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# Go SDK (experimental)

The Go SDK is currently an experimental feature of Apache Beam and
not suitable for production use. It is based on the following initial 
[design](https://s.apache.org/beam-go-sdk-design-rfc).

## How to run the examples

**Prerequisites**: to use Google Cloud sources and sinks (default for
most examples), follow the setup
[here](https://beam.apache.org/documentation/runners/dataflow/). You can
verify that it works by running the corresponding Java example.

The examples are normal Go programs and are most easily run directly. They
are parameterized by Go flags. For example, to run wordcount on direct runner do:

```
$ pwd
[...]/sdks/go
$ go run examples/wordcount/wordcount.go --output=/tmp/result.txt
[{6: KV<string,int>/GW/KV<bytes,int[varintz]>}]
[{10: KV<int,string>/GW/KV<int[varintz],bytes>}]
2018/03/21 09:39:03 Pipeline:
2018/03/21 09:39:03 Nodes: {1: []uint8/GW/bytes}
{2: string/GW/bytes}
{3: string/GW/bytes}
{4: string/GW/bytes}
{5: string/GW/bytes}
{6: KV<string,int>/GW/KV<bytes,int[varintz]>}
{7: CoGBK<string,int>/GW/CoGBK<bytes,int[varintz]>}
{8: KV<string,int>/GW/KV<bytes,int[varintz]>}
{9: string/GW/bytes}
{10: KV<int,string>/GW/KV<int[varintz],bytes>}
{11: CoGBK<int,string>/GW/CoGBK<int[varintz],bytes>}
Edges: 1: Impulse [] -> [Out: []uint8 -> {1: []uint8/GW/bytes}]
2: ParDo [In(Main): []uint8 <- {1: []uint8/GW/bytes}] -> [Out: T -> {2: string/GW/bytes}]
3: ParDo [In(Main): string <- {2: string/GW/bytes}] -> [Out: string -> {3: string/GW/bytes}]
4: ParDo [In(Main): string <- {3: string/GW/bytes}] -> [Out: string -> {4: string/GW/bytes}]
5: ParDo [In(Main): string <- {4: string/GW/bytes}] -> [Out: string -> {5: string/GW/bytes}]
6: ParDo [In(Main): T <- {5: string/GW/bytes}] -> [Out: KV<T,int> -> {6: KV<string,int>/GW/KV<bytes,int[varintz]>}]
7: CoGBK [In(Main): KV<string,int> <- {6: KV<string,int>/GW/KV<bytes,int[varintz]>}] -> [Out: CoGBK<string,int> -> {7: CoGBK<string,int>/GW/CoGBK<bytes,int[varintz]>}]
8: Combine [In(Main): int <- {7: CoGBK<string,int>/GW/CoGBK<bytes,int[varintz]>}] -> [Out: KV<string,int> -> {8: KV<string,int>/GW/KV<bytes,int[varintz]>}]
9: ParDo [In(Main): KV<string,int> <- {8: KV<string,int>/GW/KV<bytes,int[varintz]>}] -> [Out: string -> {9: string/GW/bytes}]
10: ParDo [In(Main): T <- {9: string/GW/bytes}] -> [Out: KV<int,T> -> {10: KV<int,string>/GW/KV<int[varintz],bytes>}]
11: CoGBK [In(Main): KV<int,string> <- {10: KV<int,string>/GW/KV<int[varintz],bytes>}] -> [Out: CoGBK<int,string> -> {11: CoGBK<int,string>/GW/CoGBK<int[varintz],bytes>}]
12: ParDo [In(Main): CoGBK<int,string> <- {11: CoGBK<int,string>/GW/CoGBK<int[varintz],bytes>}] -> []
2018/03/21 09:39:03 Reading from gs://apache-beam-samples/shakespeare/kinglear.txt
2018/03/21 09:39:04 Writing to /tmp/result.txt
```

The debugging output is currently quite verbose and likely to change. The output is a local
file in this case:

```
$ head /tmp/result.txt 
while: 2
darkling: 1
rail'd: 1
ford: 1
bleed's: 1
hath: 52
Remain: 1
disclaim: 1
sentence: 1
purse: 6
```

To run wordcount on dataflow runner do:

```
$  go run wordcount.go --runner=dataflow --project=<YOUR_GCP_PROJECT> --staging_location=<YOUR_GCS_LOCATION>/staging --worker_harness_container_image=<YOUR_SDK_HARNESS_IMAGE_LOCATION> --output=<YOUR_GCS_LOCATION>/output
```

The output is a GCS file in this case:

```
$ gsutil cat <YOUR_GCS_LOCATION>/output* | head
Blanket: 1
blot: 1
Kneeling: 3
cautions: 1
appears: 4
Deserved: 1
nettles: 1
OSWALD: 53
sport: 3
Crown'd: 1
```


See [BUILD.md](./BUILD.md) for how to build Go code in general. See
[CONTAINERS.md](../CONTAINERS.md) for how to build and push the Go
SDK harness container image.

## Issues

Please use the [`sdk-go`](https://issues.apache.org/jira/issues/?jql=project%20%3D%20BEAM%20AND%20resolution%20%3D%20Unresolved%20AND%20component%20%3D%20sdk-go%20ORDER%20BY%20priority%20DESC%2C%20updated%20DESC) component for any bugs or feature requests.

## Contributing to the Go SDK

### New to developing Go?
https://tour.golang.org : The Go Tour gives you the basics of the language, interactively no installation required.

https://github.com/campoy/go-tooling-workshop is a great start on learning good (optional) development tools for Go. 

### Developing Go Beam SDK on Github

To make and test changes when working with Go, it's neecessary to clone your repository 
in a subdirectory of your GOPATH. This permits existing gradle tools to use your in progress changes.

```
# Create a Go compatible place for the repo, using src/github.com/apache/
# matches where Go will look for the files, or go get would put them.
$ mkdir -p $GOPATH/src/github.com/apache/
$ cd $GOPATH/src/github.com/apache/


# Clone the repo, and update your branch as normal
$ git clone https://github.com/apache/beam.git
$ cd beam
$ git remote add <GitHub_user> git@github.com:<GitHub_user>/beam.git
$ git fetch --all

# Get or Update all the Go SDK dependencies
$ go get -u ./...
# Test that the system compiles and runs.
$ go test ./...
```

If you don’t have a GOPATH set, follow [these instructions](https://github.com/golang/go/wiki/SettingGOPATH) to create a new directory in your home directory, and use that.

Follow the [contribution guide](https://beam.apache.org/contribute/contribution-guide/#code) to create branches, and submit pull requests as normal.

### Dependency management
Until [BEAM-5379](https://issues.apache.org/jira/browse/BEAM-5379) is resolved,
Beam locks versions of packages with the gogradle plugin. If new dependencies
are added in a PR then the lock file needs to be updated. 
From the `$GOPATH/src/github.com/apache/beam` directory run

```
$ ./gradlew :sdks:go:goLock
`./gradlew :goPostcommit`
```

 to update the lock file, and test your code under the locked versions. gogradle
will add vendor directories with the locked versions of the code.

You can sanity check a PR on Jenkins by commenting `Run Go PostCommit` to trigger 
the integration tests. This is important so that the Beam testing done on the
jenkins cluster can produce consistent results, and have the packages available.


