LibC: Implement dirname() and basename()

And write section 3 man pages for them.

Base/usr/share/man/man3/basename.md

@@ -0,0 +1,53 @@
+## Name
+
+basename - extract file name from a path
+
+## Synopsis
+
+```**c++
+#include <libgen.h>
+
+char* basename(char* path);
+```
+
+## Description
+
+Given a file path, `basename()` returns that file's name. `basename()` works
+purely lexically, meaning it only manipulates the path as a string, and does
+not check if such a file actually exists.
+
+A call to `basename()` may reuse and modify the passed in `path` buffer. Do not
+expect it to have the same value after calling `basename()`.
+
+## Return value
+
+`basename()` returns the file name as a string. This string may be allocated
+in static memory, or it may point to some part of the original `path` buffer.
+Do not `free()` the returned string, and do not `free()` the original `path`
+buffer while using the returned string.
+
+## Examples
+
+```c++
+#include <AK/LogStream.h>
+#include <libgen.h>
+
+int main()
+{
+    char path1[] = "/home/anon/ReadMe.md";
+    dbg() << basename(path1); // should be "ReadMe.md"
+
+    char path2[] = "foo/bar/";
+    dbg() << basename(path2); // should be "bar"
+
+    char path3[] = "foo";
+    dbg() << basename(path3); // should be "foo"
+
+    char path4[] = "/";
+    dbg() << basename(path4); // should be "/"
+}
+```
+
+## See also
+
+* [`dirname`(3)](dirname.md)

Base/usr/share/man/man3/dirname.md

@@ -0,0 +1,54 @@
+## Name
+
+dirname - get a file's containing directory path
+
+## Synopsis
+
+```**c++
+#include <libgen.h>
+
+char* dirname(char* path);
+```
+
+## Description
+
+Given a file path, `dirname()` returns a path to the directory that contains the
+file. `dirname()` works purely lexically, meaning it only manipulates the path
+as a string, and does not check if such a file or its containing directory
+actually exist.
+
+A call to `dirname()` may reuse and modify the passed in `path` buffer. Do not
+expect it to have the same value after calling `dirname()`.
+
+## Return value
+
+`dirname()` returns the directory path as a string. This string may be allocated
+in static memory, or it may point to some part of the original `path` buffer.
+Do not `free()` the returned string, and do not `free()` the original `path`
+buffer while using the returned string.
+
+## Examples
+
+```c++
+#include <AK/LogStream.h>
+#include <libgen.h>
+
+int main()
+{
+    char path1[] = "/home/anon/ReadMe.md";
+    dbg() << dirname(path1); // should be "/home/anon"
+
+    char path2[] = "foo/bar/";
+    dbg() << dirname(path2); // should be "foo"
+
+    char path3[] = "foo";
+    dbg() << dirname(path3); // should be "."
+
+    char path4[] = "/";
+    dbg() << dirname(path4); // should be "/"
+}
+```
+
+## See also
+
+* [`basename`(3)](basename.md)

Libraries/LibC/Makefile

@@ -51,7 +51,8 @@ LIBC_OBJS = \
        arpa/inet.o \
        netdb.o \
        sched.o \
-       dlfcn.o
+       dlfcn.o \
+       libgen.o
 
 ASM_OBJS = setjmp.ao crti.ao crtn.ao
 

Libraries/LibC/libgen.cpp

@@ -0,0 +1,58 @@
+#include <AK/Assertions.h>
+#include <libgen.h>
+#include <string.h>
+
+static char dot[] = ".";
+static char slash[] = "/";
+
+char* dirname(char* path)
+{
+    if (path == nullptr)
+        return dot;
+
+    int len = strlen(path);
+    if (len == 0)
+        return dot;
+
+    while (len > 1 && path[len - 1] == '/') {
+        path[len - 1] = 0;
+        len--;
+    }
+
+    char* last_slash = strrchr(path, '/');
+    if (last_slash == nullptr)
+        return dot;
+
+    if (last_slash == path)
+        return slash;
+
+    *last_slash = 0;
+    return path;
+}
+
+char* basename(char* path)
+{
+    if (path == nullptr)
+        return dot;
+
+    int len = strlen(path);
+    if (len == 0)
+        return dot;
+
+    while (len > 1 && path[len - 1] == '/') {
+        path[len - 1] = 0;
+        len--;
+    }
+
+    char* last_slash = strrchr(path, '/');
+    if (last_slash == nullptr)
+        return path;
+
+    if (len == 1) {
+        ASSERT(last_slash == path);
+        ASSERT(path[0] == '/');
+        return slash;
+    }
+
+    return last_slash + 1;
+}

Libraries/LibC/libgen.h

@@ -0,0 +1,10 @@
+#pragma once
+
+#include <sys/cdefs.h>
+
+__BEGIN_DECLS
+
+char* dirname(char* path);
+char* basename(char* path);
+
+__END_DECLS