1 files changed, 112 insertions, 0 deletions
diff --git a/src/precheck.c b/src/precheck.c
new file mode 100644
index 0000000..a9fce35
--- /dev/null
+++ b/src/precheck.c
@@ -0,0 +1,112 @@
+//
+// Created by Anshul Gupta on 4/7/25.
+//
+
+#include "precheck.h"
+
+#include <stdio.h>
+#include <sys/errno.h>
+#include <sys/stat.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#ifdef __linux__
+#include <sys/capability.h>
+#endif
+
+/**
+ * Check if git is installed and available in the PATH.
+ * @return 1 if git is available, 0 if not.
+ */
+static int has_git(void)
+{
+	pid_t pid = fork();
+	if (pid < 0) {
+		perror("fork");
+		return 0;
+	}
+
+	if (pid == 0) {
+		// Child process
+		char *args[] = {"git", "--version", NULL};
+		execvp("git", args);
+		_exit(127); // execvp only returns on error
+	}
+
+	// Parent process
+	int status;
+	pid_t result;
+	do {
+		result = waitpid(pid, &status, 0);
+	} while (result == -1 && errno == EINTR);
+	if (result == -1) {
+		perror("waitpid");
+		return 0;
+	}
+
+	// Check exit status
+	if (WIFEXITED(status) && WEXITSTATUS(status) == 0) {
+		return 1; // git is available
+	}
+
+	fprintf(stderr, "Error: git is not installed or not found in PATH\n");
+	return 0; // git is not available
+}
+
+/**
+ * Check if we have CAP_CHOWN capability or if we are root.
+ * @return 1 if we have chown capability, 0 if not.
+ */
+static int has_chown(void)
+{
+#ifdef __linux__
+	cap_t caps = cap_get_proc();
+	if (caps == NULL) {
+		perror("cap_get_proc");
+		return 0;
+	}
+
+	cap_flag_value_t cap_value;
+	if (cap_get_flag(caps, CAP_CHOWN, CAP_EFFECTIVE, &cap_value) == -1) {
+		perror("cap_get_flag");
+		cap_free(caps);
+		return 0;
+	}
+	cap_free(caps);
+
+	if (cap_value == CAP_SET)
+		return 1; // We have CAP_CHOWN capability
+	fprintf(stderr, "Error: CAP_CHOWN capability is not set\n");
+	return 0; // We don't have CAP_CHOWN capability
+#else
+	if (geteuid() == 0)
+		return 1;
+	fprintf(stderr, "Error: not running as root\n");
+	return 0;
+#endif
+}
+
+/**
+ * Check if the git base directory exists.
+ * @param path Path to the directory to check
+ * @return 1 if the directory exists, 0 if not.
+ */
+static int git_base_exists(const char *path)
+{
+	struct stat st;
+	if (stat(path, &st) == 0 && S_ISDIR(st.st_mode)) {
+		return 1;
+	}
+	fprintf(stderr, "Error: git base directory does not exist: %s\n", path);
+	return 0;
+}
+
+int precheck_self(const struct config *cfg)
+{
+	if (!has_git())
+		return -1;
+	if (!has_chown())
+		return -1;
+	if (!git_base_exists(cfg->git_base))
+		return -1;
+	return 0;
+}