seek should return cursor position (#4211)

6 files changed, 79 insertions, 40 deletions

diff --git a/cli/js/files.ts b/cli/js/files.ts
index d66870309..dafdd0b32 100644
--- a/cli/js/files.ts
+++ b/cli/js/files.ts
@@ -216,24 +216,32 @@ export async function write(rid: number, p: Uint8Array): Promise<number> {
 
 /** Synchronously seek a file ID to the given offset under mode given by `whence`.
  *
+ * Returns the number of cursor position.
+ *
  *       const file = Deno.openSync("/foo/bar.txt");
- *       Deno.seekSync(file.rid, 0, 0);
+ *       const position = Deno.seekSync(file.rid, 0, 0);
  */
-export function seekSync(rid: number, offset: number, whence: SeekMode): void {
-  sendSyncJson("op_seek", { rid, offset, whence });
+export function seekSync(
+  rid: number,
+  offset: number,
+  whence: SeekMode
+): number {
+  return sendSyncJson("op_seek", { rid, offset, whence });
 }
 
 /** Seek a file ID to the given offset under mode given by `whence`.
  *
+ * Resolves with the number of cursor position.
+ *
  *      const file = await Deno.open("/foo/bar.txt");
- *      await Deno.seek(file.rid, 0, 0);
+ *      const position = await Deno.seek(file.rid, 0, 0);
  */
 export async function seek(
   rid: number,
   offset: number,
   whence: SeekMode
-): Promise<void> {
-  await sendAsyncJson("op_seek", { rid, offset, whence });
+): Promise<number> {
+  return await sendAsyncJson("op_seek", { rid, offset, whence });
 }
 
 /** Close the given resource ID. */
@@ -269,11 +277,11 @@ export class File
     return readSync(this.rid, p);
   }
 
-  seek(offset: number, whence: SeekMode): Promise<void> {
+  seek(offset: number, whence: SeekMode): Promise<number> {
     return seek(this.rid, offset, whence);
   }
 
-  seekSync(offset: number, whence: SeekMode): void {
+  seekSync(offset: number, whence: SeekMode): number {
     return seekSync(this.rid, offset, whence);
   }
 
diff --git a/cli/js/files_test.ts b/cli/js/files_test.ts
index 7e3479798..81c379020 100644
--- a/cli/js/files_test.ts
+++ b/cli/js/files_test.ts
@@ -280,6 +280,7 @@ testPerm(
     const data = encoder.encode("Hello world!\n");
 
     const file = await Deno.open(filename, "w+");
+    const seekPosition = 0;
     // assert file was created
     let fileInfo = Deno.statSync(filename);
     assert(fileInfo.isFile());
@@ -290,7 +291,12 @@ testPerm(
     assertEquals(fileInfo.len, 13);
 
     const buf = new Uint8Array(20);
-    await file.seek(0, Deno.SeekMode.SEEK_START);
+    // seeking from beginning of a file
+    const cursorPosition = await file.seek(
+      seekPosition,
+      Deno.SeekMode.SEEK_START
+    );
+    assertEquals(seekPosition, cursorPosition);
     const result = await file.read(buf);
     assertEquals(result, 13);
     file.close();
@@ -302,10 +308,16 @@ testPerm(
 testPerm({ read: true }, async function seekStart(): Promise<void> {
   const filename = "cli/tests/hello.txt";
   const file = await Deno.open(filename);
+  const seekPosition = 6;
   // Deliberately move 1 step forward
   await file.read(new Uint8Array(1)); // "H"
   // Skipping "Hello "
-  await file.seek(6, Deno.SeekMode.SEEK_START);
+  // seeking from beginning of a file plus seekPosition
+  const cursorPosition = await file.seek(
+    seekPosition,
+    Deno.SeekMode.SEEK_START
+  );
+  assertEquals(seekPosition, cursorPosition);
   const buf = new Uint8Array(6);
   await file.read(buf);
   const decoded = new TextDecoder().decode(buf);
@@ -316,10 +328,13 @@ testPerm({ read: true }, async function seekStart(): Promise<void> {
 testPerm({ read: true }, function seekSyncStart(): void {
   const filename = "cli/tests/hello.txt";
   const file = Deno.openSync(filename);
+  const seekPosition = 6;
   // Deliberately move 1 step forward
   file.readSync(new Uint8Array(1)); // "H"
   // Skipping "Hello "
-  file.seekSync(6, Deno.SeekMode.SEEK_START);
+  // seeking from beginning of a file plus seekPosition
+  const cursorPosition = file.seekSync(seekPosition, Deno.SeekMode.SEEK_START);
+  assertEquals(seekPosition, cursorPosition);
   const buf = new Uint8Array(6);
   file.readSync(buf);
   const decoded = new TextDecoder().decode(buf);
@@ -333,7 +348,13 @@ testPerm({ read: true }, async function seekCurrent(): Promise<void> {
   // Deliberately move 1 step forward
   await file.read(new Uint8Array(1)); // "H"
   // Skipping "ello "
-  await file.seek(5, Deno.SeekMode.SEEK_CURRENT);
+  const seekPosition = 5;
+  // seekPosition is relative to current cursor position after read
+  const cursorPosition = await file.seek(
+    seekPosition,
+    Deno.SeekMode.SEEK_CURRENT
+  );
+  assertEquals(seekPosition + 1, cursorPosition);
   const buf = new Uint8Array(6);
   await file.read(buf);
   const decoded = new TextDecoder().decode(buf);
@@ -347,7 +368,13 @@ testPerm({ read: true }, function seekSyncCurrent(): void {
   // Deliberately move 1 step forward
   file.readSync(new Uint8Array(1)); // "H"
   // Skipping "ello "
-  file.seekSync(5, Deno.SeekMode.SEEK_CURRENT);
+  const seekPosition = 5;
+  // seekPosition is relative to current cursor position after read
+  const cursorPosition = file.seekSync(
+    seekPosition,
+    Deno.SeekMode.SEEK_CURRENT
+  );
+  assertEquals(seekPosition + 1, cursorPosition);
   const buf = new Uint8Array(6);
   file.readSync(buf);
   const decoded = new TextDecoder().decode(buf);
@@ -358,7 +385,10 @@ testPerm({ read: true }, function seekSyncCurrent(): void {
 testPerm({ read: true }, async function seekEnd(): Promise<void> {
   const filename = "cli/tests/hello.txt";
   const file = await Deno.open(filename);
-  await file.seek(-6, Deno.SeekMode.SEEK_END);
+  const seekPosition = -6;
+  // seek from end of file that has 12 chars, 12 - 6  = 6
+  const cursorPosition = await file.seek(seekPosition, Deno.SeekMode.SEEK_END);
+  assertEquals(6, cursorPosition);
   const buf = new Uint8Array(6);
   await file.read(buf);
   const decoded = new TextDecoder().decode(buf);
@@ -369,7 +399,10 @@ testPerm({ read: true }, async function seekEnd(): Promise<void> {
 testPerm({ read: true }, function seekSyncEnd(): void {
   const filename = "cli/tests/hello.txt";
   const file = Deno.openSync(filename);
-  file.seekSync(-6, Deno.SeekMode.SEEK_END);
+  const seekPosition = -6;
+  // seek from end of file that has 12 chars, 12 - 6  = 6
+  const cursorPosition = file.seekSync(seekPosition, Deno.SeekMode.SEEK_END);
+  assertEquals(6, cursorPosition);
   const buf = new Uint8Array(6);
   file.readSync(buf);
   const decoded = new TextDecoder().decode(buf);
diff --git a/cli/js/io.ts b/cli/js/io.ts
index 151c69f22..e7311d0f4 100644
--- a/cli/js/io.ts
+++ b/cli/js/io.ts
@@ -105,23 +105,15 @@ export interface Seeker {
    * and `SEEK_END` means relative to the end.
    *
    * Seeking to an offset before the start of the file is an error. Seeking to
-   * any positive offset is legal, but the behavior of subsequent I/O
-   * operations on the underlying object is implementation-dependent.
+   * any positive offset is legal, but the behavior of subsequent I/O operations
+   * on the underlying object is implementation-dependent. It returns the cursor
+   * position.
    */
-  seek(offset: number, whence: SeekMode): Promise<void>;
+  seek(offset: number, whence: SeekMode): Promise<number>;
 }
 
 export interface SyncSeeker {
-  /** Seek sets the offset for the next `readSync()` or `writeSync()` to
-   * offset, interpreted according to `whence`: `SEEK_START` means relative
-   * to the start of the file, `SEEK_CURRENT` means relative to the current
-   * offset, and `SEEK_END` means relative to the end.
-   *
-   * Seeking to an offset before the start of the file is an error. Seeking to
-   * any positive offset is legal, but the behavior of subsequent I/O
-   * operations on the underlying object is implementation-dependent.
-   */
-  seekSync(offset: number, whence: SeekMode): void;
+  seekSync(offset: number, whence: SeekMode): number;
 }
 
 // https://golang.org/pkg/io/#ReadCloser
diff --git a/cli/js/lib.deno.ns.d.ts b/cli/js/lib.deno.ns.d.ts
index c54876008..50aab6a35 100644
--- a/cli/js/lib.deno.ns.d.ts
+++ b/cli/js/lib.deno.ns.d.ts
@@ -383,8 +383,9 @@ declare namespace Deno {
      * Seeking to an offset before the start of the file is an error. Seeking to
      * any positive offset is legal, but the behavior of subsequent I/O
      * operations on the underlying object is implementation-dependent.
+     * It returns the number of cursor position.
      */
-    seek(offset: number, whence: SeekMode): Promise<void>;
+    seek(offset: number, whence: SeekMode): Promise<number>;
   }
 
   export interface SyncSeeker {
@@ -397,7 +398,7 @@ declare namespace Deno {
      * any positive offset is legal, but the behavior of subsequent I/O
      * operations on the underlying object is implementation-dependent.
      */
-    seekSync(offset: number, whence: SeekMode): void;
+    seekSync(offset: number, whence: SeekMode): number;
   }
 
   export interface ReadCloser extends Reader, Closer {}
@@ -525,7 +526,11 @@ declare namespace Deno {
    *       const file = Deno.openSync("/foo/bar.txt");
    *       Deno.seekSync(file.rid, 0, 0);
    */
-  export function seekSync(rid: number, offset: number, whence: SeekMode): void;
+  export function seekSync(
+    rid: number,
+    offset: number,
+    whence: SeekMode
+  ): number;
 
   /** Seek a file ID to the given offset under mode given by `whence`.
    *
@@ -536,7 +541,7 @@ declare namespace Deno {
     rid: number,
     offset: number,
     whence: SeekMode
-  ): Promise<void>;
+  ): Promise<number>;
 
   /** Close the given resource ID. */
   export function close(rid: number): void;
@@ -557,8 +562,8 @@ declare namespace Deno {
     writeSync(p: Uint8Array): number;
     read(p: Uint8Array): Promise<number | EOF>;
     readSync(p: Uint8Array): number | EOF;
-    seek(offset: number, whence: SeekMode): Promise<void>;
-    seekSync(offset: number, whence: SeekMode): void;
+    seek(offset: number, whence: SeekMode): Promise<number>;
+    seekSync(offset: number, whence: SeekMode): number;
     close(): void;
   }
 
diff --git a/cli/js/lib.deno.shared_globals.d.ts b/cli/js/lib.deno.shared_globals.d.ts
index bec9469c5..fef155f3d 100644
--- a/cli/js/lib.deno.shared_globals.d.ts
+++ b/cli/js/lib.deno.shared_globals.d.ts
@@ -1191,13 +1191,14 @@ declare namespace __io {
      * relative to the start of the file and an error, if any.
      *
      * Seeking to an offset before the start of the file is an error. Seeking to
-     * any positive offset is legal, but the behavior of subsequent I/O
-     * operations on the underlying object is implementation-dependent.
+     * any positive offset is legal, but the behavior of subsequent I/O operations
+     * on the underlying object is implementation-dependent.
+     * It returns the cursor position.
      */
-    seek(offset: number, whence: SeekMode): Promise<void>;
+    seek(offset: number, whence: SeekMode): Promise<number>;
   }
   export interface SyncSeeker {
-    seekSync(offset: number, whence: SeekMode): void;
+    seekSync(offset: number, whence: SeekMode): number;
   }
   export interface ReadCloser extends Reader, Closer {}
   export interface WriteCloser extends Writer, Closer {}
diff --git a/cli/ops/files.rs b/cli/ops/files.rs
index 916cbdc69..60fc452a3 100644
--- a/cli/ops/files.rs
+++ b/cli/ops/files.rs
@@ -204,8 +204,8 @@ fn op_seek(
   let mut file = futures::executor::block_on(tokio_file.try_clone())?;
 
   let fut = async move {
-    file.seek(seek_from).await?;
-    Ok(json!({}))
+    let pos = file.seek(seek_from).await?;
+    Ok(json!(pos))
   };
 
   if args.promise_id.is_none() {