Serve public icon files

src/main/kotlin/com/android/trisolarisserver/controller/IconFiles.kt

@@ -1,7 +1,12 @@
 package com.android.trisolarisserver.controller
 
 import org.springframework.beans.factory.annotation.Value
+import org.springframework.core.io.FileSystemResource
+import org.springframework.http.HttpHeaders
+import org.springframework.http.MediaType
+import org.springframework.http.ResponseEntity
 import org.springframework.web.bind.annotation.GetMapping
+import org.springframework.web.bind.annotation.PathVariable
 import org.springframework.web.bind.annotation.RequestMapping
 import org.springframework.web.bind.annotation.RestController
 import java.nio.file.Files
@@ -29,4 +34,21 @@ class IconFiles(
                 .toList()
         }
     }
+
+    @GetMapping("/png/{filename}")
+    fun getPng(@PathVariable filename: String): ResponseEntity<FileSystemResource> {
+        if (filename.contains("..") || filename.contains("/") || filename.contains("\\")) {
+            return ResponseEntity.badRequest().build()
+        }
+        val file = Paths.get(pngRoot, filename)
+        if (!Files.exists(file) || !Files.isRegularFile(file)) {
+            return ResponseEntity.notFound().build()
+        }
+        val resource = FileSystemResource(file)
+        return ResponseEntity.ok()
+            .contentType(MediaType.IMAGE_PNG)
+            .header(HttpHeaders.CONTENT_DISPOSITION, "inline; filename=\"${file.fileName}\"")
+            .contentLength(resource.contentLength())
+            .body(resource)
+    }
 }