/*          __                               _
*    ____  / /_  ____ ___  __  ___________ _(_)
*   / __ \/ __ \/ __ `__ \/ / / / ___/ __ `/ /
*  / /_/ / / / / / / / / / /_/ / /__/ /_/ / /
*  \____/_/ /_/_/ /_/ /_/\__, /\___/\__, /_/
*                       /____/     /____/
*
* SPDX-License-Identifier: BSD-2-Clause-FreeBSD
*
* Copyright (c) 2021, Max Christian Pohle <max@coderonline.de>
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
*    notice, this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright
*    notice, this list of conditions and the following disclaimer in the
*    documentation and/or other materials provided with the distribution.
*
* {{{ DISCLAIMER
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
* }}}
*/

// {{{ INCLUDES
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <err.h>
#include <errno.h>
#include <arpa/inet.h>
#include <fcntl.h>
#include <sys/sendfile.h>
#include <sys/stat.h>
// #include <pthread.h>      // maybe later
// }}}
// {{{ MACROS
#define EWOULDBLOCK_DELAY     100
#define READ_BUFFER_LENGTH    9000 // jumboframe?
#define POST_DATA_MAX_LENGTH  18000
#define DEBUG_SLEEP_TIME      50000

#ifndef DEBUG
#define DEBUG(X, ...) // (X, ...)
#else
#include <stdarg.h>
static inline int verbose(const char * format, ...) {
	va_list va; va_start(va, format); usleep(DEBUG_SLEEP_TIME); return vprintf(format, va);
}
#undef DEBUG
#define DEBUG verbose
#endif
// }}}

typedef struct {
	int    newline_length; // lenght of one newline in bytes (\n has 1, CR/LF has 2)
	char * method;         // GET/POST or something like that
	char * url;            // request URL (e.g. /index.html)
	char * boundary;       // usually looks similar to ------1234
	size_t boundary_size;  // size in bytes, calculated after first header complete; is an indicator for the first header
	char * content_type;   // sometimes 'text/html', also sometimes 'text/html; boundary=------1234'
	char * content_disposition; // includes file names of uploaded files or field names with form-data (e.g. curl -F)
} Http_Header;

void send_answer(int fd_socket, Http_Header * http_header) {
	FILE * f = fdopen((size_t) fd_socket, "w");
	fputs("HTTP/1.0 200 OK\n", f);
	fputs("content-type: text/plain\n\n", f);
	fflush(f);

	int file = open(&http_header->url[1], O_RDONLY);
	if(0 < file) {
		struct stat stat;
		fstat(file, &stat);
		sendfile (fileno(f), file, NULL, stat.st_size);
	} else {
		if(http_header->url) // TODO: too dangerous to check that here, that is too late.
			fprintf(f, "could not open file \"%s\"\n", &http_header->url[1]);
	}

	fclose(f);
}

int read_everything(FILE * f_r, FILE * output) {
	const int read_buffer_length = READ_BUFFER_LENGTH;
	char read_buffer[read_buffer_length];
	for(size_t size = -2 ; ; size = fread(read_buffer, 1, read_buffer_length, f_r)) {
		if(-2 == size || (-1 == size && EWOULDBLOCK == errno)) {
			usleep(EWOULDBLOCK_DELAY); // try again a little later
			continue;
		}

		fwrite(read_buffer, read_buffer_length, 1, output);

		if (read_buffer_length > POST_DATA_MAX_LENGTH)
			return EXIT_FAILURE;

		if (size < read_buffer_length) { // I expect one nmemb of data
			break;
		}
	}
	fflush(output);
	return EXIT_SUCCESS;
}

void * next_customer(size_t new_socket) {
	FILE * f_r = fdopen((size_t) new_socket, "r");

	char * output_buffer = NULL;
	size_t output_buffer_length = 0;
	FILE * output = open_memstream(&output_buffer, &output_buffer_length);

	read_everything(f_r, output);  // TODO: catch return value and error handling
	shutdown(new_socket, SHUT_RD); // shutdown the reading half of the connection

	char * start = output_buffer;
	char * end = NULL;
	char * search = "\r\n";

	Http_Header http_header = {0};

	char * name = NULL;
	while(NULL != (end = strpbrk(start, search))) { // TODO: try harder to break things (are SEGFAULTs possible?)

		size_t matchlen = strspn(end, search);
		switch(end[0]) {
			case ':':
				end[0] = '\0'; // {{{ remember header 'names' and search for the value
				end++;         // jump over the colon

				name = start;  // remember, where name starts, will be important in the newline case

				if (0 == strcasecmp("Content-Type", start)) {
					search = "\r\n;"; // (more unlikely) also search for a semicolon in Content-Type: [...]; boundary=[...]
				} else {
					search = "\r\n";  // (likely) search for some kind of newline
				} // }}}
				break;
			case ';':
				// {{{ find the form-data boundary in the main header
				start += strspn(start, "; "); // remove spaces and semicolons (boundary check implicit; also stops at '\0')

				const char s_multipart_form_data[] = "boundary=";
				if(NULL == http_header.boundary && 0 < strcasecmp(start, s_multipart_form_data))
				{
					http_header.boundary = end + sizeof(s_multipart_form_data) + 1;
					http_header.boundary += strspn(http_header.boundary, "-");
					DEBUG("> Boundary found, now looking where it ends...\n");
					search = "\r\n";
					continue;
				} /// }}}
				break;
			case '\r': // fallthrough
			case '\n':
				// {{{ newlines are special: sometimes content parts follow and sometimes headers, guess what...
				end[0] = '\0';
				search = ":"; // we will continue to search for headers
				if(NULL == name) {
					if(NULL == http_header.method) {
						DEBUG("[%ld]> HTTP REQUEST LINE :: %s \n", matchlen, start);
						end[0] = '\0';

						while(NULL != (start = memchr(start, ' ', end - start))) {
							if(NULL == http_header.url)
								http_header.url = ++start;
							else
								start[0] = '\0';
						}
						http_header.method = start;
						http_header.newline_length = matchlen;
					} else {
						DEBUG("[...]\n"); // if we want to intentially skip something, we land here by setting name = NUL;
						break;
					}
				} else { // we know that name is not NULL and can work with it
					if (0 == strcasecmp("Content-Disposition", name))
					{ http_header.content_disposition = start; }
				} // }}}
				DEBUG("\033[32m[%ld]> '% 20s' = '%s'\033[0m\n", matchlen, name, start);
				// {{{ check if a http header ended (e.g. two newlines)
				if(matchlen > http_header.newline_length) {
					DEBUG("> END HEADERS, because there were %d newlines; boundary='%s'[%ld]\n", matchlen / http_header.newline_length, http_header.boundary, http_header.boundary_size);
					end += matchlen;

					// if it was the first header, we calculate the boundary size and expect more headers to come after a boundary
					if(http_header.boundary && http_header.boundary_size == 0) {
						DEBUG("================================================================================\n");
						http_header.boundary_size = strlen(http_header.boundary);
						// skip the first header and boundary...
						start = end;
						start += strspn(start, "-");
						start += http_header.boundary_size;
						start += http_header.newline_length;
						continue;
					} else {
						char * content_start = end;
						while(1)
						{
							size_t size_remaining = (size_t)  output_buffer_length - (end - output_buffer) - 1;
							DEBUG("%ld remaining.\n", size_remaining);

							if(size_remaining <= 0) {
								DEBUG("> not even the boundary would fit in that what is left.\n");
								break;
							}

							if(NULL == (end = memchr((void*) end, '-', size_remaining))) {
								DEBUG("no further '-' found\n");
								break;
							}

							char * content_end = end - http_header.newline_length;

							end += strspn(end, "-");
							if(0 == strncmp(end, http_header.boundary, http_header.boundary_size)) {
								size_t file_size = content_end - content_start;
								DEBUG("> Content ends here, size of the last file is %ld.", file_size);

								end += http_header.boundary_size;
								matchlen = strspn(end, "\r\n");
								DEBUG("> end is at %p, matchlen is %ld\n", end, matchlen);

								search = ":";
								break;
							} else {
								end = end + 1;
							}
						}
					}
					break;
				} // }}} if condition after a header
		} // switch

		if(NULL == end)
			break;
		else
			start = end + matchlen;
	}

	DEBUG("> sending answer...");
	send_answer(new_socket, &http_header);
	DEBUG("> answer sent.");

	fclose(f_r);

	fclose(output);
	free(output_buffer);

	return NULL;
}

int serve(int server_fd)
{
	struct sockaddr_in address;
	socklen_t address_len = sizeof(address);
	DEBUG("> Waiting for connections on server file descriptor %d\n", server_fd);

	size_t new_socket = -1;
	while(-1 != (new_socket = accept(server_fd, (struct sockaddr*) &address, &address_len)))
	{
		DEBUG("> Client %ld is connected via port %d\n", new_socket, address.sin_port);

		// set non blocking mode...
		fcntl(
			(size_t) new_socket,
			F_SETFL,
			fcntl((size_t) new_socket, F_GETFL) | O_NONBLOCK
		);

		next_customer(new_socket);

#ifdef VALGRIND
		break; // only run once, so that valgrind can test allocations&frees
#endif
	}

	err(errno, "error serving");
	close(server_fd);
}

int main(const int argc, char const * argv[]) {
	int server_fd = -1, opt = 1;

	int port = atoi(argc > 1 ? argv[1] : "8080");
	0 == port ? port = 8080 : port;


	struct sockaddr_in address = {
		.sin_family      = AF_INET,
		.sin_addr.s_addr = INADDR_ANY,
		.sin_port        = htons(port)
	};

	// I <3 C
	0 == (server_fd = socket(AF_INET, SOCK_STREAM, 0))
	? err(errno, NULL)
	: setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR | SO_REUSEPORT, &opt, sizeof(opt))
	? err(errno, "setsockopt failed on socket with fileno %d", server_fd)
	: bind(server_fd, (struct sockaddr*) &address, sizeof(address))
	? err(errno, NULL)
	: listen(server_fd, SOMAXCONN)
	? err(errno, NULL)
	: serve(server_fd)
	? err(errno, NULL)
	: exit(EXIT_SUCCESS)
	; return EXIT_FAILURE;
}

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