README.md
1# Metadata Example
2
3## Overview
4
5This example shows you how to add custom headers on the client and server and
6how to access them.
7
8Custom metadata must follow the "Custom-Metadata" format listed in
9https://github.com/grpc/grpc/blob/master/doc/PROTOCOL-HTTP2.md, with the
10exception of binary headers, which don't have to be base64 encoded.
11
12### Get the tutorial source code
13 The example code for this and our other examples lives in the `examples` directory. Clone this repository
14 at the [latest stable release tag](https://github.com/grpc/grpc/releases) to your local machine by running the following command:
15 ```sh
16$ git clone -b RELEASE_TAG_HERE https://github.com/grpc/grpc
17```
18 Change your current directory to examples/cpp/metadata
19 ```sh
20$ cd examples/cpp/metadata
21```
22
23### Generating gRPC code
24 To generate the client and server side interfaces:
25 ```sh
26$ make helloworld.grpc.pb.cc helloworld.pb.cc
27```
28Which internally invokes the proto-compiler as:
29 ```sh
30$ protoc -I ../../protos/ --grpc_out=. --plugin=protoc-gen-grpc=grpc_cpp_plugin ../../protos/helloworld.proto
31$ protoc -I ../../protos/ --cpp_out=. ../../protos/helloworld.proto
32```
33### Try it!
34Build client and server:
35
36```sh
37$ make
38```
39
40Run the server, which will listen on port 50051:
41
42```sh
43$ ./greeter_server
44```
45
46Run the client (in a different terminal):
47
48```sh
49$ ./greeter_client
50```
51
52If things go smoothly, you will see in the client terminal:
53
54"Client received initial metadata from server: initial metadata value"
55"Client received trailing metadata from server: trailing metadata value"
56"Client received message: Hello World"
57
58
59And in the server terminal:
60
61"Header key: custom-bin , value: 01234567"
62"Header key: custom-header , value: Custom Value"
63"Header key: user-agent , value: grpc-c++/1.16.0-dev grpc-c/6.0.0-dev (linux; chttp2; gao)"
64
65We did not add the user-agent metadata as a custom header. This shows how
66the gRPC framework adds some headers under the hood that may show up in the
67metadata map.
68