From 1a8631d0621dd212a325f04510ba9091388ce9e7 Mon Sep 17 00:00:00 2001
From: PolarETech <52513329+PolarETech@users.noreply.github.com>
Date: Tue, 20 Sep 2022 04:59:02 +0900
Subject: [PATCH] fix(node/fs): position option of fs.read and fs.readSync
 works the same as Node (#2669)

---
 node/_fs/_fs_read.ts      | 24 +++++++++---
 node/_fs/_fs_read_test.ts | 81 +++++++++++++++++++++++++++++++--------
 2 files changed, 84 insertions(+), 21 deletions(-)

diff --git a/node/_fs/_fs_read.ts b/node/_fs/_fs_read.ts
index f5959923c352..9ac20be7cfa5 100644
--- a/node/_fs/_fs_read.ts
+++ b/node/_fs/_fs_read.ts
@@ -98,12 +98,18 @@ export function read(
   let err: Error | null = null,
     numberOfBytesRead: number | null = null;
 
-  if (position) {
-    Deno.seekSync(fd, position, Deno.SeekMode.Current);
-  }
-
   try {
+    let currentPosition = 0;
+    if (typeof position === "number" && position >= 0) {
+      currentPosition = Deno.seekSync(fd, 0, Deno.SeekMode.Current);
+      Deno.seekSync(fd, position, Deno.SeekMode.Start);
+    }
+
     numberOfBytesRead = Deno.readSync(fd, buffer);
+
+    if (typeof position === "number" && position >= 0) {
+      Deno.seekSync(fd, currentPosition, Deno.SeekMode.Start);
+    }
   } catch (error) {
     err = error instanceof Error ? error : new Error("[non-error thrown]");
   }
@@ -168,11 +174,17 @@ export function readSync(
     }`,
   );
 
-  if (position) {
-    Deno.seekSync(fd, position, Deno.SeekMode.Current);
+  let currentPosition = 0;
+  if (typeof position === "number" && position >= 0) {
+    currentPosition = Deno.seekSync(fd, 0, Deno.SeekMode.Current);
+    Deno.seekSync(fd, position, Deno.SeekMode.Start);
   }
 
   const numberOfBytesRead = Deno.readSync(fd, buffer);
 
+  if (typeof position === "number" && position >= 0) {
+    Deno.seekSync(fd, currentPosition, Deno.SeekMode.Start);
+  }
+
   return numberOfBytesRead ?? 0;
 }
diff --git a/node/_fs/_fs_read_test.ts b/node/_fs/_fs_read_test.ts
index a2c8a461d09f..7eff9a7c955d 100644
--- a/node/_fs/_fs_read_test.ts
+++ b/node/_fs/_fs_read_test.ts
@@ -87,25 +87,43 @@ Deno.test({
 });
 
 Deno.test({
-  name: "[std/node/fs] Specifies where to begin reading from in the file",
+  name:
+    "[std/node/fs] position option of fs.read() specifies where to begin reading from in the file",
   async fn() {
     const moduleDir = path.dirname(path.fromFileUrl(import.meta.url));
     const testData = path.resolve(moduleDir, "testdata", "hello.txt");
-    const buf = Buffer.alloc(11);
-    await readTest(
-      testData,
-      buf,
-      buf.byteOffset,
-      buf.byteLength,
-      6,
-      (_fd, bytesRead, data) => {
-        assertStrictEquals(bytesRead, 5);
-        assertEquals(
-          data,
-          Buffer.from([119, 111, 114, 108, 100, 0, 0, 0, 0, 0, 0]),
+    const fd = openSync(testData);
+    const buf = Buffer.alloc(5);
+    const positions = [6, 0, -1, null];
+    const expected = [
+      [119, 111, 114, 108, 100],
+      [104, 101, 108, 108, 111],
+      [104, 101, 108, 108, 111],
+      [32, 119, 111, 114, 108],
+    ];
+    for (const [i, position] of positions.entries()) {
+      await new Promise((resolve) => {
+        read(
+          fd,
+          {
+            buffer: buf,
+            offset: buf.byteOffset,
+            length: buf.byteLength,
+            position,
+          },
+          (err, bytesRead, data) => {
+            assertEquals(err, null);
+            assertStrictEquals(bytesRead, 5);
+            assertEquals(
+              data,
+              Buffer.from(expected[i]),
+            );
+            return resolve(true);
+          },
         );
-      },
-    );
+      });
+    }
+    closeSync(fd);
   },
 });
 
@@ -184,6 +202,39 @@ Deno.test({
   },
 });
 
+Deno.test({
+  name:
+    "[std/node/fs] position option of fs.readSync() specifies where to begin reading from in the file",
+  fn() {
+    const moduleDir = path.dirname(path.fromFileUrl(import.meta.url));
+    const testData = path.resolve(moduleDir, "testdata", "hello.txt");
+    const fd = openSync(testData);
+    const buf = Buffer.alloc(5);
+    const positions = [6, 0, -1, null];
+    const expected = [
+      [119, 111, 114, 108, 100],
+      [104, 101, 108, 108, 111],
+      [104, 101, 108, 108, 111],
+      [32, 119, 111, 114, 108],
+    ];
+    for (const [i, position] of positions.entries()) {
+      const bytesRead = readSync(
+        fd,
+        buf,
+        buf.byteOffset,
+        buf.byteLength,
+        position,
+      );
+      assertStrictEquals(bytesRead, 5);
+      assertEquals(
+        buf,
+        Buffer.from(expected[i]),
+      );
+    }
+    closeSync(fd);
+  },
+});
+
 Deno.test({
   name: "[std/node/fs] Read fs.readSync(fd, buffer[, options]) signature",
   fn() {