support metric files with uppercase extension

README.md

@@ -52,7 +52,7 @@ $ fail2ban-prometheus-exporter -h
         path to the fail2ban server socket
   -version
         show version info and exit
-   -collector.textfile
+  -collector.textfile
         enable the textfile collector
   -collector.textfile.directory string
         directory to read text files with metrics from
@@ -256,7 +256,7 @@ To enable textfile metrics:
 Metrics collected from these files will be exposed directly alongside the other metrics without any additional processing.
 This means that it is the responsibility of the file creator to ensure the format is correct.
 
-By exporting textfile metrics, an extra metric is also exported with an error count for each file:
+By exporting textfile metrics an extra metric is also exported with an error count for each file:
 
 ```
 # HELP textfile_error Checks for errors while reading text files
@@ -264,4 +264,4 @@ By exporting textfile metrics, an extra metric is also exported with an error co
 textfile_error{path="file.prom"} 0
 ```
 
-**NOTE:** Only files ending with `.prom` will be considered.
+**NOTE:** Any file not ending with `.prom` will be ignored.

src/textfile/file.go

@@ -27,7 +27,7 @@ func (c *Collector) collectFileContents() {
 
 	for _, file := range files {
 		fileName := file.Name()
-		if !strings.HasSuffix(fileName, ".prom") {
+		if !strings.HasSuffix(strings.ToLower(fileName), ".prom") {
 			continue
 		}
 		c.fileMap[fileName] = &fileData{