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import { parseSrvUrl } from "./uri.ts";import { ConnectOptions } from "../types.ts";
enum AllowedOption {  authSource = "authSource",  replicaSet = "replicaSet",  loadBalanced = "loadBalanced",}
function isAllowedOption(key: unknown): key is AllowedOption {  return Object.values(AllowedOption).includes(key as AllowedOption);}
interface Resolver {  resolveDns: typeof Deno.resolveDns;}
interface SRVResolveResultOptions {  authSource?: string;  replicaSet?: string;  loadBalanced?: string;}
interface SRVResolveResult {  servers: { host: string; port: number }[];  options: SRVResolveResultOptions;}
class SRVError extends Error {  constructor(message?: string) {    super(message);    this.name = "SRVError";  }}
export class Srv {  resolver: Resolver;
  constructor(resolver = { resolveDns: Deno.resolveDns }) {    this.resolver = resolver;  }
  async resolveSrvUrl(urlString: string): Promise<ConnectOptions> {    const options = parseSrvUrl(urlString);    const { srvServer, ...connectOptions } = options;    if (!srvServer) {      throw new SRVError(        `Could not parse srv server address from ${urlString}`,      );    }    const resolveResult = await this.resolve(srvServer);    return {      servers: resolveResult.servers,      // TODO: Check and throw on invalid options      ...resolveResult.options,      ...connectOptions,    };  }
  async resolve(url: string): Promise<SRVResolveResult> {    const tokens = url.split(".");    if (tokens.length < 3) {      throw new SRVError(        `Expected url in format 'host.domain.tld', received ${url}`,      );    }
    const srvRecord = await this.resolver.resolveDns(      `_mongodb._tcp.${url}`,      "SRV",    );    if (!(srvRecord?.length > 0)) {      throw new SRVError(        `Expected at least one SRV record, received ${srvRecord          ?.length} for url ${url}`,      );    }    const txtRecords = await this.resolver.resolveDns(url, "TXT");    if (txtRecords?.length !== 1) {      throw new SRVError(        `Expected exactly one TXT record, received ${txtRecords          ?.length} for url ${url}`,      );    }
    const servers = srvRecord.map((record) => {      return {        host: record.target,        port: record.port,      };    });
    const optionsUri = txtRecords[0].join("");    const options: { valid: SRVResolveResultOptions; illegal: string[] } = {      valid: {},      illegal: [],    };    optionsUri.split("&").forEach((option: string) => {      const [key, value] = option.split("=");      if (isAllowedOption(key) && !!value) options.valid[key] = value;      else options.illegal.push(option);    });
    if (options.illegal.length !== 0) {      throw new SRVError(        `Illegal uri options: ${options.illegal}. Allowed options: ${          Object.values(AllowedOption)        }`,      );    }
    return {      servers,      options: options.valid,    };  }}