public File download()

in core/src/main/java/hudson/model/UpdateCenter.java [1243:1323]
64 lines of code
17 McCabe index (conditional complexity)

        public File download(DownloadJob job, URL src) throws IOException {
            MessageDigest sha1 = null;
            MessageDigest sha256 = null;
            MessageDigest sha512 = null;
            try {
                // Java spec says SHA-1 and SHA-256 exist, and SHA-512 might not, so one try/catch block should be fine
                sha1 = MessageDigest.getInstance("SHA-1");
                sha256 = MessageDigest.getInstance("SHA-256");
                sha512 = MessageDigest.getInstance("SHA-512");
            } catch (NoSuchAlgorithmException nsa) {
                LOGGER.log(Level.WARNING, "Failed to instantiate message digest algorithm, may only have weak or no verification of downloaded file", nsa);
            }

            URLConnection con = null;
            try {
                con = connect(job,src);
                //JENKINS-34174 - set timeout for downloads, may hang indefinitely
                // particularly noticeable during 2.0 install when downloading
                // many plugins
                con.setReadTimeout(PLUGIN_DOWNLOAD_READ_TIMEOUT);
                
                int total = con.getContentLength();
                byte[] buf = new byte[8192];
                int len;

                File dst = job.getDestination();
                File tmp = new File(dst.getPath()+".tmp");

                LOGGER.info("Downloading "+job.getName());
                Thread t = Thread.currentThread();
                String oldName = t.getName();
                t.setName(oldName + ": " + src);
                try (OutputStream _out = Files.newOutputStream(tmp.toPath());
                     OutputStream out =
                             sha1 != null ? new DigestOutputStream(
                                     sha256 != null ? new DigestOutputStream(
                                             sha512 != null ? new DigestOutputStream(_out, sha512) : _out, sha256) : _out, sha1) : _out;
                     InputStream in = con.getInputStream();
                     CountingInputStream cin = new CountingInputStream(in)) {
                    while ((len = cin.read(buf)) >= 0) {
                        out.write(buf,0,len);
                        job.status = job.new Installing(total == -1 ? -1 : cin.getCount() * 100 / total);
                    }
                } catch (IOException | InvalidPathException e) {
                    throw new IOException("Failed to load "+src+" to "+tmp,e);
                } finally {
                    t.setName(oldName);
                }

                if (total!=-1 && total!=tmp.length()) {
                    // don't know exactly how this happens, but report like
                    // http://www.ashlux.com/wordpress/2009/08/14/hudson-and-the-sonar-plugin-fail-maveninstallation-nosuchmethoderror/
                    // indicates that this kind of inconsistency can happen. So let's be defensive
                    throw new IOException("Inconsistent file length: expected "+total+" but only got "+tmp.length());
                }

                if (sha1 != null) {
                    byte[] digest = sha1.digest();
                    job.computedSHA1 = Base64.getEncoder().encodeToString(digest);
                }
                if (sha256 != null) {
                    byte[] digest = sha256.digest();
                    job.computedSHA256 = Base64.getEncoder().encodeToString(digest);
                }
                if (sha512 != null) {
                    byte[] digest = sha512.digest();
                    job.computedSHA512 = Base64.getEncoder().encodeToString(digest);
                }
                return tmp;
            } catch (IOException e) {
                // assist troubleshooting in case of e.g. "too many redirects" by printing actual URL
                String extraMessage = "";
                if (con != null && con.getURL() != null && !src.toString().equals(con.getURL().toString())) {
                    // Two URLs are considered equal if different hosts resolve to same IP. Prefer to log in case of string inequality,
                    // because who knows how the server responds to different host name in the request header?
                    // Also, since it involved name resolution, it'd be an expensive operation.
                    extraMessage = " (redirected to: " + con.getURL() + ")";
                }
                throw new IOException("Failed to download from "+src+extraMessage,e);
            }
        }