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