echo then close connection

readline.s

@@ -0,0 +1,36 @@
+; Returns length in rax
+; Errors (in rax):
+; -1024 - line too long
+; other negative - error from read(2)
+; Arguments:
+; rdi - fd
+; rsi - buffer
+; rdx - max length
+readline:
+    push rdi
+    push rsi
+    push rdx
+    mov rax, SYS_READ
+    syscall
+    pop rdx
+    pop rsi
+    pop rdi
+    cmp rax, 0
+    jl return
+    mov r10, 0
+
+readline__scan:
+    cmp r10, rax
+    jge readline__overflow
+    mov r11b, [rsi + r10]
+    add r10, 1
+    cmp r11b, 0x0a  ; '\n'
+    jne readline__scan
+
+readline__return:
+    mov rax, r10
+    ret
+
+readline__overflow:
+    mov rax, -1024
+    ret