Merge pull request #93 from Automattic/GH-73

fix: handle file truncation

Author: sjinks

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+## [1.0.1](https://github.com/Automattic/vscode-logwatcher/releases/tag/v1.0.1)
+
+* Properly handle file truncation
+
 ## [1.0.0](https://github.com/Automattic/vscode-logwatcher/releases/tag/v1.0.0)
 
 * First official release
@@ -17,4 +21,4 @@
 
 ## [0.0.1](https://github.com/Automattic/vscode-logwatcher/releases/tag/v0.0.1)
 
-- Initial release.
+* Initial release.

src/test/suite/watchfilecommand.test.ts

@@ -1,7 +1,7 @@
 import { deepEqual, equal, match, notEqual } from 'node:assert/strict';
 import { EventEmitter, once } from 'node:events';
 import { WriteStream, createWriteStream } from 'node:fs';
-import { mkdtemp, rm, unlink, writeFile } from 'node:fs/promises';
+import { mkdtemp, rm, unlink, writeFile, truncate } from 'node:fs/promises';
 import { EOL, platform, tmpdir } from 'node:os';
 import { join } from 'node:path';
 import { setTimeout } from 'node:timers/promises';
@@ -177,4 +177,41 @@ suite('WatchFileCommand', function () {
         const actual = getFilenames();
         deepEqual(actual, expected);
     });
+
+
+    test('file truncation', async function () {
+        const fname = join(tmpDir, '0006.txt');
+
+        const expectedContent = '0123456789';
+        await writeFile(fname, expectedContent);
+
+        const [editor, emitter] = await Promise.all([
+            waitForOutputWindow(`extension-output-`),
+            commands.executeCommand<EventEmitter>('logwatcher.watchFile', fname),
+        ]);
+
+        notEqual(editor, undefined);
+        notEqual(emitter, undefined);
+
+        if (!editor.document.getText()) {
+            await waitForVisibleRangesChange(editor);
+        }
+
+        let actual = editor.document.getText();
+        equal(actual, expectedContent);
+
+        const waitForVisibleRangesChangePromise = waitForVisibleRangesChange(editor);
+        const onceFileChangedPromise = once(emitter, 'fileChanged');
+
+        const expectedSize = 5;
+        await truncate(fname, expectedSize);
+
+        await Promise.all([
+            waitForVisibleRangesChangePromise,
+            onceFileChangedPromise,
+        ]);
+
+        actual = editor.document.getText();
+        equal(actual, expectedContent + expectedContent.slice(0, expectedSize));
+    });
 });

src/watchfilecommand.ts

@@ -109,13 +109,23 @@ async function setUpWatcher(filename: string): Promise<Resource | null> {
         let fd: FileHandle | undefined;
         let stats: FileStat | null;
         try {
-            [fd, stats] = await Promise.all([open(filename, 'r'), statFile(filename)]);
-
+            stats = await statFile(filename);
             if (stats) {
-                const buffer = Buffer.alloc(stats.size - offset);
-                await fd.read(buffer, 0, buffer.length, offset);
-                offset += buffer.length;
-                outputChannel.append(buffer.toString('ascii'));
+                if (stats.size > offset) {
+                    fd = await open(filename, 'r');
+                    const buffer = Buffer.alloc(stats.size - offset);
+                    await fd.read(buffer, 0, buffer.length, offset);
+                    offset += buffer.length;
+                    outputChannel.append(buffer.toString('ascii'));
+                } else {
+                    offset = stats.size;
+                    const data = await readInitialData(filename, offset);
+                    if (typeof data === 'string') {
+                        outputChannel.append(data);
+                    } else {
+                        throw data;
+                    }
+                }
             }
         } catch (err) {
             outputChannel.appendLine(`*** Failed to read file ${filename}: ${(err as Error).message}`);