middleware.go

Documentation: github.com/aws/smithy-go/middleware

     1  package middleware
     2  
     3  import (
     4  	"context"
     5  )
     6  
     7  // Handler provides the interface for performing the logic to obtain an output,
     8  // or error for the given input.
     9  type Handler interface {
    10  	// Handle performs logic to obtain an output for the given input. Handler
    11  	// should be decorated with middleware to perform input specific behavior.
    12  	Handle(ctx context.Context, input interface{}) (
    13  		output interface{}, metadata Metadata, err error,
    14  	)
    15  }
    16  
    17  // HandlerFunc provides a wrapper around a function pointer to be used as a
    18  // middleware handler.
    19  type HandlerFunc func(ctx context.Context, input interface{}) (
    20  	output interface{}, metadata Metadata, err error,
    21  )
    22  
    23  // Handle invokes the underlying function, returning the result.
    24  func (fn HandlerFunc) Handle(ctx context.Context, input interface{}) (
    25  	output interface{}, metadata Metadata, err error,
    26  ) {
    27  	return fn(ctx, input)
    28  }
    29  
    30  // Middleware provides the interface to call handlers in a chain.
    31  type Middleware interface {
    32  	// ID provides a unique identifier for the middleware.
    33  	ID() string
    34  
    35  	// Performs the middleware's handling of the input, returning the output,
    36  	// or error. The middleware can invoke the next Handler if handling should
    37  	// continue.
    38  	HandleMiddleware(ctx context.Context, input interface{}, next Handler) (
    39  		output interface{}, metadata Metadata, err error,
    40  	)
    41  }
    42  
    43  // decoratedHandler wraps a middleware in order to to call the next handler in
    44  // the chain.
    45  type decoratedHandler struct {
    46  	// The next handler to be called.
    47  	Next Handler
    48  
    49  	// The current middleware decorating the handler.
    50  	With Middleware
    51  }
    52  
    53  // Handle implements the Handler interface to handle a operation invocation.
    54  func (m decoratedHandler) Handle(ctx context.Context, input interface{}) (
    55  	output interface{}, metadata Metadata, err error,
    56  ) {
    57  	return m.With.HandleMiddleware(ctx, input, m.Next)
    58  }
    59  
    60  // DecorateHandler decorates a handler with a middleware. Wrapping the handler
    61  // with the middleware.
    62  func DecorateHandler(h Handler, with ...Middleware) Handler {
    63  	for i := len(with) - 1; i >= 0; i-- {
    64  		h = decoratedHandler{
    65  			Next: h,
    66  			With: with[i],
    67  		}
    68  	}
    69  
    70  	return h
    71  }
    72
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