// A Code is an unsigned 32-bit error code as defined in the gRPC spec.
type Code uint32

const (
    // OK is returned on success.
    OK Code = 0

    // Canceled indicates the operation was canceled (typically by the caller).
    Canceled Code = 1

    // Unknown error. An example of where this error may be returned is
    // if a Status value received from another address space belongs to
    // an error-space that is not known in this address space. Also
    // errors raised by APIs that do not return enough error information
    // may be converted to this error.
    Unknown Code = 2

    // InvalidArgument indicates client specified an invalid argument.
    // Note that this differs from FailedPrecondition. It indicates arguments
    // that are problematic regardless of the state of the system
    // (e.g., a malformed file name).
    InvalidArgument Code = 3

    // DeadlineExceeded means operation expired before completion.
    // For operations that change the state of the system, this error may be
    // returned even if the operation has completed successfully. For
    // example, a successful response from a server could have been delayed
    // long enough for the deadline to expire.
    DeadlineExceeded Code = 4

    // NotFound means some requested entity (e.g., file or directory) was
    // not found.
    NotFound Code = 5

    // AlreadyExists means an attempt to create an entity failed because one
    // already exists.
    AlreadyExists Code = 6

    // PermissionDenied indicates the caller does not have permission to
    // execute the specified operation. It must not be used for rejections
    // caused by exhausting some resource (use ResourceExhausted
    // instead for those errors). It must not be
    // used if the caller cannot be identified (use Unauthenticated
    // instead for those errors).
    PermissionDenied Code = 7

    // ResourceExhausted indicates some resource has been exhausted, perhaps
    // a per-user quota, or perhaps the entire file system is out of space.
    ResourceExhausted Code = 8

    // FailedPrecondition indicates operation was rejected because the
    // system is not in a state required for the operation's execution.
    // For example, directory to be deleted may be non-empty, an rmdir
    // operation is applied to a non-directory, etc.
    FailedPrecondition Code = 9

    // Aborted indicates the operation was aborted, typically due to a
    // concurrency issue like sequencer check failures, transaction aborts,
    // etc.
    Aborted Code = 10

    // OutOfRange means operation was attempted past the valid range.
    // E.g., seeking or reading past end of file.
    OutOfRange Code = 11

    // Unimplemented indicates operation is not implemented or not
    // supported/enabled in this service.
    Unimplemented Code = 12

    // Internal errors. Means some invariants expected by underlying
    // system has been broken. If you see one of these errors,
    // something is very broken.
    Internal Code = 13

    // Unavailable indicates the service is currently unavailable.
    // This is a most likely a transient condition and may be corrected
    // by retrying with a backoff. Note that it is not always safe to retry
    // non-idempotent operations.
    Unavailable Code = 14

    // DataLoss indicates unrecoverable data loss or corruption.
    DataLoss Code = 15

    // Unauthenticated indicates the request does not have valid
    // authentication credentials for the operation.
    Unauthenticated Code = 16

    _maxCode = 17
)

syntax = "proto3";

option go_package="echopb";

package echo;

// EchoRequest is the request for echo.
message EchoRequest {
    string message = 1;
}

// EchoResponse is the response for echo.
message EchoResponse {
    string message = 1;
}

// Echo is the echo service.
service Echo {
    // UnaryEcho is unary echo.
    rpc UnaryEcho(EchoRequest) returns (EchoResponse) {}
    // ServerStreamingEcho is server side streaming.
    rpc ServerStreamingEcho(EchoRequest) returns (stream EchoResponse) {}
    // ClientStreamingEcho is client side streaming.
    rpc ClientStreamingEcho(stream EchoRequest) returns (EchoResponse) {}
    // BidirectionalStreamingEcho is bidi streaming.
    rpc BidirectionalStreamingEcho(stream EchoRequest) returns (stream EchoResponse) {}
}

[root@CentOS ~]# cd grpc-go-tutorial/features/echopb/
[root@CentOS echopb]# protoc --go_out=plugins=grpc:. *.proto

// EchoServer is the server API for Echo service.
type EchoServer interface {
    // UnaryEcho is unary echo.
    UnaryEcho(context.Context, *EchoRequest) (*EchoResponse, error)
    // ServerStreamingEcho is server side streaming.
    ServerStreamingEcho(*EchoRequest, Echo_ServerStreamingEchoServer) error