Initial commit

5 files changed, 339 insertions, 0 deletions

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..17ed007
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,13 @@
+.idea/
+cmake-build-*/
+CMakeLists.txt.user
+CMakeCache.txt
+CMakeFiles
+CMakeScripts
+Testing
+Makefile
+cmake_install.cmake
+install_manifest.txt
+compile_commands.json
+CTestTestfile.cmake
+_deps
diff --git a/CMakeLists.txt b/CMakeLists.txt
new file mode 100644
index 0000000..18a7186
--- /dev/null
+++ b/CMakeLists.txt
@@ -0,0 +1,6 @@
+cmake_minimum_required(VERSION 2.8)
+project(idcmp C)
+
+set(CMAKE_C_STANDARD 99)
+
+add_executable(idcmp main.c)
diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..7f0691d
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,29 @@
+BSD 3-Clause License
+
+Copyright (c) 2020, Joseph Hunkeler
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+1. Redistributions of source code must retain the above copyright notice, this
+   list of conditions and the following disclaimer.
+
+2. Redistributions in binary form must reproduce the above copyright notice,
+   this list of conditions and the following disclaimer in the documentation
+   and/or other materials provided with the distribution.
+
+3. Neither the name of the copyright holder nor the names of its
+   contributors may be used to endorse or promote products derived from
+   this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..1773bba
--- /dev/null
+++ b/README.md
@@ -0,0 +1 @@
+# idcmp
diff --git a/main.c b/main.c
new file mode 100644
index 0000000..b86de60
--- /dev/null
+++ b/main.c
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+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <grp.h>
+#include <pwd.h>
+#include <limits.h>
+#include <unistd.h>
+
+#if defined(__APPLE__)
+    // Force Darwin to emit more than 32 damn groups
+    #undef NGROUPS_MAX
+    #define NGROUPS_MAX 0x10000
+#endif
+
+struct Groups {
+    gid_t *gids;
+    int ngids;
+    struct group **group;
+};
+
+struct User {
+    struct passwd *pw;
+    struct Groups *gr;
+};
+
+struct User *user_init() {
+    struct User *result;
+
+    result = malloc(sizeof(*result));
+    result->pw = malloc(sizeof(*result->pw));
+    result->gr = malloc(sizeof(*result->gr));
+    result->gr->ngids = NGROUPS_MAX;
+    result->gr->gids = malloc(NGROUPS_MAX * sizeof(*result->gr->gids));
+    result->gr->group = calloc(result->gr->ngids, sizeof(**result->gr->group));
+    return result;
+}
+
+struct User *get_account_info(char *user) {
+    struct passwd *pw;
+    struct group *gr;
+    struct User *result;
+
+    if ((pw = getpwnam(user)) == NULL) {
+        return NULL;
+    }
+
+    // getpwnam returns static storage, so copy contents.
+    result = user_init();
+    result->pw->pw_name = strdup(pw->pw_name);
+    result->pw->pw_gid = pw->pw_gid;
+    result->pw->pw_dir = strdup(pw->pw_dir);
+    result->pw->pw_gecos = strdup(pw->pw_gecos);
+    result->pw->pw_shell = strdup(pw->pw_shell);
+    result->pw->pw_uid = pw->pw_uid;
+    result->pw->pw_passwd = strdup(pw->pw_passwd);
+
+    // populate gid list
+    if (getgrouplist(result->pw->pw_name, result->pw->pw_gid, result->gr->gids, &result->gr->ngids) == -1) {
+        perror("oh no");
+        exit(EXIT_FAILURE);
+    }
+
+    // getgrgid returns static storage, so copy contents.
+    for (size_t i = 0; i < result->gr->ngids; i++) {
+        result->gr->group[i] = calloc(1, sizeof(*result->gr->group[i]));
+        gr = getgrgid(result->gr->gids[i]);
+        if (!gr) {
+            fprintf(stderr, "Failed to read group information for GID: %d\n", result->gr->gids[i]);
+            result->gr->group[i]->gr_name = strdup("(no name)");
+            result->gr->group[i]->gr_gid = result->gr->gids[i];
+            result->gr->group[i]->gr_mem = NULL;
+            result->gr->group[i]->gr_passwd = strdup("");
+            continue;
+        }
+        result->gr->group[i]->gr_name = strdup(gr->gr_name);
+        result->gr->group[i]->gr_gid = gr->gr_gid;
+
+        size_t j = 0;
+        for (j = 0; gr->gr_mem[j] != NULL; j++);
+        result->gr->group[i]->gr_mem = calloc(j + 1, sizeof(*result->gr->group[i]->gr_mem));
+
+        for (j = 0; gr->gr_mem[j] != NULL; j++) {
+            result->gr->group[i]->gr_mem[j] = strdup(gr->gr_mem[j]);
+        }
+
+        result->gr->group[i]->gr_passwd = strdup(gr->gr_passwd);
+    }
+
+    return result;
+}
+
+void free_account_info(struct User *user) {
+    free(user->pw->pw_name);
+    free(user->pw->pw_shell);
+    free(user->pw->pw_gecos);
+    free(user->pw->pw_dir);
+    free(user->pw->pw_passwd);
+    free(user->pw);
+
+    for (size_t i = 0; i < user->gr->ngids; i++) {
+        for (size_t j = 0; user->gr->group[i]->gr_mem != NULL && user->gr->group[i]->gr_mem[j] != NULL; j++) {
+            free(user->gr->group[i]->gr_mem[j]);
+        }
+        free(user->gr->group[i]->gr_mem);
+        free(user->gr->group[i]->gr_passwd);
+        free(user->gr->group[i]->gr_name);
+        free(user->gr->group[i]);
+    }
+    free(user->gr->group);
+    free(user->gr->gids);
+    free(user->gr);
+    free(user);
+}
+
+int has_group(struct User *user, char *name) {
+    int found;
+
+    found = 0;
+    for (size_t i = 0; i < user->gr->ngids; i++) {
+        if (user->gr->group[i] == NULL) {
+            continue;
+        }
+        if (strcmp(user->gr->group[i]->gr_name, name) == 0) {
+            found = 1;
+            break;
+        }
+    }
+    return found;
+}
+
+int group_compare(struct User *a, struct User *b, char *name) {
+    int b_contains_a, a_contains_b;
+
+    a_contains_b = has_group(b, name);
+    b_contains_a = has_group(a, name);
+
+    if(a_contains_b < b_contains_a) {
+        return -1;
+    } else if (a_contains_b > b_contains_a) {
+        return 1;
+    }
+    return 0;
+}
+
+static int group_sort_name(const void *a, const void *b) {
+    struct group *aa = (*(struct group **) a);
+    struct group *bb = (*(struct group **) b);
+
+    if (strcmp(aa->gr_name, bb->gr_name) < 0) {
+        return -1;
+    } else if (strcmp(aa->gr_name, bb->gr_name) > 0) {
+        return 1;
+    }
+    return 0;
+}
+
+static int group_sort_id(const void *a, const void *b) {
+    struct group *aa = (*(struct group **) a);
+    struct group *bb = (*(struct group **) b);
+
+    if (aa->gr_gid < bb->gr_gid) {
+        return -1;
+    } else if (aa->gr_gid > bb->gr_gid) {
+        return 1;
+    }
+    return 0;
+}
+
+/**
+ * Return the length of the longest string in an array
+ */
+size_t strmax(char **arr) {
+    size_t result;
+
+    result = 0;
+    for (int i = 1; arr[i] != NULL; i++) {
+        if (strlen(arr[i]) > strlen(arr[result])) {
+            result = i;
+        }
+    }
+    return strlen(arr[result]);
+}
+
+
+typedef int (*compar)(const void *, const void *);
+
+int main(int argc, char *argv[]) {
+    struct User *user_a, *user_b;
+    int rec;
+    int ngroup_all;
+    struct group **group_all;
+    char **group_names;
+    compar fn_sort = &group_sort_id;
+
+    if (argc < 3) {
+        fprintf(stderr, "usage: %s [-n] {user_a} {user_b}\n", argv[0]);
+        exit(EXIT_FAILURE);
+    }
+
+    int arg;
+    size_t positional;
+    char *users[2];
+    for (arg = 1, positional = 0; arg < argc; arg++) {
+        if (strcmp(argv[arg], "-n") == 0) {
+            fn_sort = &group_sort_name;
+            continue;
+        }
+        if (positional > 1) {
+            break;
+        }
+        users[positional] = argv[arg];
+        positional++;
+    }
+
+    if ((user_a = get_account_info(users[0])) == NULL) {
+        fprintf(stderr, "Invalid user: '%s'\n", argv[1]);
+        exit(EXIT_FAILURE);
+    }
+
+    if ((user_b = get_account_info(users[1])) == NULL) {
+        fprintf(stderr, "Invalid user: '%s'\n", argv[2]);
+        exit(EXIT_FAILURE);
+    }
+
+    ngroup_all = user_a->gr->ngids + user_b->gr->ngids;
+    group_all = calloc(ngroup_all, sizeof(struct group *));
+    group_names = calloc(ngroup_all, sizeof(char *));
+
+    // Merge all group into a single list
+    rec = 0;
+    for (rec = 0; rec < user_a->gr->ngids; rec++) {
+        group_all[rec] = user_a->gr->group[rec];
+    }
+    for (int i = 0; i < user_b->gr->ngids; i++) {
+        if (has_group(user_a, user_b->gr->group[i]->gr_name)) {
+            continue;
+        }
+        group_all[rec] = user_b->gr->group[i];
+        rec++;
+    }
+
+    qsort(group_all, rec, sizeof(struct group *), fn_sort);
+
+    // Extract all group names from both users
+    for (size_t i = 0; group_all[i] != NULL; i++) {
+        group_names[i] = group_all[i]->gr_name;
+    }
+
+    // Construct dynamic width output header
+    int maxfmt = 255;
+    char *fmthdr = malloc(maxfmt);
+    char *fmt = malloc(maxfmt);
+    char *hdr[] = {
+            "GID NAME", "GID", "COMMON TO", NULL
+    };
+    size_t longest_group = strmax(group_names);
+
+    // Generate column titles
+    sprintf(fmthdr, "%%-%zus   %%-5s   %%s\n", longest_group);
+    printf(fmthdr, hdr[0], hdr[1], hdr[2]);
+
+    // Display records
+    sprintf(fmt, "%%-%zus | %%-5d | ", longest_group);
+    for (size_t i = 0; i < rec; i++) {
+        int contains;
+
+        printf(fmt, group_all[i]->gr_name, group_all[i]->gr_gid);
+
+        contains = group_compare(user_a, user_b, group_all[i]->gr_name);
+        if (contains < 0) {
+            puts(user_a->pw->pw_name);
+        } else if (contains > 0){
+            puts(user_b->pw->pw_name);
+        } else {
+            puts("both");
+        }
+    }
+
+    free(fmthdr);
+    free(fmt);
+    free_account_info(user_a);
+    free_account_info(user_b);
+    free(group_names);
+    for (size_t i = 0; i < ngroup_all; i++) {
+        group_all[i] = NULL;
+        free(group_all[i]);
+    }
+    free(group_all);
+    return 0;
+}