Package 'porcelain'

Title: Turn a Package into an HTTP API
Description: Wrapper around the plumber package to turn a package into an HTTP API. This adds some conventions that we find useful, such as some testing infrastructure and automatic validation of responses against a json schema.
Authors: Rich FitzJohn [aut, cre], Imperial College of Science, Technology and Medicine [cph]
Maintainer: Rich FitzJohn <[email protected]>
License: MIT + file LICENSE
Version: 0.1.15
Built: 2024-09-26 04:13:51 UTC
Source: https://github.com/reside-ic/porcelain

Help Index

A porcelain object

Description

A porcelain object. This extends (via inheritance) a plumber object, and so only changes to the plumber API are documented here.

Super classes

plumber::Hookable -> plumber::Plumber -> porcelain

Methods

Public methods

Inherited methods

Method new()

Create a porcelain object

Usage
porcelain$new(..., validate = FALSE, logger = NULL)
Arguments
...

Parameters passed to plumber

validate

Logical, indicating if any validation (implemented by the validate_response argument) should be enabled. This should be set to FALSE in production environments. By default (if validate is NULL), we look at the value of the environment PORCELAIN_VALIDATE - if true (case insensitive) then we will validate. This is intended to support easy use of validation on continuous integration systems.

logger

Optional logger, from the lgr package, perhaps created with porcelain_logger. If given, then we will log at the beginning and end of the request.

Method include_package_endpoints()

Include package endpoints

Usage
porcelain$include_package_endpoints(state = NULL, package = NULL)
Arguments
state

A named list of state, if your package requires any state-binding endpoints. Typically these will be mutable state (database connections, job queues, or similar). You must provide all states as required by the combination of all endpoints.

package

Either a package name or environment (optional, usually we'll find the right thing)

Method handle()

Handle an endpoint

Usage
porcelain$handle(...)
Arguments
...

Either a single argument, being a porcelain_endpoint object representing an endpoint, or arguments to pass through to plumber.

Method request()

Send a request to plumber for debugging

Sends a request to plumber so that the API can be easily tested without running the whole API. The interface here will probably change, and may end up using the interface of httr.

Usage
porcelain$request(
  method,
  path,
  query = NULL,
  body = NULL,
  content_type = NULL,
  request_id = NULL
)
Arguments
method

Name of HTTP method to use (e.g., GET)

path

Path to send the request to

query

Optional query parameters as a named list or character vector.

body

Optional body (only valid with PUT, POST, etc).

content_type

Optional content type (mime) which can be provided alongside body. If not provided it is set to application/octet-stream if body is raw, or application/json otherwise.

request_id

Optional request ID. An ID which is attached to every log raised by this request. Used for tracing purposes.

Method clone()

The objects of this class are cloneable with this method.

Usage
porcelain$clone(deep = FALSE)
Arguments
deep

Whether to make a deep clone.

Add headers to endpoint output data

Description

Intended to be used from endpoint target function. Note Content-Type headers are handled by returning arg to endpoint.

Usage

porcelain_add_headers(data, headers)

Arguments

data

Response data
headers

Named list of headers to add.

Value

Data from endpoint target with headers

Examples

porcelain_add_headers("output",
                   list("Content-Dispotition" = "output_file.txt"))

While porcelain makes it easy to test endpoints individually, you may still want some integration or end-to-end tests where you bring the entire API up and interact with it from your tests. This class provides a helper for doing this in a way that is reasonably tidy.

Description

While porcelain makes it easy to test endpoints individually, you may still want some integration or end-to-end tests where you bring the entire API up and interact with it from your tests. This class provides a helper for doing this in a way that is reasonably tidy.

While porcelain makes it easy to test endpoints individually, you may still want some integration or end-to-end tests where you bring the entire API up and interact with it from your tests. This class provides a helper for doing this in a way that is reasonably tidy.

Public fields

log

The path to the log file (read-only)

port

The port used by the background server (read-only)

Methods

Public methods

Method new()

Create a background server object

Usage
porcelain_background$new(
  create,
  args = NULL,
  port = NULL,
  log = NULL,
  verbose = FALSE,
  timeout = 60,
  env = NULL
)
Arguments
create

A function that will create an api object

args

Arguments that will be passed to create when creating the api object in the background process

port

The port to use for the background server. If not given then a random free port will be used in the range 8000 to 10000 - you can find the created port using the port field in the resulting object, or use the ⁠$url()⁠ or ⁠$request()⁠ methods.

log

The path to a log file to use

verbose

Logical, indicating if we should print informational messages to the console on start/stop etc.

timeout

The number of seconds to wait for the server to become available. This needs to cover the time taken to spawn the R process, and create your API object (loading all packages needed) up to the point where the server is responsive. In most cases this will take 1-2s but if you use packages that use many S4 methods or run this on a slow computer (e.g., a continuous integration server) it may take longer than you expect. The default is one minute which should be sufficient in almost all cases.

env

A named character vector of environment variables (e.g., c(VARIABLE = "value")) to set in the background process before launching the server. You can use this to control the behaviour of the background server using variables your api recognises. In addition, we export callr::rcmd_safe_env() and the value of PORCELAIN_VALIDATE.

Method start()

Start the server. It is an error to try and start a server that is already running.

Usage
porcelain_background$start()

Method status()

Return the background server status. This will be one of:

  • running: The server is running

  • stopped: The server is stopped

  • blocked: The server is stopped, but something else is running on the port that we would use

  • starting: The server is starting up (not visible in normal usage)

Usage
porcelain_background$status()

Method stop()

Stop a running server. If the server is not running, this has no effect.

Usage
porcelain_background$stop()

Method url()

Create a url string for the server, interpolating the (possibly random) port number. You can use this in your tests like bg$url("/path")

Usage
porcelain_background$url(path)
Arguments
path

String representing the absolute path

Method request()

Run a request to the server, using httr. This presents a similar inteface to the request method on the porcelain object.

Usage
porcelain_background$request(method, path, ...)
Arguments
method

The http method as a string (e.g., "GET"), passed to httr::VERB as the verb argument

path

String representing the absolute path, passed to ⁠$url()⁠

...

Additional arguments passed to httr::VERB, such as query, or the body for a POST request.

Basic endpoint object

Description

Create a porcelain_endpoint object that collects together an HTTP method (e.g., GET), a path (e.g., /path) and a target R function. Unlike plumber endpoints, porcelain endpoints are meant to be used in testing.

Public fields

method

HTTP method

path

HTTP path

target

R function used for the endpoint

validate

Logical, indicating if response validation is used

inputs

Input control

state

Possibly mutable state

returning

An porcelain_returning object controlling the return type (content type, status code, serialisation and validation information).

Methods

Public methods

Method new()

Create an endpoint

Usage
porcelain_endpoint$new(method, path, target, ..., returning, validate = NULL)
Arguments
method

The HTTP method to support

path

The server path for the endpoint

target

An R function to run as the endpoint

...

Additional parameters, currently representing inputs. You can use the functions porcelain_input_query, porcelain_input_body_binary and porcelain_input_body_json to define inputs and pass them into this method. The names used must match those in target.

returning

Information about what the endpoint returns, as created by porcelain_returning

validate

Logical, indicating if any validation (implemented by the validate_response argument) should be enabled. This should be set to FALSE in production environments. By default (if validate is NULL), we look at the value of the environment PORCELAIN_VALIDATE - if true (case insensitive) then we will validate. This is intended to support easy use of validation on continuous integration systems.

validate_response

Optional function that throws an error of the processed body is "invalid".

Method run()

Run the endpoint. This will produce a standardised response object that contains status_code, content_type, body (the serialised output as run through the process method and returned by plumber) and data (the result of running the target function)

Usage
porcelain_endpoint$run(...)
Arguments
...

Arguments passed through to the target function

Method request()

Test the endpoint. This creates a full plumber object and serves one request to the endpoint. Argument are as passed through to porcelain's $request() method, except that method and path are automatically taken from the endpoint itself.

Usage
porcelain_endpoint$request(...)
Arguments
...

Arguments passed through to the request method (query, body and content_type).

Method plumber()

Helper method for use with plumber - not designed for end-user use. This is what gets called by plumber when the endpoint receives a request.

Usage
porcelain_endpoint$plumber(req, res, ...)
Arguments
req, res

Conventional plumber request/response objects

...

Additional arguments passed through to run

Method create()

Create a plumber endpoint

Usage
porcelain_endpoint$create(envir, validate)
Arguments
envir

Environment as used by plumber (currently unclear)

validate

Logical, allowing override of validation at the api level. This takes precedence over the value set when creating the endpoint.

Method clone()

The objects of this class are cloneable with this method.

Usage
porcelain_endpoint$clone(deep = FALSE)
Arguments
deep

Whether to make a deep clone.

Control for body parameters

Description

Control for body parameters. This might change. There are several types of HTTP bodies that we want to consider here - the primary ones are a body uploaded in binary, the other is a json object. In the latter we want to validate the body against a schema (at least if validation is used). In future we might also support a form input here too.

Usage

porcelain_input_body_binary(name, content_type = NULL)

porcelain_input_body_json(name, schema = NULL, root = NULL, extract = NULL)

Arguments

name

Name of the parameter
content_type

Content type for the input. If not given, then application/octet-stream is used. Provide a vector of valid types to allow any of the types to be passed.
schema

The name of the json schema to use
root

The root of the schema directory.
extract

Optionally, the name of an element to extract from the json. If given, then the body must be a json object (not an array, for example) and extract must refer to a top-level key within it. We will extract the JSON string corresponding to this key and forward that to the argument name. Deserialisation of the json is still the target function's responsibility but there will be less of it.

Control for query parameters

Description

Control for query parameters.

Usage

porcelain_input_query(..., .parameters = list(...))

Arguments

...

Named arguments representing accepted parameters. The value of each must be a type.
.parameters

A list of named parameters to accept, instead of using ... - this interface is considerably easier to program against if building an API programmatically, avoiding the use of do.call.

Examples

porcelain::porcelain_input_query(number = "integer")

Create logger

Description

Create a json-emitting logger, using the 'lgr' package.

Usage

porcelain_logger(log_level = "info", name = NULL, path = NULL)

Arguments

log_level

The level of detail to log to. See lgr::get_log_levels() for possible values; this could be a string ("off", "info", "all", etc) or an integer level.
name

The name of the logger. By default we use one derived from the package name, though this may not always be accurate.
path

Optionally, the path to log into. If not given then we log to the console.

Value

A "Logger" object (see lgr::Logger)

Examples

logger <- porcelain::porcelain_logger(name = "example")
logger$log("info", "hello")
logger$log("trace", "silent")

Find roxygen-defined endpoint

Description

Find an endpoint defined implicitly through roxygen comments (rather than explicitly via writing porcelain_endpoint.

Usage

porcelain_package_endpoint(
  package,
  method,
  path,
  state = NULL,
  validate = NULL
)

Arguments

package

The name of the package to look in, provided as a string or as a namespace
method

The HTTP method (i.e., verb), such as GET or POST, as a string
path

The path of the method (e.g., ⁠/my/path⁠)
state

A list of state to bind into the method, if your endpoint requires any
validate

Logical, indicating if the method should be created with schema validation enabled.

Value

The endpoint, a porcelain_endpoint object

Support for endpoint return types

Description

Support for describing and controlling expected return types. The high-level functions (porcelain_returning_json and porcelain_returning_binary) should be generally used.

Usage

porcelain_returning(content_type, process, validate, status_code = 200L)

porcelain_returning_json(schema = NULL, root = NULL, status_code = 200L)

porcelain_returning_binary(status_code = 200L)

porcelain_returning_text(status_code = 200L)

Arguments

content_type

The MIME content type for the endpoint, e.g. text/plain, application/json.
process

A processing function that will convert the output of the handler function into something of the type content_type. This should be independent of arguments passed to the endpoint, so practically this is the final stage of serialisation.
validate

A function that validates the return value and throws an error if the output is not expected. This will only be used if the endpoint is created with validate = TRUE.
status_code

The HTTP status code that the endpoint will use on a successful return. The default of 200 should be reasonable.
schema

The name of the json schema to use
root

The root of the schema directory.

Define API using roxygen tags

Description

A roclet for processing ⁠@porcelain⁠ tags within a package. This presents an automated declarative approach to defining porcelain APIs using roxygen tags. When you roxygenise your package (e.g., with devtools::document() or roxygen2::roxygenise()) this roclet will create a file R/porcelain.R within your package that will be included into your package API.

Usage

porcelain_roclet()

Value

A roclet, used by roxygen2 (not typically called by users directly)

Bind state into an endpoint

Description

Bind state into an endpoint

Usage

porcelain_state(..., .state = list(...))

Arguments

...

Named arguments representing state to bind; see Details.
.state

A list of named state to bind, instead of using ... - this interface is considerably easier to program against if building an API programmatically, avoiding the use of do.call.

Details

This method allows state to be bound to the target function. Each element of ... (or .state) is named with the argument to the target function being bound, and the value is the value that argument will take. Once bound, the arguments to the target function may not be provided by an input.

The primary use case for this is to bind mutable state (database connections, etc) that may be shared amongst different endpoints within an API.

Throw an error from an endpoint

Description

Throw an error from an endpoint. This function is intended to allow target functions to throw nice errors back through the API.

Usage

porcelain_stop(message, code = "ERROR", errors = NULL, status_code = 400L, ...)

Arguments

message

The human-readable message of the error. Ignored if errors is given.
code

Optional code for the error - if not given, then ERROR is used. Ignored if errors is given.
errors

A named list of errors - use this to signal multiple error conditions as key/value pairs.
status_code

The HTTP status code to use. The default (400) means "bad request" which should be a reasonable catch-all for bad user data.
...

Additional named args to be included as fields in the error response JSON. The values must be in format ready for serialization to JSON using jsonlite::toJSON() i.e. any unboxing using jsonlite::unbox() needs to already have been done.

Value

Nothing, as this function throws an error