Add tests for splitAnsiCarryover function

src/ansi-carryover.ts

@@ -0,0 +1,62 @@
+/**
+ * Detect and split any incomplete ANSI control sequence at the end of a chunk.
+ *
+ * ANSI sequences can span multiple network packets. This function identifies
+ * incomplete sequences at the end of a chunk to prevent them from being
+ * rendered as partial/broken control codes.
+ *
+ * @param chunk - Raw output string potentially containing ANSI sequences
+ * @returns Tuple of [body, carry] where:
+ *   - body: Complete portion safe to render
+ *   - carry: Incomplete sequence to prepend to next chunk
+ *
+ * @example
+ * const [body, carry] = splitAnsiCarryover("hello\x1b[31");
+ * // body = "hello", carry = "\x1b[31"
+ */
+export function splitAnsiCarryover(chunk: string): [string, string] {
+  if (!chunk) return ["", ""];
+
+  const ESC = 0x1b;
+  const len = chunk.length;
+
+  // If last char is ESC, entire ESC starts a sequence we can't complete
+  if (chunk.charCodeAt(len - 1) === ESC) {
+    return [chunk.slice(0, -1), "\x1b"];
+  }
+
+  // Search from the last ESC backwards for a potentially incomplete sequence
+  for (let i = len - 2; i >= 0; i--) {
+    if (chunk.charCodeAt(i) !== ESC) continue;
+    const next = chunk[i + 1];
+    // OSC: ESC ] ... (terminated by BEL 0x07 or ST = ESC \
+    if (next === "]") {
+      const tail = chunk.slice(i + 2);
+      const hasBEL = tail.indexOf("\x07") !== -1;
+      const hasST = tail.indexOf("\x1b\\") !== -1;
+      if (!hasBEL && !hasST) {
+        return [chunk.slice(0, i), chunk.slice(i)];
+      }
+      // else complete; continue scanning
+      continue;
+    }
+    // CSI: ESC [ params final — ensure we have a final byte 0x40-0x7E
+    if (next === "[") {
+      let j = i + 2;
+      while (j < len && /[0-9;?]/.test(chunk[j] || "")) j++;
+      // If we reached end without a final byte, it's incomplete
+      if (j >= len) {
+        return [chunk.slice(0, i), chunk.slice(i)];
+      }
+      // Final byte exists at chunk[j]; sequence complete
+      continue;
+    }
+    // DCS/PM/APC and other ESC-prefixed two-char intros — if ESC is near end and likely incomplete, carry
+    // If ESC is the penultimate and we're at end, treat as incomplete unknown sequence
+    if (i >= len - 2) {
+      return [chunk.slice(0, i), chunk.slice(i)];
+    }
+    // Otherwise, unknown but complete; continue
+  }
+  return [chunk, ""];
+}

src/server.test.ts

@@ -1,5 +1,62 @@
 import { expect, test } from "bun:test";
+import { splitAnsiCarryover } from "./ansi-carryover";
 
-test("placeholder", () => {
-  expect(true).toBe(true);
+test("splitAnsiCarryover: complete chunk with no incomplete sequences", () => {
+  const [body, carry] = splitAnsiCarryover("hello world");
+  expect(body).toBe("hello world");
+  expect(carry).toBe("");
+});
+
+test("splitAnsiCarryover: ESC at end of chunk", () => {
+  const [body, carry] = splitAnsiCarryover("hello\x1b");
+  expect(body).toBe("hello");
+  expect(carry).toBe("\x1b");
+});
+
+test("splitAnsiCarryover: incomplete CSI sequence without final byte", () => {
+  const [body, carry] = splitAnsiCarryover("hello\x1b[31");
+  expect(body).toBe("hello");
+  expect(carry).toBe("\x1b[31");
+});
+
+test("splitAnsiCarryover: incomplete OSC without BEL terminator", () => {
+  const [body, carry] = splitAnsiCarryover("hello\x1b]0;title");
+  expect(body).toBe("hello");
+  expect(carry).toBe("\x1b]0;title");
+});
+
+test("splitAnsiCarryover: complete OSC with BEL terminator", () => {
+  const [body, carry] = splitAnsiCarryover("hello\x1b]0;title\x07world");
+  expect(body).toBe("hello\x1b]0;title\x07world");
+  expect(carry).toBe("");
+});
+
+test("splitAnsiCarryover: complete CSI sequence", () => {
+  const [body, carry] = splitAnsiCarryover("hello\x1b[31mworld");
+  expect(body).toBe("hello\x1b[31mworld");
+  expect(carry).toBe("");
+});
+
+test("splitAnsiCarryover: empty string", () => {
+  const [body, carry] = splitAnsiCarryover("");
+  expect(body).toBe("");
+  expect(carry).toBe("");
+});
+
+test("splitAnsiCarryover: multiple complete sequences", () => {
+  const [body, carry] = splitAnsiCarryover("\x1b[1m\x1b[31mhello\x1b[0m");
+  expect(body).toBe("\x1b[1m\x1b[31mhello\x1b[0m");
+  expect(carry).toBe("");
+});
+
+test("splitAnsiCarryover: incomplete CSI at end with complete CSI before", () => {
+  const [body, carry] = splitAnsiCarryover("\x1b[31mhello\x1b[");
+  expect(body).toBe("\x1b[31mhello");
+  expect(carry).toBe("\x1b[");
+});
+
+test("splitAnsiCarryover: ESC with unknown sequence near end", () => {
+  const [body, carry] = splitAnsiCarryover("hello\x1bP");
+  expect(body).toBe("hello");
+  expect(carry).toBe("\x1bP");
 });

src/server.ts

@@ -2,6 +2,7 @@
 
 import type { ServerWebSocket } from "bun";
 import { ansiToHtml } from "./ansi";
+import { splitAnsiCarryover } from "./ansi-carryover";
 import {
   appendOutput,
   createDevice,
@@ -81,69 +82,6 @@ function broadcastSSE(event: SSEEvent): void {
   }
 }
 
-/**
- * Detect and split any incomplete ANSI control sequence at the end of a chunk.
- *
- * ANSI sequences can span multiple network packets. This function identifies
- * incomplete sequences at the end of a chunk to prevent them from being
- * rendered as partial/broken control codes.
- *
- * @param chunk - Raw output string potentially containing ANSI sequences
- * @returns Tuple of [body, carry] where:
- *   - body: Complete portion safe to render
- *   - carry: Incomplete sequence to prepend to next chunk
- *
- * @example
- * const [body, carry] = splitAnsiCarryover("hello\x1b[31");
- * // body = "hello", carry = "\x1b[31"
- */
-function splitAnsiCarryover(chunk: string): [string, string] {
-  if (!chunk) return ["", ""];
-
-  const ESC = 0x1b;
-  const len = chunk.length;
-
-  // If last char is ESC, entire ESC starts a sequence we can't complete
-  if (chunk.charCodeAt(len - 1) === ESC) {
-    return [chunk.slice(0, -1), "\x1b"];
-  }
-
-  // Search from the last ESC backwards for a potentially incomplete sequence
-  for (let i = len - 2; i >= 0; i--) {
-    if (chunk.charCodeAt(i) !== ESC) continue;
-    const next = chunk[i + 1];
-    // OSC: ESC ] ... (terminated by BEL 0x07 or ST = ESC \
-    if (next === "]") {
-      const tail = chunk.slice(i + 2);
-      const hasBEL = tail.indexOf("\x07") !== -1;
-      const hasST = tail.indexOf("\x1b\\") !== -1;
-      if (!hasBEL && !hasST) {
-        return [chunk.slice(0, i), chunk.slice(i)];
-      }
-      // else complete; continue scanning
-      continue;
-    }
-    // CSI: ESC [ params final — ensure we have a final byte 0x40-0x7E
-    if (next === "[") {
-      let j = i + 2;
-      while (j < len && /[0-9;?]/.test(chunk[j] || "")) j++;
-      // If we reached end without a final byte, it's incomplete
-      if (j >= len) {
-        return [chunk.slice(0, i), chunk.slice(i)];
-      }
-      // Final byte exists at chunk[j]; sequence complete
-      continue;
-    }
-    // DCS/PM/APC and other ESC-prefixed two-char intros — if ESC is near end and likely incomplete, carry
-    // If ESC is the penultimate and we're at end, treat as incomplete unknown sequence
-    if (i >= len - 2) {
-      return [chunk.slice(0, i), chunk.slice(i)];
-    }
-    // Otherwise, unknown but complete; continue
-  }
-  return [chunk, ""];
-}
-
 // Initialize database
 const port = Number.parseInt(process.env.PORT || "7200", 10);
 initDb();