dotfiles/suckless/quark/http.c

/* See LICENSE file for copyright and license details. */
#include <arpa/inet.h>
#include <ctype.h>
#include <errno.h>
#include <limits.h>
#include <netinet/in.h>
#include <regex.h>
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include <strings.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <time.h>
#include <unistd.h>

#include "config.h"
#include "http.h"
#include "util.h"

const char *req_field_str[] = {
	[REQ_HOST]              = "Host",
	[REQ_RANGE]             = "Range",
	[REQ_IF_MODIFIED_SINCE] = "If-Modified-Since",
};

const char *req_method_str[] = {
	[M_GET]  = "GET",
	[M_HEAD] = "HEAD",
};

const char *status_str[] = {
	[S_OK]                    = "OK",
	[S_PARTIAL_CONTENT]       = "Partial Content",
	[S_MOVED_PERMANENTLY]     = "Moved Permanently",
	[S_NOT_MODIFIED]          = "Not Modified",
	[S_BAD_REQUEST]           = "Bad Request",
	[S_FORBIDDEN]             = "Forbidden",
	[S_NOT_FOUND]             = "Not Found",
	[S_METHOD_NOT_ALLOWED]    = "Method Not Allowed",
	[S_REQUEST_TIMEOUT]       = "Request Time-out",
	[S_RANGE_NOT_SATISFIABLE] = "Range Not Satisfiable",
	[S_REQUEST_TOO_LARGE]     = "Request Header Fields Too Large",
	[S_INTERNAL_SERVER_ERROR] = "Internal Server Error",
	[S_VERSION_NOT_SUPPORTED] = "HTTP Version not supported",
};

const char *res_field_str[] = {
	[RES_ACCEPT_RANGES]  = "Accept-Ranges",
	[RES_ALLOW]          = "Allow",
	[RES_LOCATION]       = "Location",
	[RES_LAST_MODIFIED]  = "Last-Modified",
	[RES_CONTENT_LENGTH] = "Content-Length",
	[RES_CONTENT_RANGE]  = "Content-Range",
	[RES_CONTENT_TYPE]   = "Content-Type",
};

enum status
http_prepare_header_buf(const struct response *res, struct buffer *buf)
{
	char tstmp[FIELD_MAX];
	size_t i;

	/* reset buffer */
	memset(buf, 0, sizeof(*buf));

	/* generate timestamp */
	if (timestamp(tstmp, sizeof(tstmp), time(NULL))) {
		goto err;
	}

	/* write data */
	if (buffer_appendf(buf,
	                   "HTTP/1.1 %d %s\r\n"
	                   "Date: %s\r\n"
	                   "Connection: close\r\n",
	                   res->status, status_str[res->status], tstmp)) {
		goto err;
	}

	for (i = 0; i < NUM_RES_FIELDS; i++) {
		if (res->field[i][0] != '\0' &&
		    buffer_appendf(buf, "%s: %s\r\n", res_field_str[i],
		                   res->field[i])) {
			goto err;
		}
	}

	if (buffer_appendf(buf, "\r\n")) {
		goto err;
	}

	return 0;
err:
	memset(buf, 0, sizeof(*buf));
	return S_INTERNAL_SERVER_ERROR;
}

enum status
http_send_buf(int fd, struct buffer *buf)
{
	ssize_t r;

	if (buf == NULL) {
		return S_INTERNAL_SERVER_ERROR;
	}

	while (buf->len > 0) {
		if ((r = write(fd, buf->data, buf->len)) <= 0) {
			if (errno == EAGAIN || errno == EWOULDBLOCK) {
				/*
				 * socket is blocking, return normally.
				 * given the buffer still contains data,
				 * this indicates to the caller that we
				 * have been interrupted.
				 */
				return 0;
			} else {
				return S_REQUEST_TIMEOUT;
			}
		}
		memmove(buf->data, buf->data + r, buf->len - r);
		buf->len -= r;
	}

	return 0;
}

static void
decode(const char src[PATH_MAX], char dest[PATH_MAX])
{
	size_t i;
	uint8_t n;
	const char *s;

	for (s = src, i = 0; *s; s++, i++) {
		if (*s == '%' && (sscanf(s + 1, "%2hhx", &n) == 1)) {
			dest[i] = n;
			s += 2;
		} else {
			dest[i] = *s;
		}
	}
	dest[i] = '\0';
}

enum status
http_recv_header(int fd, struct buffer *buf, int *done)
{
	enum status s;
	ssize_t r;

	while (1) {
		if ((r = read(fd, buf->data + buf->len,
		              sizeof(buf->data) - buf->len)) < 0) {
			if (errno == EAGAIN || errno == EWOULDBLOCK) {
				/*
				 * socket is drained, return normally,
				 * but set done to zero
				 */
				*done = 0;
				return 0;
			} else {
				s = S_REQUEST_TIMEOUT;
				goto err;
			}
		} else if (r == 0) {
			/*
			 * unexpected EOF because the client probably
			 * hung up. This is technically a bad request,
			 * because it's incomplete
			 */
			s = S_BAD_REQUEST;
			goto err;
		}
		buf->len += r;

		/* check if we are done (header terminated) */
		if (buf->len >= 4 && !memcmp(buf->data + buf->len - 4,
		                             "\r\n\r\n", 4)) {
			break;
		}

		/* buffer is full or read over, but header is not terminated */
		if (r == 0 || buf->len == sizeof(buf->data)) {
			s = S_REQUEST_TOO_LARGE;
			goto err;
		}
	}

	/* header is complete, remove last \r\n and set done */
	buf->len -= 2;
	*done = 1;

	return 0;
err:
	memset(buf, 0, sizeof(*buf));
	return s;
}

enum status
http_parse_header(const char *h, struct request *req)
{
	struct in6_addr addr;
	size_t i, mlen;
	const char *p, *q, *r, *s, *t;
	char *m, *n;

	/* empty the request struct */
	memset(req, 0, sizeof(*req));

	/*
	 * parse request line
	 */

	/* METHOD */
	for (i = 0; i < NUM_REQ_METHODS; i++) {
		mlen = strlen(req_method_str[i]);
		if (!strncmp(req_method_str[i], h, mlen)) {
			req->method = i;
			break;
		}
	}
	if (i == NUM_REQ_METHODS) {
		return S_METHOD_NOT_ALLOWED;
	}

	/* a single space must follow the method */
	if (h[mlen] != ' ') {
		return S_BAD_REQUEST;
	}

	/* basis for next step */
	p = h + mlen + 1;

	/* RESOURCE */

	/*
	 * path?query#fragment
	 * ^   ^     ^        ^
	 * |   |     |        |
	 * p   r     s        q
	 *
	 */
	if (!(q = strchr(p, ' '))) {
		return S_BAD_REQUEST;
	}

	/* search for first '?' */
	for (r = p; r < q; r++) {
		if (!isprint(*r)) {
			return S_BAD_REQUEST;
		}
		if (*r == '?') {
			break;
		}
	}
	if (r == q) {
		/* not found */
		r = NULL;
	}

	/* search for first '#' */
	for (s = p; s < q; s++) {
		if (!isprint(*s)) {
			return S_BAD_REQUEST;
		}
		if (*s == '#') {
			break;
		}
	}
	if (s == q) {
		/* not found */
		s = NULL;
	}

	if (r != NULL && s != NULL && s < r) {
		/*
		 * '#' comes before '?' and thus the '?' is literal,
		 * because the query must come before the fragment
		 */
		r = NULL;
	}

	/* write path using temporary endpointer t */
	if (r != NULL) {
		/* resource contains a query, path ends at r */
		t = r;
	} else if (s != NULL) {
		/* resource contains only a fragment, path ends at s */
		t = s;
	} else {
		/* resource contains no queries, path ends at q */
		t = q;
	}
	if ((size_t)(t - p + 1) > LEN(req->path)) {
		return S_REQUEST_TOO_LARGE;
	}
	memcpy(req->path, p, t - p);
	req->path[t - p] = '\0';
	decode(req->path, req->path);

	/* write query if present */
	if (r != NULL) {
		/* query ends either at s (if fragment present) or q */
		t = (s != NULL) ? s : q;

		if ((size_t)(t - (r + 1) + 1) > LEN(req->query)) {
			return S_REQUEST_TOO_LARGE;
		}
		memcpy(req->query, r + 1, t - (r + 1));
		req->query[t - (r + 1)] = '\0';
	}

	/* write fragment if present */
	if (s != NULL) {
		/* the fragment always starts at s + 1 and ends at q */
		if ((size_t)(q - (s + 1) + 1) > LEN(req->fragment)) {
			return S_REQUEST_TOO_LARGE;
		}
		memcpy(req->fragment, s + 1, q - (s + 1));
		req->fragment[q - (s + 1)] = '\0';
	}

	/* basis for next step */
	p = q + 1;

	/* HTTP-VERSION */
	if (strncmp(p, "HTTP/", sizeof("HTTP/") - 1)) {
		return S_BAD_REQUEST;
	}
	p += sizeof("HTTP/") - 1;
	if (strncmp(p, "1.0", sizeof("1.0") - 1) &&
	    strncmp(p, "1.1", sizeof("1.1") - 1)) {
		return S_VERSION_NOT_SUPPORTED;
	}
	p += sizeof("1.*") - 1;

	/* check terminator */
	if (strncmp(p, "\r\n", sizeof("\r\n") - 1)) {
		return S_BAD_REQUEST;
	}

	/* basis for next step */
	p += sizeof("\r\n") - 1;

	/*
	 * parse request-fields
	 */

	/* match field type */
	for (; *p != '\0';) {
		for (i = 0; i < NUM_REQ_FIELDS; i++) {
			if (!strncasecmp(p, req_field_str[i],
			                 strlen(req_field_str[i]))) {
				break;
			}
		}
		if (i == NUM_REQ_FIELDS) {
			/* unmatched field, skip this line */
			if (!(q = strstr(p, "\r\n"))) {
				return S_BAD_REQUEST;
			}
			p = q + (sizeof("\r\n") - 1);
			continue;
		}

		p += strlen(req_field_str[i]);

		/* a single colon must follow the field name */
		if (*p != ':') {
			return S_BAD_REQUEST;
		}

		/* skip whitespace */
		for (++p; *p == ' ' || *p == '\t'; p++)
			;

		/* extract field content */
		if (!(q = strstr(p, "\r\n"))) {
			return S_BAD_REQUEST;
		}
		if ((size_t)(q - p + 1) > LEN(req->field[i])) {
			return S_REQUEST_TOO_LARGE;
		}
		memcpy(req->field[i], p, q - p);
		req->field[i][q - p] = '\0';

		/* go to next line */
		p = q + (sizeof("\r\n") - 1);
	}

	/*
	 * clean up host
	 */

	m = strrchr(req->field[REQ_HOST], ':');
	n = strrchr(req->field[REQ_HOST], ']');

	/* strip port suffix but don't interfere with IPv6 bracket notation
	 * as per RFC 2732 */
	if (m && (!n || m > n)) {
		/* port suffix must not be empty */
		if (*(m + 1) == '\0') {
			return S_BAD_REQUEST;
		}
		*m = '\0';
	}

	/* strip the brackets from the IPv6 notation and validate the address */
	if (n) {
		/* brackets must be on the outside */
		if (req->field[REQ_HOST][0] != '[' || *(n + 1) != '\0') {
			return S_BAD_REQUEST;
		}

		/* remove the right bracket */
		*n = '\0';
		m = req->field[REQ_HOST] + 1;

		/* validate the contained IPv6 address */
		if (inet_pton(AF_INET6, m, &addr) != 1) {
			return S_BAD_REQUEST;
		}

		/* copy it into the host field */
		memmove(req->field[REQ_HOST], m, n - m + 1);
	}

	return 0;
}

static void
encode(const char src[PATH_MAX], char dest[PATH_MAX])
{
	size_t i;
	const char *s;

	for (s = src, i = 0; *s && i < (PATH_MAX - 4); s++) {
		if (iscntrl(*s) || (unsigned char)*s > 127) {
			i += snprintf(dest + i, PATH_MAX - i, "%%%02X",
			              (unsigned char)*s);
		} else {
			dest[i] = *s;
			i++;
		}
	}
	dest[i] = '\0';
}

static enum status
path_normalize(char *uri, int *redirect)
{
	size_t len;
	int last = 0;
	char *p, *q;

	/* require and skip first slash */
	if (uri[0] != '/') {
		return S_BAD_REQUEST;
	}
	p = uri + 1;

	/* get length of URI */
	len = strlen(p);

	for (; !last; ) {
		/* bound uri component within (p,q) */
		if (!(q = strchr(p, '/'))) {
			q = strchr(p, '\0');
			last = 1;
		}

		if (*p == '\0') {
			break;
		} else if (p == q || (q - p == 1 && p[0] == '.')) {
			/* "/" or "./" */
			goto squash;
		} else if (q - p == 2 && p[0] == '.' && p[1] == '.') {
			/* "../" */
			if (p != uri + 1) {
				/* place p right after the previous / */
				for (p -= 2; p > uri && *p != '/'; p--);
				p++;
			}
			goto squash;
		} else {
			/* move on */
			p = q + 1;
			continue;
		}
squash:
		/* squash (p,q) into void */
		if (last) {
			*p = '\0';
			len = p - uri;
		} else {
			memmove(p, q + 1, len - ((q + 1) - uri) + 2);
			len -= (q + 1) - p;
		}
		if (redirect != NULL) {
			*redirect = 1;
		}
	}

	return 0;
}

static enum status
path_add_vhost_prefix(char uri[PATH_MAX], int *redirect,
                     const struct server *srv, const struct response *res)
{
	if (srv->vhost && res->vhost && res->vhost->prefix) {
		if (prepend(uri, PATH_MAX, res->vhost->prefix)) {
			return S_REQUEST_TOO_LARGE;
		}
		if (redirect != NULL) {
			*redirect = 1;
		}
	}

	return 0;
}

static enum status
path_apply_prefix_mapping(char uri[PATH_MAX], int *redirect,
                         const struct server *srv, const struct response *res)
{
	size_t i, len;

	for (i = 0; i < srv->map_len; i++) {
		len = strlen(srv->map[i].from);
		if (!strncmp(uri, srv->map[i].from, len)) {
			/*
			 * if vhosts are enabled only apply mappings
			 * defined for the current canonical host
			 */
			if (srv->vhost && res->vhost && srv->map[i].chost &&
			    strcmp(srv->map[i].chost, res->vhost->chost)) {
				continue;
			}

			/* swap out URI prefix */
			memmove(uri, uri + len, strlen(uri) + 1);
			if (prepend(uri, PATH_MAX, srv->map[i].to)) {
				return S_REQUEST_TOO_LARGE;
			}

			if (redirect != NULL) {
				*redirect = 1;
			}

			/* break so we don't possibly hit an infinite loop */
			break;
		}
	}

	return 0;
}

static enum status
path_ensure_dirslash(char uri[PATH_MAX], int *redirect)
{
	size_t len;

	/* append '/' to URI if not present */
	len = strlen(uri);
	if (len + 1 + 1 > PATH_MAX) {
		return S_REQUEST_TOO_LARGE;
	}
	if (len > 0 && uri[len - 1] != '/') {
		uri[len] = '/';
		uri[len + 1] = '\0';
		if (redirect != NULL) {
			*redirect = 1;
		}
	}

	return 0;
}

static enum status
parse_range(const char *str, size_t size, size_t *lower, size_t *upper)
{
	char first[FIELD_MAX], last[FIELD_MAX];
	const char *p, *q, *r, *err;

	/* default to the complete range */
	*lower = 0;
	*upper = size - 1;

	/* done if no range-string is given */
	if (str == NULL || *str == '\0') {
		return 0;
	}

	/* skip opening statement */
	if (strncmp(str, "bytes=", sizeof("bytes=") - 1)) {
		return S_BAD_REQUEST;
	}
	p = str + (sizeof("bytes=") - 1);

	/* check string (should only contain numbers and a hyphen) */
	for (r = p, q = NULL; *r != '\0'; r++) {
		if (*r < '0' || *r > '9') {
			if (*r == '-') {
				if (q != NULL) {
					/* we have already seen a hyphen */
					return S_BAD_REQUEST;
				} else {
					/* place q after the hyphen */
					q = r + 1;
				}
			} else if (*r == ',' && r > p) {
				/*
				 * we refuse to accept range-lists out
				 * of spite towards this horrible part
				 * of the spec
				 */
				return S_RANGE_NOT_SATISFIABLE;
			} else {
				return S_BAD_REQUEST;
			}
		}
	}
	if (q == NULL) {
		/* the input string must contain a hyphen */
		return S_BAD_REQUEST;
	}
	r = q + strlen(q);

	/*
	 *  byte-range=first-last\0
	 *             ^     ^   ^
	 *             |     |   |
	 *             p     q   r
	 */

	/* copy 'first' and 'last' to their respective arrays */
	if ((size_t)((q - 1) - p + 1) > sizeof(first) ||
	    (size_t)(r - q + 1) > sizeof(last)) {
		return S_REQUEST_TOO_LARGE;
	}
	memcpy(first, p, (q - 1) - p);
	first[(q - 1) - p] = '\0';
	memcpy(last, q, r - q);
	last[r - q] = '\0';

	if (first[0] != '\0') {
		/*
		 * range has format "first-last" or "first-",
		 * i.e. return bytes 'first' to 'last' (or the
		 * last byte if 'last' is not given),
		 * inclusively, and byte-numbering beginning at 0
		 */
		*lower = strtonum(first, 0, MIN(SIZE_MAX, LLONG_MAX),
		                  &err);
		if (!err) {
			if (last[0] != '\0') {
				*upper = strtonum(last, 0,
				                  MIN(SIZE_MAX, LLONG_MAX),
				                  &err);
			} else {
				*upper = size - 1;
			}
		}
		if (err) {
			/* one of the strtonum()'s failed */
			return S_BAD_REQUEST;
		}

		/* check ranges */
		if (*lower > *upper || *lower >= size) {
			return S_RANGE_NOT_SATISFIABLE;
		}

		/* adjust upper limit to be at most the last byte */
		*upper = MIN(*upper, size - 1);
	} else {
		/* last must not also be empty */
		if (last[0] == '\0') {
			return S_BAD_REQUEST;
		}

		/*
		 * Range has format "-num", i.e. return the 'num'
		 * last bytes
		 */

		/*
		 * use upper as a temporary storage for 'num',
		 * as we know 'upper' is size - 1
		 */
		*upper = strtonum(last, 0, MIN(SIZE_MAX, LLONG_MAX), &err);
		if (err) {
			return S_BAD_REQUEST;
		}

		/* determine lower */
		if (*upper > size) {
			/* more bytes requested than we have */
			*lower = 0;
		} else {
			*lower = size - *upper;
		}

		/* set upper to the correct value */
		*upper = size - 1;
	}

	return 0;
}

void
http_prepare_response(const struct request *req, struct response *res,
                      const struct server *srv)
{
	enum status s, tmps;
	struct in6_addr addr;
	struct stat st;
	struct tm tm = { 0 };
	size_t i;
	int redirect, hasport, ipv6host;
	static char tmppath[PATH_MAX];
	char *p, *mime;

	/* empty all response fields */
	memset(res, 0, sizeof(*res));

	/* determine virtual host */
	if (srv->vhost) {
		for (i = 0; i < srv->vhost_len; i++) {
			if (!regexec(&(srv->vhost[i].re),
			             req->field[REQ_HOST], 0, NULL, 0)) {
				/* we have a matching vhost */
				res->vhost = &(srv->vhost[i]);
				break;
			}
		}
		if (i == srv->vhost_len) {
			s = S_NOT_FOUND;
			goto err;
		}
	}

	/* copy request-path to response-path and clean it up */
	redirect = 0;
	memcpy(res->path, req->path, MIN(sizeof(res->path), sizeof(req->path)));
	if ((tmps = path_normalize(res->path, &redirect)) ||
	    (tmps = path_add_vhost_prefix(res->path, &redirect, srv, res)) ||
	    (tmps = path_apply_prefix_mapping(res->path, &redirect, srv, res)) ||
	    (tmps = path_normalize(res->path, &redirect))) {
		s = tmps;
		goto err;
	}

	/* redirect all non-canonical hosts to their canonical forms */
	if (srv->vhost && res->vhost &&
	    strcmp(req->field[REQ_HOST], res->vhost->chost)) {
		redirect = 1;
	}

	/* reject all non-well-known hidden targets (see RFC 8615) */
	if (strstr(res->path, "/.") && strncmp(res->path, "/.well-known/",
	                                  sizeof("/.well-known/") - 1)) {
		s = S_FORBIDDEN;
		goto err;
	}

	/*
	 * generate and stat internal path based on the cleaned up request
	 * path and the virtual host while ignoring query and fragment
	 * (valid according to RFC 3986)
	 */
	if (esnprintf(res->internal_path, sizeof(res->internal_path), "/%s/%s",
	              (srv->vhost && res->vhost) ? res->vhost->dir : "",
		      res->path)) {
		s = S_REQUEST_TOO_LARGE;
		goto err;
	}
	if ((tmps = path_normalize(res->internal_path, NULL))) {
		s = tmps;
		goto err;
	}
	if (stat(res->internal_path, &st) < 0) {
		s = (errno == EACCES) ? S_FORBIDDEN : S_NOT_FOUND;
		goto err;
	}

	/*
	 * if the path points at a directory, make sure both the path
	 * and internal path have a trailing slash
	 */
	if (S_ISDIR(st.st_mode)) {
		if ((tmps = path_ensure_dirslash(res->path, &redirect)) ||
		    (tmps = path_ensure_dirslash(res->internal_path, NULL))) {
			s = tmps;
			goto err;
		}
	}

	/* redirect if the path-cleanup necessitated it earlier */
	if (redirect) {
		res->status = S_MOVED_PERMANENTLY;

		/* encode path */
		encode(res->path, tmppath);

		/* determine target location */
		if (srv->vhost && res->vhost) {
			/* absolute redirection URL */

			/* do we need to add a port to the Location? */
			hasport = srv->port && strcmp(srv->port, "80");

			/* RFC 2732 specifies to use brackets for IPv6-addresses
			 * in URLs, so we need to check if our host is one and
			 * honor that later when we fill the "Location"-field */
			if ((ipv6host = inet_pton(AF_INET6, res->vhost->chost,
			                          &addr)) < 0) {
				s = S_INTERNAL_SERVER_ERROR;
				goto err;
			}

			/*
			 * write location to response struct (re-including
			 * the query and fragment, if present)
			 */
			if (esnprintf(res->field[RES_LOCATION],
			              sizeof(res->field[RES_LOCATION]),
			              "//%s%s%s%s%s%s%s%s%s%s",
			              ipv6host ? "[" : "",
			              res->vhost->chost,
			              ipv6host ? "]" : "",
				      hasport ? ":" : "",
			              hasport ? srv->port : "",
				      tmppath,
				      req->query[0] ? "?" : "",
				      req->query,
				      req->fragment[0] ? "#" : "",
				      req->fragment)) {
				s = S_REQUEST_TOO_LARGE;
				goto err;
			}
		} else {
			/*
			 * write relative redirection URI to response struct
			 * (re-including the query and fragment, if present)
			 */
			if (esnprintf(res->field[RES_LOCATION],
			              sizeof(res->field[RES_LOCATION]),
			              "%s%s%s%s%s",
				      tmppath,
				      req->query[0] ? "?" : "",
				      req->query,
				      req->fragment[0] ? "#" : "",
				      req->fragment)) {
				s = S_REQUEST_TOO_LARGE;
				goto err;
			}
		}

		return;
	}

	if (S_ISDIR(st.st_mode)) {
		/*
		 * when we serve a directory, we first check if there
		 * exists a directory index. If not, we either make
		 * a directory listing (if enabled) or send an error
		 */

		/*
		 * append docindex to internal_path temporarily
		 * (internal_path is guaranteed to end with '/')
		 */
		if (esnprintf(tmppath, sizeof(tmppath), "%s%s",
		              res->internal_path, srv->docindex)) {
			s = S_REQUEST_TOO_LARGE;
			goto err;
		}

		/* stat the temporary path, which must be a regular file */
		if (stat(tmppath, &st) < 0 || !S_ISREG(st.st_mode)) {
			if (srv->listdirs) {
				/* serve directory listing */

				/* check if directory is accessible */
				if (access(res->internal_path, R_OK) != 0) {
					s = S_FORBIDDEN;
					goto err;
				} else {
					res->status = S_OK;
				}
				res->type = RESTYPE_DIRLISTING;

				if (esnprintf(res->field[RES_CONTENT_TYPE],
				              sizeof(res->field[RES_CONTENT_TYPE]),
					      "%s", "text/html; charset=utf-8")) {
					s = S_INTERNAL_SERVER_ERROR;
					goto err;
				}

				return;
			} else {
				/* reject */
				s = (!S_ISREG(st.st_mode) || errno == EACCES) ?
				    S_FORBIDDEN : S_NOT_FOUND;
				goto err;
			}
		} else {
			/* the docindex exists; copy tmppath to internal path */
			if (esnprintf(res->internal_path,
			              sizeof(res->internal_path), "%s",
			              tmppath)) {
				s = S_REQUEST_TOO_LARGE;
				goto err;
			}
		}
	}

	/* modified since */
	if (req->field[REQ_IF_MODIFIED_SINCE][0]) {
		/* parse field */
		if (!strptime(req->field[REQ_IF_MODIFIED_SINCE],
		              "%a, %d %b %Y %T GMT", &tm)) {
			s = S_BAD_REQUEST;
			goto err;
		}

		/* compare with last modification date of the file */
		if (difftime(st.st_mtim.tv_sec, timegm(&tm)) <= 0) {
			res->status = S_NOT_MODIFIED;
			return;
		}
	}

	/* range */
	if ((s = parse_range(req->field[REQ_RANGE], st.st_size,
	                     &(res->file.lower), &(res->file.upper)))) {
		if (s == S_RANGE_NOT_SATISFIABLE) {
			res->status = S_RANGE_NOT_SATISFIABLE;

			if (esnprintf(res->field[RES_CONTENT_RANGE],
			              sizeof(res->field[RES_CONTENT_RANGE]),
			              "bytes */%zu", st.st_size)) {
				s = S_INTERNAL_SERVER_ERROR;
				goto err;
			}

			return;
		} else {
			goto err;
		}
	}

	/* mime */
	mime = "application/octet-stream";
	if ((p = strrchr(res->internal_path, '.'))) {
		for (i = 0; i < LEN(mimes); i++) {
			if (!strcmp(mimes[i].ext, p + 1)) {
				mime = mimes[i].type;
				break;
			}
		}
	}

	/* fill response struct */
	res->type = RESTYPE_FILE;

	/* check if file is readable */
	res->status = (access(res->internal_path, R_OK)) ? S_FORBIDDEN :
	              (req->field[REQ_RANGE][0] != '\0') ?
	              S_PARTIAL_CONTENT : S_OK;

	if (esnprintf(res->field[RES_ACCEPT_RANGES],
	              sizeof(res->field[RES_ACCEPT_RANGES]),
		      "%s", "bytes")) {
		s = S_INTERNAL_SERVER_ERROR;
		goto err;
	}

	if (esnprintf(res->field[RES_CONTENT_LENGTH],
	              sizeof(res->field[RES_CONTENT_LENGTH]),
	              "%zu", res->file.upper - res->file.lower + 1)) {
		s = S_INTERNAL_SERVER_ERROR;
		goto err;
	}
	if (req->field[REQ_RANGE][0] != '\0') {
		if (esnprintf(res->field[RES_CONTENT_RANGE],
		              sizeof(res->field[RES_CONTENT_RANGE]),
		              "bytes %zd-%zd/%zu", res->file.lower,
			      res->file.upper, st.st_size)) {
			s = S_INTERNAL_SERVER_ERROR;
			goto err;
		}
	}
	if (esnprintf(res->field[RES_CONTENT_TYPE],
	              sizeof(res->field[RES_CONTENT_TYPE]),
	              "%s", mime)) {
		s = S_INTERNAL_SERVER_ERROR;
		goto err;
	}
	if (timestamp(res->field[RES_LAST_MODIFIED],
	              sizeof(res->field[RES_LAST_MODIFIED]),
	              st.st_mtim.tv_sec)) {
		s = S_INTERNAL_SERVER_ERROR;
		goto err;
	}

	return;
err:
	http_prepare_error_response(req, res, s);
}

void
http_prepare_error_response(const struct request *req,
                            struct response *res, enum status s)
{
	/* used later */
	(void)req;

	/* empty all response fields */
	memset(res, 0, sizeof(*res));

	res->type = RESTYPE_ERROR;
	res->status = s;

	if (esnprintf(res->field[RES_CONTENT_TYPE],
	              sizeof(res->field[RES_CONTENT_TYPE]),
	              "text/html; charset=utf-8")) {
		res->status = S_INTERNAL_SERVER_ERROR;
	}

	if (res->status == S_METHOD_NOT_ALLOWED) {
		if (esnprintf(res->field[RES_ALLOW],
		              sizeof(res->field[RES_ALLOW]),
			      "Allow: GET, HEAD")) {
			res->status = S_INTERNAL_SERVER_ERROR;
		}
	}
}