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cb7534dcdf
Allows to compress short arbitrary strings and returns a string using base64 url encoding. Generator for tables included and a few samples has been added. Add more to init.go Tested with fuzzing for crash resistance and symmetry, see fuzz.go
90 lines
2.1 KiB
Go
90 lines
2.1 KiB
Go
package filename
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import (
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"encoding/base64"
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"sync"
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"github.com/klauspost/compress/huff0"
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)
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// encodeURL is base64 url encoding values.
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const encodeURL = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_"
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// decodeMap will return x = decodeMap[encodeURL[byte(x)]] - 1 if x >= 0 and x < 64, otherwise -1 is returned.
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var decodeMap [256]byte
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// maxLength is the maximum length that will be attempted to be compressed.
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const maxLength = 256
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var (
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initOnce sync.Once // Used to control init of tables.
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encTables [64]*huff0.Scratch // Encoders.
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encTableLocks [64]sync.Mutex // Temporary locks for encoders since they are stateful.
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decTables [64]*huff0.Decoder // Stateless decoders.
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)
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const (
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tableUncompressed = 0
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tableRLE = 61
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tableCustom = 62
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tableReserved = 63
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)
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// predefined tables as base64 URL encoded string.
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var tablesData = [64]string{
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// Uncompressed
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tableUncompressed: "",
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// ncw home directory
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1: "MRDIEtAAMAzDMAzDSjX_ybu0w97bb-L3b2mR-rUl5LXW3lZII43kIDMzM1NXu3okgQs=",
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// ncw images
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2: "IhDIAEAA______-Pou_4Sf5z-uS-39MVWjullFLKM7EBECs=",
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// ncw Google Drive:
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3: "JxDQAIIBMDMzMwOzbv7nJJCyd_m_9D2llCarnQX33nvvlFKEhUxAAQ==",
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// Hex
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4: "ExDoSTD___-tfXfhJ0hKSkryTxU=",
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// Base64
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5: "JRDIcQf_______8PgIiIiIgINkggARHlkQwSSCCBxHFYINHdfXI=",
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// Special tables:
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// Compressed data has its own table.
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tableCustom: "",
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// Reserved for extension.
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tableReserved: "",
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}
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func initCoders() {
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initOnce.Do(func() {
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// Init base 64 decoder.
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for i, v := range encodeURL {
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decodeMap[v] = byte(i) + 1
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}
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// Initialize encoders and decoders.
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for i, dataString := range tablesData {
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if len(dataString) == 0 {
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continue
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}
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data, err := base64.URLEncoding.DecodeString(dataString)
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if err != nil {
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panic(err)
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}
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s, _, err := huff0.ReadTable(data, nil)
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if err != nil {
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panic(err)
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}
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// We want to save at least len(in) >> 5
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s.WantLogLess = 5
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s.Reuse = huff0.ReusePolicyMust
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encTables[i] = s
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decTables[i] = s.Decoder()
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}
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// Add custom table type.
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var s huff0.Scratch
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s.Reuse = huff0.ReusePolicyNone
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encTables[tableCustom] = &s
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decTables[tableCustom] = nil
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})
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}
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