From 355dd6c32b775af09d9c4a2170b32cbc32de9d6b Mon Sep 17 00:00:00 2001
From: apio <blobs.trading@gmail.com>
Date: Thu, 23 Mar 2023 22:19:54 +0100
Subject: [PATCH] apps: Add sh

---
 apps/CMakeLists.txt |   2 +-
 apps/hello.c        |  12 ------
 apps/init.c         |  12 +++---
 apps/sh.c           | 100 ++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 108 insertions(+), 18 deletions(-)
 delete mode 100644 apps/hello.c
 create mode 100644 apps/sh.c

diff --git a/apps/CMakeLists.txt b/apps/CMakeLists.txt
index 748f3695..85315b27 100644
--- a/apps/CMakeLists.txt
+++ b/apps/CMakeLists.txt
@@ -7,4 +7,4 @@ function(luna_app SOURCE_FILE APP_NAME)
 endfunction()
 
 luna_app(init.c init)
-luna_app(hello.c hello)
+luna_app(sh.c sh)
diff --git a/apps/hello.c b/apps/hello.c
deleted file mode 100644
index dea0b7e9..00000000
--- a/apps/hello.c
+++ /dev/null
@@ -1,12 +0,0 @@
-#include <stdio.h>
-
-int main(int argc, char** argv)
-{
-    printf("Hello world! argc=%d, argv[0]=%s, argv[1]=%s, argv[2]=%s\n", argc, argv[0], argv[1], argv[2]);
-
-    char buf[1024];
-    char* rc = fgets(buf, sizeof(buf), stdin);
-    if (!rc) perror("fgets");
-
-    fputs(buf, stdout);
-}
diff --git a/apps/init.c b/apps/init.c
index fb1d9b67..982af948 100644
--- a/apps/init.c
+++ b/apps/init.c
@@ -36,14 +36,16 @@ int main()
     stdout = fopen("/dev/console", "w");
     stderr = fopen("/dev/console", "w");
 
-    printf("init is running as PID %d\n", getpid());
-
     pid_t ret = fork();
 
     if (ret == 0)
     {
-        char* argv[] = { "/bin/hello", "--help", NULL };
-        execv("/bin/hello", argv);
+        char* argv[] = { "/bin/sh", NULL };
+        execv(argv[0], argv);
+        perror("execv");
+        return 1;
     }
-    else { printf("my child is PID %d!\n", ret); }
+
+    while (1)
+        ;
 }
diff --git a/apps/sh.c b/apps/sh.c
new file mode 100644
index 00000000..bafb5477
--- /dev/null
+++ b/apps/sh.c
@@ -0,0 +1,100 @@
+#include <errno.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+static char** split_command_into_argv(const char* cmd)
+{
+    size_t argc = 1;
+    char* str = strdup(cmd);
+    char** arr = calloc(sizeof(char*), argc);
+
+    char* segment = strtok(str, " \n");
+    arr[argc - 1] = segment;
+    if (segment == NULL) return arr;
+
+    argc++;
+    arr = realloc(arr, sizeof(char*) * argc);
+
+    for (;;)
+    {
+        char* segment = strtok(NULL, " \n");
+        arr[argc - 1] = segment;
+
+        if (segment == NULL) break;
+
+        argc++;
+        arr = realloc(arr, sizeof(char*) * argc);
+    }
+
+    return arr;
+}
+
+static char* join_path(const char* str1, const char* str2)
+{
+    char* buf = malloc(strlen(str1) + strlen(str2) + 1);
+    strlcpy(buf, str1, strlen(str1) + 1);
+    strncat(buf, str2, strlen(str2));
+    return buf;
+}
+
+static int execute_in_path(const char* dir, char** argv)
+{
+    char* path = join_path(dir, argv[0]);
+    int err = errno;
+
+    int status = execv(path, argv);
+    free(path);
+
+    if (errno == ENOENT)
+    {
+        errno = err;
+        return 0;
+    }
+
+    return status;
+}
+
+static int sh_execvp(char** argv)
+{
+    if (strchr(argv[0], '/'))
+    {
+        // Relative paths do not need path resolution.
+        return execv(argv[0], argv);
+    }
+
+    if (execute_in_path("/bin/", argv) != 0) return -1;
+    if (execute_in_path("/sbin/", argv) != 0) return -1;
+    if (execute_in_path("/usr/bin/", argv) != 0) return -1;
+    if (execute_in_path("/usr/local/bin/", argv) != 0) return -1;
+
+    errno = ENOENT;
+    return -1;
+}
+
+int main()
+{
+    while (1)
+    {
+        fputs("sh$ ", stdout);
+
+        char command[4096];
+        fgets(command, sizeof(command), stdin);
+
+        pid_t child = fork();
+        if (child < 0) { perror("fork"); }
+
+        if (child == 0)
+        {
+            char** argv = split_command_into_argv(command);
+            sh_execvp(argv);
+            perror(argv[0]);
+            return 1;
+        }
+
+        // Don't have sched_yield() or waitpid() yet...
+        sleep(1);
+    }
+}