/**
* mds — A micro-display server
* Copyright © 2014, 2015 Mattias Andrée (maandree@member.fsf.org)
*
* This program 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, either version 3 of the License, or
* (at your option) any later version.
*
* This program 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/>.
*/
#include "inbound.h"
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <sys/socket.h>
#define try(INSTRUCTION) if ((r = INSTRUCTION) < 0) return r
/**
* Initialise a message slot so that it can
* be used by `mds_message_read`
*
* @param this Memory slot in which to store the new message
* @return Non-zero on error, `errno` will be set accordingly.
* Destroy the message on error.
*/
int libmds_message_initialise(libmds_message_t* restrict this)
{
this->headers = NULL;
this->header_count = 0;
this->payload = NULL;
this->payload_size = 0;
this->payload_ptr = 0;
this->buffer_size = 128;
this->buffer_ptr = 0;
this->stage = 0;
this->buffer = malloc(this->buffer_size * sizeof(char));
return this->buffer == NULL ? -1 : 0;
}
/**
* Release all resources in a message, should
* be done even if initialisation fails
*
* @param this The message
*/
void libmds_message_destroy(libmds_message_t* restrict this)
{
size_t i, n = this->header_count;
if (this->headers != NULL)
for (i = 0; i < n; i++)
free(this->headers[i]);
free(this->headers), this->headers = NULL;
free(this->payload), this->payload = NULL;
free(this->buffer), this->buffer = NULL;
}
/**
* Check whether a NUL-terminated string is encoded in UTF-8
*
* @param string The string
* @param allow_modified_nul Whether Modified UTF-8 is allowed, which allows a two-byte encoding for NUL
* @return Zero if good, -1 on encoding error
*/
__attribute__((nonnull))
static int verify_utf8(const char* string, int allow_modified_nul) /* Cannibalised from <libmdsserver/util.h> */
{
static long BYTES_TO_MIN_BITS[] = {0, 0, 8, 12, 17, 22, 37};
static long BYTES_TO_MAX_BITS[] = {0, 7, 11, 16, 21, 26, 31};
long bytes = 0, read_bytes = 0, bits = 0, c, character;
/* min bits max bits
0....... 0 7
110..... 10...... 8 11
1110.... 10...... 10...... 12 16
11110... 10...... 10...... 10...... 17 21
111110.. 10...... 10...... 10...... 10...... 22 26
1111110. 10...... 10...... 10...... 10...... 10...... 27 31
*/
while ((c = (long)(*string++)))
if (read_bytes == 0)
{
/* First byte of the character. */
if ((c & 0x80) == 0x00)
/* Single-byte character. */
continue;
if ((c & 0xC0) == 0x80)
/* Single-byte character marked as multibyte, or
a non-first byte in a multibyte character. */
return -1;
/* Multibyte character. */
while ((c & 0x80))
bytes++, c <<= 1;
read_bytes = 1;
character = c & 0x7F;
if (bytes > 6)
/* 31-bit characters can be encoded with 6-bytes,
and UTF-8 does not cover higher code points. */
return -1;
}
else
{
/* Not first byte of the character. */
if ((c & 0xC0) != 0x80)
/* Beginning of new character before a
multibyte character has ended. */
return -1;
character = (character << 6) | (c & 0x7F);
if (++read_bytes < bytes)
/* Not at last byte yet. */
continue;
/* Check that the character is not unnecessarily long. */
while (character)
character >>= 1, bits++;
bits = ((bits == 0) && (bytes == 2) && allow_modified_nul) ? 8 : bits;
if ((bits < BYTES_TO_MIN_BITS[bytes]) || (BYTES_TO_MAX_BITS[bytes] < bits))
return -1;
read_bytes = bytes = bits = 0;
}
/* Make sure we did not stop at the middle of a multibyte character. */
return read_bytes == 0 ? 0 : -1;
}
/**
* Extend the header list's allocation
*
* @param this The message
* @param extent The number of additional entries
* @return Zero on success, -1 on error
*/
__attribute__((nonnull))
static int extend_headers(libmds_message_t* restrict this, size_t extent)
{
char** new_headers = realloc(this->headers, (this->header_count + extent) * sizeof(char*));
if (new_headers == NULL)
return -1;
this->headers = new_headers;
return 0;
}
/**
* Extend the read buffer by way of doubling
*
* @param this The message
* @return Zero on success, -1 on error
*/
__attribute__((nonnull))
static int extend_buffer(libmds_message_t* restrict this)
{
char* new_buf = realloc(this->buffer, (this->buffer_size << 1) * sizeof(char));
if (new_buf == NULL)
return -1;
this->buffer = new_buf;
this->buffer_size <<= 1;
return 0;
}
/**
* Reset the header list and the payload
*
* @param this The message
*/
__attribute__((nonnull))
static void reset_message(libmds_message_t* restrict this)
{
size_t i, n = this->header_count;
if (this->headers != NULL)
{
for (i = 0; i < n; i++)
free(this->headers[i]);
free(this->headers);
this->headers = NULL;
}
this->header_count = 0;
free(this->payload);
this->payload = NULL;
this->payload_size = 0;
this->payload_ptr = 0;
}
/**
* Read the headers the message and determine, and store, its payload's length
*
* @param this The message
* @return Zero on success, negative on error (malformated message: unrecoverable state)
*/
__attribute__((pure, nonnull))
static int get_payload_length(libmds_message_t* restrict this)
{
char* header;
size_t i;
for (i = 0; i < this->header_count; i++)
if (strstr(this->headers[i], "Length: ") == this->headers[i])
{
/* Store the message length. */
header = this->headers[i] + strlen("Length: ");
this->payload_size = (size_t)atoll(header);
/* Do not except a length that is not correctly formated. */
for (; *header; header++)
if ((*header < '0') || ('9' < *header))
return -2; /* Malformated value, enters unrecoverable state. */
/* Stop searching for the ‘Length’ header, we have found and parsed it. */
break;
}
return 0;
}
/**
* Verify that a header is correctly formatted
*
* @param header The header, must be NUL-terminated
* @param length The length of the header
* @return Zero if valid, negative if invalid (malformated message: unrecoverable state)
*/
__attribute__((pure, nonnull))
static int validate_header(const char* header, size_t length)
{
char* p = memchr(header, ':', length * sizeof(char));
if (verify_utf8(header, 0) < 0)
/* Either the string is not UTF-8, or your are under an UTF-8 attack,
lets just call this unrecoverable because the client will not correct. */
return -2;
if ((p == NULL) || /* Buck you, rawmemchr should not segfault the program. */
(p[1] != ' ')) /* Also an invalid format. ' ' is mandated after the ':'. */
return -2;
return 0;
}
/**
* Remove the beginning of the read buffer
*
* @param this The message
* @param length The number of characters to remove
* @param update_ptr Whether to update the buffer pointer
*/
__attribute__((nonnull))
static void unbuffer_beginning(libmds_message_t* restrict this, size_t length, int update_ptr)
{
memmove(this->buffer, this->buffer + length, (this->buffer_ptr - length) * sizeof(char));
if (update_ptr)
this->buffer_ptr -= length;
}
/**
* Remove the header–payload delimiter from the buffer,
* get the payload's size and allocate the payload
*
* @param this The message
* @return The return value follows the rules of `mds_message_read`
*/
__attribute__((nonnull))
static int initialise_payload(libmds_message_t* restrict this)
{
/* Remove the \n (end of empty line) we found from the buffer. */
unbuffer_beginning(this, 1, 1);
/* Get the length of the payload. */
if (get_payload_length(this) < 0)
return -2; /* Malformated value, enters unrecoverable state. */
/* Allocate the payload buffer. */
if (this->payload_size > 0)
if ((this->payload = malloc(this->payload_size * sizeof(char))) == NULL)
return -1;
return 0;
}
/**
* Create a header from the buffer and store it
*
* @param this The message
* @param length The length of the header, including LF-termination
* @return The return value follows the rules of `mds_message_read`
*/
__attribute__((nonnull))
static int store_header(libmds_message_t* restrict this, size_t length)
{
char* header;
/* Allocate the header. */
header = malloc(length * sizeof(char)); /* Last char is a LF, which is substituted with NUL. */
if (header == NULL)
return -1;
/* Copy the header data into the allocated header, */
memcpy(header, this->buffer, length * sizeof(char));
/* and NUL-terminate it. */
header[length - 1] = '\0';
/* Remove the header data from the read buffer. */
unbuffer_beginning(this, length, 1);
/* Make sure the the header syntax is correct so that
the program does not need to care about it. */
if (validate_header(header, length))
{
free(header);
return -2;
}
/* Store the header in the header list. */
this->headers[this->header_count++] = header;
return 0;
}
/**
* Continue reading from the socket into the buffer
*
* @param this The message
* @param fd The file descriptor of the socket
* @return The return value follows the rules of `mds_message_read`
*/
__attribute__((nonnull))
static int continue_read(libmds_message_t* restrict this, int fd)
{
size_t n;
ssize_t got;
int r;
/* Figure out how much space we have left in the read buffer. */
n = this->buffer_size - this->buffer_ptr;
/* If we do not have too much left, */
if (n < 128)
{
/* grow the buffer, */
try (extend_buffer(this));
/* and recalculate how much space we have left. */
n = this->buffer_size - this->buffer_ptr;
}
/* Then read from the socket. */
errno = 0;
got = recv(fd, this->buffer + this->buffer_ptr, n, 0);
this->buffer_ptr += (size_t)(got < 0 ? 0 : got);
if (errno)
return -1;
if (got == 0)
return errno = ECONNRESET, -1;
return 0;
}
/**
* Read the next message from a file descriptor
*
* @param this Memory slot in which to store the new message
* @param fd The file descriptor
* @return Non-zero on error or interruption, `errno` will be
* set accordingly. Destroy the message on error,
* be aware that the reading could have been
* interrupted by a signal rather than canonical error.
* If -2 is returned `errno` will not have been set,
* -2 indicates that the message is malformated,
* which is a state that cannot be recovered from.
*/
int libmds_message_read(libmds_message_t* restrict this, int fd)
{
size_t header_commit_buffer = 0;
int r;
/* If we are at stage 2, we are done and it is time to start over.
This is important because the function could have been interrupted. */
if (this->stage == 2)
{
reset_message(this);
this->stage = 0;
}
/* Read from file descriptor until we have a full message. */
for (;;)
{
char* p;
size_t length;
/* Stage 0: headers. */
/* Read all headers that we have stored into the read buffer. */
while ((this->stage == 0) &&
((p = memchr(this->buffer, '\n', this->buffer_ptr * sizeof(char))) != NULL))
if ((length = (size_t)(p - this->buffer)))
{
/* We have found a header. */
/* On every eighth header found with this function call,
we prepare the header list for eight more headers so
that it does not need to be reallocated again and again. */
if (header_commit_buffer == 0)
try (extend_headers(this, header_commit_buffer = 8));
/* Create and store header. */
try (store_header(this, length + 1));
header_commit_buffer -= 1;
}
else
{
/* We have found an empty line, i.e. the end of the headers. */
/* Remove the header–payload delimiter from the buffer,
get the payload's size and allocate the payload. */
try (initialise_payload(this));
/* Mark end of stage, next stage is getting the payload. */
this->stage = 1;
}
/* Stage 1: payload. */
if ((this->stage == 1) && (this->payload_size > 0))
{
/* How much of the payload that has not yet been filled. */
size_t need = this->payload_size - this->payload_ptr;
/* How much we have of that what is needed. */
size_t move = this->buffer_ptr < need ? this->buffer_ptr : need;
/* Copy what we have, and remove it from the the read buffer. */
memcpy(this->payload + this->payload_ptr, this->buffer, move * sizeof(char));
unbuffer_beginning(this, move, 1);
/* Keep track of how much we have read. */
this->payload_ptr += move;
}
if ((this->stage == 1) && (this->payload_ptr == this->payload_size))
{
/* If we have filled the payload (or there was no payload),
mark the end of this stage, i.e. that the message is
complete, and return with success. */
this->stage = 2;
return 0;
}
/* If stage 1 was not completed. */
/* Continue reading from the socket into the buffer. */
try (continue_read(this, fd));
}
}
