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133 lines
5.3 KiB
Markdown
133 lines
5.3 KiB
Markdown
# go-autorest
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[](https://godoc.org/github.com/Azure/go-autorest/autorest) [](https://travis-ci.org/Azure/go-autorest) [](https://goreportcard.com/report/Azure/go-autorest)
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## Usage
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Package autorest implements an HTTP request pipeline suitable for use across multiple go-routines
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and provides the shared routines relied on by AutoRest (see https://github.com/Azure/autorest/)
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generated Go code.
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The package breaks sending and responding to HTTP requests into three phases: Preparing, Sending,
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and Responding. A typical pattern is:
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```go
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req, err := Prepare(&http.Request{},
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token.WithAuthorization())
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resp, err := Send(req,
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WithLogging(logger),
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DoErrorIfStatusCode(http.StatusInternalServerError),
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DoCloseIfError(),
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DoRetryForAttempts(5, time.Second))
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err = Respond(resp,
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ByDiscardingBody(),
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ByClosing())
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```
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Each phase relies on decorators to modify and / or manage processing. Decorators may first modify
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and then pass the data along, pass the data first and then modify the result, or wrap themselves
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around passing the data (such as a logger might do). Decorators run in the order provided. For
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example, the following:
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```go
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req, err := Prepare(&http.Request{},
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WithBaseURL("https://microsoft.com/"),
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WithPath("a"),
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WithPath("b"),
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WithPath("c"))
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```
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will set the URL to:
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```
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https://microsoft.com/a/b/c
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```
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Preparers and Responders may be shared and re-used (assuming the underlying decorators support
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sharing and re-use). Performant use is obtained by creating one or more Preparers and Responders
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shared among multiple go-routines, and a single Sender shared among multiple sending go-routines,
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all bound together by means of input / output channels.
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Decorators hold their passed state within a closure (such as the path components in the example
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above). Be careful to share Preparers and Responders only in a context where such held state
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applies. For example, it may not make sense to share a Preparer that applies a query string from a
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fixed set of values. Similarly, sharing a Responder that reads the response body into a passed
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struct (e.g., `ByUnmarshallingJson`) is likely incorrect.
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Errors raised by autorest objects and methods will conform to the `autorest.Error` interface.
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See the included examples for more detail. For details on the suggested use of this package by
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generated clients, see the Client described below.
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## Helpers
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### Handling Swagger Dates
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The Swagger specification (https://swagger.io) that drives AutoRest
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(https://github.com/Azure/autorest/) precisely defines two date forms: date and date-time. The
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github.com/Azure/go-autorest/autorest/date package provides time.Time derivations to ensure correct
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parsing and formatting.
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### Handling Empty Values
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In JSON, missing values have different semantics than empty values. This is especially true for
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services using the HTTP PATCH verb. The JSON submitted with a PATCH request generally contains
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only those values to modify. Missing values are to be left unchanged. Developers, then, require a
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means to both specify an empty value and to leave the value out of the submitted JSON.
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The Go JSON package (`encoding/json`) supports the `omitempty` tag. When specified, it omits
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empty values from the rendered JSON. Since Go defines default values for all base types (such as ""
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for string and 0 for int) and provides no means to mark a value as actually empty, the JSON package
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treats default values as meaning empty, omitting them from the rendered JSON. This means that, using
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the Go base types encoded through the default JSON package, it is not possible to create JSON to
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clear a value at the server.
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The workaround within the Go community is to use pointers to base types in lieu of base types within
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structures that map to JSON. For example, instead of a value of type `string`, the workaround uses
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`*string`. While this enables distinguishing empty values from those to be unchanged, creating
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pointers to a base type (notably constant, in-line values) requires additional variables. This, for
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example,
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```go
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s := struct {
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S *string
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}{ S: &"foo" }
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```
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fails, while, this
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```go
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v := "foo"
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s := struct {
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S *string
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}{ S: &v }
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```
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succeeds.
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To ease using pointers, the subpackage `to` contains helpers that convert to and from pointers for
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Go base types which have Swagger analogs. It also provides a helper that converts between
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`map[string]string` and `map[string]*string`, enabling the JSON to specify that the value
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associated with a key should be cleared. With the helpers, the previous example becomes
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```go
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s := struct {
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S *string
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}{ S: to.StringPtr("foo") }
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```
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## Install
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```bash
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go get github.com/Azure/go-autorest/autorest
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go get github.com/Azure/go-autorest/autorest/azure
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go get github.com/Azure/go-autorest/autorest/date
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go get github.com/Azure/go-autorest/autorest/to
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```
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## License
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See LICENSE file.
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-----
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This project has adopted the [Microsoft Open Source Code of Conduct](https://opensource.microsoft.com/codeofconduct/). For more information see the [Code of Conduct FAQ](https://opensource.microsoft.com/codeofconduct/faq/) or contact [opencode@microsoft.com](mailto:opencode@microsoft.com) with any additional questions or comments.
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