88 lines
2.7 KiB
Go
88 lines
2.7 KiB
Go
package tcp
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import (
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"errors"
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)
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// Constructor A constructor for a piece of TCP middleware.
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// Some TCP middleware use this constructor out of the box,
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// so in most cases you can just pass somepackage.New.
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type Constructor func(Handler) (Handler, error)
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// Chain is a chain for TCP handlers.
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// Chain acts as a list of tcp.Handler constructors.
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// Chain is effectively immutable:
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// once created, it will always hold
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// the same set of constructors in the same order.
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type Chain struct {
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constructors []Constructor
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}
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// NewChain creates a new TCP chain,
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// memorizing the given list of TCP middleware constructors.
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// New serves no other function,
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// constructors are only called upon a call to Then().
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func NewChain(constructors ...Constructor) Chain {
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return Chain{constructors: constructors}
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}
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// Then adds an handler at the end of the chain.
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func (c Chain) Then(h Handler) (Handler, error) {
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if h == nil {
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return nil, errors.New("cannot add a nil handler to the chain")
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}
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for i := range c.constructors {
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handler, err := c.constructors[len(c.constructors)-1-i](h)
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if err != nil {
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return nil, err
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}
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h = handler
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}
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return h, nil
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}
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// Append extends a chain, adding the specified constructors
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// as the last ones in the request flow.
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//
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// Append returns a new chain, leaving the original one untouched.
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//
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// stdChain := tcp.NewChain(m1, m2)
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// extChain := stdChain.Append(m3, m4)
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// // requests in stdChain go m1 -> m2
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// // requests in extChain go m1 -> m2 -> m3 -> m4
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func (c Chain) Append(constructors ...Constructor) Chain {
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newCons := make([]Constructor, 0, len(c.constructors)+len(constructors))
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newCons = append(newCons, c.constructors...)
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newCons = append(newCons, constructors...)
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return Chain{newCons}
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}
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// Extend extends a chain by adding the specified chain
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// as the last one in the request flow.
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//
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// Extend returns a new chain, leaving the original one untouched.
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//
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// stdChain := tcp.NewChain(m1, m2)
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// ext1Chain := tcp.NewChain(m3, m4)
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// ext2Chain := stdChain.Extend(ext1Chain)
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// // requests in stdChain go m1 -> m2
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// // requests in ext1Chain go m3 -> m4
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// // requests in ext2Chain go m1 -> m2 -> m3 -> m4
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//
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// Another example:
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//
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// aHtmlAfterNosurf := tcp.NewChain(m2)
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// aHtml := tcp.NewChain(m1, func(h tcp.Handler) tcp.Handler {
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// csrf := nosurf.New(h)
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// csrf.SetFailureHandler(aHtmlAfterNosurf.ThenFunc(csrfFail))
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// return csrf
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// }).Extend(aHtmlAfterNosurf)
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// // requests to aHtml hitting nosurfs success handler go m1 -> nosurf -> m2 -> target-handler
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// // requests to aHtml hitting nosurfs failure handler go m1 -> nosurf -> m2 -> csrfFail
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func (c Chain) Extend(chain Chain) Chain {
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return c.Append(chain.constructors...)
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}
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