gRPC with Kotlin Coroutines on Android

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Mohit Sarveiya gRPC with Kotlin Coroutines on Android @heyitsmohit

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gRPC with Kotlin Coroutines ● Using gRPC on Android ● Authentication ● Retries & Hedging ● Debugging tools

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RPC g RPC (Remote Procedure Call) Framework

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• Polyglot implementation • Coroutines Support gRPC

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Server(Go) gRPC Client(Kotlin) Client(Swift)

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Server(Go) gRPC service Client(Kotlin) Client(Swift)

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Server(Go) gRPC service service MyService { rpc subscribe( . . ) }

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• Unary RPC call • Server streaming • Client streaming • Bidirectional streaming RPC Calls

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gRPC service MyService { rpc subscribe( . . ) } Proto buffer file Protoc Service Class

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• Generated class • Handles incoming requests • Send back data Service Class

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Server(Go) gRPC service Client(Kotlin) Client(Swift)

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Server(Go) gRPC service Client(Kotlin) Client(Swift) service service

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gRPC service MyService { rpc subscribe( . . ) } Proto buffer file Protoc Client Stub

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• Generated class. • Make Requests. • Creates response types. Client Stub

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Server(Go) gRPC service Client(Kotlin) Client(Swift) Client Stub

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Server(Go) gRPC service Client(Kotlin) Client(Swift) rpc rpc

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Server(Go) gRPC service Client(Kotlin) Client(Swift) rpc rpc HTTP 2

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Android gRPC Server

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grpc/grpc-kotlin Code ! Issues Pull Requests gRPC-Kotlin/JVM - An RPC library and framework grpc-kotlin-stub v0.1.4 protoc-gen-grpc-kotlinstub v0.1.4 grpc-kotlin-stub-lite v0.1.4 Bazel Build passing Gradle Build passing A Kotlin/JVM implementation of gRPC: A high performance, open source, general RPC framework that puts mobile and HTTP/2 first.

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Use Case ● Tracks your route.

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Use Case ● Tracks your route. ● Get a place from location.

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Use Case ● Tracks your route. ● Get a place from location. ● List Places around location.

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Use Case ● Tracks your route. ● Get a place from location. ● List Places around location. ● Chat with others at location. Shoreline Golf links 2940 N Shoreline Blvd Mountain View, CA 94043 Start typing

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Android gRPC Server gRPC

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gRPC service service MyService { rpc subscribe( . . ) } gRPC Server

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protocolbuffers/protobuf Code ! Issues Pull Requests Protocol Buffers - Google’s data interchange format Protocol Buffers (a.k.a., protobuf) are Google's language-neutral, platform-neutral, extensible mechanism for serializing structured data. Gradle Build passing

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Service syntax = “proto3”; Protocol Buffer Version

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Service syntax = “proto3”; service Places { } Declare Service

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RPC Call Types ● Unary ● Server Streaming ● Client Streaming ● Bidirectional

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Use Case ● Get a place from location   (Latitude, Longitude) Place

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Unary RPC Call Client Server Location

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syntax = “proto3”; service Places { rpc GetPlace(Location) returns (Place) {}; } Unary RPC Call keyword

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Unary RPC Call Name of RPC call service Places { rpc GetPlace() }

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Unary RPC Call service Places { rpc GetPlace(Location) } Request

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Unary RPC Call service Places { rpc GetPlace(Location) returns (Place) {}; } Response

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Unary RPC Call syntax = “proto3”; service Places { rpc GetPlace(Location) returns (Place) {}; } Unary RPC Call

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Unary RPC Call syntax = “proto3”; service Places { rpc GetPlace(Location) returns (Place) {}; } Define messages

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Unary RPC Call message Location { double latitude = 1; double longitude = 2; } } Keyword

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Unary RPC Call service Places { message Location double latitude = 1; double longitude = 2; } } Message name

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Unary RPC Call message Location { double latitude = 1; double longitude = 2; } Fields

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message Location { double latitude = 1; double longitude = 2; } Unary RPC Call Type

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message Location { double latitude = 1; double longitude = 2; } Unary RPC Call .proto Type C++ Java Go double double Double * f l oat64 int32 int32 int *int32 Int64 long int/long *int64 https://developers.google.com/protocol-bu f f ers/docs/overview#scalar

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message Location { double latitude = 1; double longitude = 2; } Unary RPC Call Field numbers

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Unary RPC Call syntax = “proto3”; service Places { rpc GetPlace(Location) returns (Place) {}; } Define Place

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Unary RPC Call message Place { string name = 1; Location location = 2; } Name & Location

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Unary RPC Call message Place { string name = 1; Location location = 2;   PlaceType placeType = 3; } Enum

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Unary RPC Call message Place {   PlaceType placeType = 3; enum PlaceType { Landmark = 0; Driving_Range = 1; Golf_Course = 2; Restaurant = 3; Retail = 4; } Enum

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Unary RPC Call message Place { string name = 1; Location location = 2;   PlaceType placeType = 3; enum PlaceType { … }   int64 checkins = 4; int64 comments = 5; } Int Scaler Types

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Unary RPC Call syntax = “proto3”; service Places { rpc GetPlace(Location) returns (Place) {}; }

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Use Case ● Check into place   Location Empty Response

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Unary RPC Call syntax = “proto3”; service Places { rpc CheckIn(Location) returns () {}; }

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Unary RPC Call syntax = “proto3”; service Places { rpc CheckIn(Location) returns () {}; } How do we return an empty?

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Code ! Issues Pull Requests protocolbuffers/protobuf protobuf/src/google/protobuf/empty.proto message Empty { }

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Well Known Types ● Empty ● Timestamp ● Duration

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Unary RPC Call syntax = “proto3”;   import "google/protobuf/empty.proto"; service Places { rpc CheckIn(Place) returns () {}; } Import

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Unary RPC Call syntax = “proto3”; service Places { rpc CheckIn(Location) returns (google.protobuf.Empty) {}; } How do we return an empty?

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RPC Call Types ● Unary ● Server Streaming ● Client Streaming ● Bidirectional

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Use Case ● List Places around location. Location(s) List

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Server Streaming Client Server Location(s)

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Server Streaming Client Server Stream of Places

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Server Streaming service Places { rpc ListPlaces(Area) returns (stream Place) {}; } Server Streaming RPC Call

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Server Streaming service Places { rpc ListPlaces(Area) returns (stream Place) {}; } Cluster of Locations

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Server Streaming message Area { Location lo = 1; Location hi = 2;   } Cluster of Locations

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Server Streaming service Places { rpc ListPlaces(Area) returns (stream Place) {}; } stream keyword

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Server Streaming service Places { rpc ListPlaces(Area) returns (stream Place) {}; } Server Streaming RPC Call

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RPC Call Types ● Unary ● Server Streaming ● Client Streaming ● Bidirectional

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Use Case ● Tracks your route Location(s)   Trip Summary

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Client Streaming Client Server Location(s)

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Client Streaming Client Server Trip Summary

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Client Streaming service Places { rpc RecordTrip(stream Location) returns (TripSummary) {}; }

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Client Streaming service Places { rpc RecordTrip(stream Location) returns (TripSummary) {}; } Client Stream

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Client Streaming service Places { rpc RecordTrip(stream Location) returns (TripSummary) {}; } Return single message

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Client Streaming service Places { rpc RecordTrip(stream Location) returns (TripSummary) {}; }

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RPC Call Types ● Unary ● Server Streaming ● Client Streaming ● Bidirectional

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Use Case ● Chat with others at location ● Stream of messages Shoreline Golf links 2940 N Shoreline Blvd Mountain View, CA 94043 Start typing

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Bidirectional RPC Call Client Server Comments

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Bidirectional RPC Call Client Server Replies

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Bidirectional RPC Call service Places { rpc Chat(stream Comment) returns (stream Comment) {}; } Bidirectional RPC Call

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Bidirectional RPC Call service Places { rpc Chat(stream Comment) returns (stream Comment) {}; } stream keyword

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RPC Call Types ● Unary ● Server Streaming ● Client Streaming ● Bidirectional

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RPC Call Types service Places { rpc GetPlace(Location) returns (Place) {}; rpc ListPlaces(Area) returns (stream Place) {}; rpc CheckIn(Place) returns (google.protobuf.Empty) {}; rpc Chat(stream Comment) returns (stream Comment) {}; }

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gRPC service MyService { rpc subscribe( . . ) } gRPC Server Service

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Android gRPC Server gRPC Service Service

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Android gRPC Client Stub

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Generating Client Stub ● Class for messages ● Coroutine bindings for rpc calls

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Generating Builders Proto buffer file Protoc Message Builders class Message { static class Builder { Builder set(double value) Location build() } }

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Creating Messages message Location { double latitude = 1; double longitude = 2; } class Location { static class Builder { Builder setLatitude(double value) Builder setLongitude(double value) Location build() } }

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Creating Messages message Location { double latitude = 1; double longitude = 2; } Location.newBuilder() .setLatitude(40.9888341) .setLongitude(-73.8502007) .build()

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protocolbuffers/protobuf Code ! Issues Pull Requests Kotlin support request #3742 ! Open issue opened on Oct 12, 2017 comment on opened on Oct 12, 2017 Please support convert to Kotlin 168

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Generating Service Proto buffer file Protoc Service class Service { fun rpcMethod1(): Flow   fun rpcMethod2(): Flow }

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Generated Client class CoroutineStub { }

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Generated Client class CoroutineStub { } rpc GetPlace(Location) returns (Place) {};

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Generated Client class CoroutineStub { } rpc GetPlace(Location) returns (Place) {}; suspend fun getPlace(request: Location): Place

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Generated Client class CoroutineStub { } rpc ListPlaces(Area) returns (stream Place) {};

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Generated Client class CoroutineStub { } rpc ListPlaces(Area) returns (stream Place) {}; fun listPlaces(request: Area): Flow Stream is map to Flow

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Generated Client class CoroutineStub { } rpc Chat(stream Comment) returns (stream Comment) {};

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Generated Client class CoroutineStub { } rpc Chat(stream Comment) returns (stream Comment) {}; fun chat(requests: Flow): Flow Stream is map to Flow

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Generated Client class CoroutineStub { } suspend fun getPlace(request: Location): Place fun recordTrip(requests: Flow): TripSummary fun listPlaces(request: Area): Flow fun chat(requests: Flow): Flow

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• Create Managed Channel • Specify server url, port • Create Client Stub Using Client

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Using Client val managedChannel = ManagedChannelBuilder .forAddress(host, port) .useTransportSecurity() .build()

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Using Client val managedChannel = ManagedChannelBuilder .forAddress(host, port) .useTransportSecurity() .build() Specify host and port

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Using Client val managedChannel = ManagedChannelBuilder .forAddress(host, port) .useTransportSecurity() for https

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Using Client val managedChannel = ManagedChannelBuilder .intercept(object : ClientInterceptor { fun interceptCall(method, callOptions, channel) { }) Intercept RPC Calls

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Using Client val managedChannel = ManagedChannelBuilder .forAddress(host, port) .useTransportSecurity() .build()

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Using Client val managedChannel = ManagedChannelBuilder .forAddress(host, port) .useTransportSecurity() .build() val client = CoroutineStub(managedChannel)

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View Model gRPC Client Stub

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Using Client class GrpcViewModel(val client: CoroutineStub): ViewModel() { }

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Unary RPC Call class CoroutineStub { } suspend fun getPlace(request: Location): Place

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Unary RPC Call fun getPlace(location: Location) { viewModelScope.launch { } }

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Unary RPC Call fun getPlace(location: Location) { viewModelScope.launch { val place = client.getPlace(location) } }

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Unary RPC Call fun getPlace(location: Location) { viewModelScope.launch { withContext(Dispatchers.IO) { val place = client.getPlace(location) } } }

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Server Streaming class CoroutineStub { } fun listPlaces(request: Area): Flow

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Server Streaming fun listPlaces(area: Area) { }

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Server Streaming fun listPlaces(area: Area) { viewModelScope.launch { } }

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Server Streaming fun listPlaces(area: Area) { viewModelScope.launch { val places: Flow = client.listPlaces(area) } }

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Server Streaming fun listPlaces(area: Area) { viewModelScope.launch { val places: Flow = client.listPlaces(area) places.collect { } } }

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Bidirectional RPC Call class CoroutineStub { } fun chat(requests: Flow): Flow

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Bidirectional RPC Call class CoroutineStub { } fun chat(requests: Flow): Flow

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Bidirectional RPC Call Client Stub Comments

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Bidirectional RPC Call State Flow Comments

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Bidirectional RPC Call State Flow Comments Comments Client Stub

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Using Client fun chat(comments: Flow) { } Stream of comments

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Using Client fun chat(comments: Flow) { viewModelScope.launch { } } } }

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Using Client fun chat(comments: Flow) { viewModelScope.launch { client.chat(comments) } } } }

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Using Client fun chat(comments: Flow) { viewModelScope.launch { client.chat(comments) .collect { } } } }

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Using Client class GrpcViewModel(val client: CoroutineStub): ViewModel() { fun getPlace(location: Location) fun listPlaces(area: Area): Flow fun chat(chat: Flow) }

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gRPC Client Stub How does it use coroutines?

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Consumer Coroutine

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gRPC-java client Start Consumer Coroutine

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gRPC-java client Request Consumer Coroutine Producer Coroutine Response

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gRPC-java client Request Consumer Coroutine Producer Coroutine Response Channel (size = 1)

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gRPC-java client Request Consumer Coroutine Producer Coroutine Response Channel (size = 1)

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gRPC-java client Request Consumer Coroutine Producer Coroutine Response Channel (size = 1) Flow

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gRPC Client Stub How does it use coroutines?

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Android gRPC Client Stub Auth

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Auth Methods ● JWT Token ● Certificate Auth ● HTTP Basic Auth

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Auth Client Server RPC Call

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Auth Client Server Metadata

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Auth Metadata headers = new Metadata();

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Auth Metadata headers = new Metadata(); headers.put(“auth_token","token");

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Auth val client = CoroutineStub(managedChannel)

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Auth val client = CoroutineStub(managedChannel) .withCallCredentials( . . . )

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withCallCredentials(object: CallCredentials { override fun applyRequestMetadata() { } } Auth

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withCallCredentials(object: CallCredentials { override fun applyRequestMetadata(applier: MetadataApplier) { } } Auth

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withCallCredentials(object: CallCredentials { override fun applyRequestMetadata(applier: MetadataApplier) { Metadata headers = new Metadata(); headers.put(“auth_token","token"); } } Auth

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withCallCredentials(object: CallCredentials { override fun applyRequestMetadata(applier: MetadataApplier) { Metadata headers = new Metadata(); headers.put(“auth_token","token"); applier.apply(headers); } } Auth

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Auth Client Server RPC Call

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Auth Client Server Metadata

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Errors Client Server RPC Call

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Errors Client Server Retry

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Enable Retry val managedChannel = ManagedChannelBuilder .forAddress(host, port) .useTransportSecurity() .enableRetry() .build()

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Client App gRPC Client Lib Server Application

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Client App gRPC Client Lib Server Application Make   gRPC Call Sends RPC

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Client App gRPC Client Lib Server Application Failure Make   gRPC Call Sends RPC

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Client App gRPC Client Lib Server Application Failure Make   gRPC Call Sends RPC Returns UNAVAILABLE

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Client App gRPC Client Lib Server Application Failure Make   gRPC Call Sends RPC Returns UNAVAILABLE Retried RPC

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Client App gRPC Client Lib Server Application Failure Make   gRPC Call Sends RPC Returns UNAVAILABLE Retried RPC Success Return OK Receive   data

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Enable Retry "retryPolicy": { "maxAttempts": 10, "initialBackoff": "5s", "maxBackoff": "1s", "backoffMultiplier": 2, "retryableStatusCodes": [ "UNAVAILABLE" ] }

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Hedging Client Server RPC Call(s)

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Client App gRPC Client Lib Server Application Make   gRPC Call Sends RPC

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Client App gRPC Client Lib Server Application Make   gRPC Call Sends RPC Return OK

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Client App gRPC Client Lib Server Application Make   gRPC Call Sends RPC Cancel

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Hedging Policy "hedgingPolicy": { "maxAttempts": 10, "hedgingDelay": “1.5s", "nonFatalStatusCodes": [ "UNAVAILABLE", "INTERNAL", "ABORTED" ] }

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uw-labs/bloom-rpc Code ! Issues Pull Requests BloomRPC The missing GUI Client for GRPC services. release v1.5.2

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No content

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gRPC https: / / codingwithmohit.com/grpc/grpc-kotlin-coroutines/

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Resources ● gRPC with Kotlin Coroutines     https: / / codingwithmohit.com/grpc/grpc-kotlin-coroutines/ ● Unit Testing Delays, Errors & Retries with Kotlin Flows     https: / / codingwithmohit.com/coroutines/unit-testing-delays-   errors-retries-with-kotlin-flows/    

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Thank You! www.codingwithmohit.com @heyitsmohit