file.c

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/*
 * Copyright 2010 Vincent Sanders <vince@netsurf-browser.org>
 *
 * This file is part of NetSurf.
 *
 * NetSurf is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; version 2 of the License.
 *
 * NetSurf is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
/**
 * \file
 *
 * file scheme URL handling. Based on the data fetcher by Rob Kendrick
 *
 * output dates and directory ordering are affected by the current locale
 */
 
#include "utils/config.h"
 
#include <stdlib.h>
#include <ctype.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
#include <stdbool.h>
#include <string.h>
#include <strings.h>
#include <time.h>
#include <stdio.h>
#include <stdarg.h>
#ifdef HAVE_MMAP
#include <sys/mman.h>
#endif
#include <libwapcaplet/libwapcaplet.h>
 
#include "netsurf/inttypes.h"
#include "utils/nsurl.h"
#include "utils/dirent.h"
#include "utils/corestrings.h"
#include "utils/messages.h"
#include "utils/utils.h"
#include "utils/log.h"
#include "utils/time.h"
#include "utils/ring.h"
#include "utils/file.h"
#include "netsurf/fetch.h"
#include "desktop/gui_internal.h"
 
#include "content/fetch.h"
#include "content/fetchers.h"
#include "dirlist.h"
#include "file.h"
 
/* Maximum size of read buffer */
#define FETCH_FILE_MAX_BUF_SIZE (1024 * 1024)
 
/** Context for a fetch */
struct fetch_file_context {
        struct fetch_file_context *r_next, *r_prev;
 
        struct fetch *fetchh; /**< Handle for this fetch */
 
        bool aborted; /**< Flag indicating fetch has been aborted */
        bool locked; /**< Flag indicating entry is already entered */
 
        nsurl *url; /**< The full url the fetch refers to */
        char *path; /**< The actual path to be used with open() */
 
        time_t file_etag; /**< Request etag for file (previous st.m_time) */
};
 
static struct fetch_file_context *ring = NULL;
 
/** issue fetch callbacks with locking */
static inline bool fetch_file_send_callback(const fetch_msg *msg,
                struct fetch_file_context *ctx)
{
        ctx->locked = true;
        fetch_send_callback(msg, ctx->fetchh);
        ctx->locked = false;
 
        return ctx->aborted;
}
 
static bool fetch_file_send_header(struct fetch_file_context *ctx,
                const char *fmt, ...)
{
        fetch_msg msg;
        char header[64];
        va_list ap;
        int len;
 
        va_start(ap, fmt);
        len = vsnprintf(header, sizeof header, fmt, ap);
        va_end(ap);
 
        if (len >= (int)sizeof(header) || len < 0) {
                return false;
        }
 
        msg.type = FETCH_HEADER;
        msg.data.header_or_data.buf = (const uint8_t *) header;
        msg.data.header_or_data.len = len;
 
        return fetch_file_send_callback(&msg, ctx);
}
 
/** callback to initialise the file fetcher. */
static bool fetch_file_initialise(lwc_string *scheme)
{
        return true;
}
 
/** callback to initialise the file fetcher. */
static void fetch_file_finalise(lwc_string *scheme)
{
}
 
static bool fetch_file_can_fetch(const nsurl *url)
{
        return true;
}
 
/** callback to set up a file fetch context. */
static void *
fetch_file_setup(struct fetch *fetchh,
                 nsurl *url,
                 bool only_2xx,
                 bool downgrade_tls,
                 const char *post_urlenc,
                 const struct fetch_multipart_data *post_multipart,
                 const char **headers)
{
        struct fetch_file_context *ctx;
        int i;
        nserror ret;
 
        ctx = calloc(1, sizeof(*ctx));
        if (ctx == NULL)
                return NULL;
 
        ret = guit->file->nsurl_to_path(url, &ctx->path);
        if (ret != NSERROR_OK) {
                free(ctx);
                return NULL;
        }
 
        ctx->url = nsurl_ref(url);
 
        /* Scan request headers looking for If-None-Match */
        for (i = 0; headers[i] != NULL; i++) {
                if (strncasecmp(headers[i], "If-None-Match:",
                                SLEN("If-None-Match:")) != 0) {
                        continue;
                }
 
                /* If-None-Match: "12345678" */
                const char *d = headers[i] + SLEN("If-None-Match:");
 
                /* Scan to first digit, if any */
                while (*d != '\0' && (*d < '0' || '9' < *d))
                        d++;
 
                /* Convert to time_t */
                if (*d != '\0') {
                        ret = nsc_snptimet(d, strlen(d), &ctx->file_etag);
                        if (ret != NSERROR_OK) {
                                NSLOG(fetch, WARNING,
                                                "Bad If-None-Match value");
                        }
                }
        }
 
        ctx->fetchh = fetchh;
 
        RING_INSERT(ring, ctx);
 
        return ctx;
}
 
/** callback to free a file fetch */
static void fetch_file_free(void *ctx)
{
        struct fetch_file_context *c = ctx;
        nsurl_unref(c->url);
        free(c->path);
        free(ctx);
}
 
/** callback to start a file fetch */
static bool fetch_file_start(void *ctx)
{
        return true;
}
 
/** callback to abort a file fetch */
static void fetch_file_abort(void *ctx)
{
        struct fetch_file_context *c = ctx;
 
        /* To avoid the poll loop having to deal with the fetch context
         * disappearing from under it, we simply flag the abort here.
         * The poll loop itself will perform the appropriate cleanup.
         */
        c->aborted = true;
}
 
static int fetch_file_errno_to_http_code(int error_no)
{
        switch (error_no) {
        case ENAMETOOLONG:
                return 400;
        case EACCES:
                return 403;
        case ENOENT:
                return 404;
        default:
                break;
        }
 
        return 500;
}
 
static void fetch_file_process_error(struct fetch_file_context *ctx, int code)
{
        fetch_msg msg;
        char buffer[1024];
        const char *title;
        char key[8];
 
        /* content is going to return error code */
        fetch_set_http_code(ctx->fetchh, code);
 
        /* content type */
        if (fetch_file_send_header(ctx, "Content-Type: text/html; charset=utf-8"))
                goto fetch_file_process_error_aborted;
 
        snprintf(key, sizeof key, "HTTP%03d", code);
        title = messages_get(key);
 
        snprintf(buffer, sizeof buffer,
                 "<html><head>"
                 "<title>%s</title>"
                 "<link rel=\"stylesheet\" type=\"text/css\" "
                 "href=\"resource:internal.css\">\n"
                 "</head>"
                 "<body class=\"ns-even-bg ns-even-fg ns-border\" "
                 "id =\"fetcherror\">\n"
                 "<h1 class=\"ns-border ns-odd-fg-bad\">%s</h1>\n"
                 "<p>%s %d %s %s</p>\n"
                 "</body>\n</html>\n",
                 title, title,
                 messages_get("FetchErrorCode"), code,
                 messages_get("FetchFile"), nsurl_access(ctx->url));
 
        msg.type = FETCH_DATA;
        msg.data.header_or_data.buf = (const uint8_t *) buffer;
        msg.data.header_or_data.len = strlen(buffer);
        if (fetch_file_send_callback(&msg, ctx))
                goto fetch_file_process_error_aborted;
 
        msg.type = FETCH_FINISHED;
        fetch_file_send_callback(&msg, ctx);
 
fetch_file_process_error_aborted:
        return;
}
 
 
/** Process object as a regular file */
static void fetch_file_process_plain(struct fetch_file_context *ctx,
                                     struct stat *fdstat)
{
#ifdef HAVE_MMAP
        fetch_msg msg;
        char *buf = NULL;
        size_t buf_size;
 
        int fd; /**< The file descriptor of the object */
 
        /* Check if we can just return not modified */
        if (ctx->file_etag != 0 && ctx->file_etag == fdstat->st_mtime) {
                fetch_set_http_code(ctx->fetchh, 304);
                msg.type = FETCH_NOTMODIFIED;
                fetch_file_send_callback(&msg, ctx);
                return;
        }
 
        fd = open(ctx->path, O_RDONLY);
        if (fd < 0) {
                /* process errors as appropriate */
                fetch_file_process_error(ctx,
                                fetch_file_errno_to_http_code(errno));
                return;
        }
 
        /* set buffer size */
        buf_size = fdstat->st_size;
 
        /* allocate the buffer storage */
        if (buf_size > 0) {
                buf = mmap(NULL, buf_size, PROT_READ, MAP_SHARED, fd, 0);
                if (buf == MAP_FAILED) {
                        msg.type = FETCH_ERROR;
                        msg.data.error = "Unable to map memory for file data buffer";
                        fetch_file_send_callback(&msg, ctx);
                        close(fd);
                        return;
                }
        }
 
        /* fetch is going to be successful */
        fetch_set_http_code(ctx->fetchh, 200);
 
        /* Any callback can result in the fetch being aborted.
         * Therefore, we _must_ check for this after _every_ call to
         * fetch_file_send_callback().
         */
 
        /* content type */
        if (fetch_file_send_header(ctx, "Content-Type: %s", 
                                   guit->fetch->filetype(ctx->path))) {
                goto fetch_file_process_aborted;
        }
 
        /* content length */
        if (fetch_file_send_header(ctx, "Content-Length: %" PRIsizet,
                                   fdstat->st_size)) {
                goto fetch_file_process_aborted;
        }
 
        /* create etag */
        if (fetch_file_send_header(ctx, "ETag: \"%10" PRId64 "\"",
                                   (int64_t) fdstat->st_mtime)) {
                goto fetch_file_process_aborted;
        }
 
        msg.type = FETCH_DATA;
        msg.data.header_or_data.buf = (const uint8_t *) buf;
        msg.data.header_or_data.len = buf_size;
        fetch_file_send_callback(&msg, ctx);
 
        if (ctx->aborted == false) {
                msg.type = FETCH_FINISHED;
                fetch_file_send_callback(&msg, ctx);
        }
 
fetch_file_process_aborted:
 
        if (buf != NULL)
                munmap(buf, buf_size);
        close(fd);
#else
        fetch_msg msg;
        char *buf;
        size_t buf_size;
 
        ssize_t tot_read = 0;
        ssize_t res;
 
        FILE *infile;
 
        /* Check if we can just return not modified */
        if (ctx->file_etag != 0 && ctx->file_etag == fdstat->st_mtime) {
                fetch_set_http_code(ctx->fetchh, 304);
                msg.type = FETCH_NOTMODIFIED;
                fetch_file_send_callback(&msg, ctx);
                return;
        }
 
        infile = fopen(ctx->path, "rb");
        if (infile == NULL) {
                /* process errors as appropriate */
                fetch_file_process_error(ctx,
                                fetch_file_errno_to_http_code(errno));
                return;
        }
 
        /* set buffer size */
        buf_size = fdstat->st_size;
        if (buf_size > FETCH_FILE_MAX_BUF_SIZE)
                buf_size = FETCH_FILE_MAX_BUF_SIZE;
 
        /* allocate the buffer storage */
        buf = malloc(buf_size);
        if (buf == NULL) {
                msg.type = FETCH_ERROR;
                msg.data.error =
                        "Unable to allocate memory for file data buffer";
                fetch_file_send_callback(&msg, ctx);
                fclose(infile);
                return;
        }
 
        /* fetch is going to be successful */
        fetch_set_http_code(ctx->fetchh, 200);
 
        /* Any callback can result in the fetch being aborted.
         * Therefore, we _must_ check for this after _every_ call to
         * fetch_file_send_callback().
         */
 
        /* content type */
        if (fetch_file_send_header(ctx, "Content-Type: %s", 
                                   guit->fetch->filetype(ctx->path))) {
                goto fetch_file_process_aborted;
        }
 
        /* content length */
        if (fetch_file_send_header(ctx, "Content-Length: %" PRIsizet,
                                   fdstat->st_size)) {
                goto fetch_file_process_aborted;
        }
 
        /* create etag */
        if (fetch_file_send_header(ctx, "ETag: \"%10" PRId64 "\"", 
                                   (int64_t) fdstat->st_mtime)) {
                goto fetch_file_process_aborted;
        }
 
        /* main data loop */
        while (tot_read < fdstat->st_size) {
                res = fread(buf, 1, buf_size, infile);
                if (res == 0) {
                        if (feof(infile)) {
                                msg.type = FETCH_ERROR;
                                msg.data.error = "Unexpected EOF reading file";
                                fetch_file_send_callback(&msg, ctx);
                                goto fetch_file_process_aborted;
                        } else {
                                msg.type = FETCH_ERROR;
                                msg.data.error = "Error reading file";
                                fetch_file_send_callback(&msg, ctx);
                                goto fetch_file_process_aborted;
                        }
                }
                tot_read += res;
 
                msg.type = FETCH_DATA;
                msg.data.header_or_data.buf = (const uint8_t *) buf;
                msg.data.header_or_data.len = res;
                if (fetch_file_send_callback(&msg, ctx))
                        break;
        }
 
        if (ctx->aborted == false) {
                msg.type = FETCH_FINISHED;
                fetch_file_send_callback(&msg, ctx);
        }
 
fetch_file_process_aborted:
 
        fclose(infile);
        free(buf);
#endif
        return;
}
 
static char *gen_nice_title(char *path)
{
        char *nice_path, *cnv, *tmp;
        char *title;
        int title_length;
 
        /* Convert path for display */
        nice_path = malloc(strlen(path) * SLEN("&amp;") + 1);
        if (nice_path == NULL) {
                return NULL;
        }
 
        /* Escape special HTML characters */
        for (cnv = nice_path, tmp = path; *tmp != '\0'; tmp++) {
                if (*tmp == '<') {
                        *cnv++ = '&';
                        *cnv++ = 'l';
                        *cnv++ = 't';
                        *cnv++ = ';';
                } else if (*tmp == '>') {
                        *cnv++ = '&';
                        *cnv++ = 'g';
                        *cnv++ = 't';
                        *cnv++ = ';';
                } else if (*tmp == '&') {
                        *cnv++ = '&';
                        *cnv++ = 'a';
                        *cnv++ = 'm';
                        *cnv++ = 'p';
                        *cnv++ = ';';
                } else {
                        *cnv++ = *tmp;
                }
        }
        *cnv = '\0';
 
        /* Construct a localised title string */
        title_length = (cnv - nice_path) + strlen(messages_get("FileIndex"));
        title = malloc(title_length + 1);
 
        if (title == NULL) {
                free(nice_path);
                return NULL;
        }
 
        /* Set title to localised "Index of <nice_path>" */
        snprintf(title, title_length, messages_get("FileIndex"), nice_path);
 
        free(nice_path);
 
        return title;
}
 
/**
 * Generate an output row of the directory listing.
 *
 * \param ctx The file fetching context.
 * \param ent current directory entry.
 * \param even is the row an even row.
 * \param buffer The output buffer.
 * \param buffer_len The space available in the output buffer.
 * \return NSERROR_OK or error code on faliure.
 */
static nserror
process_dir_ent(struct fetch_file_context *ctx,
                 struct dirent *ent,
                 bool even,
                 char *buffer,
                 size_t buffer_len)
{
        nserror ret;
        char *urlpath = NULL; /* buffer for leaf entry path */
        struct stat ent_stat; /* stat result of leaf entry */
        char datebuf[64]; /* buffer for date text */
        char timebuf[64]; /* buffer for time text */
        nsurl *url;
 
        /* skip hidden files */
        if (ent->d_name[0] == '.') {
                return NSERROR_BAD_PARAMETER;
        }
 
        ret = netsurf_mkpath(&urlpath, NULL, 2, ctx->path, ent->d_name);
        if (ret != NSERROR_OK) {
                return ret;
        }
 
        if (stat(urlpath, &ent_stat) != 0) {
                ent_stat.st_mode = 0;
                datebuf[0] = 0;
                timebuf[0] = 0;
        } else {
                /* Get date in output format. a (day of week) and b
                 * (month) are both affected by the locale
                 */
                if (strftime((char *)&datebuf, sizeof datebuf, "%a %d %b %Y",
                             localtime(&ent_stat.st_mtime)) == 0) {
                        datebuf[0] = '-';
                        datebuf[1] = 0;
                }
 
                /* Get time in output format */
                if (strftime((char *)&timebuf, sizeof timebuf, "%H:%M",
                             localtime(&ent_stat.st_mtime)) == 0) {
                        timebuf[0] = '-';
                        timebuf[1] = 0;
                }
        }
 
        ret = guit->file->path_to_nsurl(urlpath, &url);
        if (ret != NSERROR_OK) {
                free(urlpath);
                return ret;
        }
 
        if (S_ISREG(ent_stat.st_mode)) {
                /* regular file */
                dirlist_generate_row(even,
                                     false,
                                     url,
                                     ent->d_name,
                                     guit->fetch->filetype(urlpath),
                                     ent_stat.st_size,
                                     datebuf, timebuf,
                                     buffer, buffer_len);
        } else if (S_ISDIR(ent_stat.st_mode)) {
                /* directory */
                dirlist_generate_row(even,
                                     true,
                                     url,
                                     ent->d_name,
                                     messages_get("FileDirectory"),
                                     -1,
                                     datebuf, timebuf,
                                     buffer, buffer_len);
        } else {
                /* something else */
                dirlist_generate_row(even,
                                     false,
                                     url,
                                     ent->d_name,
                                     "",
                                     -1,
                                     datebuf, timebuf,
                                     buffer, buffer_len);
        }
 
        nsurl_unref(url);
        free(urlpath);
 
        return NSERROR_OK;
}
 
/**
 * Comparison function for sorting directories.
 *
 * Correctly orders non zero-padded numerical parts.
 * ie. produces "file1, file2, file10" rather than "file1, file10, file2".
 *
 * \param d1 first directory entry
 * \param d2 second directory entry
 */
static int dir_sort_alpha(const struct dirent **d1, const struct dirent **d2)
{
        const char *s1 = (*d1)->d_name;
        const char *s2 = (*d2)->d_name;
 
        while (*s1 != '\0' && *s2 != '\0') {
                if ((*s1 >= '0' && *s1 <= '9') &&
                                (*s2 >= '0' && *s2 <= '9')) {
                        int n1 = 0,  n2 = 0;
                        while (*s1 >= '0' && *s1 <= '9') {
                                n1 = n1 * 10 + (*s1) - '0';
                                s1++;
                        }
                        while (*s2 >= '0' && *s2 <= '9') {
                                n2 = n2 * 10 + (*s2) - '0';
                                s2++;
                        }
                        if (n1 != n2) {
                                return n1 - n2;
                        }
                        if (*s1 == '\0' || *s2 == '\0')
                                break;
                }
                if (tolower(*s1) != tolower(*s2))
                        break;
 
                s1++;
                s2++;
        }
 
        return tolower(*s1) - tolower(*s2);
}
 
static void fetch_file_process_dir(struct fetch_file_context *ctx,
                                   struct stat *fdstat)
{
        fetch_msg msg;
        char buffer[1024]; /* Output buffer */
        bool even = false; /* formatting flag */
        char *title; /* pretty printed title */
        nserror err; /* result from url routines */
        nsurl *up; /* url of parent */
 
        struct dirent **listing = NULL; /* directory entry listing */
        int i; /* directory entry index */
        int n; /* number of directory entries */
 
        n = scandir(ctx->path, &listing, 0, dir_sort_alpha);
        if (n < 0) {
                fetch_file_process_error(ctx,
                        fetch_file_errno_to_http_code(errno));
                return;
        }
 
        /* fetch is going to be successful */
        fetch_set_http_code(ctx->fetchh, 200);
 
        /* force no-cache */
        if (fetch_file_send_header(ctx, "Cache-Control: no-cache"))
                goto fetch_file_process_dir_aborted;
 
        /* content type */
        if (fetch_file_send_header(ctx, "Content-Type: text/html; charset=utf-8"))
                goto fetch_file_process_dir_aborted;
 
        msg.type = FETCH_DATA;
        msg.data.header_or_data.buf = (const uint8_t *) buffer;
 
        /* directory listing top */
        dirlist_generate_top(buffer, sizeof buffer);
        msg.data.header_or_data.len = strlen(buffer);
        if (fetch_file_send_callback(&msg, ctx))
                goto fetch_file_process_dir_aborted;
 
        /* directory listing title */
        title = gen_nice_title(ctx->path);
        dirlist_generate_title(title, buffer, sizeof buffer);
        free(title);
        msg.data.header_or_data.len = strlen(buffer);
        if (fetch_file_send_callback(&msg, ctx))
                goto fetch_file_process_dir_aborted;
 
        /* Print parent directory link */
        err = nsurl_parent(ctx->url, &up);
        if (err == NSERROR_OK) {
                if (nsurl_compare(ctx->url, up, NSURL_COMPLETE) == false) {
                        /* different URL; have parent */
                        dirlist_generate_parent_link(nsurl_access(up),
                                        buffer, sizeof buffer);
 
                        msg.data.header_or_data.len = strlen(buffer);
                        fetch_file_send_callback(&msg, ctx);
                }
                nsurl_unref(up);
 
                if (ctx->aborted)
                        goto fetch_file_process_dir_aborted;
 
        }
 
        /* directory list headings */
        dirlist_generate_headings(buffer, sizeof buffer);
        msg.data.header_or_data.len = strlen(buffer);
        if (fetch_file_send_callback(&msg, ctx))
                goto fetch_file_process_dir_aborted;
 
        for (i = 0; i < n; i++) {
 
                err = process_dir_ent(ctx, listing[i], even, buffer,
                                       sizeof(buffer));
 
                if (err == NSERROR_OK) {
                        msg.data.header_or_data.len = strlen(buffer);
                        if (fetch_file_send_callback(&msg, ctx))
                                goto fetch_file_process_dir_aborted;
 
                        even = !even;
                }
        }
 
        /* directory listing bottom */
        dirlist_generate_bottom(buffer, sizeof buffer);
        msg.data.header_or_data.len = strlen(buffer);
        if (fetch_file_send_callback(&msg, ctx))
                goto fetch_file_process_dir_aborted;
 
        msg.type = FETCH_FINISHED;
        fetch_file_send_callback(&msg, ctx);
 
fetch_file_process_dir_aborted:
 
        if (listing != NULL) {
                for (i = 0; i < n; i++) {
                        free(listing[i]);
                }
                free(listing);
        }
}
 
 
/* process a file fetch */
static void fetch_file_process(struct fetch_file_context *ctx)
{
        struct stat fdstat; /**< The objects stat */
 
        if (stat(ctx->path, &fdstat) != 0) {
                /* process errors as appropriate */
                fetch_file_process_error(ctx,
                                fetch_file_errno_to_http_code(errno));
                return;
        }
 
        if (S_ISDIR(fdstat.st_mode)) {
                /* directory listing */
                fetch_file_process_dir(ctx, &fdstat);
                return;
        } else if (S_ISREG(fdstat.st_mode)) {
                /* regular file */
                fetch_file_process_plain(ctx, &fdstat);
                return;
        } else {
                /* unhandled type of file */
                fetch_file_process_error(ctx, 501);
        }
 
        return;
}
 
/** callback to poll for additional file fetch contents */
static void fetch_file_poll(lwc_string *scheme)
{
        struct fetch_file_context *c, *save_ring = NULL;
 
        while (ring != NULL) {
                /* Take the first entry from the ring */
                c = ring;
                RING_REMOVE(ring, c);
 
                /* Ignore fetches that have been flagged as locked.
                 * This allows safe re-entrant calls to this function.
                 * Re-entrancy can occur if, as a result of a callback,
                 * the interested party causes fetch_poll() to be called
                 * again.
                 */
                if (c->locked == true) {
                        RING_INSERT(save_ring, c);
                        continue;
                }
 
                /* Only process non-aborted fetches */
                if (c->aborted == false) {
                        /* file fetches can be processed in one go */
                        fetch_file_process(c);
                }
 
                /* And now finish */
                fetch_remove_from_queues(c->fetchh);
                fetch_free(c->fetchh);
 
        }
 
        /* Finally, if we saved any fetches which were locked, put them back
         * into the ring for next time
         */
        ring = save_ring;
}
 
nserror fetch_file_register(void)
{
        lwc_string *scheme = lwc_string_ref(corestring_lwc_file);
        const struct fetcher_operation_table fetcher_ops = {
                .initialise = fetch_file_initialise,
                .acceptable = fetch_file_can_fetch,
                .setup = fetch_file_setup,
                .start = fetch_file_start,
                .abort = fetch_file_abort,
                .free = fetch_file_free,
                .poll = fetch_file_poll,
                .finalise = fetch_file_finalise
        };
 
        return fetcher_add(scheme, &fetcher_ops);
}