/**
* Utility functions for the proxy MCP server.
*/
import { networkInterfaces } from "node:os";
/**
* Maximum characters for tool output to stay within MCP token limits.
*/
const MAX_RESULT_CHARS = 24000;
/**
* Serialize data to JSON, truncating if it exceeds MCP limits.
* For arrays: binary-search for max items that fit, append truncation notice.
* For other values: slice the JSON string and append a notice.
*/
export function truncateResult(data: unknown, indent?: number): string {
const full = JSON.stringify(data, null, indent);
if (full.length <= MAX_RESULT_CHARS) return full;
if (Array.isArray(data)) {
let lo = 0;
let hi = data.length;
while (lo < hi) {
const mid = (lo + hi + 1) >>> 1;
if (JSON.stringify(data.slice(0, mid), null, indent).length <= MAX_RESULT_CHARS - 200) {
lo = mid;
} else {
hi = mid - 1;
}
}
const truncated = data.slice(0, lo);
return JSON.stringify({
items: truncated,
truncated: true,
showing: lo,
total: data.length,
message: `Showing ${lo} of ${data.length} items. Use filter/limit params to narrow results.`,
}, null, indent);
}
return full.slice(0, MAX_RESULT_CHARS - 100) + "\n... [truncated, total " + full.length + " chars]";
}
/**
* Get the first non-loopback IPv4 address for LAN proxy instructions.
*/
export function getLocalIP(): string {
let interfaces: ReturnType<typeof networkInterfaces>;
try {
interfaces = networkInterfaces();
} catch {
return "127.0.0.1";
}
for (const iface of Object.values(interfaces)) {
if (!iface) continue;
for (const addr of iface) {
if (addr.family === "IPv4" && !addr.internal) {
return addr.address;
}
}
}
return "127.0.0.1";
}
/**
* Serialize headers object to a clean record, lowercasing keys.
*/
export function serializeHeaders(headers: Record<string, string | string[] | undefined>): Record<string, string> {
const result: Record<string, string> = {};
for (const [key, value] of Object.entries(headers)) {
if (value !== undefined) {
result[key.toLowerCase()] = Array.isArray(value) ? value.join(", ") : value;
}
}
return result;
}
/**
* Cap a string to maxLen characters, appending "..." if truncated.
*/
export function capString(s: string, maxLen: number): string {
if (s.length <= maxLen) return s;
return s.slice(0, maxLen) + "...";
}
