super-graph/jsn/get.go

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package jsn
import (
"hash/maphash"
)
const (
expectKey int = iota
expectKeyClose
expectColon
expectValue
expectString
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expectNull
expectListClose
expectObjClose
expectBoolClose
expectNumClose
)
// Field struct holds a JSON key and value
type Field struct {
Key []byte
Value []byte
}
// Value function is a utility function to sanitize returned values
func Value(b []byte) []byte {
e := (len(b) - 1)
switch {
case b[0] == '"' && b[e] == '"':
return b[1:(len(b) - 1)]
case b[0] == '[' && b[e] == ']':
return nil
case b[0] == '{' && b[e] == '}':
return nil
default:
return b
}
}
// Keys function fetches values for the provided keys
func Get(b []byte, keys [][]byte) []Field {
kmap := make(map[uint64]struct{}, len(keys))
h := maphash.Hash{}
for i := range keys {
_, _ = h.Write(keys[i])
kmap[h.Sum64()] = struct{}{}
h.Reset()
}
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res := make([]Field, 0, 20)
s, e, d := 0, 0, 0
var k []byte
state := expectKey
n := 0
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instr := false
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slash := 0
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for i := 0; i < len(b); i++ {
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if instr && b[i] == '\\' {
slash++
continue
}
if b[i] == '"' && (slash%2 == 0) {
instr = !instr
}
if state == expectObjClose || state == expectListClose {
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if !instr {
switch b[i] {
case '{', '[':
d++
case '}', ']':
d--
}
}
}
switch {
case state == expectKey && b[i] == '"':
state = expectKeyClose
s = i
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case state == expectKeyClose && (b[i] == '"' && (slash%2 == 0)):
state = expectColon
k = b[(s + 1):i]
case state == expectColon && b[i] == ':':
state = expectValue
case state == expectValue && b[i] == '"':
state = expectString
s = i
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case state == expectString && (b[i] == '"' && (slash%2 == 0)):
e = i
case state == expectValue && b[i] == '[':
state = expectListClose
s = i
d++
case state == expectListClose && d == 0 && b[i] == ']':
e = i
i = s
case state == expectValue && b[i] == '{':
state = expectObjClose
s = i
d++
case state == expectObjClose && d == 0 && b[i] == '}':
e = i
i = s
case state == expectValue && (b[i] >= '0' && b[i] <= '9'):
state = expectNumClose
s = i
case state == expectNumClose &&
((b[i] < '0' || b[i] > '9') &&
(b[i] != '.' && b[i] != 'e' && b[i] != 'E' && b[i] != '+' && b[i] != '-')):
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e = i - 1
case state == expectValue &&
(b[i] == 'f' || b[i] == 'F' || b[i] == 't' || b[i] == 'T'):
state = expectBoolClose
s = i
case state == expectBoolClose && (b[i] == 'e' || b[i] == 'E'):
e = i
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case state == expectValue && b[i] == 'n':
state = expectNull
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s = i
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case state == expectNull && (b[i-1] == 'l' && b[i] == 'l'):
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e = i
}
if e != 0 {
_, _ = h.Write(k)
_, ok := kmap[h.Sum64()]
h.Reset()
if ok {
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res = append(res, Field{k, b[s:(e + 1)]})
n++
}
if state == expectListClose {
loop:
for j := i + 1; j < len(b); j++ {
switch b[j] {
case ' ', '\t', '\n':
continue
case '{':
break loop
}
i = e
break loop
}
}
state = expectKey
e = 0
}
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slash = 0
}
return res[:n]
}