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/*
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 *  This file is part of CoCalc: Copyright © 2020 Sagemath, Inc.
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 *  License: MS-RSL – see LICENSE.md for details
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 */
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/* Determine the base path for this CoCalc service.
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The default export of this module is base path, which should
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be used by the CoCalc backend hub server.
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*/
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const DEFN: string = `
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The basePath is the URL prefix for all paths, relative to the
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host root. It must start with a leading slash /, but does not
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end with one unless it is '/'.  It also should not include ://.
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Some examples of valid basePaths:
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- /
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- /10f0e544-313c-4efe-8718-1111ac97ad11/port/5000
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These are not valid:
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- //
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- "" (empty string)
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- /foo/
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- https://cocalc.com/
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If the environment variable BASE_PATH is set then use that (e.g., used
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when running a project), or throw an error if our assumptions are not satisfied.
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Otherwise, if this code is running in a CoCalc project (i.e., if the env variable
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COCALC_PROJECT_ID is set), then the base path is a combination of
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COCALC_PROJECT_ID and the port that the hub will serve on.
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If neither of the above conditions are met, then the base path is /.
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NOTES:
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- We use this code in a project started by the hub to determine the base path;
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in that case, the env variable BASE_PATH is set, since otherwise the project
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itself would view the base path as being relative to its own id.
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`;
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import PORT from "./port";
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function isValidBasePath(s: string): boolean {
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  if (s[0] != "/") return false;
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  if (s.length == 1) return true;
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  if (s[s.length - 1] == "/") return false;
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  if (s.includes("://")) return false;
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  return true;
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}
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function basePath(): string {
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  if (process.env.BASE_PATH) {
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    if (!isValidBasePath(process.env.BASE_PATH)) {
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      throw Error(
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        `BASE_PATH (="${process.env.BASE_PATH}") is invalid - ${DEFN}.`,
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      );
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    }
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    return process.env.BASE_PATH;
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  }
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  if (process.env.API_SERVER) {
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    // if an api server is set but BASE_PATH isn't (e.g., we're using a remote api server), then we
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    // deduce the base path from that URL. Examples:
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    //   API_SERVER=http://localhost:5000/6659c2e3-ff5e-4bb4-9a43-8830aa951282/port/5000 --> "/6659c2e3-ff5e-4bb4-9a43-8830aa951282/port/5000"
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    //   API_SERVER=https://compute.cocalc.io --> "/"
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    //   API_SERVER=https://cocalc.com --> "/"
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    const url = process.env.API_SERVER;
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    const i = url.indexOf("://");
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    if (i == -1) {
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      throw Error(`invalid API_SERVER url ${url}`);
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    }
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    const j = url.indexOf("/", i + 3);
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    if (j == -1) {
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      return "/";
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    }
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    return url.slice(j) ? url.slice(j) : "/";
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  }
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  if (!process.env.COCALC_PROJECT_ID) {
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    return "/";
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  }
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  // This is used by the project server, i.e., inside the project.
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  return `/${process.env.COCALC_PROJECT_ID}/port/${PORT}`;
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}
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export default basePath();
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