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package http
import (
"context"
"fmt"
"net/http"
"github.com/aws/smithy-go/middleware"
)
// WithHeaderComment instruments a middleware stack to append an HTTP field
// comment to the given header as specified in RFC 9110
// (https://www.rfc-editor.org/rfc/rfc9110#name-comments).
//
// The header is case-insensitive. If the provided header exists when the
// middleware runs, the content will be inserted as-is enclosed in parentheses.
//
// Note that per the HTTP specification, comments are only allowed in fields
// containing "comment" as part of their field value definition, but this API
// will NOT verify whether the provided header is one of them.
//
// WithHeaderComment MAY be applied more than once to a middleware stack and/or
// more than once per header.
func WithHeaderComment(header, content string) func(*middleware.Stack) error {
return func(s *middleware.Stack) error {
m, err := getOrAddHeaderComment(s)
if err != nil {
return fmt.Errorf("get or add header comment: %v", err)
}
m.values.Add(header, content)
return nil
}
}
type headerCommentMiddleware struct {
values http.Header // hijack case-insensitive access APIs
}
func (*headerCommentMiddleware) ID() string {
return "headerComment"
}
func (m *headerCommentMiddleware) HandleBuild(ctx context.Context, in middleware.BuildInput, next middleware.BuildHandler) (
out middleware.BuildOutput, metadata middleware.Metadata, err error,
) {
r, ok := in.Request.(*Request)
if !ok {
return out, metadata, fmt.Errorf("unknown transport type %T", in.Request)
}
for h, contents := range m.values {
for _, c := range contents {
if existing := r.Header.Get(h); existing != "" {
r.Header.Set(h, fmt.Sprintf("%s (%s)", existing, c))
}
}
}
return next.HandleBuild(ctx, in)
}
func getOrAddHeaderComment(s *middleware.Stack) (*headerCommentMiddleware, error) {
id := (*headerCommentMiddleware)(nil).ID()
m, ok := s.Build.Get(id)
if !ok {
m := &headerCommentMiddleware{values: http.Header{}}
if err := s.Build.Add(m, middleware.After); err != nil {
return nil, fmt.Errorf("add build: %v", err)
}
return m, nil
}
hc, ok := m.(*headerCommentMiddleware)
if !ok {
return nil, fmt.Errorf("existing middleware w/ id %s is not *headerCommentMiddleware", id)
}
return hc, nil
}
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