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* Remove lots of refs to iron and funcy oracle etc.. * more ref replacements * Replacing more refs. Treeder * Use Fn not FN
95 lines
3.4 KiB
Markdown
95 lines
3.4 KiB
Markdown
# Writing Functions
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This will give you the basic overview of writing base level functions. You can also use higher level
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abstractions that make it easier such as [lambda](lambda/README.md).
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Also, for complete examples in various languages, see the [examples directory](/examples).
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## Code
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The most basic code layout in any language is as follows, this is pseudo code and is not meant to run.
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```ruby
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# Read and parse from STDIN
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body = JSON.parse(STDIN)
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# Do something
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return_struct = doSomething(body)
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# If sync, respond:
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STDOUT.write(JSON.generate(return_struct))
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# If async, update something:
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db.update(return_struct)
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```
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## Inputs
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Inputs are provided through standard input and environment variables. We'll just talk about the default input format here, but you can find others [here](function-format.md).
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To read in the function body, just read from STDIN.
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You will also have access to a set of environment variables.
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* `FN_REQUEST_URL` - the full URL for the request ([parsing example](https://github.com/fnproject/fn/tree/master/examples/tutorial/params))
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* `FN_APP_NAME` - the name of the application that matched this route, eg: `myapp`
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* `FN_PATH` - the matched route, eg: `/hello`
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* `FN_METHOD` - the HTTP method for the request, eg: `GET` or `POST`
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* `FN_CALL_ID` - a unique ID for each function execution.
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* `FN_FORMAT` - a string representing one of the [function formats](function-format.md), currently either `default` or `http`. Default is `default`.
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* `FN_MEMORY` - a number representing the amount of memory available to the call, in MB
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* `FN_TYPE` - the type for this call, currently 'sync' or 'async'
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* `FN_HEADER_$X` - the HTTP headers that were set for this request. Replace $X with the upper cased name of the header and replace dashes in the header with underscores.
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* `$X` - any [configuration values](https://github.com/fnproject/cli/blob/master/README.md#application-level-configuration) you've set
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for the Application or the Route. Replace X with the upper cased name of the config variable you set. Ex: `minio_secret=secret` will be exposed via MINIO_SECRET env var.
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* `FN_PARAM_$Y` - any variables found from parsing the URL. Replace $Y with any `:var` from the url.
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Warning: these may change before release.
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## Logging
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Standard out is where you should write response data for synchronous functions. Standard error
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is where you should write for logging, as [it was intended](http://www.jstorimer.com/blogs/workingwithcode/7766119-when-to-use-stderr-instead-of-stdout).
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So to write output to logs, simply log to STDERR. Here are some examples in a few languages.
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In Go, simply use the [log](https://golang.org/pkg/log/) package, it writes to STDERR by default.
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```go
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log.Println("hi")
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```
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In Node.js:
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```node
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console.error("hi");
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```
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[More details for Node.js here](http://stackoverflow.com/a/27576486/105562).
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In Ruby:
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```ruby
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STDERR.puts("hi")
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```
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## Using Lambda Functions
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### Lambda everywhere
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Lambda support for Fn enables you to take your AWS Lambda functions and run them
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anywhere. You should be able to take your code and run them without any changes.
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Creating Lambda functions is not much different than using regular functions, just use
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the `lambda-node` runtime.
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```sh
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fn init --runtime lambda-node --name lambda-node
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```
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Be sure the filename for your main handler is `func.js`.
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TODO: Make Java and Python use the new workflow too.
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## Next Steps
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* [Packaging your function](packaging.md)
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