go-autorest

Usage

Package autorest implements an HTTP request pipeline suitable for use across multiple go-routines and provides the shared routines relied on by AutoRest (see https://github.com/Azure/autorest/) generated Go code.

The package breaks sending and responding to HTTP requests into three phases: Preparing, Sending, and Responding. A typical pattern is:

  req, err := Prepare(&http.Request{},
    token.WithAuthorization())

  resp, err := Send(req,
    WithLogging(logger),
    DoErrorIfStatusCode(http.StatusInternalServerError),
    DoCloseIfError(),
    DoRetryForAttempts(5, time.Second))

  err = Respond(resp,
    ByClosing())

Each phase relies on decorators to modify and / or manage processing. Decorators may first modify and then pass the data along, pass the data first and then modify the result, or wrap themselves around passing the data (such as a logger might do). Decorators run in the order provided. For example, the following:

  req, err := Prepare(&http.Request{},
    WithBaseURL("https://microsoft.com/"),
    WithPath("a"),
    WithPath("b"),
    WithPath("c"))

will set the URL to:

  https://microsoft.com/a/b/c

Preparers and Responders may be shared and re-used (assuming the underlying decorators support sharing and re-use). Performant use is obtained by creating one or more Preparers and Responders shared among multiple go-routines, and a single Sender shared among multiple sending go-routines, all bound together by means of input / output channels.

Decorators hold their passed state within a closure (such as the path components in the example above). Be careful to share Preparers and Responders only in a context where such held state applies. For example, it may not make sense to share a Preparer that applies a query string from a fixed set of values. Similarly, sharing a Responder that reads the response body into a passed struct (e.g., ByUnmarshallingJson) is likely incorrect.

Errors raised by autorest objects and methods will conform to the autorest.Error interface.

See the included examples for more detail. For details on the suggested use of this package by generated clients, see the Client described below.

Helpers

Handling Swagger Dates

The Swagger specification (https://swagger.io) that drives AutoRest (https://github.com/Azure/autorest/) precisely defines two date forms: date and date-time. The github.com/Azure/go-autorest/autorest/date package provides time.Time derivations to ensure correct parsing and formatting.

Handling Empty Values

In JSON, missing values have different semantics than empty values. This is especially true for services using the HTTP PATCH verb. The JSON submitted with a PATCH request generally contains only those values to modify. Missing values are to be left unchanged. Developers, then, require a means to both specify an empty value and to leave the value out of the submitted JSON.

The Go JSON package (encoding/json) supports the omitempty tag. When specified, it omits empty values from the rendered JSON. Since Go defines default values for all base types (such as "" for string and 0 for int) and provides no means to mark a value as actually empty, the JSON package treats default values as meaning empty, omitting them from the rendered JSON. This means that, using the Go base types encoded through the default JSON package, it is not possible to create JSON to clear a value at the server.

The workaround within the Go community is to use pointers to base types in lieu of base types within structures that map to JSON. For example, instead of a value of type string, the workaround uses *string. While this enables distinguishing empty values from those to be unchanged, creating pointers to a base type (notably constant, in-line values) requires additional variables. This, for example,

  s := struct {
    S *string
  }{ S: &"foo" }

fails, while, this

  v := "foo"
  s := struct {
    S *string
  }{ S: &v }

succeeds.

To ease using pointers, the subpackage to contains helpers that convert to and from pointers for Go base types which have Swagger analogs. It also provides a helper that converts between map[string]string and map[string]*string, enabling the JSON to specify that the value associated with a key should be cleared. With the helpers, the previous example becomes

  s := struct {
    S *string
  }{ S: to.StringPtr("foo") }

Install

go get github.com/Azure/go-autorest/autorest
go get github.com/Azure/go-autorest/autorest/azure
go get github.com/Azure/go-autorest/autorest/date
go get github.com/Azure/go-autorest/autorest/to

License

See LICENSE file.