Add getgrent() family of functions.

Author: https://github.com/awesomekling
Commit: https://github.com/SerenityOS/serenity/commit/90bab5ea717

Base/etc/group

@@ -0,0 +1,3 @@
+root:x:0:
+wheel:x:1:andreas
+users:x:100:andreas

LibC/Makefile

@@ -20,6 +20,7 @@ LIBC_OBJS = \
        getopt.o \
        scanf.o \
        pwd.o \
+       grp.o \
        times.o \
        termcap.o \
        setjmp.o \

LibC/grp.cpp

@@ -0,0 +1,121 @@
+#include <grp.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sys/mman.h>
+#include <AK/String.h>
+
+extern "C" {
+
+#define GRDB_STR_MAX_LEN 256
+
+struct group_with_strings : public group {
+    char name_buffer[GRDB_STR_MAX_LEN];
+    char passwd_buffer[GRDB_STR_MAX_LEN];
+    char* members[32];
+    char members_buffer[32][32];
+};
+
+static FILE* __grdb_stream = nullptr;
+static unsigned __grdb_line_number = 0;
+static struct group_with_strings* __grdb_entry = nullptr;
+
+void setgrent()
+{
+    __grdb_line_number = 0;
+    if (__grdb_stream) {
+        rewind(__grdb_stream);
+    } else {
+        __grdb_stream = fopen("/etc/group", "r");
+        if (!__grdb_stream) {
+            perror("open /etc/group");
+        }
+        assert(__grdb_stream);
+        __grdb_entry = (struct group_with_strings*)mmap(nullptr, getpagesize());
+        set_mmap_name(__grdb_entry, getpagesize(), "setgrent");
+    }
+}
+
+void endgrent()
+{
+    __grdb_line_number = 0;
+    if (__grdb_stream) {
+        fclose(__grdb_stream);
+        __grdb_stream = nullptr;
+    }
+    if (__grdb_entry) {
+        munmap(__grdb_entry, getpagesize());
+        __grdb_entry = nullptr;
+    }
+}
+
+struct group* getgrgid(gid_t gid)
+{
+    setgrent();
+    while (auto* gr = getgrent()) {
+        if (gr->gr_gid == gid)
+            return gr;
+    }
+    return nullptr;
+}
+
+struct group* getgrname(const char* name)
+{
+    setgrent();
+    while (auto* gr = getgrent()) {
+        if (!strcmp(gr->gr_name, name))
+            return gr;
+    }
+    return nullptr;
+}
+
+struct group* getgrent()
+{
+    if (!__grdb_stream)
+        setgrent();
+
+    assert(__grdb_stream);
+    if (feof(__grdb_stream))
+        return nullptr;
+
+next_entry:
+    char buffer[1024];
+    ++__grdb_line_number;
+    char* s = fgets(buffer, sizeof(buffer), __grdb_stream);
+    if (!s)
+        return nullptr;
+    assert(__grdb_stream);
+    if (feof(__grdb_stream))
+        return nullptr;
+    String line(s);
+    auto parts = line.split(':');
+    if (parts.size() != 4) {
+        fprintf(stderr, "getgrent(): Malformed entry on line %u\n", __grdb_line_number);
+        goto next_entry;
+    }
+    auto& e_name = parts[0];
+    auto& e_passwd = parts[1];
+    auto& e_gid_string = parts[2];
+    auto& e_members_string = parts[3];
+    bool ok;
+    gid_t e_gid = e_gid_string.toUInt(ok);
+    if (!ok) {
+        fprintf(stderr, "getgrent(): Malformed GID on line %u\n", __grdb_line_number);
+        goto next_entry;
+    }
+    auto members = e_members_string.split(',');
+    __grdb_entry->gr_gid = e_gid;
+    __grdb_entry->gr_name = __grdb_entry->name_buffer;
+    __grdb_entry->gr_passwd = __grdb_entry->passwd_buffer;
+    for (size_t i = 0; i < parts.size(); ++i) {
+        __grdb_entry->members[i] = __grdb_entry->members_buffer[i];
+        strcpy(__grdb_entry->members_buffer[i], parts[i].characters());
+    }
+    __grdb_entry->members[parts.size()] = nullptr;
+    __grdb_entry->gr_mem = __grdb_entry->members;
+    strncpy(__grdb_entry->name_buffer, e_name.characters(), GRDB_STR_MAX_LEN);
+    strncpy(__grdb_entry->passwd_buffer, e_passwd.characters(), GRDB_STR_MAX_LEN);
+    return __grdb_entry;
+}
+
+}

LibC/grp.h

@@ -0,0 +1,21 @@
+#pragma once
+
+#include <sys/cdefs.h>
+#include <sys/types.h>
+
+__BEGIN_DECLS
+
+struct group {
+    char* gr_name;
+    char* gr_passwd;
+    gid_t gr_gid;
+    char** gr_mem;
+};
+
+struct group* getgrent();
+void setgrent();
+void endgrent();
+struct group* getgrnam(const char* name);
+struct group* getgrgid(gid_t);
+
+__END_DECLS

Userland/id.cpp

@@ -1,6 +1,7 @@
 #include <LibC/unistd.h>
 #include <LibC/stdio.h>
 #include <LibC/pwd.h>
+#include <LibC/grp.h>
 
 int main(int c, char** v)
 {
@@ -8,8 +9,9 @@ int main(int c, char** v)
     gid_t gid = getgid();
 
     struct passwd* pw = getpwuid(uid);
+    struct group* gr = getgrgid(gid);
 
-    printf("uid=%u(%s), gid=%u, pid=%u\n", uid, pw ? pw->pw_name : "n/a", gid, getpid());
+    printf("uid=%u(%s), gid=%u(%s)\n", uid, pw ? pw->pw_name : "n/a", gid, gr ? gr->gr_name : "n/a", getpid());
     return 0;
 }