fix: send a one-byte asset with its byte instead of Content-Length 0

src/middleware.js

@@ -703,6 +703,7 @@ function wrapper(context) {
               extra.outputFileSystem,
               start,
               end,
+              len,
             );
 
             ({ bufferOrStream, byteLength } = result);
@@ -848,6 +849,7 @@ function wrapper(context) {
             extra.outputFileSystem,
             start,
             end,
+            len,
           ));
         } catch (error) {
           await errorHandler(/** @type {NodeJS.ErrnoException} */ (error));

src/utils/compatibleAPI.js

@@ -218,13 +218,15 @@ function finish(res, data) {
  * @param {OutputFileSystem} outputFileSystem output file system
  * @param {number} start start
  * @param {number} end end
+ * @param {number} len byte length of the range, or of the whole file
  * @returns {{ bufferOrStream: (Buffer | import("fs").ReadStream), byteLength: number }} result with buffer or stream and byte length
  */
 function createReadStreamOrReadFileSync(
   filename,
   outputFileSystem,
   start,
   end,
+  len,
 ) {
   /** @type {Buffer | import("fs").ReadStream} */
   let bufferOrStream;
@@ -243,8 +245,9 @@ function createReadStreamOrReadFileSync(
         end,
       });
 
-    // Handle files with zero bytes
-    byteLength = end === 0 ? 0 : end - start + 1;
+    // An empty file and a one-byte file both end at offset 0, so the length
+    // is the caller's byte count. A stat without a size keeps the arithmetic
+    byteLength = Number.isFinite(len) ? len : end - start + 1;
   } else {
     bufferOrStream = outputFileSystem.readFileSync(filename);
     ({ byteLength } = bufferOrStream);

test/middleware.test.js

@@ -1053,6 +1053,10 @@ describe.each([
             path.resolve(outputPath, "empty-file.txt"),
             "",
           );
+          instance.context.outputFileSystem.writeFileSync(
+            path.resolve(outputPath, "one-byte.txt"),
+            "a",
+          );
         });
 
         afterAll(async () => {
@@ -1463,6 +1467,25 @@ describe.each([
           );
         });
 
+        it('should return "200" code for the "GET" request and "Content-Length" of "1" when file has one byte', async () => {
+          const response = await req.get("/one-byte.txt");
+
+          expect(response.statusCode).toBe(200);
+          expect(response.headers["content-length"]).toBe("1");
+          expect(response.text).toBe("a");
+        });
+
+        it('should return "206" code for the "GET" request with a one-byte range', async () => {
+          const response = await req
+            .get("/one-byte.txt")
+            .set("Range", "bytes=0-0");
+
+          expect(response.statusCode).toBe(206);
+          expect(response.headers["content-range"]).toBe("bytes 0-0/1");
+          expect(response.headers["content-length"]).toBe("1");
+          expect(response.text).toBe("a");
+        });
+
         it('should return the "200" code for the "GET" request to the "image image.svg" file', async () => {
           const fileData = instance.context.outputFileSystem.readFileSync(
             path.resolve(outputPath, "image image.svg"),

types/utils/compatibleAPI.d.ts

@@ -218,13 +218,15 @@ declare function finish<
  * @param {OutputFileSystem} outputFileSystem output file system
  * @param {number} start start
  * @param {number} end end
+ * @param {number} len byte length of the range, or of the whole file
  * @returns {{ bufferOrStream: (Buffer | import("fs").ReadStream), byteLength: number }} result with buffer or stream and byte length
  */
 declare function createReadStreamOrReadFileSync(
   filename: string,
   outputFileSystem: OutputFileSystem,
   start: number,
   end: number,
+  len: number,
 ): {
   bufferOrStream: Buffer | import("fs").ReadStream;
   byteLength: number;