ci(docs-infra): rename 'upload-server' to 'preview-server'

The server no longer has files uploaded to it. Instead it is more
accurate to refer to it as dealing with "previews" of PRs.

aio/aio-builds-setup/dockerbuild/scripts-js/lib/preview-server/build-retriever.ts

@@ -0,0 +1,83 @@
+import * as fs from 'fs';
+import fetch from 'node-fetch';
+import {dirname} from 'path';
+import {mkdir} from 'shelljs';
+import {promisify} from 'util';
+import {CircleCiApi} from '../common/circle-ci-api';
+import {assert, assertNotMissingOrEmpty, computeArtifactDownloadPath, createLogger} from '../common/utils';
+import {PreviewServerError} from './preview-error';
+
+export interface GithubInfo {
+  org: string;
+  pr: number;
+  repo: string;
+  sha: string;
+  success: boolean;
+}
+
+/**
+ * A helper that can get information about builds and download build artifacts.
+ */
+export class BuildRetriever {
+  private logger = createLogger('BuildRetriever');
+  constructor(private api: CircleCiApi, private downloadSizeLimit: number, private downloadDir: string) {
+    assert(downloadSizeLimit > 0, 'Invalid parameter "downloadSizeLimit" should be a number greater than 0.');
+    assertNotMissingOrEmpty('downloadDir', downloadDir);
+  }
+
+  /**
+   * Get GitHub information about a build
+   * @param buildNum The number of the build for which to retrieve the info.
+   * @returns The Github org, repo, PR and latest SHA for the specified build.
+   */
+  public async getGithubInfo(buildNum: number): Promise<GithubInfo> {
+    const buildInfo = await this.api.getBuildInfo(buildNum);
+    const githubInfo: GithubInfo = {
+      org: buildInfo.username,
+      pr: getPrfromBranch(buildInfo.branch),
+      repo: buildInfo.reponame,
+      sha: buildInfo.vcs_revision,
+      success: !buildInfo.failed,
+    };
+    return githubInfo;
+  }
+
+  /**
+   * Make a request to the given URL for a build artifact and store it locally.
+   * @param buildNum the number of the CircleCI build whose artifact we want to download.
+   * @param pr the number of the PR that triggered the CircleCI build.
+   * @param sha the commit in the PR that triggered the CircleCI build.
+   * @param artifactPath the path on CircleCI where the artifact was stored.
+   * @returns A promise to the file path where the downloaded file was stored.
+   */
+  public async downloadBuildArtifact(buildNum: number, pr: number, sha: string, artifactPath: string): Promise<string> {
+    try {
+      const outPath = computeArtifactDownloadPath(this.downloadDir, pr, sha, artifactPath);
+      const downloadExists = await new Promise(resolve => fs.exists(outPath, exists => resolve(exists)));
+      if (!downloadExists) {
+        const url = await this.api.getBuildArtifactUrl(buildNum, artifactPath);
+        const response = await fetch(url, {size: this.downloadSizeLimit});
+        if (response.status !== 200) {
+          throw new PreviewServerError(response.status, `Error ${response.status} - ${response.statusText}`);
+        }
+        const buffer = await response.buffer();
+        mkdir('-p', dirname(outPath));
+        await promisify(fs.writeFile)(outPath, buffer);
+      }
+      return outPath;
+    } catch (error) {
+      this.logger.warn(error);
+      const status = (error.type === 'max-size') ? 413 : 500;
+      throw new PreviewServerError(status, `CircleCI artifact download failed (${error.message || error})`);
+    }
+  }
+}
+
+function getPrfromBranch(branch: string): number {
+  // CircleCI only exposes PR numbers via the `branch` field :-(
+  const match = /^pull\/(\d+)$/.exec(branch);
+  if (!match) {
+    throw new Error(`No PR found in branch field: ${branch}`);
+  }
+  return +match[1];
+}