timeout in seconds.")
 	flag.BoolVar(&opts.showVersion, "V", false, "Show version information.")
+	flag.StringVar(&opts.debugLog, "debug-log", "", "Write all of the internal logging to the specified file.")
 	flag.Parse()
 	if opts.showVersion {
 		fmt.Printf("ffuf version: %s\n", ffuf.VERSION)
 		os.Exit(0)
 	}
+	if len(opts.debugLog) != 0 {
+		f, err := os.OpenFile(opts.debugLog, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "Disabling logging, encountered error(s): %s\n", err)
+			log.SetOutput(ioutil.Discard)
+		} else {
+			log.SetOutput(f)
+			defer f.Close()
+		}
+	} else {
+		log.SetOutput(ioutil.Discard)
+	}
 	if err := prepareConfig(&opts, &conf); err != nil {
 		fmt.Fprintf(os.Stderr, "Encountered error(s): %s\n", err)
 		flag.Usage()