shell: implement functions to parse command lines into an (argc, argv) tuple

Makefile

@@ -37,6 +37,7 @@ obj-y += source/ftl/ftl.o
 obj-y += source/ftl/gc.o
 obj-y += source/ftl/map.o
 
+obj-y += source/shell/args.o
 obj-y += source/shell/cmd.o
 obj-y += source/shell/flash.o
 obj-y += source/shell/ftl.o

include/shell.h

@@ -1,5 +1,8 @@
 #pragma once
 
+size_t count_args(char *line);
+char **parse_args(char *line, size_t *argc);
+
 struct cmd {
 	const char *key;
 	void (* exec)(const char *line);

source/shell/args.c

@@ -0,0 +1,75 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <shell.h>
+
+size_t count_args(char *line)
+{
+	char *p = line;
+	size_t n = 0;
+
+	while (*p != '\0') {
+		p += strspn(p, " \n\r");
+
+		while (*p != '\0' && *p != ' ') {
+			if (*p++ != '\"')
+				continue;
+
+			while (*p != '\0' && *p != '\"')
+				++p;
+
+			if (*p == '\"')
+				++p;
+		}
+
+		++n;
+	}
+
+	return n;
+}
+
+char **parse_args(char *line, size_t *argc)
+{
+	char **argv;
+	char **arg;
+	char *p = line;
+	char *s;
+	size_t n;
+
+	if (!argc)
+		argc = &n;
+
+	*argc = count_args(line);
+
+	if (!(argv = malloc(*argc * sizeof(char *) + strlen(line) + 1)))
+		return NULL;
+
+	arg = argv;
+	s = (char *)argv + *argc * sizeof(char *);
+
+	while (*p != '\0') {
+		p += strspn(p, " \n\r");
+		*arg++ = s;
+
+		while (*p != '\0' && *p != ' ') {
+			if (*p != '\"') {
+				*s++ = *p++;
+				continue;
+			}
+
+			++p;
+
+			while (*p != '\0' && *p != '\"')
+				*s++ = *p++;
+
+			if (*p == '\"')
+				++p;
+		}
+
+		*s++ = '\0';
+	}
+
+	return argv;
+}
+