xref: /aosp_15_r20/external/grpc-grpc/include/grpc/grpc.h (revision cc02d7e222339f7a4f6ba5f422e6413f4bd931f2)
1 /*
2  *
3  * Copyright 2015-2016 gRPC authors.
4  *
5  * Licensed under the Apache License, Version 2.0 (the "License");
6  * you may not use this file except in compliance with the License.
7  * You may obtain a copy of the License at
8  *
9  *     http://www.apache.org/licenses/LICENSE-2.0
10  *
11  * Unless required by applicable law or agreed to in writing, software
12  * distributed under the License is distributed on an "AS IS" BASIS,
13  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14  * See the License for the specific language governing permissions and
15  * limitations under the License.
16  *
17  */
18 
19 #ifndef GRPC_GRPC_H
20 #define GRPC_GRPC_H
21 
22 #include <stddef.h>
23 
24 #include <grpc/byte_buffer.h>
25 #include <grpc/impl/connectivity_state.h>  // IWYU pragma: export
26 #include <grpc/impl/grpc_types.h>          // IWYU pragma: export
27 #include <grpc/impl/propagation_bits.h>
28 #include <grpc/slice.h>
29 #include <grpc/status.h>
30 #include <grpc/support/port_platform.h>
31 #include <grpc/support/time.h>
32 
33 #ifdef __cplusplus
34 extern "C" {
35 #endif
36 
37 /*! \mainpage GRPC Core
38  *
39  * The GRPC Core library is a low-level library designed to be wrapped by higher
40  * level libraries. The top-level API is provided in grpc.h. Security related
41  * functionality lives in grpc_security.h.
42  */
43 
44 GRPCAPI void grpc_metadata_array_init(grpc_metadata_array* array);
45 GRPCAPI void grpc_metadata_array_destroy(grpc_metadata_array* array);
46 
47 GRPCAPI void grpc_call_details_init(grpc_call_details* details);
48 GRPCAPI void grpc_call_details_destroy(grpc_call_details* details);
49 
50 /** Initialize the grpc library.
51 
52     After it's called, a matching invocation to grpc_shutdown() is expected.
53 
54     It is not safe to call any other grpc functions before calling this.
55     (To avoid overhead, little checking is done, and some things may work. We
56     do not warrant that they will continue to do so in future revisions of this
57     library). */
58 GRPCAPI void grpc_init(void);
59 
60 /** Shut down the grpc library.
61 
62     Before it's called, there should haven been a matching invocation to
63     grpc_init().
64 
65     The last call to grpc_shutdown will initiate cleaning up of grpc library
66     internals, which can happen in another thread. Once the clean-up is done,
67     no memory is used by grpc, nor are any instructions executing within the
68     grpc library.  Prior to calling, all application owned grpc objects must
69     have been destroyed. */
70 GRPCAPI void grpc_shutdown(void);
71 
72 /** EXPERIMENTAL. Returns 1 if the grpc library has been initialized.
73     TODO(ericgribkoff) Decide if this should be promoted to non-experimental as
74     part of stabilizing the fork support API, as tracked in
75     https://github.com/grpc/grpc/issues/15334 */
76 GRPCAPI int grpc_is_initialized(void);
77 
78 /** DEPRECATED. Recommend to use grpc_shutdown only */
79 GRPCAPI void grpc_shutdown_blocking(void);
80 
81 /** Return a string representing the current version of grpc */
82 GRPCAPI const char* grpc_version_string(void);
83 
84 /** Return a string specifying what the 'g' in gRPC stands for */
85 GRPCAPI const char* grpc_g_stands_for(void);
86 
87 /** Returns the completion queue factory based on the attributes. MAY return a
88     NULL if no factory can be found */
89 GRPCAPI const grpc_completion_queue_factory*
90 grpc_completion_queue_factory_lookup(
91     const grpc_completion_queue_attributes* attributes);
92 
93 /** Helper function to create a completion queue with grpc_cq_completion_type
94     of GRPC_CQ_NEXT and grpc_cq_polling_type of GRPC_CQ_DEFAULT_POLLING */
95 GRPCAPI grpc_completion_queue* grpc_completion_queue_create_for_next(
96     void* reserved);
97 
98 /** Helper function to create a completion queue with grpc_cq_completion_type
99     of GRPC_CQ_PLUCK and grpc_cq_polling_type of GRPC_CQ_DEFAULT_POLLING */
100 GRPCAPI grpc_completion_queue* grpc_completion_queue_create_for_pluck(
101     void* reserved);
102 
103 /** Helper function to create a completion queue with grpc_cq_completion_type
104     of GRPC_CQ_CALLBACK and grpc_cq_polling_type of GRPC_CQ_DEFAULT_POLLING.
105     This function is experimental. */
106 GRPCAPI grpc_completion_queue* grpc_completion_queue_create_for_callback(
107     grpc_completion_queue_functor* shutdown_callback, void* reserved);
108 
109 /** Create a completion queue */
110 GRPCAPI grpc_completion_queue* grpc_completion_queue_create(
111     const grpc_completion_queue_factory* factory,
112     const grpc_completion_queue_attributes* attributes, void* reserved);
113 
114 /** Blocks until an event is available, the completion queue is being shut down,
115     or deadline is reached.
116 
117     Returns a grpc_event with type GRPC_QUEUE_TIMEOUT on timeout,
118     otherwise a grpc_event describing the event that occurred.
119 
120     Callers must not call grpc_completion_queue_next and
121     grpc_completion_queue_pluck simultaneously on the same completion queue. */
122 GRPCAPI grpc_event grpc_completion_queue_next(grpc_completion_queue* cq,
123                                               gpr_timespec deadline,
124                                               void* reserved);
125 
126 /** Blocks until an event with tag 'tag' is available, the completion queue is
127     being shutdown or deadline is reached.
128 
129     Returns a grpc_event with type GRPC_QUEUE_TIMEOUT on timeout,
130     otherwise a grpc_event describing the event that occurred.
131 
132     Callers must not call grpc_completion_queue_next and
133     grpc_completion_queue_pluck simultaneously on the same completion queue.
134 
135     Completion queues support a maximum of GRPC_MAX_COMPLETION_QUEUE_PLUCKERS
136     concurrently executing plucks at any time. */
137 GRPCAPI grpc_event grpc_completion_queue_pluck(grpc_completion_queue* cq,
138                                                void* tag, gpr_timespec deadline,
139                                                void* reserved);
140 
141 /** Maximum number of outstanding grpc_completion_queue_pluck executions per
142     completion queue */
143 #define GRPC_MAX_COMPLETION_QUEUE_PLUCKERS 6
144 
145 /** Begin destruction of a completion queue. Once all possible events are
146     drained then grpc_completion_queue_next will start to produce
147     GRPC_QUEUE_SHUTDOWN events only. At that point it's safe to call
148     grpc_completion_queue_destroy.
149 
150     After calling this function applications should ensure that no
151     NEW work is added to be published on this completion queue. */
152 GRPCAPI void grpc_completion_queue_shutdown(grpc_completion_queue* cq);
153 
154 /** Destroy a completion queue. The caller must ensure that the queue is
155     drained and no threads are executing grpc_completion_queue_next */
156 GRPCAPI void grpc_completion_queue_destroy(grpc_completion_queue* cq);
157 
158 /*********** EXPERIMENTAL API ************/
159 /** Initializes a thread local cache for \a cq.
160  * grpc_flush_cq_tls_cache() MUST be called on the same thread,
161  * with the same cq.
162  */
163 GRPCAPI void grpc_completion_queue_thread_local_cache_init(
164     grpc_completion_queue* cq);
165 
166 /*********** EXPERIMENTAL API ************/
167 /** Flushes the thread local cache for \a cq.
168  * Returns 1 if there was contents in the cache.  If there was an event
169  * in \a cq tls cache, its tag is placed in tag, and ok is set to the
170  * event success.
171  */
172 GRPCAPI int grpc_completion_queue_thread_local_cache_flush(
173     grpc_completion_queue* cq, void** tag, int* ok);
174 
175 /** Check the connectivity state of a channel. */
176 GRPCAPI grpc_connectivity_state grpc_channel_check_connectivity_state(
177     grpc_channel* channel, int try_to_connect);
178 
179 /** Watch for a change in connectivity state.
180     Once the channel connectivity state is different from last_observed_state,
181     tag will be enqueued on cq with success=1.
182     If deadline expires BEFORE the state is changed, tag will be enqueued on cq
183     with success=0. */
184 GRPCAPI void grpc_channel_watch_connectivity_state(
185     grpc_channel* channel, grpc_connectivity_state last_observed_state,
186     gpr_timespec deadline, grpc_completion_queue* cq, void* tag);
187 
188 /** Check whether a grpc channel supports connectivity watcher */
189 GRPCAPI int grpc_channel_support_connectivity_watcher(grpc_channel* channel);
190 
191 /** Create a call given a grpc_channel, in order to call 'method'. All
192     completions are sent to 'completion_queue'. 'method' and 'host' need only
193     live through the invocation of this function.
194     If parent_call is non-NULL, it must be a server-side call. It will be used
195     to propagate properties from the server call to this new client call,
196     depending on the value of \a propagation_mask (see propagation_bits.h for
197     possible values). */
198 GRPCAPI grpc_call* grpc_channel_create_call(
199     grpc_channel* channel, grpc_call* parent_call, uint32_t propagation_mask,
200     grpc_completion_queue* completion_queue, grpc_slice method,
201     const grpc_slice* host, gpr_timespec deadline, void* reserved);
202 
203 /** Pre-register a method/host pair on a channel.
204     method and host are not owned and must remain alive while the channel is
205     alive. */
206 GRPCAPI void* grpc_channel_register_call(grpc_channel* channel,
207                                          const char* method, const char* host,
208                                          void* reserved);
209 
210 /** Create a call given a handle returned from grpc_channel_register_call.
211     \sa grpc_channel_create_call. */
212 GRPCAPI grpc_call* grpc_channel_create_registered_call(
213     grpc_channel* channel, grpc_call* parent_call, uint32_t propagation_mask,
214     grpc_completion_queue* completion_queue, void* registered_call_handle,
215     gpr_timespec deadline, void* reserved);
216 
217 /** Allocate memory in the grpc_call arena: this memory is automatically
218     discarded at call completion */
219 GRPCAPI void* grpc_call_arena_alloc(grpc_call* call, size_t size);
220 
221 /** Start a batch of operations defined in the array ops; when complete, post a
222     completion of type 'tag' to the completion queue bound to the call.
223     The order of ops specified in the batch has no significance.
224     Only one operation of each type can be active at once in any given
225     batch.
226     If a call to grpc_call_start_batch returns GRPC_CALL_OK you must call
227     grpc_completion_queue_next or grpc_completion_queue_pluck on the completion
228     queue associated with 'call' for work to be performed. If a call to
229     grpc_call_start_batch returns any value other than GRPC_CALL_OK it is
230     guaranteed that no state associated with 'call' is changed and it is not
231     appropriate to call grpc_completion_queue_next or
232     grpc_completion_queue_pluck consequent to the failed grpc_call_start_batch
233     call.
234     If a call to grpc_call_start_batch with an empty batch returns
235     GRPC_CALL_OK, the tag is put in the completion queue immediately.
236     THREAD SAFETY: access to grpc_call_start_batch in multi-threaded environment
237     needs to be synchronized. As an optimization, you may synchronize batches
238     containing just send operations independently from batches containing just
239     receive operations. Access to grpc_call_start_batch with an empty batch is
240     thread-compatible. */
241 GRPCAPI grpc_call_error grpc_call_start_batch(grpc_call* call,
242                                               const grpc_op* ops, size_t nops,
243                                               void* tag, void* reserved);
244 
245 /** Returns a newly allocated string representing the endpoint to which this
246     call is communicating with. The string is in the uri format accepted by
247     grpc_channel_create.
248     The returned string should be disposed of with gpr_free().
249 
250     WARNING: this value is never authenticated or subject to any security
251     related code. It must not be used for any authentication related
252     functionality. Instead, use grpc_auth_context. */
253 GRPCAPI char* grpc_call_get_peer(grpc_call* call);
254 
255 struct census_context;
256 
257 /** Set census context for a call; Must be called before first call to
258    grpc_call_start_batch(). */
259 GRPCAPI void grpc_census_call_set_context(grpc_call* call,
260                                           struct census_context* context);
261 
262 /** Retrieve the calls current census context. */
263 GRPCAPI struct census_context* grpc_census_call_get_context(grpc_call* call);
264 
265 /** Return a newly allocated string representing the target a channel was
266     created for. */
267 GRPCAPI char* grpc_channel_get_target(grpc_channel* channel);
268 
269 /** Request info about the channel.
270     \a channel_info indicates what information is being requested and
271     how that information will be returned.
272     \a channel_info is owned by the caller. */
273 GRPCAPI void grpc_channel_get_info(grpc_channel* channel,
274                                    const grpc_channel_info* channel_info);
275 
276 /** EXPERIMENTAL.  Resets the channel's connect backoff.
277     TODO(roth): When we see whether this proves useful, either promote
278     to non-experimental or remove it. */
279 GRPCAPI void grpc_channel_reset_connect_backoff(grpc_channel* channel);
280 
281 /** --- grpc_channel_credentials object. ---
282 
283    A channel credentials object represents a way to authenticate a client on a
284    channel. Different types of channel credentials are declared in
285    grpc_security.h. */
286 
287 typedef struct grpc_channel_credentials grpc_channel_credentials;
288 
289 /** Releases a channel credentials object.
290    The creator of the credentials object is responsible for its release. */
291 
292 GRPCAPI void grpc_channel_credentials_release(grpc_channel_credentials* creds);
293 
294 /** --- grpc_server_credentials object. ---
295 
296    A server credentials object represents a way to authenticate a server.
297    Different types of server credentials are declared in grpc_security.h. */
298 
299 typedef struct grpc_server_credentials grpc_server_credentials;
300 
301 /** Releases a server_credentials object.
302    The creator of the server_credentials object is responsible for its release.
303    */
304 GRPCAPI void grpc_server_credentials_release(grpc_server_credentials* creds);
305 
306 /** Creates a secure channel using the passed-in credentials. Additional
307     channel level configuration MAY be provided by grpc_channel_args, though
308     the expectation is that most clients will want to simply pass NULL. The
309     user data in 'args' need only live through the invocation of this function.
310     However, if any args of the 'pointer' type are passed, then the referenced
311     vtable must be maintained by the caller until grpc_channel_destroy
312     terminates. See grpc_channel_args definition for more on this. */
313 GRPCAPI grpc_channel* grpc_channel_create(const char* target,
314                                           grpc_channel_credentials* creds,
315                                           const grpc_channel_args* args);
316 
317 /** Create a lame client: this client fails every operation attempted on it. */
318 GRPCAPI grpc_channel* grpc_lame_client_channel_create(
319     const char* target, grpc_status_code error_code, const char* error_message);
320 
321 /** Close and destroy a grpc channel */
322 GRPCAPI void grpc_channel_destroy(grpc_channel* channel);
323 
324 /** Error handling for grpc_call
325    Most grpc_call functions return a grpc_error. If the error is not GRPC_OK
326    then the operation failed due to some unsatisfied precondition.
327    If a grpc_call fails, it's guaranteed that no change to the call state
328    has been made. */
329 
330 /** Cancel an RPC.
331     Can be called multiple times, from any thread.
332     THREAD-SAFETY grpc_call_cancel and grpc_call_cancel_with_status
333     are thread-safe, and can be called at any point before grpc_call_unref
334     is called.*/
335 GRPCAPI grpc_call_error grpc_call_cancel(grpc_call* call, void* reserved);
336 
337 /** Cancel an RPC.
338     Can be called multiple times, from any thread.
339     If a status has not been received for the call, set it to the status code
340     and description passed in.
341     Importantly, this function does not send status nor description to the
342     remote endpoint.
343     Note that \a description doesn't need be a static string.
344     It doesn't need to be alive after the call to
345     grpc_call_cancel_with_status completes.
346     */
347 GRPCAPI grpc_call_error grpc_call_cancel_with_status(grpc_call* call,
348                                                      grpc_status_code status,
349                                                      const char* description,
350                                                      void* reserved);
351 
352 /* Returns whether or not the call's receive message operation failed because of
353  * an error (as opposed to a graceful end-of-stream) */
354 GRPCAPI int grpc_call_failed_before_recv_message(const grpc_call* c);
355 
356 /** Ref a call.
357     THREAD SAFETY: grpc_call_ref is thread-compatible */
358 GRPCAPI void grpc_call_ref(grpc_call* call);
359 
360 /** Unref a call.
361     THREAD SAFETY: grpc_call_unref is thread-compatible */
362 GRPCAPI void grpc_call_unref(grpc_call* call);
363 
364 /** Request notification of a new call.
365     Once a call is received, a notification tagged with \a tag_new is added to
366     \a cq_for_notification. \a call, \a details and \a request_metadata are
367     updated with the appropriate call information. \a cq_bound_to_call is bound
368     to \a call, and batch operation notifications for that call will be posted
369     to \a cq_bound_to_call.
370     Note that \a cq_for_notification must have been registered to the server via
371     \a grpc_server_register_completion_queue. */
372 GRPCAPI grpc_call_error grpc_server_request_call(
373     grpc_server* server, grpc_call** call, grpc_call_details* details,
374     grpc_metadata_array* request_metadata,
375     grpc_completion_queue* cq_bound_to_call,
376     grpc_completion_queue* cq_for_notification, void* tag_new);
377 
378 /** How to handle payloads for a registered method */
379 typedef enum {
380   /** Don't try to read the payload */
381   GRPC_SRM_PAYLOAD_NONE,
382   /** Read the initial payload as a byte buffer */
383   GRPC_SRM_PAYLOAD_READ_INITIAL_BYTE_BUFFER
384 } grpc_server_register_method_payload_handling;
385 
386 /** Registers a method in the server.
387     Methods to this (host, method) pair will not be reported by
388     grpc_server_request_call, but instead be reported by
389     grpc_server_request_registered_call when passed the appropriate
390     registered_method (as returned by this function).
391     Must be called before grpc_server_start.
392     Returns NULL on failure. */
393 GRPCAPI void* grpc_server_register_method(
394     grpc_server* server, const char* method, const char* host,
395     grpc_server_register_method_payload_handling payload_handling,
396     uint32_t flags);
397 
398 /** Request notification of a new pre-registered call. 'cq_for_notification'
399     must have been registered to the server via
400     grpc_server_register_completion_queue. */
401 GRPCAPI grpc_call_error grpc_server_request_registered_call(
402     grpc_server* server, void* registered_method, grpc_call** call,
403     gpr_timespec* deadline, grpc_metadata_array* request_metadata,
404     grpc_byte_buffer** optional_payload,
405     grpc_completion_queue* cq_bound_to_call,
406     grpc_completion_queue* cq_for_notification, void* tag_new);
407 
408 /** Create a server. Additional configuration for each incoming channel can
409     be specified with args. If no additional configuration is needed, args can
410     be NULL. The user data in 'args' need only live through the invocation of
411     this function. However, if any args of the 'pointer' type are passed, then
412     the referenced vtable must be maintained by the caller until
413     grpc_server_destroy terminates. See grpc_channel_args definition for more
414     on this. */
415 GRPCAPI grpc_server* grpc_server_create(const grpc_channel_args* args,
416                                         void* reserved);
417 
418 /** Register a completion queue with the server. Must be done for any
419     notification completion queue that is passed to grpc_server_request_*_call
420     and to grpc_server_shutdown_and_notify. Must be performed prior to
421     grpc_server_start. */
422 GRPCAPI void grpc_server_register_completion_queue(grpc_server* server,
423                                                    grpc_completion_queue* cq,
424                                                    void* reserved);
425 
426 // More members might be added in later, so users should take care to memset
427 // this to 0 before using it.
428 typedef struct {
429   grpc_status_code code;
430   const char* error_message;
431 } grpc_serving_status_update;
432 
433 // There might be more methods added later, so users should take care to memset
434 // this to 0 before using it.
435 typedef struct {
436   void (*on_serving_status_update)(void* user_data, const char* uri,
437                                    grpc_serving_status_update update);
438   void* user_data;
439 } grpc_server_xds_status_notifier;
440 
441 typedef struct grpc_server_config_fetcher grpc_server_config_fetcher;
442 
443 /** EXPERIMENTAL.  Creates an xDS config fetcher. */
444 GRPCAPI grpc_server_config_fetcher* grpc_server_config_fetcher_xds_create(
445     grpc_server_xds_status_notifier notifier, const grpc_channel_args* args);
446 
447 /** EXPERIMENTAL.  Destroys a config fetcher. */
448 GRPCAPI void grpc_server_config_fetcher_destroy(
449     grpc_server_config_fetcher* config_fetcher);
450 
451 /** EXPERIMENTAL.  Sets the server's config fetcher.  Takes ownership.
452     Must be called before adding ports */
453 GRPCAPI void grpc_server_set_config_fetcher(
454     grpc_server* server, grpc_server_config_fetcher* config_fetcher);
455 
456 /** Add a HTTP2 over an encrypted link over tcp listener.
457    Returns bound port number on success, 0 on failure.
458    REQUIRES: server not started */
459 GRPCAPI int grpc_server_add_http2_port(grpc_server* server, const char* addr,
460                                        grpc_server_credentials* creds);
461 
462 /** Start a server - tells all listeners to start listening */
463 GRPCAPI void grpc_server_start(grpc_server* server);
464 
465 /** Begin shutting down a server.
466     After completion, no new calls or connections will be admitted.
467     Existing calls will be allowed to complete.
468     Send a GRPC_OP_COMPLETE event when there are no more calls being serviced.
469     Shutdown is idempotent, and all tags will be notified at once if multiple
470     grpc_server_shutdown_and_notify calls are made. 'cq' must have been
471     registered to this server via grpc_server_register_completion_queue. */
472 GRPCAPI void grpc_server_shutdown_and_notify(grpc_server* server,
473                                              grpc_completion_queue* cq,
474                                              void* tag);
475 
476 /** Cancel all in-progress calls.
477     Only usable after shutdown. */
478 GRPCAPI void grpc_server_cancel_all_calls(grpc_server* server);
479 
480 /** Destroy a server.
481     Shutdown must have completed beforehand (i.e. all tags generated by
482     grpc_server_shutdown_and_notify must have been received, and at least
483     one call to grpc_server_shutdown_and_notify must have been made). */
484 GRPCAPI void grpc_server_destroy(grpc_server* server);
485 
486 /** Enable or disable a tracer.
487 
488     Tracers (usually controlled by the environment variable GRPC_TRACE)
489     allow printf-style debugging on GRPC internals, and are useful for
490     tracking down problems in the field.
491 
492     Use of this function is not strictly thread-safe, but the
493     thread-safety issues raised by it should not be of concern. */
494 GRPCAPI int grpc_tracer_set_enabled(const char* name, int enabled);
495 
496 /** Check whether a metadata key is legal (will be accepted by core) */
497 GRPCAPI int grpc_header_key_is_legal(grpc_slice slice);
498 
499 /** Check whether a non-binary metadata value is legal (will be accepted by
500     core) */
501 GRPCAPI int grpc_header_nonbin_value_is_legal(grpc_slice slice);
502 
503 /** Check whether a metadata key corresponds to a binary value */
504 GRPCAPI int grpc_is_binary_header(grpc_slice slice);
505 
506 /** Convert grpc_call_error values to a string */
507 GRPCAPI const char* grpc_call_error_to_string(grpc_call_error error);
508 
509 /** Create a buffer pool */
510 GRPCAPI grpc_resource_quota* grpc_resource_quota_create(const char* trace_name);
511 
512 /** Add a reference to a buffer pool */
513 GRPCAPI void grpc_resource_quota_ref(grpc_resource_quota* resource_quota);
514 
515 /** Drop a reference to a buffer pool */
516 GRPCAPI void grpc_resource_quota_unref(grpc_resource_quota* resource_quota);
517 
518 /** Update the size of a buffer pool */
519 GRPCAPI void grpc_resource_quota_resize(grpc_resource_quota* resource_quota,
520                                         size_t new_size);
521 
522 /** Update the size of the maximum number of threads allowed */
523 GRPCAPI void grpc_resource_quota_set_max_threads(
524     grpc_resource_quota* resource_quota, int new_max_threads);
525 
526 /** EXPERIMENTAL.  Dumps xDS configs as a serialized ClientConfig proto.
527     The full name of the proto is envoy.service.status.v3.ClientConfig. */
528 GRPCAPI grpc_slice grpc_dump_xds_configs(void);
529 
530 /** Fetch a vtable for a grpc_channel_arg that points to a grpc_resource_quota
531  */
532 GRPCAPI const grpc_arg_pointer_vtable* grpc_resource_quota_arg_vtable(void);
533 
534 /************* CHANNELZ API *************/
535 /** Channelz is under active development. The following APIs will see some
536     churn as the feature is implemented. This comment will be removed once
537     channelz is officially supported, and these APIs become stable. For now
538     you may track the progress by following this github issue:
539     https://github.com/grpc/grpc/issues/15340
540 
541     the following APIs return allocated JSON strings that match the response
542     objects from the channelz proto, found here:
543     https://github.com/grpc/grpc/blob/master/src/proto/grpc/channelz/channelz.proto.
544 
545     For easy conversion to protobuf, The JSON is formatted according to:
546     https://developers.google.com/protocol-buffers/docs/proto3#json. */
547 
548 /* Gets all root channels (i.e. channels the application has directly
549    created). This does not include subchannels nor non-top level channels.
550    The returned string is allocated and must be freed by the application. */
551 GRPCAPI char* grpc_channelz_get_top_channels(intptr_t start_channel_id);
552 
553 /* Gets all servers that exist in the process. */
554 GRPCAPI char* grpc_channelz_get_servers(intptr_t start_server_id);
555 
556 /* Returns a single Server, or else a NOT_FOUND code. */
557 GRPCAPI char* grpc_channelz_get_server(intptr_t server_id);
558 
559 /* Gets all server sockets that exist in the server. */
560 GRPCAPI char* grpc_channelz_get_server_sockets(intptr_t server_id,
561                                                intptr_t start_socket_id,
562                                                intptr_t max_results);
563 
564 /* Returns a single Channel, or else a NOT_FOUND code. The returned string
565    is allocated and must be freed by the application. */
566 GRPCAPI char* grpc_channelz_get_channel(intptr_t channel_id);
567 
568 /* Returns a single Subchannel, or else a NOT_FOUND code. The returned string
569    is allocated and must be freed by the application. */
570 GRPCAPI char* grpc_channelz_get_subchannel(intptr_t subchannel_id);
571 
572 /* Returns a single Socket, or else a NOT_FOUND code. The returned string
573    is allocated and must be freed by the application. */
574 GRPCAPI char* grpc_channelz_get_socket(intptr_t socket_id);
575 
576 /**
577  * EXPERIMENTAL - Subject to change.
578  * Fetch a vtable for grpc_channel_arg that points to
579  * grpc_authorization_policy_provider.
580  */
581 GRPCAPI const grpc_arg_pointer_vtable*
582 grpc_authorization_policy_provider_arg_vtable(void);
583 
584 #ifdef __cplusplus
585 }
586 #endif
587 
588 #endif /* GRPC_GRPC_H */
589