[Init] Initial commit - NetMesh terminal manager

components/terminal/connectionLogBuffer.ts

@@ -0,0 +1,94 @@
+/**
+ * A bounded, append-only text buffer that retains only the last `maxChars`
+ * characters — the connection log used for diagnostics/replay.
+ *
+ * The naive implementation (`log += chunk; if (log.length > max) log =
+ * log.slice(-max)`) flattens a ~max-length string on *every* append once the
+ * cap is reached — on the render thread, for every output chunk including each
+ * echoed keystroke.
+ *
+ * Instead, data is coalesced into a small, bounded number of fixed-size blocks
+ * (~`maxChars / blockSize`, e.g. ~16 for the 1 MB cap). New data accumulates in
+ * an open `tail`; once it reaches `blockSize` it is sealed into a block. Trimming
+ * the oldest data therefore only ever drops/slices a handful of blocks — never
+ * one array element per append, which would make trim O(number of appends) and
+ * defeat the purpose. Append is amortized O(chunk); the full string is
+ * materialized only on `toString()` (called rarely, on finalize).
+ */
+export interface ConnectionLogBuffer {
+  append(chunk: string): void;
+  toString(): string;
+  reset(): void;
+  /**
+   * Number of internal string segments currently retained. Exposed for tests
+   * to assert the bounded-memory / bounded-trim property.
+   */
+  segmentCount(): number;
+}
+
+const DEFAULT_BLOCK_SIZE = 64 * 1024;
+
+export function createConnectionLogBuffer(
+  maxChars: number,
+  blockSize: number = DEFAULT_BLOCK_SIZE,
+): ConnectionLogBuffer {
+  let blocks: string[] = []; // sealed blocks, oldest first, each up to ~blockSize
+  let tail = ""; // open block currently being filled (newest data)
+  let total = 0; // total retained length across blocks + tail
+
+  const trim = () => {
+    let overflow = total - maxChars;
+    if (overflow <= 0) return;
+    // Drop/slice whole blocks from the front. `blocks.length` is bounded by
+    // ~maxChars/blockSize, so this shift is O(small constant), not O(appends).
+    while (overflow > 0 && blocks.length > 0) {
+      const head = blocks[0];
+      if (head.length <= overflow) {
+        blocks.shift();
+        total -= head.length;
+        overflow -= head.length;
+      } else {
+        blocks[0] = head.slice(overflow);
+        total -= overflow;
+        overflow = 0;
+      }
+    }
+    // Only reachable when the tail alone exceeds the cap (e.g. blockSize >=
+    // maxChars); keep its last `maxChars` characters.
+    if (overflow > 0) {
+      tail = tail.slice(overflow);
+      total -= overflow;
+    }
+  };
+
+  return {
+    append(chunk: string): void {
+      if (!chunk) return;
+      // A single chunk at/over the cap can only contribute its own tail.
+      if (chunk.length >= maxChars) {
+        blocks = [];
+        tail = chunk.slice(chunk.length - maxChars);
+        total = tail.length;
+        return;
+      }
+      tail += chunk;
+      total += chunk.length;
+      if (tail.length >= blockSize) {
+        blocks.push(tail);
+        tail = "";
+      }
+      if (total > maxChars) trim();
+    },
+    toString(): string {
+      return blocks.length > 0 ? blocks.join("") + tail : tail;
+    },
+    reset(): void {
+      blocks = [];
+      tail = "";
+      total = 0;
+    },
+    segmentCount(): number {
+      return blocks.length + (tail.length > 0 ? 1 : 0);
+    },
+  };
+}