path: root/src/objective-c/GRPCClient/GRPCCall.m

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 *
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#import "GRPCCall.h"

#import <RxLibrary/GRXConcurrentWriteable.h>
#include <grpc/grpc.h>
#include <grpc/support/time.h>

#import "private/GRPCConnectivityMonitor.h"
#import "private/GRPCHost.h"
#import "private/GRPCRequestHeaders.h"
#import "private/GRPCWrappedCall.h"
#import "private/NSData+GRPC.h"
#import "private/NSDictionary+GRPC.h"
#import "private/NSError+GRPC.h"

NSString *const kGRPCHeadersKey = @"io.grpc.HeadersKey";
NSString *const kGRPCTrailersKey = @"io.grpc.TrailersKey";
static NSMutableDictionary *callFlags;

@interface GRPCCall ()<GRXWriteable>
// Make them read-write.
@property(atomic, strong) NSDictionary *responseHeaders;
@property(atomic, strong) NSDictionary *responseTrailers;
@end

// The following methods of a C gRPC call object aren't reentrant, and thus
// calls to them must be serialized:
// - start_batch
// - destroy
//
// start_batch with a SEND_MESSAGE argument can only be called after the
// OP_COMPLETE event for any previous write is received. This is achieved by
// pausing the requests writer immediately every time it writes a value, and
// resuming it again when OP_COMPLETE is received.
//
// Similarly, start_batch with a RECV_MESSAGE argument can only be called after
// the OP_COMPLETE event for any previous read is received.This is easier to
// enforce, as we're writing the received messages into the writeable:
// start_batch is enqueued once upon receiving the OP_COMPLETE event for the
// RECV_METADATA batch, and then once after receiving each OP_COMPLETE event for
// each RECV_MESSAGE batch.
@implementation GRPCCall {
  dispatch_queue_t _callQueue;

  NSString *_host;
  NSString *_path;
  GRPCWrappedCall *_wrappedCall;
  GRPCConnectivityMonitor *_connectivityMonitor;

  // The C gRPC library has less guarantees on the ordering of events than we
  // do. Particularly, in the face of errors, there's no ordering guarantee at
  // all. This wrapper over our actual writeable ensures thread-safety and
  // correct ordering.
  GRXConcurrentWriteable *_responseWriteable;

  // The network thread wants the requestWriter to resume (when the server is
  // ready for more input), or to stop (on errors), concurrently with user
  // threads that want to start it, pause it or stop it. Because a writer isn't
  // thread-safe, we'll synchronize those operations on it.
  // We don't use a dispatch queue for that purpose, because the writer can call
  // writeValue: or writesFinishedWithError: on this GRPCCall as part of those
  // operations. We want to be able to pause the writer immediately on
  // writeValue:, so we need our locking to be recursive.
  GRXWriter *_requestWriter;

  // To create a retain cycle when a call is started, up until it finishes. See
  // |startWithWriteable:| and |finishWithError:|. This saves users from having
  // to retain a
  // reference to the call object if all they're interested in is the handler
  // being executed when
  // the response arrives.
  GRPCCall *_retainSelf;

  GRPCRequestHeaders *_requestHeaders;
}

@synthesize state = _state;

// TODO(jcanizales): If grpc_init is idempotent, this should be changed from
// load to initialize.
+ (void)load {
  grpc_init();
  callFlags = [NSMutableDictionary dictionary];
}

+ (void)setCallSafety:(GRPCCallSafety)callSafety
                 host:(NSString *)host
                 path:(NSString *)path {
  NSString *hostAndPath = [NSString stringWithFormat:@"%@/%@", host, path];
  switch (callSafety) {
    case GRPCCallSafetyDefault:
      callFlags[hostAndPath] = @0;
      break;
    case GRPCCallSafetyIdempotentRequest:
      callFlags[hostAndPath] = @GRPC_INITIAL_METADATA_IDEMPOTENT_REQUEST;
      break;
    case GRPCCallSafetyCacheableRequest:
      callFlags[hostAndPath] = @GRPC_INITIAL_METADATA_CACHEABLE_REQUEST;
      break;
    default:
      break;
  }
}

+ (uint32_t)callFlagsForHost:(NSString *)host path:(NSString *)path {
  NSString *hostAndPath = [NSString stringWithFormat:@"%@/%@", host, path];
  return [callFlags[hostAndPath] intValue];
}

- (instancetype)init {
  return [self initWithHost:nil path:nil requestsWriter:nil];
}

// Designated initializer
- (instancetype)initWithHost:(NSString *)host
                        path:(NSString *)path
              requestsWriter:(GRXWriter *)requestWriter {
  if (!host || !path) {
    [NSException raise:NSInvalidArgumentException
                format:@"Neither host nor path can be nil."];
  }
  if (requestWriter.state != GRXWriterStateNotStarted) {
    [NSException raise:NSInvalidArgumentException
                format:@"The requests writer can't be already started."];
  }
  if ((self = [super init])) {
    _host = [host copy];
    _path = [path copy];

    // Serial queue to invoke the non-reentrant methods of the grpc_call object.
    _callQueue = dispatch_queue_create("io.grpc.call", NULL);

    _requestWriter = requestWriter;

    _requestHeaders = [[GRPCRequestHeaders alloc] initWithCall:self];
  }
  return self;
}

#pragma mark Finish

- (void)finishWithError:(NSError *)errorOrNil {
  @synchronized(self) {
    _state = GRXWriterStateFinished;
  }

  // If the call isn't retained anywhere else, it can be deallocated now.
  _retainSelf = nil;

  // If there were still request messages coming, stop them.
  @synchronized(_requestWriter) {
    _requestWriter.state = GRXWriterStateFinished;
  }

  if (errorOrNil) {
    [_responseWriteable cancelWithError:errorOrNil];
  } else {
    [_responseWriteable enqueueSuccessfulCompletion];
  }
}

- (void)cancelCall {
  // Can be called from any thread, any number of times.
  [_wrappedCall cancel];
}

- (void)cancel {
  [self finishWithError:[NSError errorWithDomain:kGRPCErrorDomain
                                            code:GRPCErrorCodeCancelled
                                        userInfo:@{
                                          NSLocalizedDescriptionKey :
                                              @"Canceled by app"
                                        }]];
  [self cancelCall];
}

- (void)dealloc {
  __block GRPCWrappedCall *wrappedCall = _wrappedCall;
  dispatch_async(_callQueue, ^{
    wrappedCall = nil;
  });
}

#pragma mark Read messages

// Only called from the call queue.
// The handler will be called from the network queue.
- (void)startReadWithHandler:(void (^)(grpc_byte_buffer *))handler {
  // TODO(jcanizales): Add error handlers for async failures
  [_wrappedCall startBatchWithOperations:@[ [[GRPCOpRecvMessage alloc]
                                             initWithHandler:handler] ]];
}

// Called initially from the network queue once response headers are received,
// then "recursively" from the responseWriteable queue after each response from
// the
// server has been written.
// If the call is currently paused, this is a noop. Restarting the call will
// invoke this
// method.
// TODO(jcanizales): Rename to readResponseIfNotPaused.
- (void)startNextRead {
  if (self.state == GRXWriterStatePaused) {
    return;
  }
  __weak GRPCCall *weakSelf = self;
  __weak GRXConcurrentWriteable *weakWriteable = _responseWriteable;

  dispatch_async(_callQueue, ^{
    [weakSelf startReadWithHandler:^(grpc_byte_buffer *message) {
      if (message == NULL) {
        // No more messages from the server
        return;
      }
      NSData *data = [NSData grpc_dataWithByteBuffer:message];
      grpc_byte_buffer_destroy(message);
      if (!data) {
        // The app doesn't have enough memory to hold the server response. We
        // don't want to throw, because the app shouldn't crash for a behavior
        // that's on the hands of any server to have. Instead we finish and ask
        // the server to cancel.
        [weakSelf
            finishWithError:[NSError
                                errorWithDomain:kGRPCErrorDomain
                                           code:GRPCErrorCodeResourceExhausted
                                       userInfo:@{
                                         NSLocalizedDescriptionKey :
                                             @"Client does not have enough "
                                             @"memory to hold the server "
                                             @"response."
                                       }]];
        [weakSelf cancelCall];
        return;
      }
      [weakWriteable enqueueValue:data
                completionHandler:^{
                  [weakSelf startNextRead];
                }];
    }];
  });
}

#pragma mark Send headers

- (void)sendHeaders:(NSDictionary *)headers {
  // TODO(jcanizales): Add error handlers for async failures
  [_wrappedCall startBatchWithOperations:@[
    [[GRPCOpSendMetadata alloc]
        initWithMetadata:headers
                   flags:[GRPCCall callFlagsForHost:_host path:_path]
                 handler:nil]
  ]];
}

#pragma mark GRXWriteable implementation

// Only called from the call queue. The error handler will be called from the
// network queue if the write didn't succeed.
- (void)writeMessage:(NSData *)message
    withErrorHandler:(void (^)())errorHandler {
  __weak GRPCCall *weakSelf = self;
  void (^resumingHandler)(void) = ^{
    // Resume the request writer.
    GRPCCall *strongSelf = weakSelf;
    if (strongSelf) {
      @synchronized(strongSelf->_requestWriter) {
        strongSelf->_requestWriter.state = GRXWriterStateStarted;
      }
    }
  };
  [_wrappedCall startBatchWithOperations:@[ [[GRPCOpSendMessage alloc]
                                             initWithMessage:message
                                                     handler:resumingHandler] ]
                            errorHandler:errorHandler];
}

- (void)writeValue:(id)value {
  // TODO(jcanizales): Throw/assert if value isn't NSData.

  // Pause the input and only resume it when the C layer notifies us that writes
  // can proceed.
  @synchronized(_requestWriter) {
    _requestWriter.state = GRXWriterStatePaused;
  }

  __weak GRPCCall *weakSelf = self;
  dispatch_async(_callQueue, ^{
    [weakSelf writeMessage:value
          withErrorHandler:^{
            [weakSelf
                finishWithError:[NSError errorWithDomain:kGRPCErrorDomain
                                                    code:GRPCErrorCodeInternal
                                                userInfo:nil]];
          }];
  });
}

// Only called from the call queue. The error handler will be called from the
// network queue if the requests stream couldn't be closed successfully.
- (void)finishRequestWithErrorHandler:(void (^)())errorHandler {
  [_wrappedCall startBatchWithOperations:@[ [[GRPCOpSendClose alloc] init] ]
                            errorHandler:errorHandler];
}

- (void)writesFinishedWithError:(NSError *)errorOrNil {
  if (errorOrNil) {
    [self cancel];
  } else {
    __weak GRPCCall *weakSelf = self;
    dispatch_async(_callQueue, ^{
      [weakSelf finishRequestWithErrorHandler:^{
        [weakSelf finishWithError:[NSError errorWithDomain:kGRPCErrorDomain
                                                      code:GRPCErrorCodeInternal
                                                  userInfo:nil]];
      }];
    });
  }
}

#pragma mark Invoke

// Both handlers will eventually be called, from the network queue. Writes can
// start immediately after this.
// The first one (headersHandler), when the response headers are received.
// The second one (completionHandler), whenever the RPC finishes for any reason.
- (void)invokeCallWithHeadersHandler:(void (^)(NSDictionary *))headersHandler
                   completionHandler:
                       (void (^)(NSError *, NSDictionary *))completionHandler {
  // TODO(jcanizales): Add error handlers for async failures
  [_wrappedCall startBatchWithOperations:@[ [[GRPCOpRecvMetadata alloc]
                                             initWithHandler:headersHandler] ]];
  [_wrappedCall
      startBatchWithOperations:@[ [[GRPCOpRecvStatus alloc]
                                   initWithHandler:completionHandler] ]];
}

- (void)invokeCall {
  [self invokeCallWithHeadersHandler:^(NSDictionary *headers) {
    // Response headers received.
    self.responseHeaders = headers;
    [self startNextRead];
  }
      completionHandler:^(NSError *error, NSDictionary *trailers) {
        self.responseTrailers = trailers;

        if (error) {
          NSMutableDictionary *userInfo = [NSMutableDictionary dictionary];
          if (error.userInfo) {
            [userInfo addEntriesFromDictionary:error.userInfo];
          }
          userInfo[kGRPCTrailersKey] = self.responseTrailers;
          // TODO(jcanizales): The C gRPC library doesn't guarantee that the
          // headers block will be called before this one, so an error might end
          // up with trailers but no headers. We shouldn't call finishWithError
          // until ater both blocks are called. It is also when this is done
          // that we can provide a merged view of response headers and trailers
          // in a thread-safe way.
          if (self.responseHeaders) {
            userInfo[kGRPCHeadersKey] = self.responseHeaders;
          }
          error = [NSError errorWithDomain:error.domain
                                      code:error.code
                                  userInfo:userInfo];
        }
        [self finishWithError:error];
      }];
  // Now that the RPC has been initiated, request writes can start.
  @synchronized(_requestWriter) {
    [_requestWriter startWithWriteable:self];
  }
}

#pragma mark GRXWriter implementation

- (void)startWithWriteable:(id<GRXWriteable>)writeable {
  @synchronized(self) {
    _state = GRXWriterStateStarted;
  }

  // Create a retain cycle so that this instance lives until the RPC finishes
  // (or is cancelled). This makes RPCs in which the call isn't externally
  // retained possible (as long as it is started before being autoreleased).
  // Care is taken not to retain self strongly in any of the blocks used in this
  // implementation, so that the life of the instance is determined by this
  // retain cycle.
  _retainSelf = self;

  _responseWriteable =
      [[GRXConcurrentWriteable alloc] initWithWriteable:writeable];

  _wrappedCall = [[GRPCWrappedCall alloc] initWithHost:_host path:_path];
  NSAssert(_wrappedCall, @"Error allocating RPC objects. Low memory?");

  [self sendHeaders:_requestHeaders];
  [self invokeCall];

  // TODO(jcanizales): Extract this logic somewhere common.
  NSString *host =
  [NSURL URLWithString:[@"https://" stringByAppendingString:_host]].host;
  if (!host) {
    // TODO(jcanizales): Check this on init.
    [NSException raise:NSInvalidArgumentException
                format:@"host of %@ is nil", _host];
  }
  __weak typeof(self) weakSelf = self;
  _connectivityMonitor = [GRPCConnectivityMonitor monitorWithHost:host];
  void (^handler)() = ^{
    typeof(self) strongSelf = weakSelf;
    if (strongSelf) {
      [strongSelf
       finishWithError:[NSError errorWithDomain:kGRPCErrorDomain
                                           code:GRPCErrorCodeUnavailable
                                       userInfo:@{
                                                  NSLocalizedDescriptionKey :
                                                    @"Connectivity lost."
                                                  }]];
    }
  };
  [_connectivityMonitor handleLossWithHandler:handler
                      wifiStatusChangeHandler:^{
                      }];
}

- (void)setState:(GRXWriterState)newState {
  @synchronized(self) {
    // Manual transitions are only allowed from the started or paused states.
    if (_state == GRXWriterStateNotStarted ||
        _state == GRXWriterStateFinished) {
      return;
    }

    switch (newState) {
      case GRXWriterStateFinished:
        _state = newState;
        // Per GRXWriter's contract, setting the state to Finished manually
        // means one doesn't wish the writeable to be messaged anymore.
        [_responseWriteable cancelSilently];
        _responseWriteable = nil;
        return;
      case GRXWriterStatePaused:
        _state = newState;
        return;
      case GRXWriterStateStarted:
        if (_state == GRXWriterStatePaused) {
          _state = newState;
          [self startNextRead];
        }
        return;
      case GRXWriterStateNotStarted:
        return;
    }
  }
}

@end