/* See LICENSE file for copyright and license details. */
#include "types-message.h"
#include "util.h"

#include <sys/socket.h>
#include <errno.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>


/**
 * Initialise a message slot so that it can
 * be used by to read messages
 * 
 * @param   this  Memory slot in which to store the new message
 * @return        Non-zero on error, `errno` will be set accordingly
 */
int
message_initialise(struct message *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);
	if (!this->buffer)
		return -1;
	return 0;
}


/**
 * Release all resources in a message, should
 * be done even if initialisation fails
 * 
 * @param  this  The message
 */
void
message_destroy(struct message *restrict this)
{
	size_t i;

	if (this->headers) {
		for (i = 0; i < this->header_count; i++)
			free(this->headers[i]);
		free(this->headers);
	}
	free(this->payload);
	free(this->buffer);
}


#if defined(__clang__)
# pragma GCC diagnostic push
# pragma GCC diagnostic ignored "-Wcast-align"
#endif


/**
 * Marshal a message for state serialisation
 * 
 * @param  this  The message
 * @param  buf   Output buffer for the marshalled data,
 *               `NULL` just measure how large the buffers
 *               needs to be
 * @return       The number of marshalled byte
 */
size_t
message_marshal(const struct message *restrict this, void *restrict buf)
{
	size_t i, n, off = 0;
	char *bs = buf;

	if (bs)
		*(size_t *)&bs[off] = this->header_count;
	off += sizeof(size_t);

	if (bs)
		*(size_t *)&bs[off] = this->payload_size;
	off += sizeof(size_t);

	if (bs)
		*(size_t *)&bs[off] = this->payload_ptr;
	off += sizeof(size_t);

	if (bs)
		*(size_t *)&bs[off] = this->buffer_ptr;
	off += sizeof(size_t);

	if (bs)
		*(int *)&bs[off] = this->stage;
	off += sizeof(int);

	for (i = 0; i < this->header_count; i++) {
		n = strlen(this->headers[i]) + 1;
		if (bs)
			memcpy(&bs[off], this->headers[i], n);
		off += n;
	}

	if (bs)
		memcpy(&bs[off], this->payload, this->payload_ptr);
	off += this->payload_ptr;

	if (bs)
		memcpy(&bs[off], this->buffer, this->buffer_ptr);
	off += this->buffer_ptr;

	return off;
}


/**
 * Unmarshal a message for state deserialisation
 * 
 * @param   this  Memory slot in which to store the new message
 * @param   buf   In buffer with the marshalled data
 * @return        The number of unmarshalled bytes, 0 on error
 */
size_t
message_unmarshal(struct message *restrict this, const void *restrict buf)
{
	size_t i, n, off = 0, header_count;
	const char *bs = buf;

	this->header_count = 0;

	header_count = *(const size_t *)&bs[off];
	off += sizeof(size_t);

	this->payload_size = *(const size_t *)&bs[off];
	off += sizeof(size_t);

	this->payload_ptr = *(const size_t *)&bs[off];
	off += sizeof(size_t);

	this->buffer_size = this->buffer_ptr = *(const size_t *)&bs[off];
	off += sizeof(size_t);

	this->stage = *(const int *)&bs[off];
	off += sizeof(int);

	/* Make sure that the pointers are NULL so that they are
	   not freed without being allocated when the message is
	   destroyed if this function fails. */
	this->headers = NULL;
	this->payload = NULL;
	this->buffer  = NULL;

	/* To 2-power-multiple of 128 bytes. */
	this->buffer_size >>= 7;
	if (!this->buffer_size) {
		this->buffer_size = 1;
	} else {
		this->buffer_size -= 1;
		this->buffer_size |= this->buffer_size >> 1;
		this->buffer_size |= this->buffer_size >> 2;
		this->buffer_size |= this->buffer_size >> 4;
		this->buffer_size |= this->buffer_size >> 8;
		this->buffer_size |= this->buffer_size >> 16;
#if SIZE_MAX == UINT64_MAX
		this->buffer_size |= this->buffer_size >> 32;
#endif
		this->buffer_size += 1;
	}
	this->buffer_size <<= 7;

	/* Allocate header list, payload and read buffer. */

	if (header_count > 0)
		if (!(this->headers = malloc(header_count * sizeof(char*))))
			goto fail;

	if (this->payload_size > 0)
		if (!(this->payload = malloc(this->payload_size)))
			goto fail;

	if (!(this->buffer = malloc(this->buffer_size)))
		goto fail;

	/* Fill the header list, payload and read buffer. */

	for (i = 0; i < header_count; i++) {
		n = strlen(&bs[off]) + 1;
		this->headers[i] = memdup(&bs[off], n);
		if (!this->headers[i])
			goto fail;
		off += n;
		this->header_count++;
	}

	memcpy(this->payload, &bs[off], this->payload_ptr);
	off += this->payload_ptr;

	memcpy(this->buffer, &bs[off], this->buffer_ptr);
	off += this->buffer_ptr;

	return off;

fail:
	return 0;
}


#if defined(__clang__)
# pragma GCC diagnostic pop
#endif



/**
 * Extend the header list's allocation
 * 
 * @param   this    The message
 * @param   extent  The number of additional entries
 * @return          Zero on success, -1 on error
 */
GCC_ONLY(__attribute__((__nonnull__)))
static int
extend_headers(struct message *restrict this, size_t extent)
{
	char **new = realloc(this->headers, (this->header_count + extent) * sizeof(char *));
	if (!new)
		return -1;
	this->headers = new;
	return 0;
}


/**
 * Extend the read buffer by way of doubling
 * 
 * @param   this  The message
 * @return        Zero on success, -1 on error
 */
GCC_ONLY(__attribute__((__nonnull__)))
static int
extend_buffer(struct message *restrict this)
{
	char *restrict new = realloc(this->buffer, (this->buffer_size << 1) * sizeof(char));
	if (!new)
		return -1;
	this->buffer = new;
	this->buffer_size <<= 1;
	return 0;
}


/**
 * Reset the header list and the payload
 * 
 * @param  this  The message
 */
GCC_ONLY(__attribute__((__nonnull__)))
static void
reset_message(struct message *restrict this)
{
	size_t i;
	if (this->headers) {
		for (i = 0; i < this->header_count; 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)
 */
GCC_ONLY(__attribute__((__pure__, __nonnull__)))
static int
get_payload_length(struct message *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)atol(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)
 */
GCC_ONLY(__attribute__((__pure__, __nonnull__)))
static int
validate_header(const char *restrict header, size_t length)
{
	char *restrict p = memchr(header, ':', length * sizeof(char));

	if (verify_utf8(header) < 0) {
		/* Either the string is not UTF-8, or your are under an UTF-8 attack,
		   let's just call this unrecoverable because the client will not correct. */
		return -2;
	}

	if (!p ||        /* 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
 */
GCC_ONLY(__attribute__((__nonnull__)))
static void
unbuffer_beginning(struct message *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 `message_read`
 */
GCC_ONLY(__attribute__((__nonnull__)))
static int
initialise_payload(struct message *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) {
		this->payload = malloc(this->payload_size);
		if (!this->payload)
			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 `message_read`
 */
GCC_ONLY(__attribute__((__nonnull__)))
static int
store_header(struct message *restrict this, size_t length)
{
	char *restrict header;
  
	/* Allocate the header. */
	header = malloc(length); /* Last char is a LF, which is substituted with NUL. */
	if (!header)
		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 `message_read`
 */
GCC_ONLY(__attribute__((__nonnull__)))
static int
continue_read(struct message *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, */
		if ((r = extend_buffer(this)) < 0)
			return r;

		/* 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) {
		errno = ECONNRESET;
		return -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        0:  At least one message is available
 *                -1: Exceptional connection:
 *                  EINTR:        System call interrupted
 *                  EAGAIN:       No message is available
 *                  EWOULDBLOCK:  No message is available
 *                  ECONNRESET:   Connection closed
 *                  Other:        Failure
 *                -2: Corrupt message (unrecoverable)
 */
GCC_ONLY(__attribute__((__nonnull__)))
int
message_read(struct message *restrict this, int fd)
{
	size_t header_commit_buffer = 0;
	size_t length, need, move;
	int r;
	char *p;

	/* 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 (;;) {      
		/* 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))))) {
			length = (size_t)(p - this->buffer);
			if (length) {
				/* 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)
					if ((r = extend_headers(this, header_commit_buffer = 8)) < 0)
						return r;

				/* Create and store header. */
				if ((r = store_header(this, length + 1)) < 0)
					return r;
				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. */
				if ((r = initialise_payload(this)) < 0)
					return r;

				/* 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. */
			need = this->payload_size - this->payload_ptr;
			/* How much we have of that what is needed. */
			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. */
		if ((r = continue_read(this, fd)) < 0)
			return r;
	}
}