Source / Include Folder (#88)

Moved Source Files Into `src` Folder

1 files changed, 318 insertions, 0 deletions

diff --git a/src/xspawn.c b/src/xspawn.c
new file mode 100644
index 0000000..93c270a
--- /dev/null
+++ b/src/xspawn.c
@@ -0,0 +1,318 @@
+/****************************************************************************
+ * bfs                                                                      *
+ * Copyright (C) 2018-2022 Tavian Barnes <tavianator@tavianator.com>        *
+ *                                                                          *
+ * Permission to use, copy, modify, and/or distribute this software for any *
+ * purpose with or without fee is hereby granted.                           *
+ *                                                                          *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES *
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF         *
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR  *
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES   *
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN    *
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF  *
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.           *
+ ****************************************************************************/
+
+#include "xspawn.h"
+#include "util.h"
+#include <errno.h>
+#include <fcntl.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+/**
+ * Types of spawn actions.
+ */
+enum bfs_spawn_op {
+	BFS_SPAWN_CLOSE,
+	BFS_SPAWN_DUP2,
+	BFS_SPAWN_FCHDIR,
+	BFS_SPAWN_SETRLIMIT,
+};
+
+/**
+ * A spawn action.
+ */
+struct bfs_spawn_action {
+	struct bfs_spawn_action *next;
+
+	enum bfs_spawn_op op;
+	int in_fd;
+	int out_fd;
+	int resource;
+	struct rlimit rlimit;
+};
+
+int bfs_spawn_init(struct bfs_spawn *ctx) {
+	ctx->flags = 0;
+	ctx->actions = NULL;
+	ctx->tail = &ctx->actions;
+	return 0;
+}
+
+int bfs_spawn_destroy(struct bfs_spawn *ctx) {
+	struct bfs_spawn_action *action = ctx->actions;
+	while (action) {
+		struct bfs_spawn_action *next = action->next;
+		free(action);
+		action = next;
+	}
+	return 0;
+}
+
+int bfs_spawn_setflags(struct bfs_spawn *ctx, enum bfs_spawn_flags flags) {
+	ctx->flags = flags;
+	return 0;
+}
+
+/** Add a spawn action to the chain. */
+static struct bfs_spawn_action *bfs_spawn_add(struct bfs_spawn *ctx, enum bfs_spawn_op op) {
+	struct bfs_spawn_action *action = malloc(sizeof(*action));
+	if (action) {
+		action->next = NULL;
+		action->op = op;
+		action->in_fd = -1;
+		action->out_fd = -1;
+
+		*ctx->tail = action;
+		ctx->tail = &action->next;
+	}
+	return action;
+}
+
+int bfs_spawn_addclose(struct bfs_spawn *ctx, int fd) {
+	if (fd < 0) {
+		errno = EBADF;
+		return -1;
+	}
+
+	struct bfs_spawn_action *action = bfs_spawn_add(ctx, BFS_SPAWN_CLOSE);
+	if (action) {
+		action->out_fd = fd;
+		return 0;
+	} else {
+		return -1;
+	}
+}
+
+int bfs_spawn_adddup2(struct bfs_spawn *ctx, int oldfd, int newfd) {
+	if (oldfd < 0 || newfd < 0) {
+		errno = EBADF;
+		return -1;
+	}
+
+	struct bfs_spawn_action *action = bfs_spawn_add(ctx, BFS_SPAWN_DUP2);
+	if (action) {
+		action->in_fd = oldfd;
+		action->out_fd = newfd;
+		return 0;
+	} else {
+		return -1;
+	}
+}
+
+int bfs_spawn_addfchdir(struct bfs_spawn *ctx, int fd) {
+	if (fd < 0) {
+		errno = EBADF;
+		return -1;
+	}
+
+	struct bfs_spawn_action *action = bfs_spawn_add(ctx, BFS_SPAWN_FCHDIR);
+	if (action) {
+		action->in_fd = fd;
+		return 0;
+	} else {
+		return -1;
+	}
+}
+
+int bfs_spawn_addsetrlimit(struct bfs_spawn *ctx, int resource, const struct rlimit *rl) {
+	struct bfs_spawn_action *action = bfs_spawn_add(ctx, BFS_SPAWN_SETRLIMIT);
+	if (action) {
+		action->resource = resource;
+		action->rlimit = *rl;
+		return 0;
+	} else {
+		return -1;
+	}
+}
+
+/** Actually exec() the new process. */
+static void bfs_spawn_exec(const char *exe, const struct bfs_spawn *ctx, char **argv, char **envp, int pipefd[2]) {
+	int error;
+	const struct bfs_spawn_action *actions = ctx ? ctx->actions : NULL;
+
+	xclose(pipefd[0]);
+
+	for (const struct bfs_spawn_action *action = actions; action; action = action->next) {
+		// Move the error-reporting pipe out of the way if necessary...
+		if (action->out_fd == pipefd[1]) {
+			int fd = dup_cloexec(pipefd[1]);
+			if (fd < 0) {
+				goto fail;
+			}
+			xclose(pipefd[1]);
+			pipefd[1] = fd;
+		}
+
+		// ... and pretend the pipe doesn't exist
+		if (action->in_fd == pipefd[1]) {
+			errno = EBADF;
+			goto fail;
+		}
+
+		switch (action->op) {
+		case BFS_SPAWN_CLOSE:
+			if (close(action->out_fd) != 0) {
+				goto fail;
+			}
+			break;
+		case BFS_SPAWN_DUP2:
+			if (dup2(action->in_fd, action->out_fd) < 0) {
+				goto fail;
+			}
+			break;
+		case BFS_SPAWN_FCHDIR:
+			if (fchdir(action->in_fd) != 0) {
+				goto fail;
+			}
+			break;
+		case BFS_SPAWN_SETRLIMIT:
+			if (setrlimit(action->resource, &action->rlimit) != 0) {
+				goto fail;
+			}
+			break;
+		}
+	}
+
+	execve(exe, argv, envp);
+
+fail:
+	error = errno;
+
+	// In case of a write error, the parent will still see that we exited
+	// unsuccessfully, but won't know why
+	(void) xwrite(pipefd[1], &error, sizeof(error));
+
+	xclose(pipefd[1]);
+	_Exit(127);
+}
+
+pid_t bfs_spawn(const char *exe, const struct bfs_spawn *ctx, char **argv, char **envp) {
+	extern char **environ;
+	if (!envp) {
+		envp = environ;
+	}
+
+	enum bfs_spawn_flags flags = ctx ? ctx->flags : 0;
+	char *resolved = NULL;
+	if (flags & BFS_SPAWN_USEPATH) {
+		exe = resolved = bfs_spawn_resolve(exe);
+		if (!resolved) {
+			return -1;
+		}
+	}
+
+	// Use a pipe to report errors from the child
+	int pipefd[2];
+	if (pipe_cloexec(pipefd) != 0) {
+		free(resolved);
+		return -1;
+	}
+
+	pid_t pid = fork();
+	if (pid < 0) {
+		close_quietly(pipefd[1]);
+		close_quietly(pipefd[0]);
+		free(resolved);
+		return -1;
+	} else if (pid == 0) {
+		// Child
+		bfs_spawn_exec(exe, ctx, argv, envp, pipefd);
+	}
+
+	// Parent
+	xclose(pipefd[1]);
+	free(resolved);
+
+	int error;
+	ssize_t nbytes = xread(pipefd[0], &error, sizeof(error));
+	xclose(pipefd[0]);
+	if (nbytes == sizeof(error)) {
+		int wstatus;
+		waitpid(pid, &wstatus, 0);
+		errno = error;
+		return -1;
+	}
+
+	return pid;
+}
+
+char *bfs_spawn_resolve(const char *exe) {
+	if (strchr(exe, '/')) {
+		return strdup(exe);
+	}
+
+	const char *path = getenv("PATH");
+
+	char *confpath = NULL;
+	if (!path) {
+		path = confpath = xconfstr(_CS_PATH);
+		if (!path) {
+			return NULL;
+		}
+	}
+
+	size_t cap = 0;
+	char *ret = NULL;
+	while (true) {
+		const char *end = strchr(path, ':');
+		size_t len = end ? (size_t)(end - path) : strlen(path);
+
+		// POSIX 8.3: "A zero-length prefix is a legacy feature that
+		// indicates the current working directory."
+		if (len == 0) {
+			path = ".";
+			len = 1;
+		}
+
+		size_t total = len + 1 + strlen(exe) + 1;
+		if (cap < total) {
+			char *grown = realloc(ret, total);
+			if (!grown) {
+				goto fail;
+			}
+			ret = grown;
+			cap = total;
+		}
+
+		memcpy(ret, path, len);
+		if (ret[len - 1] != '/') {
+			ret[len++] = '/';
+		}
+		strcpy(ret + len, exe);
+
+		if (xfaccessat(AT_FDCWD, ret, X_OK) == 0) {
+			break;
+		}
+
+		if (!end) {
+			errno = ENOENT;
+			goto fail;
+		}
+
+		path = end + 1;
+	}
+
+	free(confpath);
+	return ret;
+
+fail:
+	free(confpath);
+	free(ret);
+	return NULL;
+}