Program.java

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.nio.charset.UnsupportedCharsetException;
import java.net.Socket;

public class Program {
    private static void readResponse(InputStream inputStream) throws Exception {
        try (
            BufferedReader in = new BufferedReader(
                new InputStreamReader(
                    inputStream,
                    StandardCharsets.US_ASCII
                )
            )
        ) {
            int contentLength = 0;
            String charsetName = "";
            String line = in.readLine();
            while (!line.isEmpty()) {
                System.out.println(line);
                final String[] s = line.split(":");
                if (s.length == 2) {
                    if (s[0].trim().equals("Content-Length")) {
                        contentLength = Integer.parseInt(s[1].trim());
                    } else if (s[0].trim().equals("Transfer-Encoding")) {
                        if (s[1].trim().equals("chunked")) {
                            contentLength = -1;
                        }
                    } else if (s[0].trim().equals("Content-Type")) {
                        final String[] s2 = s[1].trim().split(";");
                        if (s2.length == 2) {
                            final String[] s3 = s2[1].trim().split("=");
                            if (s3.length == 2) {
                                if (s3[0].trim().equals("charset")) {
                                    charsetName = s3[1].trim();
                                }
                            }
                        }
                    }
                }
                line = in.readLine();
            }
            /*if (!charsetName.isEmpty()) {
                if (Charset.isSupported(charsetName)) {
                    final Charset charset = Charset.forName(charsetName);
                    readBody(inputStream, charset, contentLength);
                } else {
                    throw new UnsupportedCharsetException(charsetName);
                }
            } else {
                readBody(inputStream, StandardCharsets.ISO_8859_1, contentLength);
            }*/
            readBodyData(in, contentLength);
        }
    }

    private static void readBody(InputStream inputStream, Charset charset, int contentLength) throws Exception {
        try (
            BufferedReader in = new BufferedReader(
                new InputStreamReader(
                    inputStream,
                    charset
                )
            )
        ) {
            readBodyData(in, contentLength);
        }
    }

    private static void readBodyData(BufferedReader in, int contentLength) throws Exception {
        System.out.println();
        if (contentLength > 0) {
            final StringBuilder sb = new StringBuilder();
            boolean flagError = false;
            for (int i = 0; i < contentLength && !flagError; i++) {
                int c = in.read();
                if (c >= 0) {
                    sb.append((char)c);
                } else {
                    flagError = true;
                }
            }
            System.out.println(sb.toString());
        } else if (contentLength == -1) {
            final StringBuilder sb = new StringBuilder();
            boolean flagEnd = false;
            while (!flagEnd) {
                int chunkSize = 0;
                int c = in.read();
                while (c >= (int)' ') {
                    if (c >= (int)'0' && c <= (int)'9') {
                        chunkSize *= 16;
                        chunkSize += c - (int)'0';
                    } else if (c >= (int)'A' && c <= (int)'F') {
                        chunkSize *= 16;
                        chunkSize += c - (int)'A' + 10;
                    } else if (c >= (int)'a' && c <= (int)'f') {
                        chunkSize *= 16;
                        chunkSize += c - (int)'a' + 10;
                    } else {
                        c = -1;
                    }
                    if (c >= 0) {
                        c = in.read();
                    }
                }
                flagEnd = true;
                if (c == '\r') {
                    c = in.read();
                    if (c == '\n') {
                        boolean flagError = false;
                        for (int i = 0; i < chunkSize && !flagError; i++) {
                            c = in.read();
                            if (c >= 0) {
                                sb.append((char)c);
                            } else {
                                flagError = true;
                            }
                        }
                        if (!flagError) {
                            c = in.read();
                            if (c == '\r') {
                                c = in.read();
                                if (c == '\n') {
                                    if (chunkSize > 0) {
                                        flagEnd = false;
                                    }
                                }
                            }
                        }
                    }
                }
            }
            System.out.println(sb.toString());
        } else {
            String line = in.readLine();
            while (line != null && !line.isEmpty()) {
                System.out.println(line);
                line = in.readLine();
            }
        }
    }

    private static void sendRequest(
        OutputStream outputStream, InputStream inputStream, String url,
        String method, String[] headers
    ) throws Exception {
        try (
            BufferedWriter out = new BufferedWriter(
                new OutputStreamWriter(
                    outputStream,
                    StandardCharsets.US_ASCII
                )
            )
        ) {
            out.write(method);
            out.write(' ');
            out.write(url);
            out.write(' ');
            out.write("HTTP/1.1");
            out.write('\r');
            out.write('\n');
            for (String header : headers) {
                out.write(header);
                out.write('\r');
                out.write('\n');
            }
            out.write('\r');
            out.write('\n');
            out.flush();
            readResponse(inputStream);
        }
    }

    public static void main(String[] args) {
        if (args.length != 4) {
            System.err.println("Syntax: java Program <host> <port> <method> <url>");
            System.err.println("Example: java Program www.lib.ru 80 GET /");
            System.exit(1);
        }
        try (
            Socket client = new Socket(args[0], Integer.parseInt(args[1]));
            InputStream cis = client.getInputStream();
            OutputStream cos = client.getOutputStream()
        ) {
            sendRequest(cos, cis, args[3], args[2], new String[] { "Host: " + args[0], "User-Agent: application" });
        } catch (Exception ex) {
            System.err.println("ERROR: " + ex.getMessage());
        }
    }
}