67 lines
1.6 KiB
Go
67 lines
1.6 KiB
Go
package qpack
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// copied from the Go standard library HPACK implementation
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import "errors"
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var errVarintOverflow = errors.New("varint integer overflow")
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// appendVarInt appends i, as encoded in variable integer form using n
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// bit prefix, to dst and returns the extended buffer.
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//
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// See
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// http://http2.github.io/http2-spec/compression.html#integer.representation
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func appendVarInt(dst []byte, n byte, i uint64) []byte {
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k := uint64((1 << n) - 1)
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if i < k {
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return append(dst, byte(i))
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}
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dst = append(dst, byte(k))
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i -= k
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for ; i >= 128; i >>= 7 {
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dst = append(dst, byte(0x80|(i&0x7f)))
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}
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return append(dst, byte(i))
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}
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// readVarInt reads an unsigned variable length integer off the
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// beginning of p. n is the parameter as described in
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// http://http2.github.io/http2-spec/compression.html#rfc.section.5.1.
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//
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// n must always be between 1 and 8.
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//
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// The returned remain buffer is either a smaller suffix of p, or err != nil.
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// The error is errNeedMore if p doesn't contain a complete integer.
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func readVarInt(n byte, p []byte) (i uint64, remain []byte, err error) {
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if n < 1 || n > 8 {
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panic("bad n")
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}
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if len(p) == 0 {
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return 0, p, errNeedMore
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}
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i = uint64(p[0])
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if n < 8 {
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i &= (1 << uint64(n)) - 1
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}
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if i < (1<<uint64(n))-1 {
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return i, p[1:], nil
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}
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origP := p
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p = p[1:]
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var m uint64
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for len(p) > 0 {
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b := p[0]
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p = p[1:]
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i += uint64(b&127) << m
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if b&128 == 0 {
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return i, p, nil
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}
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m += 7
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if m >= 63 { // TODO: proper overflow check. making this up.
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return 0, origP, errVarintOverflow
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}
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}
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return 0, origP, errNeedMore
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}
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