httpread.c

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/*
 * httpread - Manage reading file(s) from HTTP/TCP socket
 * Author: Ted Merrill
 * Copyright 2008 Atheros Communications
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * Alternatively, this software may be distributed under the terms of BSD
 * license.
 *
 * See README and COPYING for more details.
 *
 * The files are buffered via internal callbacks from eloop, then presented to
 * an application callback routine when completely read into memory. May also
 * be used if no file is expected but just to get the header, including HTTP
 * replies (e.g. HTTP/1.1 200 OK etc.).
 *
 * This does not attempt to be an optimally efficient implementation, but does
 * attempt to be of reasonably small size and memory consumption; assuming that
 * only small files are to be read. A maximum file size is provided by
 * application and enforced.
 *
 * It is assumed that the application does not expect any of the following:
 * -- transfer encoding other than chunked
 * -- trailer fields
 * It is assumed that, even if the other side requested that the connection be
 * kept open, that we will close it (thus HTTP messages sent by application
 * should have the connection closed field); this is allowed by HTTP/1.1 and
 * simplifies things for us.
 *
 * Other limitations:
 * -- HTTP header may not exceed a hard-coded size.
 *
 * Notes:
 * This code would be massively simpler without some of the new features of
 * HTTP/1.1, especially chunked data.
 */

#include "includes.h"

#include "common.h"
#include "eloop.h"
#include "httpread.h"


/* Tunable parameters */
#define HTTPREAD_READBUF_SIZE 1024      /* read in chunks of this size */
#define HTTPREAD_HEADER_MAX_SIZE 4096   /* max allowed for headers */
#define HTTPREAD_BODYBUF_DELTA 4096     /* increase allocation by this */

#if 0
/* httpread_debug -- set this global variable > 0 e.g. from debugger
 * to enable debugs (larger numbers for more debugs)
 * Make this a #define of 0 to eliminate the debugging code.
 */
int httpread_debug = 99;
#else
#define httpread_debug 0        /* eliminates even the debugging code */
#endif


/* control instance -- actual definition (opaque to application)
 */
struct httpread {
        /* information from creation */
        int sd;         /* descriptor of TCP socket to read from */
        void (*cb)(struct httpread *handle, void *cookie,
                    enum httpread_event e);  /* call on event */
        void *cookie;   /* pass to callback */
        int max_bytes;          /* maximum file size else abort it */
        int timeout_seconds;            /* 0 or total duration timeout period */

        /* dynamically used information follows */
        int sd_registered;      /* nonzero if we need to unregister socket */
        int to_registered;      /* nonzero if we need to unregister timeout */

        int got_hdr;            /* nonzero when header is finalized */
        char hdr[HTTPREAD_HEADER_MAX_SIZE+1];   /* headers stored here */
        int hdr_nbytes;

        enum httpread_hdr_type hdr_type;
        int version;            /* 1 if we've seen 1.1 */
        int reply_code;         /* for type REPLY, e.g. 200 for HTTP/1.1 200 OK */
        int got_content_length; /* true if we know content length for sure */
        int content_length;     /* body length,  iff got_content_length */
        int chunked;            /* nonzero for chunked data */
        char *uri;

        int got_body;           /* nonzero when body is finalized */
        char *body;
        int body_nbytes;
        int body_alloc_nbytes;  /* amount allocated */

        int got_file;           /* here when we are done */

        /* The following apply if data is chunked: */
        int in_chunk_data;      /* 0=in/at header, 1=in the data or tail*/
        int chunk_start;        /* offset in body of chunk hdr or data */
        int chunk_size;         /* data of chunk (not hdr or ending CRLF)*/
        int in_trailer;         /* in header fields after data (chunked only)*/
        enum trailer_state {
                trailer_line_begin = 0,
                trailer_empty_cr,       /* empty line + CR */
                trailer_nonempty,
                trailer_nonempty_cr,
        } trailer_state;
};


/* Check words for equality, where words consist of graphical characters
 * delimited by whitespace
 * Returns nonzero if "equal" doing case insensitive comparison.
 */
static int word_eq(char *s1, char *s2)
{
        int c1;
        int c2;
        int end1 = 0;
        int end2 = 0;
        for (;;) {
                c1 = *s1++;
                c2 = *s2++;
                if (isalpha(c1) && isupper(c1))
                        c1 = tolower(c1);
                if (isalpha(c2) && isupper(c2))
                        c2 = tolower(c2);
                end1 = !isgraph(c1);
                end2 = !isgraph(c2);
                if (end1 || end2 || c1 != c2)
                        break;
        }
        return end1 && end2;  /* reached end of both words? */
}


/* convert hex to binary
 * Requires that c have been previously tested true with isxdigit().
 */
static int hex_value(int c)
{
        if (isdigit(c))
                return c - '0';
        if (islower(c))
                return 10 + c - 'a';
        return 10 + c - 'A';
}


static void httpread_timeout_handler(void *eloop_data, void *user_ctx);

/* httpread_destroy -- if h is non-NULL, clean up
 * This must eventually be called by the application following
 * call of the application's callback and may be called
 * earlier if desired.
 */
void httpread_destroy(struct httpread *h)
{
        if (httpread_debug >= 10)
                wpa_printf(MSG_DEBUG, "ENTER httpread_destroy(%p)", h);
        if (!h)
                return;

        if (h->to_registered)
                eloop_cancel_timeout(httpread_timeout_handler, NULL, h);
        h->to_registered = 0;
        if (h->sd_registered)
                eloop_unregister_sock(h->sd, EVENT_TYPE_READ);
        h->sd_registered = 0;
        os_free(h->body);
        os_free(h->uri);
        os_memset(h, 0, sizeof(*h));  /* aid debugging */
        h->sd = -1;     /* aid debugging */
        os_free(h);
}


/* httpread_timeout_handler -- called on excessive total duration
 */
static void httpread_timeout_handler(void *eloop_data, void *user_ctx)
{
        struct httpread *h = user_ctx;
        wpa_printf(MSG_DEBUG, "httpread timeout (%p)", h);
        h->to_registered = 0;   /* is self-cancelling */
        (*h->cb)(h, h->cookie, HTTPREAD_EVENT_TIMEOUT);
}


/* Analyze options only so far as is needed to correctly obtain the file.
 * The application can look at the raw header to find other options.
 */
static int httpread_hdr_option_analyze(
        struct httpread *h,
        char *hbp       /* pointer to current line in header buffer */
        )
{
        if (word_eq(hbp, "CONTENT-LENGTH:")) {
                while (isgraph(*hbp))
                        hbp++;
                while (*hbp == ' ' || *hbp == '\t')
                        hbp++;
                if (!isdigit(*hbp))
                        return -1;
                h->content_length = atol(hbp);
                h->got_content_length = 1;
                return 0;
        }
        if (word_eq(hbp, "TRANSFER_ENCODING:") ||
            word_eq(hbp, "TRANSFER-ENCODING:")) {
                while (isgraph(*hbp))
                        hbp++;
                while (*hbp == ' ' || *hbp == '\t')
                        hbp++;
                /* There should (?) be no encodings of interest
                 * other than chunked...
                 */
                if (word_eq(hbp, "CHUNKED")) {
                        h->chunked = 1;
                        h->in_chunk_data = 0;
                        /* ignore possible ;<parameters> */
                }
                return 0;
        }
        /* skip anything we don't know, which is a lot */
        return 0;
}


static int httpread_hdr_analyze(struct httpread *h)
{
        char *hbp = h->hdr;      /* pointer into h->hdr */
        int standard_first_line = 1;

        /* First line is special */
        h->hdr_type = HTTPREAD_HDR_TYPE_UNKNOWN;
        if (!isgraph(*hbp))
                goto bad;
        if (os_strncmp(hbp, "HTTP/", 5) == 0) {
                h->hdr_type = HTTPREAD_HDR_TYPE_REPLY;
                standard_first_line = 0;
                hbp += 5;
                if (hbp[0] == '1' && hbp[1] == '.' &&
                    isdigit(hbp[2]) && hbp[2] != '0')
                        h->version = 1;
                while (isgraph(*hbp))
                        hbp++;
                while (*hbp == ' ' || *hbp == '\t')
                        hbp++;
                if (!isdigit(*hbp))
                        goto bad;
                h->reply_code = atol(hbp);
        } else if (word_eq(hbp, "GET"))
                h->hdr_type = HTTPREAD_HDR_TYPE_GET;
        else if (word_eq(hbp, "HEAD"))
                h->hdr_type = HTTPREAD_HDR_TYPE_HEAD;
        else if (word_eq(hbp, "POST"))
                h->hdr_type = HTTPREAD_HDR_TYPE_POST;
        else if (word_eq(hbp, "PUT"))
                h->hdr_type = HTTPREAD_HDR_TYPE_PUT;
        else if (word_eq(hbp, "DELETE"))
                h->hdr_type = HTTPREAD_HDR_TYPE_DELETE;
        else if (word_eq(hbp, "TRACE"))
                h->hdr_type = HTTPREAD_HDR_TYPE_TRACE;
        else if (word_eq(hbp, "CONNECT"))
                h->hdr_type = HTTPREAD_HDR_TYPE_CONNECT;
        else if (word_eq(hbp, "NOTIFY"))
                h->hdr_type = HTTPREAD_HDR_TYPE_NOTIFY;
        else if (word_eq(hbp, "M-SEARCH"))
                h->hdr_type = HTTPREAD_HDR_TYPE_M_SEARCH;
        else if (word_eq(hbp, "M-POST"))
                h->hdr_type = HTTPREAD_HDR_TYPE_M_POST;
        else if (word_eq(hbp, "SUBSCRIBE"))
                h->hdr_type = HTTPREAD_HDR_TYPE_SUBSCRIBE;
        else if (word_eq(hbp, "UNSUBSCRIBE"))
                h->hdr_type = HTTPREAD_HDR_TYPE_UNSUBSCRIBE;
        else {
        }

        if (standard_first_line) {
                char *rawuri;
                char *uri;
                /* skip type */
                while (isgraph(*hbp))
                        hbp++;
                while (*hbp == ' ' || *hbp == '\t')
                        hbp++;
                /* parse uri.
                 * Find length, allocate memory for translated
                 * copy, then translate by changing %<hex><hex>
                 * into represented value.
                 */
                rawuri = hbp;
                while (isgraph(*hbp))
                        hbp++;
                h->uri = os_malloc((hbp - rawuri) + 1);
                if (h->uri == NULL)
                        goto bad;
                uri = h->uri;
                while (rawuri < hbp) {
                        int c = *rawuri;
                        if (c == '%' &&
                            isxdigit(rawuri[1]) && isxdigit(rawuri[2])) {
                                *uri++ = (hex_value(rawuri[1]) << 4) |
                                        hex_value(rawuri[2]);
                                rawuri += 3;
                        } else {
                                *uri++ = c;
                                rawuri++;
                        }
                }
                *uri = 0;       /* null terminate */
                while (isgraph(*hbp))
                        hbp++;
                while (*hbp == ' ' || *hbp == '\t')
                        hbp++;
                /* get version */
                if (0 == strncmp(hbp, "HTTP/", 5)) {
                        hbp += 5;
                        if (hbp[0] == '1' && hbp[1] == '.' &&
                            isdigit(hbp[2]) && hbp[2] != '0')
                                h->version = 1;
                }
        }
        /* skip rest of line */
        while (*hbp)
                if (*hbp++ == '\n')
                        break;

        /* Remainder of lines are options, in any order;
         * or empty line to terminate
         */
        for (;;) {
                /* Empty line to terminate */
                if (hbp[0] == '\n' ||
                    (hbp[0] == '\r' && hbp[1] == '\n'))
                        break;
                if (!isgraph(*hbp))
                        goto bad;
                if (httpread_hdr_option_analyze(h, hbp))
                        goto bad;
                /* skip line */
                while (*hbp)
                        if (*hbp++ == '\n')
                                break;
        }

        /* chunked overrides content-length always */
        if (h->chunked)
                h->got_content_length = 0;

        /* For some types, we should not try to read a body
         * This is in addition to the application determining
         * that we should not read a body.
         */
        switch (h->hdr_type) {
        case HTTPREAD_HDR_TYPE_REPLY:
                /* Some codes can have a body and some not.
                 * For now, just assume that any other than 200
                 * do not...
                 */
                if (h->reply_code != 200)
                        h->max_bytes = 0;
                break;
        case HTTPREAD_HDR_TYPE_GET:
        case HTTPREAD_HDR_TYPE_HEAD:
                /* in practice it appears that it is assumed
                 * that GETs have a body length of 0... ?
                 */
                if (h->chunked == 0 && h->got_content_length == 0)
                        h->max_bytes = 0;
                break;
        case HTTPREAD_HDR_TYPE_POST:
        case HTTPREAD_HDR_TYPE_PUT:
        case HTTPREAD_HDR_TYPE_DELETE:
        case HTTPREAD_HDR_TYPE_TRACE:
        case HTTPREAD_HDR_TYPE_CONNECT:
        case HTTPREAD_HDR_TYPE_NOTIFY:
        case HTTPREAD_HDR_TYPE_M_SEARCH:
        case HTTPREAD_HDR_TYPE_M_POST:
        case HTTPREAD_HDR_TYPE_SUBSCRIBE:
        case HTTPREAD_HDR_TYPE_UNSUBSCRIBE:
        default:
                break;
        }

        return 0;

bad:
        /* Error */
        return -1;
}


/* httpread_read_handler -- called when socket ready to read
 *
 * Note: any extra data we read past end of transmitted file is ignored;
 * if we were to support keeping connections open for multiple files then
 * this would have to be addressed.
 */
static void httpread_read_handler(int sd, void *eloop_ctx, void *sock_ctx)
{
        struct httpread *h = sock_ctx;
        int nread;
        char *rbp;      /* pointer into read buffer */
        char *hbp;      /* pointer into header buffer */
        char *bbp;      /* pointer into body buffer */
        char readbuf[HTTPREAD_READBUF_SIZE];  /* temp use to read into */

        if (httpread_debug >= 20)
                wpa_printf(MSG_DEBUG, "ENTER httpread_read_handler(%p)", h);

        /* read some at a time, then search for the interal
         * boundaries between header and data and etc.
         */
        nread = read(h->sd, readbuf, sizeof(readbuf));
        if (nread < 0)
                goto bad;
        if (nread == 0) {
                /* end of transmission... this may be normal
                 * or may be an error... in some cases we can't
                 * tell which so we must assume it is normal then.
                 */
                if (!h->got_hdr) {
                        /* Must at least have completed header */
                        wpa_printf(MSG_DEBUG, "httpread premature eof(%p)", h);
                        goto bad;
                }
                if (h->chunked || h->got_content_length) {
                        /* Premature EOF; e.g. dropped connection */
                        wpa_printf(MSG_DEBUG,
                                   "httpread premature eof(%p) %d/%d",
                                   h, h->body_nbytes,
                                   h->content_length);
                        goto bad;
                }
                /* No explicit length, hopefully we have all the data
                 * although dropped connections can cause false
                 * end
                 */
                if (httpread_debug >= 10)
                        wpa_printf(MSG_DEBUG, "httpread ok eof(%p)", h);
                        h->got_body = 1;
                        goto got_file;
        }
        rbp = readbuf;

        /* Header consists of text lines (terminated by both CR and LF)
         * and an empty line (CR LF only).
         */
        if (!h->got_hdr) {
                hbp = h->hdr + h->hdr_nbytes;
                /* add to headers until:
                 *      -- we run out of data in read buffer
                 *      -- or, we run out of header buffer room
                 *      -- or, we get double CRLF in headers
                 */
                for (;;) {
                        if (nread == 0)
                                goto get_more;
                        if (h->hdr_nbytes == HTTPREAD_HEADER_MAX_SIZE) {
                                goto bad;
                        }
                        *hbp++ = *rbp++;
                        nread--;
                        h->hdr_nbytes++;
                        if (h->hdr_nbytes >= 4 &&
                            hbp[-1] == '\n' &&
                            hbp[-2] == '\r' &&
                            hbp[-3] == '\n' &&
                            hbp[-4] == '\r' ) {
                                h->got_hdr = 1;
                                *hbp = 0;       /* null terminate */
                                break;
                        }
                }
                /* here we've just finished reading the header */
                if (httpread_hdr_analyze(h)) {
                        wpa_printf(MSG_DEBUG, "httpread bad hdr(%p)", h);
                        goto bad;
                }
                if (h->max_bytes == 0) {
                        if (httpread_debug >= 10)
                                wpa_printf(MSG_DEBUG,
                                           "httpread no body hdr end(%p)", h);
                        goto got_file;
                }
                if (h->got_content_length && h->content_length == 0) {
                        if (httpread_debug >= 10)
                                wpa_printf(MSG_DEBUG,
                                           "httpread zero content length(%p)",
                                           h);
                        goto got_file;
                }
        }

        /* Certain types of requests never have data and so
         * must be specially recognized.
         */
        if (!os_strncasecmp(h->hdr, "SUBSCRIBE", 9) ||
            !os_strncasecmp(h->hdr, "UNSUBSCRIBE", 11) ||
            !os_strncasecmp(h->hdr, "HEAD", 4) ||
            !os_strncasecmp(h->hdr, "GET", 3)) {
                if (!h->got_body) {
                        if (httpread_debug >= 10)
                                wpa_printf(MSG_DEBUG,
                                           "httpread NO BODY for sp. type");
                }
                h->got_body = 1;
                goto got_file;
        }

        /* Data can be just plain binary data, or if "chunked"
         * consists of chunks each with a header, ending with
         * an ending header.
         */
        if (nread == 0)
                goto get_more;
        if (!h->got_body) {
                /* Here to get (more of) body */
                /* ensure we have enough room for worst case for body
                 * plus a null termination character
                 */
                if (h->body_alloc_nbytes < (h->body_nbytes + nread + 1)) {
                        char *new_body;
                        int new_alloc_nbytes;

                        if (h->body_nbytes >= h->max_bytes)
                                goto bad;
                        new_alloc_nbytes = h->body_alloc_nbytes +
                                HTTPREAD_BODYBUF_DELTA;
                        /* For content-length case, the first time
                         * through we allocate the whole amount
                         * we need.
                         */
                        if (h->got_content_length &&
                            new_alloc_nbytes < (h->content_length + 1))
                                new_alloc_nbytes = h->content_length + 1;
                        if ((new_body = os_realloc(h->body, new_alloc_nbytes))
                            == NULL)
                                goto bad;

                        h->body = new_body;
                        h->body_alloc_nbytes = new_alloc_nbytes;
                }
                /* add bytes */
                bbp = h->body + h->body_nbytes;
                for (;;) {
                        int ncopy;
                        /* See if we need to stop */
                        if (h->chunked && h->in_chunk_data == 0) {
                                /* in chunk header */
                                char *cbp = h->body + h->chunk_start;
                                if (bbp-cbp >= 2 && bbp[-2] == '\r' &&
                                    bbp[-1] == '\n') {
                                        /* end of chunk hdr line */
                                        /* hdr line consists solely
                                         * of a hex numeral and CFLF
                                         */
                                        if (!isxdigit(*cbp))
                                                goto bad;
                                        h->chunk_size = strtoul(cbp, NULL, 16);
                                        /* throw away chunk header
                                         * so we have only real data
                                         */
                                        h->body_nbytes = h->chunk_start;
                                        bbp = cbp;
                                        if (h->chunk_size == 0) {
                                                /* end of chunking */
                                                /* trailer follows */
                                                h->in_trailer = 1;
                                                if (httpread_debug >= 20)
                                                        wpa_printf(
                                                                MSG_DEBUG,
                                                                "httpread end chunks(%p)", h);
                                                break;
                                        }
                                        h->in_chunk_data = 1;
                                        /* leave chunk_start alone */
                                }
                        } else if (h->chunked) {
                                /* in chunk data */
                                if ((h->body_nbytes - h->chunk_start) ==
                                    (h->chunk_size + 2)) {
                                        /* end of chunk reached,
                                         * new chunk starts
                                         */
                                        /* check chunk ended w/ CRLF
                                         * which we'll throw away
                                         */
                                        if (bbp[-1] == '\n' &&
                                            bbp[-2] == '\r') {
                                        } else
                                                goto bad;
                                        h->body_nbytes -= 2;
                                        bbp -= 2;
                                        h->chunk_start = h->body_nbytes;
                                        h->in_chunk_data = 0;
                                        h->chunk_size = 0; /* just in case */
                                }
                        } else if (h->got_content_length &&
                                   h->body_nbytes >= h->content_length) {
                                h->got_body = 1;
                                if (httpread_debug >= 10)
                                        wpa_printf(
                                                MSG_DEBUG,
                                                "httpread got content(%p)", h);
                                goto got_file;
                        }
                        if (nread <= 0)
                                break;
                        /* Now transfer. Optimize using memcpy where we can. */
                        if (h->chunked && h->in_chunk_data) {
                                /* copy up to remainder of chunk data
                                 * plus the required CR+LF at end
                                 */
                                ncopy = (h->chunk_start + h->chunk_size + 2) -
                                        h->body_nbytes;
                        } else if (h->chunked) {
                                /*in chunk header -- don't optimize */
                                *bbp++ = *rbp++;
                                nread--;
                                h->body_nbytes++;
                                continue;
                        } else if (h->got_content_length) {
                                ncopy = h->content_length - h->body_nbytes;
                        } else {
                                ncopy = nread;
                        }
                        /* Note: should never be 0 */
                        if (ncopy > nread)
                                ncopy = nread;
                        os_memcpy(bbp, rbp, ncopy);
                        bbp += ncopy;
                        h->body_nbytes += ncopy;
                        rbp += ncopy;
                        nread -= ncopy;
                }       /* body copy loop */
        }       /* !got_body */
        if (h->chunked && h->in_trailer) {
                /* If "chunked" then there is always a trailer,
                 * consisting of zero or more non-empty lines
                 * ending with CR LF and then an empty line w/ CR LF.
                 * We do NOT support trailers except to skip them --
                 * this is supported (generally) by the http spec.
                 */
                bbp = h->body + h->body_nbytes;
                for (;;) {
                        int c;
                        if (nread <= 0)
                                break;
                        c = *rbp++;
                        nread--;
                        switch (h->trailer_state) {
                        case trailer_line_begin:
                                if (c == '\r')
                                        h->trailer_state = trailer_empty_cr;
                                else
                                        h->trailer_state = trailer_nonempty;
                                break;
                        case trailer_empty_cr:
                                /* end empty line */
                                if (c == '\n') {
                                        h->trailer_state = trailer_line_begin;
                                        h->in_trailer = 0;
                                        if (httpread_debug >= 10)
                                                wpa_printf(
                                                        MSG_DEBUG,
                                                        "httpread got content(%p)", h);
                                        h->got_body = 1;
                                        goto got_file;
                                }
                                h->trailer_state = trailer_nonempty;
                                break;
                        case trailer_nonempty:
                                if (c == '\r')
                                        h->trailer_state = trailer_nonempty_cr;
                                break;
                        case trailer_nonempty_cr:
                                if (c == '\n')
                                        h->trailer_state = trailer_line_begin;
                                else
                                        h->trailer_state = trailer_nonempty;
                                break;
                        }
                }
        }
        goto get_more;

bad:
        /* Error */
        wpa_printf(MSG_DEBUG, "httpread read/parse failure (%p)", h);
        (*h->cb)(h, h->cookie, HTTPREAD_EVENT_ERROR);
        return;

get_more:
        return;

got_file:
        if (httpread_debug >= 10)
                wpa_printf(MSG_DEBUG,
                           "httpread got file %d bytes type %d",
                           h->body_nbytes, h->hdr_type);
        /* Null terminate for convenience of some applications */
        if (h->body)
                h->body[h->body_nbytes] = 0; /* null terminate */
        h->got_file = 1;
        /* Assume that we do NOT support keeping connection alive,
         * and just in case somehow we don't get destroyed right away,
         * unregister now.
         */
        if (h->sd_registered)
                eloop_unregister_sock(h->sd, EVENT_TYPE_READ);
        h->sd_registered = 0;
        /* The application can destroy us whenever they feel like...
         * cancel timeout.
         */
        if (h->to_registered)
                eloop_cancel_timeout(httpread_timeout_handler, NULL, h);
        h->to_registered = 0;
        (*h->cb)(h, h->cookie, HTTPREAD_EVENT_FILE_READY);
}


/* httpread_create -- start a new reading session making use of eloop.
 * The new instance will use the socket descriptor for reading (until
 * it gets a file and not after) but will not close the socket, even
 * when the instance is destroyed (the application must do that).
 * Return NULL on error.
 *
 * Provided that httpread_create successfully returns a handle,
 * the callback fnc is called to handle httpread_event events.
 * The caller should do destroy on any errors or unknown events.
 *
 * Pass max_bytes == 0 to not read body at all (required for e.g.
 * reply to HEAD request).
 */
struct httpread * httpread_create(
        int sd,  /* descriptor of TCP socket to read from */
        void (*cb)(struct httpread *handle, void *cookie,
                   enum httpread_event e),  /* call on event */
        void *cookie,    /* pass to callback */
        int max_bytes,    /* maximum body size else abort it */
        int timeout_seconds     /* 0; or total duration timeout period */
        )
{
        struct httpread *h = NULL;

        h = os_zalloc(sizeof(*h));
        if (h == NULL)
                goto fail;
        h->sd = sd;
        h->cb = cb;
        h->cookie = cookie;
        h->max_bytes = max_bytes;
        h->timeout_seconds = timeout_seconds;

        if (timeout_seconds > 0) {
                if (eloop_register_timeout(timeout_seconds, 0,
                                           httpread_timeout_handler,
                                           NULL, h)) {
                        /* No way to recover (from malloc failure) */
                        goto fail;
                }
                h->to_registered = 1;
        }
        if (eloop_register_sock(sd, EVENT_TYPE_READ, httpread_read_handler,
                                NULL, h)) {
                /* No way to recover (from malloc failure) */
                goto fail;
        }
        h->sd_registered = 1;
        return h;

fail:

        /* Error */
        httpread_destroy(h);
        return NULL;
}


/* httpread_hdr_type_get -- When file is ready, returns header type. */
enum httpread_hdr_type httpread_hdr_type_get(struct httpread *h)
{
        return h->hdr_type;
}


/* httpread_uri_get -- When file is ready, uri_get returns (translated) URI
 * or possibly NULL (which would be an error).
 */
char * httpread_uri_get(struct httpread *h)
{
        return h->uri;
}


/* httpread_reply_code_get -- When reply is ready, returns reply code */
int httpread_reply_code_get(struct httpread *h)
{
        return h->reply_code;
}


/* httpread_length_get -- When file is ready, returns file length. */
int httpread_length_get(struct httpread *h)
{
        return h->body_nbytes;
}


/* httpread_data_get -- When file is ready, returns file content
 * with null byte appened.
 * Might return NULL in some error condition.
 */
void * httpread_data_get(struct httpread *h)
{
        return h->body ? h->body : "";
}


/* httpread_hdr_get -- When file is ready, returns header content
 * with null byte appended.
 * Might return NULL in some error condition.
 */
char * httpread_hdr_get(struct httpread *h)
{
        return h->hdr;
}


/* httpread_hdr_line_get -- When file is ready, returns pointer
 * to line within header content matching the given tag
 * (after the tag itself and any spaces/tabs).
 *
 * The tag should end with a colon for reliable matching.
 *
 * If not found, returns NULL;
 */
char * httpread_hdr_line_get(struct httpread *h, const char *tag)
{
        int tag_len = os_strlen(tag);
        char *hdr = h->hdr;
        hdr = os_strchr(hdr, '\n');
        if (hdr == NULL)
                return NULL;
        hdr++;
        for (;;) {
                if (!os_strncasecmp(hdr, tag, tag_len)) {
                        hdr += tag_len;
                        while (*hdr == ' ' || *hdr == '\t')
                                hdr++;
                        return hdr;
                }
                hdr = os_strchr(hdr, '\n');
                if (hdr == NULL)
                        return NULL;
                hdr++;
        }
}