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107 lines
1.9 KiB
Go
107 lines
1.9 KiB
Go
package main
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import (
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"crypto/sha256"
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"fmt"
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"net/http"
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"sync"
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"unsafe"
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)
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// cacheRecorder is a thread-safe implementation of http.ResponseWriter
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type cacheRecorder struct {
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mu sync.Mutex
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item cacheItem
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done bool
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}
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type cacheItem struct {
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expiration int
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eTag string
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code int
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header http.Header
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body []byte
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}
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func newCacheRecorder() *cacheRecorder {
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return &cacheRecorder{
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item: cacheItem{
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code: http.StatusOK,
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header: make(http.Header),
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},
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}
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}
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func (c *cacheRecorder) finish() *cacheItem {
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c.mu.Lock()
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defer c.mu.Unlock()
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if c.done {
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return &c.item
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}
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c.done = true
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c.item.eTag = c.item.header.Get("ETag")
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if c.item.eTag == "" {
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c.item.eTag = fmt.Sprintf("%x", sha256.Sum256(c.item.body))
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}
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return &c.item
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}
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// Header implements http.ResponseWriter.
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func (c *cacheRecorder) Header() http.Header {
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c.mu.Lock()
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defer c.mu.Unlock()
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if c.done {
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return nil
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}
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return c.item.header
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}
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// Write implements http.ResponseWriter.
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func (c *cacheRecorder) Write(buf []byte) (int, error) {
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c.mu.Lock()
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defer c.mu.Unlock()
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if c.done {
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return 0, fmt.Errorf("write after finish")
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}
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c.item.body = append(c.item.body, buf...)
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return len(buf), nil
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}
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// WriteString implements io.StringWriter.
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func (c *cacheRecorder) WriteString(str string) (int, error) {
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return c.Write([]byte(str))
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}
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// WriteHeader implements http.ResponseWriter.
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func (c *cacheRecorder) WriteHeader(code int) {
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c.mu.Lock()
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defer c.mu.Unlock()
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if c.done {
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return
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}
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c.item.code = code
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}
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func (ci *cacheItem) cost() int64 {
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size := int64(unsafe.Sizeof(*ci)) // Base struct size
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// Add sizes of variable-length fields
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size += int64(len(ci.eTag))
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size += int64(len(ci.body))
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// Calculate header size
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for key, values := range ci.header {
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size += int64(len(key))
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for _, value := range values {
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size += int64(len(value))
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}
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}
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return size
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}
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