/* vi: set sw=4 ts=4: */
/*
 * wget - retrieve a file using HTTP or FTP
 *
 * Chip Rosenthal Covad Communications <chip@laserlink.net>
 * Licensed under GPLv2, see file LICENSE in this source tree.
 *
 * Copyright (C) 2010 Bradley M. Kuhn <bkuhn@ebb.org>
 * Kuhn's copyrights are licensed GPLv2-or-later.  File as a whole remains GPLv2.
 */
//config:config WGET
//config:       bool "wget (38 kb)"
//config:       default y
//config:       help
//config:       wget is a utility for non-interactive download of files from HTTP
//config:       and FTP servers.
//config:
//config:config FEATURE_WGET_LONG_OPTIONS
//config:       bool "Enable long options"
//config:       default y
//config:       depends on WGET && LONG_OPTS
//config:
//config:config FEATURE_WGET_STATUSBAR
//config:       bool "Enable progress bar (+2k)"
//config:       default y
//config:       depends on WGET
//config:
//config:config FEATURE_WGET_FTP
//config:       bool "Enable FTP protocol (+1k)"
//config:       default y
//config:       depends on WGET
//config:       help
//config:       To support FTPS, enable FEATURE_WGET_HTTPS as well.
//config:
//config:config FEATURE_WGET_AUTHENTICATION
//config:       bool "Enable HTTP authentication"
//config:       default y
//config:       depends on WGET
//config:       help
//config:       Support authenticated HTTP transfers.
//config:
//config:config FEATURE_WGET_TIMEOUT
//config:       bool "Enable timeout option -T SEC"
//config:       default y
//config:       depends on WGET
//config:       help
//config:       Supports network read and connect timeouts for wget,
//config:       so that wget will give up and timeout, through the -T
//config:       command line option.
//config:
//config:       Currently only connect and network data read timeout are
//config:       supported (i.e., timeout is not applied to the DNS query). When
//config:       FEATURE_WGET_LONG_OPTIONS is also enabled, the --timeout option
//config:       will work in addition to -T.
//config:
//config:config FEATURE_WGET_HTTPS
//config:       bool "Support HTTPS using internal TLS code"
//config:       default y
//config:       depends on WGET
//config:       select TLS
//config:       help
//config:       wget will use internal TLS code to connect to https:// URLs.
//config:       It also enables FTPS support, but it's not well tested yet.
//config:       Note:
//config:       On NOMMU machines, ssl_helper applet should be available
//config:       in the $PATH for this to work. Make sure to select that applet.
//config:
//config:       Note: currently, TLS code only makes TLS I/O work, it
//config:       does *not* check that the peer is who it claims to be, etc.
//config:       IOW: it uses peer-supplied public keys to establish encryption
//config:       and signing keys, then encrypts and signs outgoing data and
//config:       decrypts incoming data.
//config:       It does not check signature hashes on the incoming data:
//config:       this means that attackers manipulating TCP packets can
//config:       send altered data and we unknowingly receive garbage.
//config:       (This check might be relatively easy to add).
//config:       It does not check public key's certificate:
//config:       this means that the peer may be an attacker impersonating
//config:       the server we think we are talking to.
//config:
//config:       If you think this is unacceptable, consider this. As more and more
//config:       servers switch to HTTPS-only operation, without such "crippled"
//config:       TLS code it is *impossible* to simply download a kernel source
//config:       from kernel.org. Which can in real world translate into
//config:       "my small automatic tooling to build cross-compilers from sources
//config:       no longer works, I need to additionally keep a local copy
//config:       of ~4 megabyte source tarball of a SSL library and ~2 megabyte
//config:       source of wget, need to compile and built both before I can
//config:       download anything. All this despite the fact that the build
//config:       is done in a QEMU sandbox on a machine with absolutely nothing
//config:       worth stealing, so I don't care if someone would go to a lot
//config:       of trouble to intercept my HTTPS download to send me an altered
//config:       kernel tarball".
//config:
//config:       If you still think this is unacceptable, send patches.
//config:
//config:       If you still think this is unacceptable, do not want to send
//config:       patches, but do want to waste bandwidth expaining how wrong
//config:       it is, you will be ignored.
//config:
//config:       FEATURE_WGET_OPENSSL does implement TLS verification
//config:       using the certificates available to OpenSSL.
//config:
//config:config FEATURE_WGET_OPENSSL
//config:       bool "Try to connect to HTTPS using openssl"
//config:       default y
//config:       depends on WGET
//config:       help
//config:       Try to use openssl to handle HTTPS.
//config:
//config:       OpenSSL has a simple SSL client for debug purposes.
//config:       If you select this option, wget will effectively run:
//config:       "openssl s_client -quiet -connect hostname:443
//config:       -servername hostname 2>/dev/null" and pipe its data
//config:       through it. -servername is not used if hostname is numeric.
//config:       Note inconvenient API: host resolution is done twice,
//config:       and there is no guarantee openssl's idea of IPv6 address
//config:       format is the same as ours.
//config:       Another problem is that s_client prints debug information
//config:       to stderr, and it needs to be suppressed. This means
//config:       all error messages get suppressed too.
//config:       openssl is also a big binary, often dynamically linked
//config:       against ~15 libraries.
//config:
//config:       If openssl can't be executed, internal TLS code will be used
//config:       (if you enabled it); if openssl can be executed but fails later,
//config:       wget can't detect this, and download will fail.
//config:
//config:       By default TLS verification is performed, unless
//config:       --no-check-certificate option is passed.

//applet:IF_WGET(APPLET(wget, BB_DIR_USR_BIN, BB_SUID_DROP))

//kbuild:lib-$(CONFIG_WGET) += wget.o

//usage:#define wget_trivial_usage
//usage:        IF_FEATURE_WGET_LONG_OPTIONS(
//usage:       "[-cqS] [--spider] [-O FILE] [-o LOGFILE] [--header STR]\n"
//usage:       "        [--post-data STR | --post-file FILE] [-Y on/off]\n"
/* Since we ignore these opts, we don't show them in --help */
/* //usage:    "        [--no-cache] [--passive-ftp] [-t TRIES]" */
/* //usage:    "        [-nv] [-nc] [-nH] [-np]" */
//usage:       "        "IF_FEATURE_WGET_OPENSSL("[--no-check-certificate] ")"[-P DIR] [-U AGENT]"IF_FEATURE_WGET_TIMEOUT(" [-T SEC]")" URL..."
//usage:        )
//usage:        IF_NOT_FEATURE_WGET_LONG_OPTIONS(
//usage:       "[-cqS] [-O FILE] [-o LOGFILE] [-Y on/off] [-P DIR] [-U AGENT]"IF_FEATURE_WGET_TIMEOUT(" [-T SEC]")" URL..."
//usage:        )
//usage:#define wget_full_usage "\n\n"
//usage:       "Retrieve files via HTTP or FTP\n"
//usage:        IF_FEATURE_WGET_LONG_OPTIONS(
//usage:     "\n        --spider        Only check URL existence: $? is 0 if exists"
//usage:     "\n        --header STR    Add STR (of form 'header: value') to headers"
//usage:     "\n        --post-data STR Send STR using POST method"
//usage:     "\n        --post-file FILE        Send FILE using POST method"
//usage:        IF_FEATURE_WGET_OPENSSL(
//usage:     "\n        --no-check-certificate  Don't validate the server's certificate"
//usage:        )
//usage:        )
//usage:     "\n        -c              Continue retrieval of aborted transfer"
//usage:     "\n        -q              Quiet"
//usage:     "\n        -P DIR          Save to DIR (default .)"
//usage:     "\n        -S              Show server response"
//usage:        IF_FEATURE_WGET_TIMEOUT(
//usage:     "\n        -T SEC          Network read timeout is SEC seconds"
//usage:        )
//usage:     "\n        -O FILE         Save to FILE ('-' for stdout)"
//usage:     "\n        -o LOGFILE      Log messages to FILE"
//usage:     "\n        -U STR          Use STR for User-Agent header"
//usage:     "\n        -Y on/off       Use proxy"

#include "libbb.h"

#if 0
# define log_io(...) bb_error_msg(__VA_ARGS__)
# define SENDFMT(fp, fmt, ...) \
        do { \
                log_io("> " fmt, ##__VA_ARGS__); \
                fprintf(fp, fmt, ##__VA_ARGS__); \
        } while (0);
#else
# define log_io(...) ((void)0)
# define SENDFMT(fp, fmt, ...) fprintf(fp, fmt, ##__VA_ARGS__)
#endif


#define SSL_SUPPORTED (ENABLE_FEATURE_WGET_OPENSSL || ENABLE_FEATURE_WGET_HTTPS)
#define FTPS_SUPPORTED (ENABLE_FEATURE_WGET_FTP && ENABLE_FEATURE_WGET_HTTPS)

struct host_info {
        char *allocated;
        const char *path;
        char       *user;
        const char *protocol;
        char       *host;
        int         port;
};
static const char P_HTTP[] ALIGN1 = "http";
#if SSL_SUPPORTED
static const char P_HTTPS[] ALIGN1 = "https";
#endif
#if ENABLE_FEATURE_WGET_FTP
static const char P_FTP[] ALIGN1 = "ftp";
#endif
#if FTPS_SUPPORTED
static const char P_FTPS[] ALIGN1 = "ftps";
#endif

#if ENABLE_FEATURE_WGET_LONG_OPTIONS
/* User-specified headers prevent using our corresponding built-in headers.  */
enum {
        HDR_HOST          = (1<<0),
        HDR_USER_AGENT    = (1<<1),
        HDR_RANGE         = (1<<2),
        HDR_CONTENT_TYPE  = (1<<3),
        HDR_AUTH          = (1<<4) * ENABLE_FEATURE_WGET_AUTHENTICATION,
        HDR_PROXY_AUTH    = (1<<5) * ENABLE_FEATURE_WGET_AUTHENTICATION,
};
static const char wget_user_headers[] ALIGN1 =
        "Host:\0"
        "User-Agent:\0"
        "Range:\0"
        "Content-Type:\0"
# if ENABLE_FEATURE_WGET_AUTHENTICATION
        "Authorization:\0"
        "Proxy-Authorization:\0"
# endif
        ;
# define USR_HEADER_HOST         (G.user_headers & HDR_HOST)
# define USR_HEADER_USER_AGENT   (G.user_headers & HDR_USER_AGENT)
# define USR_HEADER_RANGE        (G.user_headers & HDR_RANGE)
# define USR_HEADER_CONTENT_TYPE (G.user_headers & HDR_CONTENT_TYPE)
# define USR_HEADER_AUTH         (G.user_headers & HDR_AUTH)
# define USR_HEADER_PROXY_AUTH   (G.user_headers & HDR_PROXY_AUTH)
#else /* No long options, no user-headers :( */
# define USR_HEADER_HOST         0
# define USR_HEADER_USER_AGENT   0
# define USR_HEADER_RANGE        0
# define USR_HEADER_CONTENT_TYPE 0
# define USR_HEADER_AUTH         0
# define USR_HEADER_PROXY_AUTH   0
#endif

/* Globals */
struct globals {
        off_t content_len;        /* Content-length of the file */
        off_t beg_range;          /* Range at which continue begins */
#if ENABLE_FEATURE_WGET_STATUSBAR
        off_t transferred;        /* Number of bytes transferred so far */
        const char *curfile;      /* Name of current file being transferred */
        bb_progress_t pmt;
#endif
        char *dir_prefix;
#if ENABLE_FEATURE_WGET_LONG_OPTIONS
        char *post_data;
        char *post_file;
        char *extra_headers;
        unsigned char user_headers; /* Headers mentioned by the user */
#endif
        char *fname_out;        /* where to direct output (-O) */
        char *fname_log;        /* where to direct log (-o) */
        const char *proxy_flag; /* Use proxies if env vars are set */
        const char *user_agent; /* "User-Agent" header field */
        int output_fd;
        int log_fd;
        int o_flags;
#if ENABLE_FEATURE_WGET_TIMEOUT
        unsigned timeout_seconds;
        smallint die_if_timed_out;
#endif
        smallint chunked;         /* chunked transfer encoding */
        smallint got_clen;        /* got content-length: from server  */
        /* Local downloads do benefit from big buffer.
         * With 512 byte buffer, it was measured to be
         * an order of magnitude slower than with big one.
         */
        char wget_buf[CONFIG_FEATURE_COPYBUF_KB*1024] ALIGNED(16);
} FIX_ALIASING;
#define G (*ptr_to_globals)
#define INIT_G() do { \
        SET_PTR_TO_GLOBALS(xzalloc(sizeof(G))); \
} while (0)
#define FINI_G() do { \
        FREE_PTR_TO_GLOBALS(); \
} while (0)


/* Must match option string! */
enum {
        WGET_OPT_CONTINUE   = (1 << 0),
        WGET_OPT_QUIET      = (1 << 1),
        WGET_OPT_SERVER_RESPONSE = (1 << 2),
        WGET_OPT_OUTNAME    = (1 << 3),
        WGET_OPT_LOGNAME    = (1 << 4),
        WGET_OPT_PREFIX     = (1 << 5),
        WGET_OPT_PROXY      = (1 << 6),
        WGET_OPT_USER_AGENT = (1 << 7),
        WGET_OPT_NETWORK_READ_TIMEOUT = (1 << 8),
        WGET_OPT_RETRIES    = (1 << 9),
        WGET_OPT_nsomething = (1 << 10),
        WGET_OPT_HEADER     = (1 << 11) * ENABLE_FEATURE_WGET_LONG_OPTIONS,
        WGET_OPT_POST_DATA  = (1 << 12) * ENABLE_FEATURE_WGET_LONG_OPTIONS,
        WGET_OPT_SPIDER     = (1 << 13) * ENABLE_FEATURE_WGET_LONG_OPTIONS,
        WGET_OPT_NO_CHECK_CERT = (1 << 14) * ENABLE_FEATURE_WGET_LONG_OPTIONS,
        WGET_OPT_POST_FILE  = (1 << 15) * ENABLE_FEATURE_WGET_LONG_OPTIONS,
        /* hijack this bit for other than opts purposes: */
        WGET_NO_FTRUNCATE   = (1 << 31)
};

#define WGET_OPT_POST (WGET_OPT_POST_DATA | WGET_OPT_POST_FILE)

enum {
        PROGRESS_START = -1,
        PROGRESS_END   = 0,
        PROGRESS_BUMP  = 1,
};
#if ENABLE_FEATURE_WGET_STATUSBAR
static void progress_meter(int flag)
{
        int notty;

        if (option_mask32 & WGET_OPT_QUIET)
                return;

        /* Don't save progress to log file */
        if (G.log_fd >= 0)
                return;

        if (flag == PROGRESS_START)
                bb_progress_init(&G.pmt, G.curfile);

        notty = bb_progress_update(&G.pmt,
                        G.beg_range,
                        G.transferred,
                        (G.chunked || !G.got_clen) ? 0 : G.beg_range + G.transferred + G.content_len
        );

        if (flag == PROGRESS_END) {
                bb_progress_free(&G.pmt);
                if (notty == 0)
                        bb_putchar_stderr('\n'); /* it's tty */
                G.transferred = 0;
        }
}
#else
static ALWAYS_INLINE void progress_meter(int flag UNUSED_PARAM) {}
#endif


/* IPv6 knows scoped address types i.e. link and site local addresses. Link
 * local addresses can have a scope identifier to specify the
 * interface/link an address is valid on (e.g. fe80::1%eth0). This scope
 * identifier is only valid on a single node.
 *
 * RFC 4007 says that the scope identifier MUST NOT be sent across the wire,
 * unless all nodes agree on the semantic. Apache e.g. regards zone identifiers
 * in the Host header as invalid requests, see
 * https://issues.apache.org/bugzilla/show_bug.cgi?id=35122
 */
static void strip_ipv6_scope_id(char *host)
{
        char *scope, *cp;

        /* bbox wget actually handles IPv6 addresses without [], like
         * wget "http://::1/xxx", but this is not standard.
         * To save code, _here_ we do not support it. */

        if (host[0] != '[')
                return; /* not IPv6 */

        scope = strchr(host, '%');
        if (!scope)
                return;

        /* Remove the IPv6 zone identifier from the host address */
        cp = strchr(host, ']');
        if (!cp || (cp[1] != ':' && cp[1] != '\0')) {
                /* malformed address (not "[xx]:nn" or "[xx]") */
                return;
        }

        /* cp points to "]...", scope points to "%eth0]..." */
        overlapping_strcpy(scope, cp);
}

#if ENABLE_FEATURE_WGET_AUTHENTICATION
/* Base64-encode character string. */
static char *base64enc(const char *str)
{
        /* paranoia */
        unsigned len = strnlen(str, sizeof(G.wget_buf)/4*3 - 10);
        bb_uuencode(G.wget_buf, str, len, bb_uuenc_tbl_base64);
        return G.wget_buf;
}
#endif

#if ENABLE_FEATURE_WGET_TIMEOUT
static void alarm_handler(int sig UNUSED_PARAM)
{
        /* This is theoretically unsafe (uses stdio and malloc in signal handler) */
        if (G.die_if_timed_out)
                bb_simple_error_msg_and_die("download timed out");
}
static void set_alarm(void)
{
        if (G.timeout_seconds) {
                alarm(G.timeout_seconds);
                G.die_if_timed_out = 1;
        }
}
# define clear_alarm() ((void)(G.die_if_timed_out = 0))
#else
# define set_alarm()   ((void)0)
# define clear_alarm() ((void)0)
#endif

#if ENABLE_FEATURE_WGET_OPENSSL
/*
 * is_ip_address() attempts to verify whether or not a string
 * contains an IPv4 or IPv6 address (vs. an FQDN).  The result
 * of inet_pton() can be used to determine this.
 */
static int is_ip_address(const char *string)
{
        struct sockaddr_in sa;

        int result = inet_pton(AF_INET, string, &(sa.sin_addr));
# if ENABLE_FEATURE_IPV6
        if (result == 0) {
                struct sockaddr_in6 sa6;
                result = inet_pton(AF_INET6, string, &(sa6.sin6_addr));
        }
# endif
        return (result == 1);
}
#endif

static FILE *open_socket(len_and_sockaddr *lsa)
{
        int fd;
        FILE *fp;

        set_alarm();
        fd = xconnect_stream(lsa);
        clear_alarm();

        /* glibc 2.4 seems to try seeking on it - ??! */
        /* hopefully it understands what ESPIPE means... */
        fp = fdopen(fd, "r+");
        if (!fp)
                bb_die_memory_exhausted();

        return fp;
}

/* We balk at any control chars in other side's messages.
 * This prevents nasty surprises (e.g. ESC sequences) in "Location:" URLs
 * and error messages.
 *
 * The only exception is tabs, which are converted to (one) space:
 * HTTP's "headers: <whitespace> values" may have those.
 */
static char* sanitize_string(char *s)
{
        unsigned char *p = (void *) s;
        while (*p) {
                if (*p < ' ') {
                        if (*p != '\t')
                                break;
                        *p = ' ';
                }
                p++;
        }
        *p = '\0';
        return s;
}

/* Returns '\n' if it was seen, else '\0'. Trims at first '\r' or '\n' */
static char fgets_trim_sanitize(FILE *fp, const char *fmt)
{
        char c;
        char *buf_ptr;

        set_alarm();
        if (fgets(G.wget_buf, sizeof(G.wget_buf), fp) == NULL)
                bb_simple_perror_msg_and_die("error getting response");
        clear_alarm();

        buf_ptr = strchrnul(G.wget_buf, '\n');
        c = *buf_ptr;
#if 1
        /* Disallow any control chars: trim at first char < 0x20 */
        sanitize_string(G.wget_buf);
#else
        *buf_ptr = '\0';
        buf_ptr = strchrnul(G.wget_buf, '\r');
        *buf_ptr = '\0';
#endif

        log_io("< %s", G.wget_buf);

        if (fmt && (option_mask32 & WGET_OPT_SERVER_RESPONSE))
                fprintf(stderr, fmt, G.wget_buf);

        return c;
}

#if ENABLE_FEATURE_WGET_FTP
static int ftpcmd(const char *s1, const char *s2, FILE *fp)
{
        int result;
        if (s1) {
                if (!s2)
                        s2 = "";
                fprintf(fp, "%s%s\r\n", s1, s2);
                /* With --server-response, wget also shows its ftp commands */
                if (option_mask32 & WGET_OPT_SERVER_RESPONSE)
                        fprintf(stderr, "--> %s%s\n\n", s1, s2);
                fflush(fp);
                log_io("> %s%s", s1, s2);
        }

        /* Read until "Nxx something" is received */
        G.wget_buf[3] = 0;
        do {
                fgets_trim_sanitize(fp, "%s\n");
        } while (!isdigit(G.wget_buf[0]) || G.wget_buf[3] != ' ');

        G.wget_buf[3] = '\0';
        result = xatoi_positive(G.wget_buf);
        G.wget_buf[3] = ' ';
        return result;
}
#endif

static void parse_url(const char *src_url, struct host_info *h)
{
        char *url, *p, *sp;

        free(h->allocated);
        h->allocated = url = xstrdup(src_url);

        h->protocol = P_HTTP;
        p = strstr(url, "://");
        if (p) {
                *p = '\0';
                h->host = p + 3;
#if ENABLE_FEATURE_WGET_FTP
                if (strcmp(url, P_FTP) == 0) {
                        h->port = bb_lookup_std_port(P_FTP, "tcp", 21);
                        h->protocol = P_FTP;
                } else
#endif
#if FTPS_SUPPORTED
                if (strcmp(url, P_FTPS) == 0) {
                        h->port = bb_lookup_std_port(P_FTPS, "tcp", 990);
                        h->protocol = P_FTPS;
                } else
#endif
#if SSL_SUPPORTED
                if (strcmp(url, P_HTTPS) == 0) {
                        h->port = bb_lookup_std_port(P_HTTPS, "tcp", 443);
                        h->protocol = P_HTTPS;
                } else
#endif
                if (strcmp(url, P_HTTP) == 0) {
                        goto http;
                } else {
                        *p = ':';
                        bb_error_msg_and_die("not an http or ftp url: %s", url);
                }
        } else {
                // GNU wget is user-friendly and falls back to http://
                h->host = url;
 http:
                h->port = bb_lookup_std_port(P_HTTP, "tcp", 80);
        }

        // FYI:
        // "Real" wget 'http://busybox.net?var=a/b' sends this request:
        //   'GET /?var=a/b HTTP/1.0'
        //   and saves 'index.html?var=a%2Fb' (we save 'b')
        // wget 'http://busybox.net?login=john@doe':
        //   request: 'GET /?login=john@doe HTTP/1.0'
        //   saves: 'index.html?login=john@doe' (we save 'login=john@doe')
        // wget 'http://busybox.net#test/test':
        //   request: 'GET / HTTP/1.0'
        //   saves: 'index.html' (we save 'test')
        //
        // We also don't add unique .N suffix if file exists...
        sp = strchr(h->host, '/');
        p = strchr(h->host, '?'); if (!sp || (p && sp > p)) sp = p;
        p = strchr(h->host, '#'); if (!sp || (p && sp > p)) sp = p;
        if (!sp) {
                h->path = "";
        } else if (*sp == '/') {
                *sp = '\0';
                h->path = sp + 1;
        } else {
                // sp points to '#' or '?'
                // Note:
                // http://busybox.net?login=john@doe is a valid URL
                // (without '/' between ".net" and "?"),
                // can't store NUL at sp[-1] - this destroys hostname.
                *sp++ = '\0';
                h->path = sp;
        }

        sp = strrchr(h->host, '@');
        if (sp != NULL) {
                // URL-decode "user:password" string before base64-encoding:
                // wget http://test:my%20pass@example.com should send
                // Authorization: Basic dGVzdDpteSBwYXNz
                // which decodes to "test:my pass".
                // Standard wget and curl do this too.
                *sp = '\0';
                free(h->user);
                h->user = xstrdup(percent_decode_in_place(h->host, /*strict:*/ 0));
                h->host = sp + 1;
        }
        /* else: h->user remains NULL, or as set by original request
         * before redirect (if we are here after a redirect).
         */
}

static char *get_sanitized_hdr(FILE *fp)
{
        char *s, *hdrval;
        int c;

        /* retrieve header line */
        c = fgets_trim_sanitize(fp, "  %s\n");

        /* end of the headers? */
        if (G.wget_buf[0] == '\0')
                return NULL;

        /* convert the header name to lower case */
        for (s = G.wget_buf; isalnum(*s) || *s == '-' || *s == '.' || *s == '_'; ++s) {
                /*
                 * No-op for 20-3f and 60-7f. "0-9a-z-." are in these ranges.
                 * 40-5f range ("@A-Z[\]^_") maps to 60-7f.
                 * "A-Z" maps to "a-z".
                 * "@[\]" can't occur in header names.
                 * "^_" maps to "~,DEL" (which is wrong).
                 * "^" was never seen yet, "_" was seen from web.archive.org
                 * (x-archive-orig-x_commoncrawl_Signature: HEXSTRING).
                 */
                *s |= 0x20;
        }

        /* verify we are at the end of the header name */
        if (*s != ':')
                bb_error_msg_and_die("bad header line: %s", G.wget_buf);

        /* locate the start of the header value */
        *s++ = '\0';
        hdrval = skip_whitespace(s);

        if (c != '\n') {
                /* Rats! The buffer isn't big enough to hold the entire header value */
                while (c = getc(fp), c != EOF && c != '\n')
                        continue;
        }

        return hdrval;
}

static void reset_beg_range_to_zero(void)
{
        bb_simple_error_msg("restart failed");
        G.beg_range = 0;
        xlseek(G.output_fd, 0, SEEK_SET);
        /* Done at the end instead: */
        /* ftruncate(G.output_fd, 0); */
}

#if ENABLE_FEATURE_WGET_OPENSSL
static int spawn_https_helper_openssl(const char *host, unsigned port)
{
        char *allocated = NULL;
        char *servername;
        int sp[2];
        int pid;
        IF_FEATURE_WGET_HTTPS(volatile int child_failed = 0;)

        if (socketpair(AF_UNIX, SOCK_STREAM, 0, sp) != 0)
                /* Kernel can have AF_UNIX support disabled */
                bb_simple_perror_msg_and_die("socketpair");

        if (!strchr(host, ':'))
                host = allocated = xasprintf("%s:%u", host, port);
        servername = xstrdup(host);
        strrchr(servername, ':')[0] = '\0';

        fflush_all();
        pid = xvfork();
        if (pid == 0) {
                /* Child */
                char *argv[13];
                char **argp;

                close(sp[0]);
                xmove_fd(sp[1], 0);
                xdup2(0, 1);
                /*
                 * openssl s_client -quiet -connect www.kernel.org:443 2>/dev/null
                 * It prints some debug stuff on stderr, don't know how to suppress it.
                 * Work around by dev-nulling stderr. We lose all error messages :(
                 */
                xmove_fd(2, 3);
                xopen("/dev/null", O_RDWR);
                memset(&argv, 0, sizeof(argv));
                argv[0] = (char*)"openssl";
                argv[1] = (char*)"s_client";
                argv[2] = (char*)"-quiet";
                argv[3] = (char*)"-connect";
                argv[4] = (char*)host;
                /*
                 * Per RFC 6066 Section 3, the only permitted values in the
                 * TLS server_name (SNI) field are FQDNs (DNS hostnames).
                 * IPv4 and IPv6 addresses, port numbers are not allowed.
                 */
                argp = &argv[5];
                if (!is_ip_address(servername)) {
                        *argp++ = (char*)"-servername"; //[5]
                        *argp++ = (char*)servername;    //[6]
                }
                if (!(option_mask32 & WGET_OPT_NO_CHECK_CERT)) {
                        /* Abort on bad server certificate */
                        *argp++ = (char*)"-verify";              //[7]
                        *argp++ = (char*)"100";                  //[8]
                        *argp++ = (char*)"-verify_return_error"; //[9]
                        if (!is_ip_address(servername)) {
                                *argp++ = (char*)"-verify_hostname"; //[10]
                                *argp++ = (char*)servername;         //[11]
                        } else {
                                *argp++ = (char*)"-verify_ip"; //[10]
                                *argp++ = (char*)host;         //[11]
                        }
                }
                //[12] (or earlier) is NULL terminator

                BB_EXECVP(argv[0], argv);
                xmove_fd(3, 2);
# if ENABLE_FEATURE_WGET_HTTPS
                child_failed = 1;
                xfunc_die();
# else
                bb_perror_msg_and_die("can't execute '%s'", argv[0]);
# endif
                /* notreached */
        }

        /* Parent */
        free(servername);
        free(allocated);
        close(sp[1]);
# if ENABLE_FEATURE_WGET_HTTPS
        if (child_failed) {
                close(sp[0]);
                return -1;
        }
# endif
        return sp[0];
}
#endif

#if ENABLE_FEATURE_WGET_HTTPS
static void spawn_ssl_client(const char *host, int network_fd, int flags)
{
        int sp[2];
        int pid;
        char *servername, *p;

        if (!(option_mask32 & WGET_OPT_NO_CHECK_CERT)) {
                option_mask32 |= WGET_OPT_NO_CHECK_CERT;
                bb_simple_error_msg("note: TLS certificate validation not implemented");
        }

        servername = xstrdup(host);
        p = strrchr(servername, ':');
        if (p) *p = '\0';

        if (socketpair(AF_UNIX, SOCK_STREAM, 0, sp) != 0)
                /* Kernel can have AF_UNIX support disabled */
                bb_simple_perror_msg_and_die("socketpair");

        fflush_all();
        pid = BB_MMU ? xfork() : xvfork();
        if (pid == 0) {
                /* Child */
                close(sp[0]);
                xmove_fd(sp[1], 0);
                xdup2(0, 1);
                if (BB_MMU) {
                        tls_state_t *tls = new_tls_state();
                        tls->ifd = tls->ofd = network_fd;
                        tls_handshake(tls, servername);
                        tls_run_copy_loop(tls, flags);
                        exit(0);
                } else {
                        char *argv[6];

                        xmove_fd(network_fd, 3);
                        argv[0] = (char*)"ssl_client";
                        argv[1] = (char*)"-s3";
                        //TODO: if (!is_ip_address(servername))...
                        argv[2] = (char*)"-n";
                        argv[3] = servername;
                        argv[4] = (flags & TLSLOOP_EXIT_ON_LOCAL_EOF ? (char*)"-e" : NULL);
                        argv[5] = NULL;
                        BB_EXECVP(argv[0], argv);
                        bb_perror_msg_and_die("can't execute '%s'", argv[0]);
                }
                /* notreached */
        }

        /* Parent */
        free(servername);
        close(sp[1]);
        xmove_fd(sp[0], network_fd);
}
#endif

#if ENABLE_FEATURE_WGET_FTP
static FILE* prepare_ftp_session(FILE **dfpp, struct host_info *target, len_and_sockaddr *lsa)
{
        FILE *sfp;
        char *pass;
        int port;

        sfp = open_socket(lsa);
#if FTPS_SUPPORTED
        if (target->protocol == P_FTPS)
                spawn_ssl_client(target->host, fileno(sfp), TLSLOOP_EXIT_ON_LOCAL_EOF);
#endif

        if (ftpcmd(NULL, NULL, sfp) != 220)
                bb_simple_error_msg_and_die(G.wget_buf);
                /* note: ftpcmd() sanitizes G.wget_buf, ok to print */

        /* Split username:password pair */
        pass = (char*)"busybox"; /* password for "anonymous" */
        if (target->user) {
                pass = strchr(target->user, ':');
                if (pass)
                        *pass++ = '\0';
        }

        /* Log in */
        switch (ftpcmd("USER ", target->user ?: "anonymous", sfp)) {
        case 230:
                break;
        case 331:
                if (ftpcmd("PASS ", pass, sfp) == 230)
                        break;
                /* fall through (failed login) */
        default:
                bb_error_msg_and_die("ftp login: %s", G.wget_buf);
        }

        ftpcmd("TYPE I", NULL, sfp);

        /* Query file size */
        if (ftpcmd("SIZE ", target->path, sfp) == 213) {
                G.content_len = BB_STRTOOFF(G.wget_buf + 4, NULL, 10);
                if (G.content_len < 0 || errno) {
                        bb_error_msg_and_die("bad SIZE value '%s'", G.wget_buf + 4);
                }
                G.got_clen = 1;
        }

        /* Enter passive mode */
        if (ENABLE_FEATURE_IPV6 && ftpcmd("EPSV", NULL, sfp) == 229) {
                /* good */
        } else
        if (ftpcmd("PASV", NULL, sfp) != 227) {
 pasv_error:
                bb_error_msg_and_die("bad response to %s: %s", "PASV", G.wget_buf);
        }
        port = parse_pasv_epsv(G.wget_buf);
        if (port < 0)
                goto pasv_error;

        set_nport(&lsa->u.sa, htons(port));

        *dfpp = open_socket(lsa);

#if FTPS_SUPPORTED
        if (target->protocol == P_FTPS) {
                /* "PROT P" enables encryption of data stream.
                 * Without it (or with "PROT C"), data is sent unencrypted.
                 */
                if (ftpcmd("PROT P", NULL, sfp) == 200)
                        spawn_ssl_client(target->host, fileno(*dfpp), /*flags*/ 0);
        }
#endif

        if (G.beg_range != 0) {
                sprintf(G.wget_buf, "REST %"OFF_FMT"u", G.beg_range);
                if (ftpcmd(G.wget_buf, NULL, sfp) == 350)
                        G.content_len -= G.beg_range;
                else
                        reset_beg_range_to_zero();
        }

//TODO: needs ftp-escaping 0xff and '\n' bytes here.
//Or disallow '\n' altogether via sanitize_string() in parse_url().
//But 0xff's are possible in valid utf8 filenames.
        if (ftpcmd("RETR ", target->path, sfp) > 150)
                bb_error_msg_and_die("bad response to %s: %s", "RETR", G.wget_buf);

        return sfp;
}
#endif

static void NOINLINE retrieve_file_data(FILE *dfp)
{
#if ENABLE_FEATURE_WGET_STATUSBAR || ENABLE_FEATURE_WGET_TIMEOUT
# if ENABLE_FEATURE_WGET_TIMEOUT
        unsigned second_cnt = G.timeout_seconds;
# endif
        struct pollfd polldata;

        polldata.fd = fileno(dfp);
        polldata.events = POLLIN | POLLPRI;
#endif
        if (!(option_mask32 & WGET_OPT_QUIET)) {
                if (G.output_fd == 1)
                        fprintf(stderr, "writing to stdout\n");
                else
                        fprintf(stderr, "saving to '%s'\n", G.fname_out);
        }
        progress_meter(PROGRESS_START);

        if (G.chunked)
                goto get_clen;

        /* Loops only if chunked */
        while (1) {

#if ENABLE_FEATURE_WGET_STATUSBAR || ENABLE_FEATURE_WGET_TIMEOUT
                /* Must use nonblocking I/O, otherwise fread will loop
                 * and *block* until it reads full buffer,
                 * which messes up progress bar and/or timeout logic.
                 * Because of nonblocking I/O, we need to dance
                 * very carefully around EAGAIN. See explanation at
                 * clearerr() calls.
                 */
                ndelay_on(polldata.fd);
#endif
                while (1) {
                        int n;
                        unsigned rdsz;

#if ENABLE_FEATURE_WGET_STATUSBAR || ENABLE_FEATURE_WGET_TIMEOUT
                        /* fread internally uses read loop, which in our case
                         * is usually exited when we get EAGAIN.
                         * In this case, libc sets error marker on the stream.
                         * Need to clear it before next fread to avoid possible
                         * rare false positive ferror below. Rare because usually
                         * fread gets more than zero bytes, and we don't fall
                         * into if (n <= 0) ...
                         */
                        clearerr(dfp);
#endif
                        errno = 0;
                        rdsz = sizeof(G.wget_buf);
                        if (G.got_clen) {
                                if (G.content_len < (off_t)sizeof(G.wget_buf)) {
                                        if ((int)G.content_len <= 0)
                                                break;
                                        rdsz = (unsigned)G.content_len;
                                }
                        }
                        n = fread(G.wget_buf, 1, rdsz, dfp);

                        if (n > 0) {
                                xwrite(G.output_fd, G.wget_buf, n);
#if ENABLE_FEATURE_WGET_STATUSBAR
                                G.transferred += n;
#endif
                                if (G.got_clen) {
                                        G.content_len -= n;
                                        if (G.content_len == 0)
                                                break;
                                }
#if ENABLE_FEATURE_WGET_TIMEOUT
                                second_cnt = G.timeout_seconds;
#endif
                                goto bump;
                        }

                        /* n <= 0.
                         * man fread:
                         * If error occurs, or EOF is reached, the return value
                         * is a short item count (or zero).
                         * fread does not distinguish between EOF and error.
                         */
                        if (errno != EAGAIN) {

                                if (ferror(dfp)) {
                                        progress_meter(PROGRESS_END);
                                        bb_simple_perror_msg_and_die(bb_msg_read_error);
                                }
                                break; /* EOF, not error */
                        }

#if ENABLE_FEATURE_WGET_STATUSBAR || ENABLE_FEATURE_WGET_TIMEOUT
                        /* It was EAGAIN. There is no data. Wait up to one second
                         * then abort if timed out, or update the bar and try reading again.
                         */
                        if (safe_poll(&polldata, 1, 1000) == 0) {
# if ENABLE_FEATURE_WGET_TIMEOUT
                                if (second_cnt != 0 && --second_cnt == 0) {
                                        progress_meter(PROGRESS_END);
                                        bb_simple_error_msg_and_die("download timed out");
                                }
# endif
                                /* We used to loop back to poll here,
                                 * but there is no great harm in letting fread
                                 * to try reading anyway.
                                 */
                        }
#endif
 bump:
                        /* Need to do it _every_ second for "stalled" indicator
                         * to be shown properly.
                         */
                        progress_meter(PROGRESS_BUMP);
                } /* while (reading data) */

#if ENABLE_FEATURE_WGET_STATUSBAR || ENABLE_FEATURE_WGET_TIMEOUT
                clearerr(dfp);
                ndelay_off(polldata.fd); /* else fgets can get very unhappy */
#endif
                if (!G.chunked)
                        break;

                /* Each chunk ends with "\r\n" - eat it */
                fgets_trim_sanitize(dfp, NULL);
 get_clen:
                /* chunk size format is "HEXNUM[;name[=val]]\r\n" */
                fgets_trim_sanitize(dfp, NULL);
                errno = 0;
                G.content_len = STRTOOFF(G.wget_buf, NULL, 16);
                /*
                 * Had a bug with inputs like "ffffffff0001f400"
                 * smashing the heap later. Ensure >= 0.
                 */
                if (G.content_len < 0 || errno)
                        bb_error_msg_and_die("bad chunk length '%s'", G.wget_buf);
                if (G.content_len == 0)
                        break; /* all done! */
                G.got_clen = 1;
                /*
                 * Note that fgets may result in some data being buffered in dfp.
                 * We loop back to fread, which will retrieve this data.
                 * Also note that code has to be arranged so that fread
                 * is done _before_ one-second poll wait - poll doesn't know
                 * about stdio buffering and can result in spurious one second waits!
                 */
        }

        /* Draw full bar and free its resources */
        G.chunked = 0;  /* makes it show 100% even for chunked download */
        G.got_clen = 1; /* makes it show 100% even for download of (formerly) unknown size */
        progress_meter(PROGRESS_END);
        if (G.content_len != 0) {
                bb_simple_perror_msg_and_die("connection closed prematurely");
                /* GNU wget says "DATE TIME (NN MB/s) - Connection closed at byte NNN. Retrying." */
        }

        /* If -c failed, we restart from the beginning,
         * but we do not truncate file then, we do it only now, at the end.
         * This lets user to ^C if his 99% complete 10 GB file download
         * failed to restart *without* losing the almost complete file.
         */
        {
                off_t pos = lseek(G.output_fd, 0, SEEK_CUR);
                if (pos != (off_t)-1) {
                        /* do not truncate if -O- is in use, a user complained about
                         * "wget -qO- 'http://example.com/empty' >>FILE" truncating FILE.
                         */
                        if (!(option_mask32 & WGET_NO_FTRUNCATE))
                                ftruncate(G.output_fd, pos);
                }
        }

        if (!(option_mask32 & WGET_OPT_QUIET)) {
                if (G.output_fd == 1)
                        fprintf(stderr, "written to stdout\n");
                else
                        fprintf(stderr, "'%s' saved\n", G.fname_out);
        }
}

static void download_one_url(const char *url)
{
        bool use_proxy;                 /* Use proxies if env vars are set  */
        int redir_limit;
        len_and_sockaddr *lsa;
        FILE *sfp;                      /* socket to web/ftp server         */
        FILE *dfp;                      /* socket to ftp server (data)      */
        char *fname_out_alloc;
        char *redirected_path = NULL;
        struct host_info server;
        struct host_info target;

        server.allocated = NULL;
        target.allocated = NULL;
        server.user = NULL;
        target.user = NULL;

        parse_url(url, &target);

        /* Use the proxy if necessary */
        use_proxy = (strcmp(G.proxy_flag, "off") != 0);
        if (use_proxy) {
                char *proxy = getenv(target.protocol[0] == 'f' ? "ftp_proxy" : "http_proxy");
//FIXME: what if protocol is https? Ok to use http_proxy?
                use_proxy = (proxy && proxy[0]);
                if (use_proxy)
                        parse_url(proxy, &server);
        }
        if (!use_proxy) {
                server.protocol = target.protocol;
                server.port = target.port;
                if (ENABLE_FEATURE_IPV6) {
                        //free(server.allocated); - can't be non-NULL
                        server.host = server.allocated = xstrdup(target.host);
                } else {
                        server.host = target.host;
                }
        }

        if (ENABLE_FEATURE_IPV6)
                strip_ipv6_scope_id(target.host);

        /* If there was no -O FILE, guess output filename */
        fname_out_alloc = NULL;
        if (!(option_mask32 & WGET_OPT_OUTNAME)) {
                G.fname_out = bb_get_last_path_component_nostrip(target.path);
                /* handle "wget http://kernel.org//" */
                if (G.fname_out[0] == '/' || !G.fname_out[0])
                        G.fname_out = (char*)"index.html";
                /* -P DIR is considered only if there was no -O FILE */
                if (G.dir_prefix)
                        G.fname_out = fname_out_alloc = concat_path_file(G.dir_prefix, G.fname_out);
                else {
                        /* redirects may free target.path later, need to make a copy */
                        G.fname_out = fname_out_alloc = xstrdup(G.fname_out);
                }
        }
#if ENABLE_FEATURE_WGET_STATUSBAR
        G.curfile = bb_get_last_path_component_nostrip(G.fname_out);
#endif

        /* Determine where to start transfer */
        G.beg_range = 0;
        if (option_mask32 & WGET_OPT_CONTINUE) {
                G.output_fd = open(G.fname_out, O_WRONLY);
                if (G.output_fd >= 0) {
                        G.beg_range = xlseek(G.output_fd, 0, SEEK_END);
                }
                /* File doesn't exist. We do not create file here yet.
                 * We are not sure it exists on remote side */
        }

        redir_limit = 16;
 resolve_lsa:
        lsa = xhost2sockaddr(server.host, server.port);
        if (!(option_mask32 & WGET_OPT_QUIET)) {
                char *s = xmalloc_sockaddr2dotted(&lsa->u.sa);
                fprintf(stderr, "Connecting to %s (%s)\n", server.host, s);
                free(s);
        }
 establish_session:
        /*G.content_len = 0; - redundant, got_clen = 0 is enough */
        G.got_clen = 0;
        G.chunked = 0;
        if (use_proxy || target.protocol[0] != 'f' /*not ftp[s]*/) {
                /*
                 *  HTTP session
                 */
                char *str;
                int status;

                /* Open socket to http(s) server */
#if ENABLE_FEATURE_WGET_OPENSSL
                /* openssl (and maybe internal TLS) support is configured */
                if (server.protocol == P_HTTPS) {
                        /* openssl-based helper
                         * Inconvenient API since we can't give it an open fd
                         */
                        int fd = spawn_https_helper_openssl(server.host, server.port);
# if ENABLE_FEATURE_WGET_HTTPS
                        if (fd < 0) { /* no openssl? try internal */
                                sfp = open_socket(lsa);
                                spawn_ssl_client(server.host, fileno(sfp), /*flags*/ 0);
                                goto socket_opened;
                        }
# else
                        /* We don't check for exec("openssl") failure in this case */
# endif
                        sfp = fdopen(fd, "r+");
                        if (!sfp)
                                bb_die_memory_exhausted();
                        goto socket_opened;
                }
                sfp = open_socket(lsa);
 socket_opened:
#elif ENABLE_FEATURE_WGET_HTTPS
                /* Only internal TLS support is configured */
                sfp = open_socket(lsa);
                if (server.protocol == P_HTTPS)
                        spawn_ssl_client(server.host, fileno(sfp), /*flags*/ 0);
#else
                /* ssl (https) support is not configured */
                sfp = open_socket(lsa);
#endif
                /* Send HTTP request */
                if (use_proxy) {
                        SENDFMT(sfp, "GET %s://%s/%s HTTP/1.1\r\n",
                                target.protocol, target.host,
                                target.path);
                } else {
                        SENDFMT(sfp, "%s /%s HTTP/1.1\r\n",
                                (option_mask32 & WGET_OPT_POST) ? "POST" : "GET",
                                target.path);
                }
                if (!USR_HEADER_HOST)
                        SENDFMT(sfp, "Host: %s\r\n", target.host);
                if (!USR_HEADER_USER_AGENT)
                        SENDFMT(sfp, "User-Agent: %s\r\n", G.user_agent);

                /* Ask server to close the connection as soon as we are done
                 * (IOW: we do not intend to send more requests)
                 */
                SENDFMT(sfp, "Connection: close\r\n");

#if ENABLE_FEATURE_WGET_AUTHENTICATION
                if (target.user && !USR_HEADER_AUTH) {
                        SENDFMT(sfp, "Proxy-Authorization: Basic %s\r\n"+6,
                                base64enc(target.user));
                }
                if (use_proxy && server.user && !USR_HEADER_PROXY_AUTH) {
                        SENDFMT(sfp, "Proxy-Authorization: Basic %s\r\n",
                                base64enc(server.user));
                }
#endif

                if (G.beg_range != 0 && !USR_HEADER_RANGE)
                        SENDFMT(sfp, "Range: bytes=%"OFF_FMT"u-\r\n", G.beg_range);

#if ENABLE_FEATURE_WGET_LONG_OPTIONS
                if (G.extra_headers) {
                        log_io(G.extra_headers);
                        fputs(G.extra_headers, sfp);
                }

                if (option_mask32 & WGET_OPT_POST_FILE) {
                        int fd = xopen_stdin(G.post_file);
                        G.post_data = xmalloc_read(fd, NULL);
                        close(fd);
                }

                if (G.post_data) {
                        /* If user did not override it... */
                        if (!USR_HEADER_CONTENT_TYPE) {
                                SENDFMT(sfp,
                                        "Content-Type: application/x-www-form-urlencoded\r\n"
                                );
                        }
                        SENDFMT(sfp,
                                "Content-Length: %u\r\n"
                                "\r\n"
                                "%s",
                                (int) strlen(G.post_data), G.post_data
                        );
                } else
#endif
                {
                        SENDFMT(sfp, "\r\n");
                }

                fflush(sfp);

/* Tried doing this unconditionally.
 * Cloudflare and nginx/1.11.5 are shocked to see SHUT_WR on non-HTTPS.
 */
#if SSL_SUPPORTED
                if (target.protocol == P_HTTPS) {
                        /* If we use SSL helper, keeping our end of the socket open for writing
                         * makes our end (i.e. the same fd!) readable (EAGAIN instead of EOF)
                         * even after child closes its copy of the fd.
                         * This helps:
                         */
                        shutdown(fileno(sfp), SHUT_WR);
                }
#endif

                /*
                 * Retrieve HTTP response line and check for "200" status code.
                 */
 read_response:
                fgets_trim_sanitize(sfp, "  %s\n");

                str = G.wget_buf;
                str = skip_non_whitespace(str);
                str = skip_whitespace(str);
                // FIXME: no error check
                // xatou wouldn't work: "200 OK"
                status = atoi(str);
                switch (status) {
                case 0:
                case 100:
                        while (get_sanitized_hdr(sfp) != NULL)
                                /* eat all remaining headers */;
                        goto read_response;

                /* Success responses */
                case 200:
                        /* fall through */
                case 201: /* 201 Created */
/* "The request has been fulfilled and resulted in a new resource being created" */
                        /* Standard wget is reported to treat this as success */
                        /* fall through */
                case 202: /* 202 Accepted */
/* "The request has been accepted for processing, but the processing has not been completed" */
                        /* Treat as success: fall through */
                case 203: /* 203 Non-Authoritative Information */
/* "Use of this response code is not required and is only appropriate when the response would otherwise be 200 (OK)" */
                        /* fall through */
                case 204: /* 204 No Content */
/*
Response 204 doesn't say "null file", it says "metadata
has changed but data didn't":

"10.2.5 204 No Content
The server has fulfilled the request but does not need to return
an entity-body, and might want to return updated metainformation.
The response MAY include new or updated metainformation in the form
of entity-headers, which if present SHOULD be associated with
the requested variant.

If the client is a user agent, it SHOULD NOT change its document
view from that which caused the request to be sent. This response
is primarily intended to allow input for actions to take place
without causing a change to the user agent's active document view,
although any new or updated metainformation SHOULD be applied
to the document currently in the user agent's active view.

The 204 response MUST NOT include a message-body, and thus
is always terminated by the first empty line after the header fields."

However, in real world it was observed that some web servers
(e.g. Boa/0.94.14rc21) simply use code 204 when file size is zero.
*/
                        if (G.beg_range != 0) {
                                /* "Range:..." was not honored by the server.
                                 * Restart download from the beginning.
                                 */
                                reset_beg_range_to_zero();
                        }
                        break;
                /* 205 Reset Content ?? what to do on this ??   */

                case 300:  /* redirection */
                case 301:
                case 302:
                case 303:
                case 307:
                case 308:
                        break;

                case 206: /* Partial Content */
                        if (G.beg_range != 0)
                                /* "Range:..." worked. Good. */
                                break;
                        /* Partial Content even though we did not ask for it??? */
                        /* fall through */
                default:
                        bb_error_msg_and_die("server returned error: %s", G.wget_buf);
                }

                /*
                 * Retrieve HTTP headers.
                 */
                while ((str = get_sanitized_hdr(sfp)) != NULL) {
                        static const char keywords[] ALIGN1 =
                                "content-length\0""transfer-encoding\0""location\0";
                        enum {
                                KEY_content_length = 1, KEY_transfer_encoding, KEY_location
                        };
                        smalluint key;

                        /* get_sanitized_hdr converted "FOO:" string to lowercase */

                        /* strip trailing whitespace */
                        char *s = strchrnul(str, '\0') - 1;
                        while (s >= str && (*s == ' ' || *s == '\t')) {
                                *s = '\0';
                                s--;
                        }
                        key = index_in_strings(keywords, G.wget_buf) + 1;
                        if (key == KEY_content_length) {
                                G.content_len = BB_STRTOOFF(str, NULL, 10);
                                if (G.content_len < 0 || errno) {
                                        bb_error_msg_and_die("content-length %s is garbage", str);
                                }
                                G.got_clen = 1;
                                continue;
                        }
                        if (key == KEY_transfer_encoding) {
                                if (strcmp(str_tolower(str), "chunked") != 0)
                                        bb_error_msg_and_die("transfer encoding '%s' is not supported", str);
                                G.chunked = 1;
                        }
                        if (key == KEY_location && status >= 300) {
                                if (--redir_limit == 0)
                                        bb_simple_error_msg_and_die("too many redirections");
                                fclose(sfp);
                                if (str[0] == '/') {
                                        free(redirected_path);
                                        target.path = redirected_path = xstrdup(str + 1);
                                        /* lsa stays the same: it's on the same server */
                                } else {
                                        parse_url(str, &target);
                                        if (!use_proxy) {
                                                /* server.user remains untouched */
                                                free(server.allocated);
                                                server.allocated = NULL;
                                                server.protocol = target.protocol;
                                                server.host = target.host;
                                                /* strip_ipv6_scope_id(target.host); - no! */
                                                /* we assume remote never gives us IPv6 addr with scope id */
                                                server.port = target.port;
                                                free(lsa);
                                                goto resolve_lsa;
                                        } /* else: lsa stays the same: we use proxy */
                                }
                                goto establish_session;
                        }
                }
//              if (status >= 300)
//                      bb_error_msg_and_die("bad redirection (no Location: header from server)");

                /* For HTTP, data is pumped over the same connection */
                dfp = sfp;
        } else {
#if ENABLE_FEATURE_WGET_FTP
                /*
                 *  FTP session
                 */
                sfp = prepare_ftp_session(&dfp, &target, lsa);
#endif
        }

        free(lsa);

        if (!(option_mask32 & WGET_OPT_SPIDER)) {
                if (G.output_fd < 0)
                        G.output_fd = xopen(G.fname_out, G.o_flags);
                retrieve_file_data(dfp);
                if (!(option_mask32 & WGET_OPT_OUTNAME)) {
                        xclose(G.output_fd);
                        G.output_fd = -1;
                }
        } else {
                if (!(option_mask32 & WGET_OPT_QUIET))
                        fprintf(stderr, "remote file exists\n");
        }

#if ENABLE_FEATURE_WGET_FTP
        if (dfp != sfp) {
                /* It's ftp. Close data connection properly */
                fclose(dfp);
                if (ftpcmd(NULL, NULL, sfp) != 226)
                        bb_error_msg_and_die("ftp error: %s", G.wget_buf);
                /* ftpcmd("QUIT", NULL, sfp); - why bother? */
        }
#endif
        fclose(sfp);

        free(server.allocated);
        free(target.allocated);
        free(server.user);
        free(target.user);
        free(fname_out_alloc);
        free(redirected_path);
}

int wget_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int wget_main(int argc UNUSED_PARAM, char **argv)
{
#if ENABLE_FEATURE_WGET_LONG_OPTIONS
        static const char wget_longopts[] ALIGN1 =
                /* name, has_arg, val */
                "continue\0"         No_argument       "c"
                "quiet\0"            No_argument       "q"
                "server-response\0"  No_argument       "S"
                "output-document\0"  Required_argument "O"
                "output-file\0"      Required_argument "o"
                "directory-prefix\0" Required_argument "P"
                "proxy\0"            Required_argument "Y"
                "user-agent\0"       Required_argument "U"
IF_FEATURE_WGET_TIMEOUT(
                "timeout\0"          Required_argument "T")
                /* Ignored: */
IF_DESKTOP(     "tries\0"            Required_argument "t")
                "header\0"           Required_argument "\xff"
                "post-data\0"        Required_argument "\xfe"
                "spider\0"           No_argument       "\xfd"
                "no-check-certificate\0" No_argument   "\xfc"
                "post-file\0"        Required_argument "\xfb"
                /* Ignored (we always use PASV): */
IF_DESKTOP(     "passive-ftp\0"      No_argument       "\xf0")
                /* Ignored (we don't support caching) */
IF_DESKTOP(     "no-cache\0"         No_argument       "\xf0")
IF_DESKTOP(     "no-verbose\0"       No_argument       "\xf0")
IF_DESKTOP(     "no-clobber\0"       No_argument       "\xf0")
IF_DESKTOP(     "no-host-directories\0" No_argument    "\xf0")
IF_DESKTOP(     "no-parent\0"        No_argument       "\xf0")
                ;
# define GETOPT32 getopt32long
# define LONGOPTS ,wget_longopts
#else
# define GETOPT32 getopt32
# define LONGOPTS
#endif

#if ENABLE_FEATURE_WGET_LONG_OPTIONS
        llist_t *headers_llist = NULL;
#endif

        INIT_G();

#if ENABLE_FEATURE_WGET_TIMEOUT
        G.timeout_seconds = 900;
        signal(SIGALRM, alarm_handler);
#endif
        G.proxy_flag = "on";   /* use proxies if env vars are set */
        G.user_agent = "Wget"; /* "User-Agent" header field */

        GETOPT32(argv, "^"
                "cqSO:o:P:Y:U:T:+"
                /*ignored:*/ "t:"
                /*ignored:*/ "n::"
                /* wget has exactly four -n<letter> opts, all of which we can ignore:
                 * -nv --no-verbose: be moderately quiet (-q is full quiet)
                 * -nc --no-clobber: abort if exists, neither download to FILE.n nor overwrite FILE
                 * -nH --no-host-directories: wget -r http://host/ won't create host/
                 * -np --no-parent
                 * "n::" above says that we accept -n[ARG].
                 * Specifying "n:" would be a bug: "-n ARG" would eat ARG!
                 */
                "\0"
                "-1" /* at least one URL */
                IF_FEATURE_WGET_LONG_OPTIONS(":\xfe--\xfb")
                IF_FEATURE_WGET_LONG_OPTIONS(":\xfe--\xfe")
                IF_FEATURE_WGET_LONG_OPTIONS(":\xfb--\xfb")
                IF_FEATURE_WGET_LONG_OPTIONS(":\xff::") /* --header is a list */
                LONGOPTS
                , &G.fname_out, &G.fname_log, &G.dir_prefix,
                &G.proxy_flag, &G.user_agent,
                IF_FEATURE_WGET_TIMEOUT(&G.timeout_seconds) IF_NOT_FEATURE_WGET_TIMEOUT(NULL),
                NULL, /* -t RETRIES */
                NULL  /* -n[ARG] */
                IF_FEATURE_WGET_LONG_OPTIONS(, &headers_llist)
                IF_FEATURE_WGET_LONG_OPTIONS(, &G.post_data)
                IF_FEATURE_WGET_LONG_OPTIONS(, &G.post_file)
        );
#if 0 /* option bits debug */
        if (option_mask32 & WGET_OPT_RETRIES) bb_error_msg("-t NUM");
        if (option_mask32 & WGET_OPT_nsomething) bb_error_msg("-nsomething");
        if (option_mask32 & WGET_OPT_HEADER) bb_error_msg("--header");
        if (option_mask32 & WGET_OPT_POST_DATA) bb_error_msg("--post-data");
        if (option_mask32 & WGET_OPT_SPIDER) bb_error_msg("--spider");
        if (option_mask32 & WGET_OPT_NO_CHECK_CERT) bb_error_msg("--no-check-certificate");
        if (option_mask32 & WGET_OPT_POST_FILE) bb_error_msg("--post-file");
        exit(0);
#endif
        argv += optind;

#if ENABLE_FEATURE_WGET_LONG_OPTIONS
        if (headers_llist) {
                int size = 0;
                char *hdr;
                llist_t *ll = headers_llist;
                while (ll) {
                        size += strlen(ll->data) + 2;
                        ll = ll->link;
                }
                G.extra_headers = hdr = xmalloc(size + 1);
                while (headers_llist) {
                        int bit;
                        const char *words;

                        size = sprintf(hdr, "%s\r\n",
                                        (char*)llist_pop(&headers_llist));
                        /* a bit like index_in_substrings but don't match full key */
                        bit = 1;
                        words = wget_user_headers;
                        while (*words) {
                                if (strstr(hdr, words) == hdr) {
                                        G.user_headers |= bit;
                                        break;
                                }
                                bit <<= 1;
                                words += strlen(words) + 1;
                        }
                        hdr += size;
                }
        }
#endif

        G.output_fd = -1;
        G.o_flags = O_WRONLY | O_CREAT | O_TRUNC | O_EXCL;
        if (G.fname_out) { /* -O FILE ? */
                if (LONE_DASH(G.fname_out)) { /* -O - ? */
                        G.output_fd = 1;
                        option_mask32 = (option_mask32 & (~WGET_OPT_CONTINUE)) | WGET_NO_FTRUNCATE;
                }
                /* compat with wget: -O FILE can overwrite */
                G.o_flags = O_WRONLY | O_CREAT | O_TRUNC;
        }

        G.log_fd = -1;
        if (G.fname_log) { /* -o FILE ? */
                if (!LONE_DASH(G.fname_log)) { /* not -o - ? */
                        /* compat with wget: -o FILE can overwrite */
                        G.log_fd = xopen(G.fname_log, O_WRONLY | O_CREAT | O_TRUNC);
                        /* Redirect only stderr to log file, so -O - will work */
                        xdup2(G.log_fd, STDERR_FILENO);
                }
        }

        while (*argv)
                download_one_url(*argv++);

        if (G.output_fd >= 0)
                xclose(G.output_fd);

        if (G.log_fd >= 0)
                xclose(G.log_fd);

#if ENABLE_FEATURE_CLEAN_UP && ENABLE_FEATURE_WGET_LONG_OPTIONS
        free(G.extra_headers);
#endif
        FINI_G();

        return EXIT_SUCCESS;
}