step_build.go

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

     1  package middleware
     2  
     3  import (
     4  	"context"
     5  )
     6  
     7  // BuildInput provides the input parameters for the BuildMiddleware to consume.
     8  // BuildMiddleware may modify the Request value before forwarding the input
     9  // along to the next BuildHandler.
    10  type BuildInput struct {
    11  	Request interface{}
    12  }
    13  
    14  // BuildOutput provides the result returned by the next BuildHandler.
    15  type BuildOutput struct {
    16  	Result interface{}
    17  }
    18  
    19  // BuildHandler provides the interface for the next handler the
    20  // BuildMiddleware will call in the middleware chain.
    21  type BuildHandler interface {
    22  	HandleBuild(ctx context.Context, in BuildInput) (
    23  		out BuildOutput, metadata Metadata, err error,
    24  	)
    25  }
    26  
    27  // BuildMiddleware provides the interface for middleware specific to the
    28  // serialize step. Delegates to the next BuildHandler for further
    29  // processing.
    30  type BuildMiddleware interface {
    31  	// Unique ID for the middleware in theBuildStep. The step does not allow
    32  	// duplicate IDs.
    33  	ID() string
    34  
    35  	// Invokes the middleware behavior which must delegate to the next handler
    36  	// for the middleware chain to continue. The method must return a result or
    37  	// error to its caller.
    38  	HandleBuild(ctx context.Context, in BuildInput, next BuildHandler) (
    39  		out BuildOutput, metadata Metadata, err error,
    40  	)
    41  }
    42  
    43  // BuildMiddlewareFunc returns a BuildMiddleware with the unique ID provided,
    44  // and the func to be invoked.
    45  func BuildMiddlewareFunc(id string, fn func(context.Context, BuildInput, BuildHandler) (BuildOutput, Metadata, error)) BuildMiddleware {
    46  	return buildMiddlewareFunc{
    47  		id: id,
    48  		fn: fn,
    49  	}
    50  }
    51  
    52  type buildMiddlewareFunc struct {
    53  	// Unique ID for the middleware.
    54  	id string
    55  
    56  	// Middleware function to be called.
    57  	fn func(context.Context, BuildInput, BuildHandler) (BuildOutput, Metadata, error)
    58  }
    59  
    60  // ID returns the unique ID for the middleware.
    61  func (s buildMiddlewareFunc) ID() string { return s.id }
    62  
    63  // HandleBuild invokes the middleware Fn.
    64  func (s buildMiddlewareFunc) HandleBuild(ctx context.Context, in BuildInput, next BuildHandler) (
    65  	out BuildOutput, metadata Metadata, err error,
    66  ) {
    67  	return s.fn(ctx, in, next)
    68  }
    69  
    70  var _ BuildMiddleware = (buildMiddlewareFunc{})
    71  
    72  // BuildStep provides the ordered grouping of BuildMiddleware to be invoked on
    73  // a handler.
    74  type BuildStep struct {
    75  	ids *orderedIDs
    76  }
    77  
    78  // NewBuildStep returns a BuildStep ready to have middleware for
    79  // initialization added to it.
    80  func NewBuildStep() *BuildStep {
    81  	return &BuildStep{
    82  		ids: newOrderedIDs(),
    83  	}
    84  }
    85  
    86  var _ Middleware = (*BuildStep)(nil)
    87  
    88  // ID returns the unique name of the step as a middleware.
    89  func (s *BuildStep) ID() string {
    90  	return "Build stack step"
    91  }
    92  
    93  // HandleMiddleware invokes the middleware by decorating the next handler
    94  // provided. Returns the result of the middleware and handler being invoked.
    95  //
    96  // Implements Middleware interface.
    97  func (s *BuildStep) HandleMiddleware(ctx context.Context, in interface{}, next Handler) (
    98  	out interface{}, metadata Metadata, err error,
    99  ) {
   100  	order := s.ids.GetOrder()
   101  
   102  	var h BuildHandler = buildWrapHandler{Next: next}
   103  	for i := len(order) - 1; i >= 0; i-- {
   104  		h = decoratedBuildHandler{
   105  			Next: h,
   106  			With: order[i].(BuildMiddleware),
   107  		}
   108  	}
   109  
   110  	sIn := BuildInput{
   111  		Request: in,
   112  	}
   113  
   114  	res, metadata, err := h.HandleBuild(ctx, sIn)
   115  	return res.Result, metadata, err
   116  }
   117  
   118  // Get retrieves the middleware identified by id. If the middleware is not present, returns false.
   119  func (s *BuildStep) Get(id string) (BuildMiddleware, bool) {
   120  	get, ok := s.ids.Get(id)
   121  	if !ok {
   122  		return nil, false
   123  	}
   124  	return get.(BuildMiddleware), ok
   125  }
   126  
   127  // Add injects the middleware to the relative position of the middleware group.
   128  // Returns an error if the middleware already exists.
   129  func (s *BuildStep) Add(m BuildMiddleware, pos RelativePosition) error {
   130  	return s.ids.Add(m, pos)
   131  }
   132  
   133  // Insert injects the middleware relative to an existing middleware id.
   134  // Returns an error if the original middleware does not exist, or the middleware
   135  // being added already exists.
   136  func (s *BuildStep) Insert(m BuildMiddleware, relativeTo string, pos RelativePosition) error {
   137  	return s.ids.Insert(m, relativeTo, pos)
   138  }
   139  
   140  // Swap removes the middleware by id, replacing it with the new middleware.
   141  // Returns the middleware removed, or an error if the middleware to be removed
   142  // doesn't exist.
   143  func (s *BuildStep) Swap(id string, m BuildMiddleware) (BuildMiddleware, error) {
   144  	removed, err := s.ids.Swap(id, m)
   145  	if err != nil {
   146  		return nil, err
   147  	}
   148  
   149  	return removed.(BuildMiddleware), nil
   150  }
   151  
   152  // Remove removes the middleware by id. Returns error if the middleware
   153  // doesn't exist.
   154  func (s *BuildStep) Remove(id string) (BuildMiddleware, error) {
   155  	removed, err := s.ids.Remove(id)
   156  	if err != nil {
   157  		return nil, err
   158  	}
   159  
   160  	return removed.(BuildMiddleware), nil
   161  }
   162  
   163  // List returns a list of the middleware in the step.
   164  func (s *BuildStep) List() []string {
   165  	return s.ids.List()
   166  }
   167  
   168  // Clear removes all middleware in the step.
   169  func (s *BuildStep) Clear() {
   170  	s.ids.Clear()
   171  }
   172  
   173  type buildWrapHandler struct {
   174  	Next Handler
   175  }
   176  
   177  var _ BuildHandler = (*buildWrapHandler)(nil)
   178  
   179  // Implements BuildHandler, converts types and delegates to underlying
   180  // generic handler.
   181  func (w buildWrapHandler) HandleBuild(ctx context.Context, in BuildInput) (
   182  	out BuildOutput, metadata Metadata, err error,
   183  ) {
   184  	res, metadata, err := w.Next.Handle(ctx, in.Request)
   185  	return BuildOutput{
   186  		Result: res,
   187  	}, metadata, err
   188  }
   189  
   190  type decoratedBuildHandler struct {
   191  	Next BuildHandler
   192  	With BuildMiddleware
   193  }
   194  
   195  var _ BuildHandler = (*decoratedBuildHandler)(nil)
   196  
   197  func (h decoratedBuildHandler) HandleBuild(ctx context.Context, in BuildInput) (
   198  	out BuildOutput, metadata Metadata, err error,
   199  ) {
   200  	return h.With.HandleBuild(ctx, in, h.Next)
   201  }
   202  
   203  // BuildHandlerFunc provides a wrapper around a function to be used as a build middleware handler.
   204  type BuildHandlerFunc func(context.Context, BuildInput) (BuildOutput, Metadata, error)
   205  
   206  // HandleBuild invokes the wrapped function with the provided arguments.
   207  func (b BuildHandlerFunc) HandleBuild(ctx context.Context, in BuildInput) (BuildOutput, Metadata, error) {
   208  	return b(ctx, in)
   209  }
   210  
   211  var _ BuildHandler = BuildHandlerFunc(nil)
   212
View as plain text