1 files changed, 362 insertions, 0 deletions
diff --git a/src/git.c b/src/git.c
new file mode 100644
index 0000000..6720e54
--- /dev/null
+++ b/src/git.c
@@ -0,0 +1,362 @@
+//
+// Created by Anshul Gupta on 4/6/25.
+//
+
+#include "git.h"
+
+#include <errno.h>
+#include <grp.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/fcntl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+extern char **environ;
+
+/**
+ * Constructs the full path to the git repository based on the base path, owner,
+ * and name. If the name is NULL, it constructs the path to the owner's
+ * directory.
+ * @param base Base path for the git repository
+ * @param owner Owner of the repository
+ * @param name Name of the repository
+ * @return A string containing the full path to the git repository or owner's
+ * directory.
+ */
+static char *get_git_path(const char *base, const char *owner, const char *name)
+{
+	if (!base || !owner)
+		return NULL;
+
+	const char *format = name ? "%s/%s/%s.git" : "%s/%s";
+
+	// Calculate the length of the string
+	const int len = snprintf(NULL, 0, format, base, owner, name);
+	if (len < 0)
+		return NULL;
+
+	// Allocate memory for the string
+	char *path = malloc(len + 1);
+	if (!path)
+		return NULL;
+
+	// Format the string
+	if (snprintf(path, len + 1, format, base, owner, name) < 0) {
+		free(path);
+		return NULL;
+	}
+	return path;
+}
+
+/**
+ * Adds authentication information to the HTTPS URL for git.
+ * @param url The HTTPS URL to modify
+ * @param user The username for authentication
+ * @param token The token for authentication
+ * @return A new string containing the modified URL with authentication
+ * information
+ */
+static char *add_url_auth(const char *url, const char *user, const char *token)
+{
+	const char *https_prefix = "https://";
+	const size_t prefix_len = strlen(https_prefix);
+	size_t new_len;
+	char *new_url;
+
+	if (!url || !user || !token)
+		return NULL;
+
+	// Find the position of "https://"
+	if (strncmp(url, https_prefix, prefix_len) != 0) {
+		fprintf(stderr, "Error: URL does not start with https://\n");
+		return NULL;
+	}
+
+	// Calculate the length of the new URL
+	new_len = strlen(url) + strlen(user) + strlen(token) +
+		  2; // 2 for "@" and ":"
+
+	// Allocate memory for the new URL
+	if (!((new_url = malloc(new_len + 1)))) {
+		perror("malloc");
+		return NULL;
+	}
+
+	// Construct the new URL
+	snprintf(new_url, new_len + 1, "https://%s:%s@%s", user, token,
+		 url + prefix_len);
+
+	return new_url;
+}
+
+/**
+ * Drops the permissions of the current process to the specified user and group.
+ * @param ctx Repository context
+ * @return 0 on success, -1 on error
+ */
+static int drop_perms(const struct repo_ctx *ctx)
+{
+	// Drop supplementary groups
+	if (setgroups(0, NULL) != 0) {
+		perror("setgroups");
+		return -1;
+	}
+	// Set gid
+	if (setgid(ctx->cfg->git_group) == -1) {
+		perror("setgid");
+		return -1;
+	}
+	// Set uid
+	if (setuid(ctx->cfg->git_owner) == -1) {
+		perror("setuid");
+		return -1;
+	}
+	return 0;
+}
+
+/**
+ * Checks if the git repository at the specified path is a mirror.
+ * @param path Path to the git repository
+ * @param ctx Repository context
+ * @return 1 if the repository is a mirror, 0 if not
+ */
+static int contains_mirror(const char *path, const struct repo_ctx *ctx)
+{
+	const pid_t pid = fork();
+	if (pid < 0) {
+		perror("fork");
+		return 0;
+	}
+
+	if (pid == 0) {
+		// Child process
+
+		// Redirect stdout to /dev/null
+		const int devnull = open("/dev/null", O_WRONLY);
+		if (devnull == -1) {
+			perror("open");
+			_exit(127);
+		}
+		if (dup2(devnull, STDOUT_FILENO) == -1) {
+			perror("dup2");
+			close(devnull);
+			_exit(127);
+		}
+		close(devnull);
+
+		// Change uid and gid to the user specified in the config
+		if (drop_perms(ctx))
+			_exit(127);
+		char *args[] = {
+				"git",	  "--git-dir", (char *) path,
+				"config", "--get",     "remote.origin.mirror",
+				NULL,
+		};
+		execvp("git", args);
+		perror("execvp");
+		_exit(127); // execvp only returns on error
+	}
+
+	int status;
+	pid_t result;
+	while ((result = waitpid(pid, &status, 0)) == -1 && errno == EINTR) {
+	}
+	if (result == -1) {
+		perror("waitpid");
+		return 0;
+	}
+	if (WIFEXITED(status)) {
+		// Check if the exit status is 0 (success)
+		if (WEXITSTATUS(status) == 0)
+			return 1; // Repo exists
+		if (WEXITSTATUS(status) == 1)
+			return 0; // Repo does not exist
+	}
+	fprintf(stderr, "Error: git command failed with status %d\n",
+		WEXITSTATUS(status));
+	return 0; // Error occurred
+}
+
+/**
+ * Creates a mirror of the git repository at the specified path.
+ * @param path Full path to the git repository
+ * @param ctx Context containing the repository information
+ * @return 0 on success, -1 on error
+ */
+static int create_mirror(const char *path, const struct repo_ctx *ctx)
+{
+	const pid_t pid = fork();
+	if (pid < 0) {
+		perror("fork");
+		return -1;
+	}
+
+	if (pid == 0) {
+		// Child process
+		// Convert the URL to a format that git can use
+		char *url = add_url_auth(ctx->url, ctx->username,
+					 ctx->cfg->token);
+
+		// Change uid and gid to the user specified in the config
+		if (drop_perms(ctx))
+			_exit(127);
+
+		char *args[] = {
+				"git", "clone",	      "--mirror",
+				url,   (char *) path, NULL,
+		};
+		execvp("git", args);
+		perror("execvp");
+		_exit(127); // execvp only returns on error
+	}
+
+	int status;
+	pid_t result;
+	while ((result = waitpid(pid, &status, 0)) == -1 && errno == EINTR) {
+	}
+	if (result == -1) {
+		perror("waitpid");
+		return -1;
+	}
+
+	if (WIFEXITED(status) && WEXITSTATUS(status) == 0)
+		return 0; // Success
+	fprintf(stderr, "Error: git clone failed with status %d\n",
+		WEXITSTATUS(status));
+	return -1; // Error occurred
+}
+
+/**
+ * Creates the directory structure for the git repository.
+ * @param ctx Repository context
+ * @return 0 on success, -1 on error
+ */
+static int create_git_path(const struct repo_ctx *ctx)
+{
+	// Create owner directory if it doesn't exist
+	char *owner_path =
+			get_git_path(ctx->cfg->git_base, ctx->cfg->owner, NULL);
+	if (!owner_path)
+		return -1;
+	if (mkdir(owner_path, 0755) == -1 && errno != EEXIST) {
+		perror("mkdir");
+		free(owner_path);
+		return -1;
+	}
+	// Set the permissions of the owner directory to 0775
+	if (chmod(owner_path, 0775) == -1) {
+		perror("chmod");
+		free(owner_path);
+		return -1;
+	}
+	free(owner_path);
+
+	// Create repo directory if it doesn't exist
+	char *repo_path = get_git_path(ctx->cfg->git_base, ctx->cfg->owner,
+				       ctx->name);
+	if (!repo_path)
+		return -1;
+	if (mkdir(repo_path, 0755) == -1 && errno != EEXIST) {
+		perror("mkdir");
+		free(repo_path);
+		return -1;
+	}
+
+	// Chown the repo directory to the specified user and group
+	if (chown(repo_path, ctx->cfg->git_owner, ctx->cfg->git_group) == -1) {
+		perror("chown");
+		free(repo_path);
+		return -1;
+	}
+
+	free(repo_path);
+	return 0;
+}
+
+/**
+ * Updates the git repository at the specified path from the remote.
+ * @param path Full path to the git repository
+ * @param ctx Context containing the repository information
+ * @return 0 on success, -1 on error
+ */
+static int update_mirror(const char *path, const struct repo_ctx *ctx)
+{
+	const pid_t pid = fork();
+	if (pid < 0) {
+		perror("fork");
+		return -1;
+	}
+
+	if (pid == 0) {
+		// Child process
+		// Change uid and gid to the user specified in the config
+		if (drop_perms(ctx))
+			_exit(127);
+
+		char *args[] = {
+				"git",	  "--git-dir", (char *) path, "remote",
+				"update", "--prune",   NULL,
+		};
+		execvp("git", args);
+		perror("execvp");
+		_exit(127); // execvp only returns on error
+	}
+
+	int status;
+	pid_t result;
+	while ((result = waitpid(pid, &status, 0)) == -1 && errno == EINTR) {
+	}
+	if (result == -1) {
+		perror("waitpid");
+		return -1;
+	}
+
+	if (WIFEXITED(status) && WEXITSTATUS(status) == 0)
+		return 0; // Success
+	fprintf(stderr, "Error: git remote update failed with status %d\n",
+		WEXITSTATUS(status));
+	return -1; // Error occurred
+}
+
+int git_mirror_repo(const struct repo_ctx *ctx)
+{
+	char *path = get_git_path(ctx->cfg->git_base, ctx->cfg->owner,
+				  ctx->name);
+	if (!path) {
+		perror("get_git_path");
+		return -1;
+	}
+
+	// Check whether repo exists
+	if (contains_mirror(path, ctx)) {
+		// Repo exists, so we can just update it
+		printf("Repo already exists, updating...\n");
+		if (update_mirror(path, ctx) == -1) {
+			perror("update_mirror");
+			free(path);
+			return -1;
+		}
+		free(path);
+		return 0;
+	}
+
+	// Repo does not exist, so we need to clone it
+	printf("Repo does not exist, cloning...\n");
+	if (create_git_path(ctx) == -1) {
+		perror("create_git_path");
+		free(path);
+		return -1;
+	}
+	if (create_mirror(path, ctx) == -1) {
+		perror("create_mirror");
+		free(path);
+		return -1;
+	}
+
+	free(path);
+	return 0;
+}