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run-command: move doc to run-command.h

Move the documentation from Documentation/technical/api-run-command.txt to run-command.h as it's easier for the developers to find the usage information beside the code instead of looking for it in another doc file. Documentation/technical/api-run-command.txt is removed because the information it has is now redundant and it'll be hard to keep it up to date and synchronized with the documentation in the header file. Signed-off-by: Heba Waly <heba.waly@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>

Heba Waly committed Nov 17, 2019 at 21:04 UTC 4c4066d95d861808f655cd29bf68aa45c0f02d19
2 files changed +245 -271
Documentation/technical/api-run-command.txt deleted
-264
@@ -1,264 +0,0 @@
1 -run-command API
2 -===============
3 -
4 -The run-command API offers a versatile tool to run sub-processes with
5 -redirected input and output as well as with a modified environment
6 -and an alternate current directory.
7 -
8 -A similar API offers the capability to run a function asynchronously,
9 -which is primarily used to capture the output that the function
10 -produces in the caller in order to process it.
11 -
12 -
13 -Functions
14 ----------
15 -
16 -`child_process_init`::
17 -
18 - Initialize a struct child_process variable.
19 -
20 -`start_command`::
21 -
22 - Start a sub-process. Takes a pointer to a `struct child_process`
23 - that specifies the details and returns pipe FDs (if requested).
24 - See below for details.
25 -
26 -`finish_command`::
27 -
28 - Wait for the completion of a sub-process that was started with
29 - start_command().
30 -
31 -`run_command`::
32 -
33 - A convenience function that encapsulates a sequence of
34 - start_command() followed by finish_command(). Takes a pointer
35 - to a `struct child_process` that specifies the details.
36 -
37 -`run_command_v_opt`, `run_command_v_opt_cd_env`::
38 -
39 - Convenience functions that encapsulate a sequence of
40 - start_command() followed by finish_command(). The argument argv
41 - specifies the program and its arguments. The argument opt is zero
42 - or more of the flags `RUN_COMMAND_NO_STDIN`, `RUN_GIT_CMD`,
43 - `RUN_COMMAND_STDOUT_TO_STDERR`, or `RUN_SILENT_EXEC_FAILURE`
44 - that correspond to the members .no_stdin, .git_cmd,
45 - .stdout_to_stderr, .silent_exec_failure of `struct child_process`.
46 - The argument dir corresponds the member .dir. The argument env
47 - corresponds to the member .env.
48 -
49 -`child_process_clear`::
50 -
51 - Release the memory associated with the struct child_process.
52 - Most users of the run-command API don't need to call this
53 - function explicitly because `start_command` invokes it on
54 - failure and `finish_command` calls it automatically already.
55 -
56 -The functions above do the following:
57 -
58 -. If a system call failed, errno is set and -1 is returned. A diagnostic
59 - is printed.
60 -
61 -. If the program was not found, then -1 is returned and errno is set to
62 - ENOENT; a diagnostic is printed only if .silent_exec_failure is 0.
63 -
64 -. Otherwise, the program is run. If it terminates regularly, its exit
65 - code is returned. No diagnostic is printed, even if the exit code is
66 - non-zero.
67 -
68 -. If the program terminated due to a signal, then the return value is the
69 - signal number + 128, ie. the same value that a POSIX shell's $? would
70 - report. A diagnostic is printed.
71 -
72 -
73 -`start_async`::
74 -
75 - Run a function asynchronously. Takes a pointer to a `struct
76 - async` that specifies the details and returns a set of pipe FDs
77 - for communication with the function. See below for details.
78 -
79 -`finish_async`::
80 -
81 - Wait for the completion of an asynchronous function that was
82 - started with start_async().
83 -
84 -`run_hook`::
85 -
86 - Run a hook.
87 - The first argument is a pathname to an index file, or NULL
88 - if the hook uses the default index file or no index is needed.
89 - The second argument is the name of the hook.
90 - The further arguments correspond to the hook arguments.
91 - The last argument has to be NULL to terminate the arguments list.
92 - If the hook does not exist or is not executable, the return
93 - value will be zero.
94 - If it is executable, the hook will be executed and the exit
95 - status of the hook is returned.
96 - On execution, .stdout_to_stderr and .no_stdin will be set.
97 - (See below.)
98 -
99 -
100 -Data structures
101 ----------------
102 -
103 -* `struct child_process`
104 -
105 -This describes the arguments, redirections, and environment of a
106 -command to run in a sub-process.
107 -
108 -The caller:
109 -
110 -1. allocates and clears (using child_process_init() or
111 - CHILD_PROCESS_INIT) a struct child_process variable;
112 -2. initializes the members;
113 -3. calls start_command();
114 -4. processes the data;
115 -5. closes file descriptors (if necessary; see below);
116 -6. calls finish_command().
117 -
118 -The .argv member is set up as an array of string pointers (NULL
119 -terminated), of which .argv[0] is the program name to run (usually
120 -without a path). If the command to run is a git command, set argv[0] to
121 -the command name without the 'git-' prefix and set .git_cmd = 1.
122 -
123 -Note that the ownership of the memory pointed to by .argv stays with the
124 -caller, but it should survive until `finish_command` completes. If the
125 -.argv member is NULL, `start_command` will point it at the .args
126 -`argv_array` (so you may use one or the other, but you must use exactly
127 -one). The memory in .args will be cleaned up automatically during
128 -`finish_command` (or during `start_command` when it is unsuccessful).
129 -
130 -The members .in, .out, .err are used to redirect stdin, stdout,
131 -stderr as follows:
132 -
133 -. Specify 0 to request no special redirection. No new file descriptor
134 - is allocated. The child process simply inherits the channel from the
135 - parent.
136 -
137 -. Specify -1 to have a pipe allocated; start_command() replaces -1
138 - by the pipe FD in the following way:
139 -
140 - .in: Returns the writable pipe end into which the caller writes;
141 - the readable end of the pipe becomes the child's stdin.
142 -
143 - .out, .err: Returns the readable pipe end from which the caller
144 - reads; the writable end of the pipe end becomes child's
145 - stdout/stderr.
146 -
147 - The caller of start_command() must close the so returned FDs
148 - after it has completed reading from/writing to it!
149 -
150 -. Specify a file descriptor > 0 to be used by the child:
151 -
152 - .in: The FD must be readable; it becomes child's stdin.
153 - .out: The FD must be writable; it becomes child's stdout.
154 - .err: The FD must be writable; it becomes child's stderr.
155 -
156 - The specified FD is closed by start_command(), even if it fails to
157 - run the sub-process!
158 -
159 -. Special forms of redirection are available by setting these members
160 - to 1:
161 -
162 - .no_stdin, .no_stdout, .no_stderr: The respective channel is
163 - redirected to /dev/null.
164 -
165 - .stdout_to_stderr: stdout of the child is redirected to its
166 - stderr. This happens after stderr is itself redirected.
167 - So stdout will follow stderr to wherever it is
168 - redirected.
169 -
170 -To modify the environment of the sub-process, specify an array of
171 -string pointers (NULL terminated) in .env:
172 -
173 -. If the string is of the form "VAR=value", i.e. it contains '='
174 - the variable is added to the child process's environment.
175 -
176 -. If the string does not contain '=', it names an environment
177 - variable that will be removed from the child process's environment.
178 -
179 -If the .env member is NULL, `start_command` will point it at the
180 -.env_array `argv_array` (so you may use one or the other, but not both).
181 -The memory in .env_array will be cleaned up automatically during
182 -`finish_command` (or during `start_command` when it is unsuccessful).
183 -
184 -To specify a new initial working directory for the sub-process,
185 -specify it in the .dir member.
186 -
187 -If the program cannot be found, the functions return -1 and set
188 -errno to ENOENT. Normally, an error message is printed, but if
189 -.silent_exec_failure is set to 1, no message is printed for this
190 -special error condition.
191 -
192 -
193 -* `struct async`
194 -
195 -This describes a function to run asynchronously, whose purpose is
196 -to produce output that the caller reads.
197 -
198 -The caller:
199 -
200 -1. allocates and clears (memset(&asy, 0, sizeof(asy));) a
201 - struct async variable;
202 -2. initializes .proc and .data;
203 -3. calls start_async();
204 -4. processes communicates with proc through .in and .out;
205 -5. closes .in and .out;
206 -6. calls finish_async().
207 -
208 -The members .in, .out are used to provide a set of fd's for
209 -communication between the caller and the callee as follows:
210 -
211 -. Specify 0 to have no file descriptor passed. The callee will
212 - receive -1 in the corresponding argument.
213 -
214 -. Specify < 0 to have a pipe allocated; start_async() replaces
215 - with the pipe FD in the following way:
216 -
217 - .in: Returns the writable pipe end into which the caller
218 - writes; the readable end of the pipe becomes the function's
219 - in argument.
220 -
221 - .out: Returns the readable pipe end from which the caller
222 - reads; the writable end of the pipe becomes the function's
223 - out argument.
224 -
225 - The caller of start_async() must close the returned FDs after it
226 - has completed reading from/writing from them.
227 -
228 -. Specify a file descriptor > 0 to be used by the function:
229 -
230 - .in: The FD must be readable; it becomes the function's in.
231 - .out: The FD must be writable; it becomes the function's out.
232 -
233 - The specified FD is closed by start_async(), even if it fails to
234 - run the function.
235 -
236 -The function pointer in .proc has the following signature:
237 -
238 - int proc(int in, int out, void *data);
239 -
240 -. in, out specifies a set of file descriptors to which the function
241 - must read/write the data that it needs/produces. The function
242 - *must* close these descriptors before it returns. A descriptor
243 - may be -1 if the caller did not configure a descriptor for that
244 - direction.
245 -
246 -. data is the value that the caller has specified in the .data member
247 - of struct async.
248 -
249 -. The return value of the function is 0 on success and non-zero
250 - on failure. If the function indicates failure, finish_async() will
251 - report failure as well.
252 -
253 -
254 -There are serious restrictions on what the asynchronous function can do
255 -because this facility is implemented by a thread in the same address
256 -space on most platforms (when pthreads is available), but by a pipe to
257 -a forked process otherwise:
258 -
259 -. It cannot change the program's state (global variables, environment,
260 - etc.) in a way that the caller notices; in other words, .in and .out
261 - are the only communication channels to the caller.
262 -
263 -. It must not change the program's state that the caller of the
264 - facility also uses.
run-command.h
+245 -7
@@ -5,8 +5,60 @@
5
6 #include "argv-array.h"
7
8 +/**
9 + * The run-command API offers a versatile tool to run sub-processes with
10 + * redirected input and output as well as with a modified environment
11 + * and an alternate current directory.
12 + *
13 + * A similar API offers the capability to run a function asynchronously,
14 + * which is primarily used to capture the output that the function
15 + * produces in the caller in order to process it.
16 + */
17 +
18 +
19 +/**
20 + * This describes the arguments, redirections, and environment of a
21 + * command to run in a sub-process.
22 + *
23 + * The caller:
24 + *
25 + * 1. allocates and clears (using child_process_init() or
26 + * CHILD_PROCESS_INIT) a struct child_process variable;
27 + * 2. initializes the members;
28 + * 3. calls start_command();
29 + * 4. processes the data;
30 + * 5. closes file descriptors (if necessary; see below);
31 + * 6. calls finish_command().
32 + *
33 + * Special forms of redirection are available by setting these members
34 + * to 1:
35 + *
36 + * .no_stdin, .no_stdout, .no_stderr: The respective channel is
37 + * redirected to /dev/null.
38 + *
39 + * .stdout_to_stderr: stdout of the child is redirected to its
40 + * stderr. This happens after stderr is itself redirected.
41 + * So stdout will follow stderr to wherever it is
42 + * redirected.
43 + */
44 struct child_process {
45 +
46 + /**
47 + * The .argv member is set up as an array of string pointers (NULL
48 + * terminated), of which .argv[0] is the program name to run (usually
49 + * without a path). If the command to run is a git command, set argv[0] to
50 + * the command name without the 'git-' prefix and set .git_cmd = 1.
51 + *
52 + * Note that the ownership of the memory pointed to by .argv stays with the
53 + * caller, but it should survive until `finish_command` completes. If the
54 + * .argv member is NULL, `start_command` will point it at the .args
55 + * `argv_array` (so you may use one or the other, but you must use exactly
56 + * one). The memory in .args will be cleaned up automatically during
57 + * `finish_command` (or during `start_command` when it is unsuccessful).
58 + *
59 + */
60 const char **argv;
61 +
62 struct argv_array args;
63 struct argv_array env_array;
64 pid_t pid;
@@ -18,8 +70,8 @@ struct child_process {
70
71 /*
72 * Using .in, .out, .err:
21 - * - Specify 0 for no redirections (child inherits stdin, stdout,
22 - * stderr from parent).
73 + * - Specify 0 for no redirections. No new file descriptor is allocated.
74 + * (child inherits stdin, stdout, stderr from parent).
75 * - Specify -1 to have a pipe allocated as follows:
76 * .in: returns the writable pipe end; parent writes to it,
77 * the readable pipe end becomes child's stdin
@@ -37,13 +89,43 @@ struct child_process {
89 int in;
90 int out;
91 int err;
92 +
93 + /**
94 + * To specify a new initial working directory for the sub-process,
95 + * specify it in the .dir member.
96 + */
97 const char *dir;
98 +
99 + /**
100 + * To modify the environment of the sub-process, specify an array of
101 + * string pointers (NULL terminated) in .env:
102 + *
103 + * - If the string is of the form "VAR=value", i.e. it contains '='
104 + * the variable is added to the child process's environment.
105 + *
106 + * - If the string does not contain '=', it names an environment
107 + * variable that will be removed from the child process's environment.
108 + *
109 + * If the .env member is NULL, `start_command` will point it at the
110 + * .env_array `argv_array` (so you may use one or the other, but not both).
111 + * The memory in .env_array will be cleaned up automatically during
112 + * `finish_command` (or during `start_command` when it is unsuccessful).
113 + */
114 const char *const *env;
115 +
116 unsigned no_stdin:1;
117 unsigned no_stdout:1;
118 unsigned no_stderr:1;
45 - unsigned git_cmd:1; /* if this is to be git sub-command */
119 + unsigned git_cmd:1; /* if this is to be git sub-command */
120 +
121 + /**
122 + * If the program cannot be found, the functions return -1 and set
123 + * errno to ENOENT. Normally, an error message is printed, but if
124 + * .silent_exec_failure is set to 1, no message is printed for this
125 + * special error condition.
126 + */
127 unsigned silent_exec_failure:1;
128 +
129 unsigned stdout_to_stderr:1;
130 unsigned use_shell:1;
131 unsigned clean_on_exit:1;
@@ -53,13 +135,63 @@ struct child_process {
135 };
136
137 #define CHILD_PROCESS_INIT { NULL, ARGV_ARRAY_INIT, ARGV_ARRAY_INIT }
138 +
139 +/**
140 + * The functions: child_process_init, start_command, finish_command,
141 + * run_command, run_command_v_opt, run_command_v_opt_cd_env, child_process_clear
142 + * do the following:
143 + *
144 + * - If a system call failed, errno is set and -1 is returned. A diagnostic
145 + * is printed.
146 + *
147 + * - If the program was not found, then -1 is returned and errno is set to
148 + * ENOENT; a diagnostic is printed only if .silent_exec_failure is 0.
149 + *
150 + * - Otherwise, the program is run. If it terminates regularly, its exit
151 + * code is returned. No diagnostic is printed, even if the exit code is
152 + * non-zero.
153 + *
154 + * - If the program terminated due to a signal, then the return value is the
155 + * signal number + 128, ie. the same value that a POSIX shell's $? would
156 + * report. A diagnostic is printed.
157 + *
158 + */
159 +
160 +/**
161 + * Initialize a struct child_process variable.
162 + */
163 void child_process_init(struct child_process *);
164 +
165 +/**
166 + * Release the memory associated with the struct child_process.
167 + * Most users of the run-command API don't need to call this
168 + * function explicitly because `start_command` invokes it on
169 + * failure and `finish_command` calls it automatically already.
170 + */
171 void child_process_clear(struct child_process *);
172 +
173 int is_executable(const char *name);
174
175 +/**
176 + * Start a sub-process. Takes a pointer to a `struct child_process`
177 + * that specifies the details and returns pipe FDs (if requested).
178 + * See below for details.
179 + */
180 int start_command(struct child_process *);
181 +
182 +/**
183 + * Wait for the completion of a sub-process that was started with
184 + * start_command().
185 + */
186 int finish_command(struct child_process *);
187 +
188 int finish_command_in_signal(struct child_process *);
189 +
190 +/**
191 + * A convenience function that encapsulates a sequence of
192 + * start_command() followed by finish_command(). Takes a pointer
193 + * to a `struct child_process` that specifies the details.
194 + */
195 int run_command(struct child_process *);
196
197 /*
@@ -68,6 +200,20 @@ int run_command(struct child_process *);
200 * overwritten by further calls to find_hook and run_hook_*.
201 */
202 const char *find_hook(const char *name);
203 +
204 +/**
205 + * Run a hook.
206 + * The first argument is a pathname to an index file, or NULL
207 + * if the hook uses the default index file or no index is needed.
208 + * The second argument is the name of the hook.
209 + * The further arguments correspond to the hook arguments.
210 + * The last argument has to be NULL to terminate the arguments list.
211 + * If the hook does not exist or is not executable, the return
212 + * value will be zero.
213 + * If it is executable, the hook will be executed and the exit
214 + * status of the hook is returned.
215 + * On execution, .stdout_to_stderr and .no_stdin will be set.
216 + */
217 LAST_ARG_MUST_BE_NULL
218 int run_hook_le(const char *const *env, const char *name, ...);
219 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);
224 #define RUN_SILENT_EXEC_FAILURE 8
225 #define RUN_USING_SHELL 16
226 #define RUN_CLEAN_ON_EXIT 32
227 +
228 +/**
229 + * Convenience functions that encapsulate a sequence of
230 + * start_command() followed by finish_command(). The argument argv
231 + * specifies the program and its arguments. The argument opt is zero
232 + * or more of the flags `RUN_COMMAND_NO_STDIN`, `RUN_GIT_CMD`,
233 + * `RUN_COMMAND_STDOUT_TO_STDERR`, or `RUN_SILENT_EXEC_FAILURE`
234 + * that correspond to the members .no_stdin, .git_cmd,
235 + * .stdout_to_stderr, .silent_exec_failure of `struct child_process`.
236 + * The argument dir corresponds the member .dir. The argument env
237 + * corresponds to the member .env.
238 + */
239 int run_command_v_opt(const char **argv, int opt);
240 int run_command_v_opt_tr2(const char **argv, int opt, const char *tr2_class);
241 /*
@@ -125,15 +283,84 @@ static inline int capture_command(struct child_process *cmd,
283 * It is expected that no synchronization and mutual exclusion between
284 * the caller and the feed function is necessary so that the function
285 * can run in a thread without interfering with the caller.
286 + *
287 + * The caller:
288 + *
289 + * 1. allocates and clears (memset(&asy, 0, sizeof(asy));) a
290 + * struct async variable;
291 + * 2. initializes .proc and .data;
292 + * 3. calls start_async();
293 + * 4. processes communicates with proc through .in and .out;
294 + * 5. closes .in and .out;
295 + * 6. calls finish_async().
296 + *
297 + * There are serious restrictions on what the asynchronous function can do
298 + * because this facility is implemented by a thread in the same address
299 + * space on most platforms (when pthreads is available), but by a pipe to
300 + * a forked process otherwise:
301 + *
302 + * - It cannot change the program's state (global variables, environment,
303 + * etc.) in a way that the caller notices; in other words, .in and .out
304 + * are the only communication channels to the caller.
305 + *
306 + * - It must not change the program's state that the caller of the
307 + * facility also uses.
308 + *
309 */
310 struct async {
130 - /*
131 - * proc reads from in; closes it before return
132 - * proc writes to out; closes it before return
133 - * returns 0 on success, non-zero on failure
311 +
312 + /**
313 + * The function pointer in .proc has the following signature:
314 + *
315 + * int proc(int in, int out, void *data);
316 + *
317 + * - in, out specifies a set of file descriptors to which the function
318 + * must read/write the data that it needs/produces. The function
319 + * *must* close these descriptors before it returns. A descriptor
320 + * may be -1 if the caller did not configure a descriptor for that
321 + * direction.
322 + *
323 + * - data is the value that the caller has specified in the .data member
324 + * of struct async.
325 + *
326 + * - The return value of the function is 0 on success and non-zero
327 + * on failure. If the function indicates failure, finish_async() will
328 + * report failure as well.
329 + *
330 */
331 int (*proc)(int in, int out, void *data);
332 +
333 void *data;
334 +
335 + /**
336 + * The members .in, .out are used to provide a set of fd's for
337 + * communication between the caller and the callee as follows:
338 + *
339 + * - Specify 0 to have no file descriptor passed. The callee will
340 + * receive -1 in the corresponding argument.
341 + *
342 + * - Specify < 0 to have a pipe allocated; start_async() replaces
343 + * with the pipe FD in the following way:
344 + *
345 + * .in: Returns the writable pipe end into which the caller
346 + * writes; the readable end of the pipe becomes the function's
347 + * in argument.
348 + *
349 + * .out: Returns the readable pipe end from which the caller
350 + * reads; the writable end of the pipe becomes the function's
351 + * out argument.
352 + *
353 + * The caller of start_async() must close the returned FDs after it
354 + * has completed reading from/writing from them.
355 + *
356 + * - Specify a file descriptor > 0 to be used by the function:
357 + *
358 + * .in: The FD must be readable; it becomes the function's in.
359 + * .out: The FD must be writable; it becomes the function's out.
360 + *
361 + * The specified FD is closed by start_async(), even if it fails to
362 + * run the function.
363 + */
364 int in; /* caller writes here and closes it */
365 int out; /* caller reads from here and closes it */
366 #ifdef NO_PTHREADS
@@ -146,8 +373,19 @@ struct async {
373 int isolate_sigpipe;
374 };
375
376 +/**
377 + * Run a function asynchronously. Takes a pointer to a `struct
378 + * async` that specifies the details and returns a set of pipe FDs
379 + * for communication with the function. See below for details.
380 + */
381 int start_async(struct async *async);
382 +
383 +/**
384 + * Wait for the completion of an asynchronous function that was
385 + * started with start_async().
386 + */
387 int finish_async(struct async *async);
388 +
389 int in_async(void);
390 int async_with_fork(void);
391 void check_pipe(int err);