diff options
Diffstat (limited to 'run-command.h')
| -rw-r--r-- | run-command.h | 252 |
1 files changed, 245 insertions, 7 deletions
diff --git a/run-command.h b/run-command.h index f769e03..592d9dc 100644 --- a/run-command.h +++ b/run-command.h @@ -5,8 +5,60 @@ #include "argv-array.h" +/** + * The run-command API offers a versatile tool to run sub-processes with + * redirected input and output as well as with a modified environment + * and an alternate current directory. + * + * A similar API offers the capability to run a function asynchronously, + * which is primarily used to capture the output that the function + * produces in the caller in order to process it. + */ + + +/** + * This describes the arguments, redirections, and environment of a + * command to run in a sub-process. + * + * The caller: + * + * 1. allocates and clears (using child_process_init() or + * CHILD_PROCESS_INIT) a struct child_process variable; + * 2. initializes the members; + * 3. calls start_command(); + * 4. processes the data; + * 5. closes file descriptors (if necessary; see below); + * 6. calls finish_command(). + * + * Special forms of redirection are available by setting these members + * to 1: + * + * .no_stdin, .no_stdout, .no_stderr: The respective channel is + * redirected to /dev/null. + * + * .stdout_to_stderr: stdout of the child is redirected to its + * stderr. This happens after stderr is itself redirected. + * So stdout will follow stderr to wherever it is + * redirected. + */ struct child_process { + + /** + * The .argv member is set up as an array of string pointers (NULL + * terminated), of which .argv[0] is the program name to run (usually + * without a path). If the command to run is a git command, set argv[0] to + * the command name without the 'git-' prefix and set .git_cmd = 1. + * + * Note that the ownership of the memory pointed to by .argv stays with the + * caller, but it should survive until `finish_command` completes. If the + * .argv member is NULL, `start_command` will point it at the .args + * `argv_array` (so you may use one or the other, but you must use exactly + * one). The memory in .args will be cleaned up automatically during + * `finish_command` (or during `start_command` when it is unsuccessful). + * + */ const char **argv; + struct argv_array args; struct argv_array env_array; pid_t pid; @@ -18,8 +70,8 @@ struct child_process { /* * Using .in, .out, .err: - * - Specify 0 for no redirections (child inherits stdin, stdout, - * stderr from parent). + * - Specify 0 for no redirections. No new file descriptor is allocated. + * (child inherits stdin, stdout, stderr from parent). * - Specify -1 to have a pipe allocated as follows: * .in: returns the writable pipe end; parent writes to it, * the readable pipe end becomes child's stdin @@ -37,13 +89,43 @@ struct child_process { int in; int out; int err; + + /** + * To specify a new initial working directory for the sub-process, + * specify it in the .dir member. + */ const char *dir; + + /** + * To modify the environment of the sub-process, specify an array of + * string pointers (NULL terminated) in .env: + * + * - If the string is of the form "VAR=value", i.e. it contains '=' + * the variable is added to the child process's environment. + * + * - If the string does not contain '=', it names an environment + * variable that will be removed from the child process's environment. + * + * If the .env member is NULL, `start_command` will point it at the + * .env_array `argv_array` (so you may use one or the other, but not both). + * The memory in .env_array will be cleaned up automatically during + * `finish_command` (or during `start_command` when it is unsuccessful). + */ const char *const *env; + unsigned no_stdin:1; unsigned no_stdout:1; unsigned no_stderr:1; - unsigned git_cmd:1; /* if this is to be git sub-command */ + unsigned git_cmd:1; /* if this is to be git sub-command */ + + /** + * If the program cannot be found, the functions return -1 and set + * errno to ENOENT. Normally, an error message is printed, but if + * .silent_exec_failure is set to 1, no message is printed for this + * special error condition. + */ unsigned silent_exec_failure:1; + unsigned stdout_to_stderr:1; unsigned use_shell:1; unsigned clean_on_exit:1; @@ -53,13 +135,63 @@ struct child_process { }; #define CHILD_PROCESS_INIT { NULL, ARGV_ARRAY_INIT, ARGV_ARRAY_INIT } + +/** + * The functions: child_process_init, start_command, finish_command, + * run_command, run_command_v_opt, run_command_v_opt_cd_env, child_process_clear + * do the following: + * + * - If a system call failed, errno is set and -1 is returned. A diagnostic + * is printed. + * + * - If the program was not found, then -1 is returned and errno is set to + * ENOENT; a diagnostic is printed only if .silent_exec_failure is 0. + * + * - Otherwise, the program is run. If it terminates regularly, its exit + * code is returned. No diagnostic is printed, even if the exit code is + * non-zero. + * + * - If the program terminated due to a signal, then the return value is the + * signal number + 128, ie. the same value that a POSIX shell's $? would + * report. A diagnostic is printed. + * + */ + +/** + * Initialize a struct child_process variable. + */ void child_process_init(struct child_process *); + +/** + * Release the memory associated with the struct child_process. + * Most users of the run-command API don't need to call this + * function explicitly because `start_command` invokes it on + * failure and `finish_command` calls it automatically already. + */ void child_process_clear(struct child_process *); + int is_executable(const char *name); +/** + * Start a sub-process. Takes a pointer to a `struct child_process` + * that specifies the details and returns pipe FDs (if requested). + * See below for details. + */ int start_command(struct child_process *); + +/** + * Wait for the completion of a sub-process that was started with + * start_command(). + */ int finish_command(struct child_process *); + int finish_command_in_signal(struct child_process *); + +/** + * A convenience function that encapsulates a sequence of + * start_command() followed by finish_command(). Takes a pointer + * to a `struct child_process` that specifies the details. + */ int run_command(struct child_process *); /* @@ -68,6 +200,20 @@ int run_command(struct child_process *); * overwritten by further calls to find_hook and run_hook_*. */ const char *find_hook(const char *name); + +/** + * Run a hook. + * The first argument is a pathname to an index file, or NULL + * if the hook uses the default index file or no index is needed. + * The second argument is the name of the hook. + * The further arguments correspond to the hook arguments. + * The last argument has to be NULL to terminate the arguments list. + * If the hook does not exist or is not executable, the return + * value will be zero. + * If it is executable, the hook will be executed and the exit + * status of the hook is returned. + * On execution, .stdout_to_stderr and .no_stdin will be set. + */ LAST_ARG_MUST_BE_NULL int run_hook_le(const char *const *env, const char *name, ...); int run_hook_ve(const char *const *env, const char *name, va_list args); @@ -78,6 +224,18 @@ int run_hook_ve(const char *const *env, const char *name, va_list args); #define RUN_SILENT_EXEC_FAILURE 8 #define RUN_USING_SHELL 16 #define RUN_CLEAN_ON_EXIT 32 + +/** + * Convenience functions that encapsulate a sequence of + * start_command() followed by finish_command(). The argument argv + * specifies the program and its arguments. The argument opt is zero + * or more of the flags `RUN_COMMAND_NO_STDIN`, `RUN_GIT_CMD`, + * `RUN_COMMAND_STDOUT_TO_STDERR`, or `RUN_SILENT_EXEC_FAILURE` + * that correspond to the members .no_stdin, .git_cmd, + * .stdout_to_stderr, .silent_exec_failure of `struct child_process`. + * The argument dir corresponds the member .dir. The argument env + * corresponds to the member .env. + */ int run_command_v_opt(const char **argv, int opt); int run_command_v_opt_tr2(const char **argv, int opt, const char *tr2_class); /* @@ -125,15 +283,84 @@ static inline int capture_command(struct child_process *cmd, * It is expected that no synchronization and mutual exclusion between * the caller and the feed function is necessary so that the function * can run in a thread without interfering with the caller. + * + * The caller: + * + * 1. allocates and clears (memset(&asy, 0, sizeof(asy));) a + * struct async variable; + * 2. initializes .proc and .data; + * 3. calls start_async(); + * 4. processes communicates with proc through .in and .out; + * 5. closes .in and .out; + * 6. calls finish_async(). + * + * There are serious restrictions on what the asynchronous function can do + * because this facility is implemented by a thread in the same address + * space on most platforms (when pthreads is available), but by a pipe to + * a forked process otherwise: + * + * - It cannot change the program's state (global variables, environment, + * etc.) in a way that the caller notices; in other words, .in and .out + * are the only communication channels to the caller. + * + * - It must not change the program's state that the caller of the + * facility also uses. + * */ struct async { - /* - * proc reads from in; closes it before return - * proc writes to out; closes it before return - * returns 0 on success, non-zero on failure + + /** + * The function pointer in .proc has the following signature: + * + * int proc(int in, int out, void *data); + * + * - in, out specifies a set of file descriptors to which the function + * must read/write the data that it needs/produces. The function + * *must* close these descriptors before it returns. A descriptor + * may be -1 if the caller did not configure a descriptor for that + * direction. + * + * - data is the value that the caller has specified in the .data member + * of struct async. + * + * - The return value of the function is 0 on success and non-zero + * on failure. If the function indicates failure, finish_async() will + * report failure as well. + * */ int (*proc)(int in, int out, void *data); + void *data; + + /** + * The members .in, .out are used to provide a set of fd's for + * communication between the caller and the callee as follows: + * + * - Specify 0 to have no file descriptor passed. The callee will + * receive -1 in the corresponding argument. + * + * - Specify < 0 to have a pipe allocated; start_async() replaces + * with the pipe FD in the following way: + * + * .in: Returns the writable pipe end into which the caller + * writes; the readable end of the pipe becomes the function's + * in argument. + * + * .out: Returns the readable pipe end from which the caller + * reads; the writable end of the pipe becomes the function's + * out argument. + * + * The caller of start_async() must close the returned FDs after it + * has completed reading from/writing from them. + * + * - Specify a file descriptor > 0 to be used by the function: + * + * .in: The FD must be readable; it becomes the function's in. + * .out: The FD must be writable; it becomes the function's out. + * + * The specified FD is closed by start_async(), even if it fails to + * run the function. + */ int in; /* caller writes here and closes it */ int out; /* caller reads from here and closes it */ #ifdef NO_PTHREADS @@ -146,8 +373,19 @@ struct async { int isolate_sigpipe; }; +/** + * Run a function asynchronously. Takes a pointer to a `struct + * async` that specifies the details and returns a set of pipe FDs + * for communication with the function. See below for details. + */ int start_async(struct async *async); + +/** + * Wait for the completion of an asynchronous function that was + * started with start_async(). + */ int finish_async(struct async *async); + int in_async(void); int async_with_fork(void); void check_pipe(int err); |