apps: Add cat

apps/Makefile

@@ -1,4 +1,4 @@
-APPS := init sym sh crash uname uptime hello ps ls args
+APPS := init sym sh crash uname uptime hello ps ls args cat
 
 APPS_DIR := $(LUNA_ROOT)/apps
 APPS_SRC := $(APPS_DIR)/src

apps/src/cat.c

@@ -0,0 +1,62 @@
+#define _GNU_SOURCE // for program_invocation_name
+#include <errno.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+
+void cat(FILE* stream)
+{
+    struct stat statbuf;
+    fstat(fileno(stream), &statbuf);
+    if (statbuf.st_mode == __VFS_DEVICE) // FIXME: Add S_ISDEV.
+    {
+        char buf[4096]; // FIXME: Do not limit ourselves to 4096 bytes. Devices which can't seek and are constant should
+                        // return EOF after the first read.
+        fgets(buf, 4096, stream);
+        if (ferror(stream))
+        {
+            perror(program_invocation_name);
+            exit(EXIT_FAILURE);
+        }
+        if (feof(stream)) return;
+        fputs(buf, stdout);
+        return;
+    }
+    char buf[BUFSIZ];
+    do {
+        fgets(buf, BUFSIZ, stream);
+        if (ferror(stream))
+        {
+            perror(program_invocation_name);
+            exit(EXIT_FAILURE);
+        }
+        fputs(buf, stdout);
+    } while (!feof(stream));
+}
+
+int main(int argc, char** argv)
+{
+    if (argc == 1) cat(stdin);
+    else
+    {
+        for (int i = 1; i < argc; i++)
+        {
+            if (strcmp(argv[i], "-") == 0) cat(stdin);
+            else if (strcmp(argv[i], "-n") == 0 || strcmp(argv[i], "--newline") == 0)
+                putchar('\n');
+            else
+            {
+                FILE* stream = fopen(argv[i], "r");
+                if (!stream)
+                {
+                    perror(program_invocation_name);
+                    return EXIT_FAILURE;
+                }
+                cat(stream);
+                fclose(stream);
+            }
+        }
+    }
+}