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* Earlier X=Y was passed as _X=Y Signed-off-by: Goutham Veeramachaneni <cs14btech11014@iith.ac.in>
73 lines
2.3 KiB
Markdown
73 lines
2.3 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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We have language libraries for [Go](https://github.com/iron-io/functions_go), [Javascript](https://github.com/iron-io/functions_js) and
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[Ruby](https://github.com/iron-io/functions_ruby).
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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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# Respond if sync:
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STDOUT.write(JSON.generate(return_struct))
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# or update something if async
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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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* REQUEST_URL - the full URL for the request
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* ROUTE - the matched route
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* METHOD - the HTTP method for the request
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* 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 you've set 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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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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## Next Steps
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* [Packaging your function](packaging.md)
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