implement content-type detection

Author: musou1500

lib/file-type-stream.d.ts

@@ -0,0 +1,10 @@
+declare module "file-type-stream" {
+  import { Transform } from "stream";
+
+  class FileTypeStream extends Transform {
+    constructor(callback: Function);
+    _transform(chunk: any, encoding: string, cb: Function): void;
+  }
+
+  export default function(cb: Function): FileTypeStream;
+}

lib/util.ts

@@ -1,3 +1,22 @@
+import { Readable } from "stream";
+import fileType = require("file-type");
+import fileTypeStream from "file-type-stream";
+
 export function toArray<T>(maybeArr: T | T[]): T[] {
   return Array.isArray(maybeArr) ? maybeArr : [maybeArr];
 }
+
+export function detectContentType(data: Buffer | Readable): Promise<string> {
+  return new Promise(resolve => {
+    const handleFileTypeResult = (result: any) => {
+      return resolve(result ? result.mime : null);
+    };
+
+    if (data instanceof Buffer) {
+      const result = fileType(data);
+      return handleFileTypeResult(result);
+    } else {
+      data.pipe(fileTypeStream(handleFileTypeResult));
+    }
+  });
+}

package.json

@@ -38,9 +38,12 @@
   ],
   "dependencies": {
     "@types/body-parser": "^1.16.3",
+    "@types/file-type": "^5.2.1",
     "@types/node": "^7.0.31",
     "axios": "^0.16.2",
-    "body-parser": "^1.17.2"
+    "body-parser": "^1.17.2",
+    "file-type": "^7.2.0",
+    "file-type-stream": "^1.0.0"
   },
   "devDependencies": {
     "@types/express": "^4.0.35",

test/helpers/LINE_Icon.png

@@ -1,5 +1,7 @@
-import { deepEqual } from "assert";
-import { toArray } from "../lib/util";
+import { deepEqual, equal } from "assert";
+import { toArray, detectContentType } from "../lib/util";
+import * as fs from "fs";
+import { join } from "path";
 
 describe("util", () => {
   describe("toArray", () => {
@@ -11,4 +13,22 @@ describe("util", () => {
       deepEqual(toArray(1), [1]);
     });
   });
+
+  describe("detectContentType", () => {
+    it("returns correct result for stream", () => {
+      const filepath = join(__dirname, "/helpers/LINE_Icon.png");
+      const readable = fs.createReadStream(filepath);
+      return detectContentType(readable).then((type: string) => {
+        equal(type, "image/png");
+      });
+    });
+
+    it("returns correct result for buffer", () => {
+      const filepath = join(__dirname, "/helpers/LINE_Icon.png");
+      const buffer = fs.readFileSync(filepath);
+      return detectContentType(buffer).then((type: string) => {
+        equal(type, "image/png");
+      });
+    });
+  });
 });