done

README.md

@@ -0,0 +1,18 @@
+# webserver
+
+Written as a tiny project to learn more about 64-bit x86 assembly and the Linux kernel ABI. The syntax here is Intel for GNU AS. The code is public domain.
+
+### Build process
+
+```
+as -g server.s -o server.o && ld server.o -o exe
+sudo ./exe 
+```
+
+### Testing
+
+```
+nc localhost 80
+GET /anything HTTP/1.0
+POST /anything HTTP/1.0
+```

server.s

@@ -0,0 +1,314 @@
+# HTTP GET/POST concurrent webserver targeting Linux ABI for x86_64 processors
+# This code is public domain
+# Author: xamidev
+
+.intel_syntax noprefix
+.global _start
+
+.equ AF_INET, 2
+.equ SOCK_STREAM, 1
+.equ NULL, 0
+.equ O_RDONLY, 0
+.equ O_WRONLY, 1
+.equ O_CREAT, 64 
+
+.section .text
+
+_start:
+	# write(unsigned int fd, char* buf, size_t count)
+	mov rax, 1
+	mov rdi, 1
+	lea rsi, [rip + str_welcome]
+	mov rdx, 24
+	syscall
+
+	# socket(AF_INET, SOCK_STREAM, NULL)
+	mov rax, 41
+	mov rdi, AF_INET
+	mov rsi, SOCK_STREAM
+	mov rdx, NULL
+	syscall
+
+	# Save sockfd somewhere
+	mov r8, rax
+
+	# bind(int sockfd, struct sockaddr_in*, int addrlen)
+	mov rax, 49
+	mov rdi, r8
+	lea rsi, [rip + sockaddr_in]
+	mov rdx, 16
+	syscall
+
+	# listen(int sockfd, int backlog)
+	mov rax, 50
+	mov rdi, r8
+	mov rsi, 0 
+	syscall
+
+	.accept_incoming_connections:
+		# accept(int sockfd, struct sockaddr_in*, int* addrlen)
+		mov rax, 43
+		mov rdi, r8
+		mov rsi, NULL
+		mov rdx, NULL
+		syscall
+
+		# Save sockfd to close it later
+		mov r14, rax
+
+	# fork() -> new child process for incoming connection; PID in rax
+	mov rax, 57
+	syscall
+
+	# If return value is zero, we're in the child process: we can process the connection
+	# If return value is non-zero, we're in the parent process: we have to get back to accepting incoming connections
+
+	test rax, rax
+	jz .continue
+	jmp .close_actual_sockfd
+
+	.close_actual_sockfd:
+		# close(unsigned int fd)
+		mov rax, 3
+		mov rdi, r14
+		syscall
+		jmp .accept_incoming_connections
+
+	.continue:	
+		# close(unsigned int fd)
+		mov rax, 3
+		mov rdi, r8
+		syscall
+	
+		# read(unsigned int fd, char* buf, size_t count)
+		mov rax, 0
+		mov rdi, r14
+		lea rsi, [rip + request_buf]
+		mov rdx, 1024
+		syscall	
+
+		# Save read bytes (full request size)
+		mov r13, rax
+	
+		.parse_http_path:
+			# Parse the HTTP request
+			# When one space is found, extract bytes until next space
+			lea rsi, [rip + request_buf]
+			xor rcx, rcx
+			.find_start:
+				mov al, byte [rsi + rcx]
+				cmp al, ' '
+				je .path_start
+				inc rcx
+				jmp .find_start
+
+			.path_start:
+				inc rcx
+				lea rdi, [rsi+rcx]
+				xor rdx, rdx
+			.path_loop:
+				mov al, byte [rdi + rdx]
+				cmp al, ' '
+				je .path_done
+				mov byte [path_buf + rdx], al
+				inc rdx
+				jmp .path_loop
+			.path_done:
+
+		# Detect if request is GET or POST (first char is G: GET, else POST)
+		.parse_get_post:
+			lea rsi, [rip + request_buf]
+			mov al, byte [rsi]
+			cmp al, 69 # 'E' (2nd letter, rsi+1)
+			je .get_request
+			jmp .post_request
+
+		.post_request:
+			# open(const char* filename, int flags, int mode)
+			mov rax, 2
+			lea rdi, [path_buf+1]
+			mov rsi, O_WRONLY | O_CREAT # O_RDONLY for GET requests
+			mov rdx, 0x1FF # All permissions	
+			syscall
+
+			# Save fd
+			mov r10, rax
+
+			.parse_request_content:
+				# When we find \r\n\r\n we know that the content follows.
+				# request_buf already contains full request.
+				lea rsi, [rip + request_buf]
+				xor rcx, rcx
+				
+				.find_body:
+					mov al, byte [rsi+rcx]
+					cmp al, 13 # \r
+					jne .next
+					mov al, byte [rsi+rcx+1]
+					cmp al, 10 # \n
+					jne .next
+					mov al, byte [rsi+rcx+2]
+					cmp al, 13
+					jne .next
+					mov al, byte[rsi+rcx+3]
+					cmp al, 10
+					jne .next
+
+					add rcx, 4
+					jmp .body_found	
+				
+				.next:
+					# Threshold to avoid infinite looping if request is malformed
+					inc rcx
+					cmp rcx, 512
+					jl .find_body
+
+					jmp .error_exit
+
+				.body_found:
+					lea rdi, [rsi+rcx]
+					lea rsi, [rip+request_content_buf]
+					mov rbx, r13
+					sub rbx, rcx
+					mov r13, rbx
+
+					# Byte amount of request content is now in r13			
+					# Now we copy this to a buffer
+					xor rcx, rcx
+
+					.content_copy_loop:
+						cmp rcx, r13
+						jge .done_copy
+
+						mov al, byte [rdi+rcx]
+						mov byte [rsi+rcx], al
+						inc rcx
+						jmp .content_copy_loop
+					.done_copy:
+					dec r13	
+					# Byte length in r13 (decrement cause of null-byte)
+					# Content in request_content_buf				
+
+			# Here, as we have a POST request, we will have to write to filename instead of reading from it.
+
+			# write(unsigned int fd, const char* buf, size_t count)
+			mov rax, 1
+			mov rdi, r10
+			lea rsi, [rip + request_content_buf+1] # ADDRESS OF REQUEST CONTENT BUFFER		
+			mov rdx, r13 # AMOUNT OF BYTES IN REQUEST CONTENT		
+			syscall
+
+			# Save read bytes
+			mov r15, rax
+
+			# close(unsigned int fd)
+			mov rax, 3
+			mov rdi, r10
+			syscall
+
+			# We simply return a 200 OK here
+
+			# write(unsigned int fd, const char* buf, size_t count)
+			mov rax, 1
+			mov rdi, r14
+			lea rsi, [rip + response]
+			mov rdx, 19
+			syscall
+
+			# close(unsigned int fd)
+			mov rax, 3
+			mov rdi, r14
+			syscall	
+			
+			jmp .normal_exit
+
+		.get_request:
+			# open(const char* filename, int flags, int mode)
+			mov rax, 2
+			lea rdi, [path_buf+1]
+			mov rsi, O_RDONLY
+			mov rdx, NULL # who cares?
+			syscall
+
+			# Save fd
+			mov r10, rax
+
+			# read(unsigned int fd, char* buf, size_t count)
+			mov rax, 0
+			mov rdi, r10
+			lea rsi, [rip + file_buf]
+			mov rdx, 1024
+			syscall
+
+			# Save read bytes
+			mov r15, rax
+	
+			# close(unsigned int fd)
+			mov rax, 3
+			mov rdi, r10
+			syscall
+
+			# write(unsigned int fd, const char* buf, size_t count)
+			mov rax, 1
+			mov rdi, r14
+			lea rsi, [rip + response]
+			mov rdx, 19
+			syscall	
+
+			# write(unsigned int fd, const char* buf, size_t count)
+			mov rax, 1
+			mov rdi, r14
+			lea rsi, [rip + file_buf]
+			mov rdx, r15
+			syscall
+			
+			# close(unsigned int fd)
+			mov rax, 3
+			mov rdi, r14
+			syscall	
+
+		.normal_exit:
+			# exit(0)
+			mov rax, 60
+			mov rdi, 0
+			syscall
+
+		.error_exit:
+			mov rax, 60
+			mov rdi, -1
+			syscall
+
+.section .data
+
+response:
+	.asciz "HTTP/1.0 200 OK\r\n\r\n"
+
+str_welcome:
+	.asciz "Starting HTTP server...\n"
+
+# Total size: 16 bytes
+sockaddr_in:
+	.word AF_INET
+	# Port 80 = 0x0050 (unsigned short, 2 bytes)
+	# Big endian: bytes are in reverse order
+	.word 0x5000
+	# 32-bits of zeroes: 0.0.0.0
+	.int 0x00000000
+	.zero 8
+
+.section .bss
+
+path_buf:
+	.zero 64
+
+request_buf:
+	.zero 1024
+
+file_buf:
+	.zero 1024
+
+stat_buf:
+	.zero 1024
+
+request_content_buf:
+	.zero 1024