refactor: split format helpers into core

packages/core/src/format.ts

@@ -0,0 +1,54 @@
+export const DEFAULT_ROW_LIMIT = 100
+export const MAX_ROW_LIMIT = 1000
+
+export const clampLimit = (
+    requested: number | undefined,
+    fallback = DEFAULT_ROW_LIMIT,
+    max = MAX_ROW_LIMIT
+): number => {
+    if (requested === undefined) {
+        return fallback
+    }
+    return Math.max(1, Math.min(Math.trunc(requested), max))
+}
+
+export const truncateRows = <T>(rows: T[], limit: number): { rows: T[]; truncated: boolean } =>
+    rows.length > limit
+        ? { rows: rows.slice(0, limit), truncated: true }
+        : { rows, truncated: false }
+
+// Slice a string to at most `maxBytes` UTF-8 bytes without splitting a
+// multi-byte sequence (back off to a code-point boundary).
+export const sliceUtf8 = (s: string, maxBytes: number): string => {
+    const buf = Buffer.from(s, 'utf8')
+    if (buf.length <= maxBytes) {
+        return s
+    }
+    let end = maxBytes
+    while (end > 0 && (buf[end] & 0xc0) === 0x80) {
+        end -= 1
+    }
+    return buf.subarray(0, end).toString('utf8')
+}
+
+// Serialize `value` to JSON and, if it exceeds `maxBytes` (UTF-8), return a
+// truncated marker object whose own serialization stays within `maxBytes`.
+export const truncateJsonBudget = (
+    value: unknown,
+    maxBytes: number
+): { body: unknown; truncated: boolean } => {
+    const text = JSON.stringify(value)
+    if (text === undefined) {
+        return { body: value, truncated: false }
+    }
+    const bytes = Buffer.byteLength(text, 'utf8')
+    if (bytes <= maxBytes) {
+        return { body: value, truncated: false }
+    }
+    const RESERVE = 256
+    const preview = sliceUtf8(text, Math.max(0, maxBytes - RESERVE))
+    return {
+        body: { _truncated: true, _originalBytes: bytes, _maxBytes: maxBytes, preview },
+        truncated: true
+    }
+}