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perf(parser): scan the input as bytes instead of runes

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Assisted-by: GLM 5.3
This commit is contained in:
petrbalvin
2026-09-17 23:11:50 +02:00
parent 3c8ac859c0
commit f1a757ec5c
3 changed files with 128 additions and 91 deletions
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CHANGELOG.md
+5
View File
@@ -42,6 +42,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
and shared with the encoder, which now resolves duplicate field keys with and shared with the encoder, which now resolves duplicate field keys with
it. Strict decoding of an array of tables of structs runs about a quarter it. Strict decoding of an array of tables of structs runs about a quarter
faster; marshalling structs gained the same layout without measurable cost. faster; marshalling structs gained the same layout without measurable cost.
- The parser scans the input bytes in place instead of building a `[]rune`
copy of the document: every character that drives the grammar is ASCII and
the input is validated UTF-8 up front, so the conversion pass and its four
bytes per rune were pure overhead. Parsing a large array-of-tables document
runs about a fifth faster and allocates about half the memory.
### Fixed ### Fixed
interpres.go
+3 -1
View File
@@ -110,7 +110,9 @@ func ParseContext(ctx context.Context, data []byte) (map[string]any, error) {
if !utf8.Valid(data) { if !utf8.Valid(data) {
return nil, &SyntaxError{Line: 1, Msg: "input is not valid UTF-8"} return nil, &SyntaxError{Line: 1, Msg: "input is not valid UTF-8"}
} }
p := &parser{src: []rune(string(data)), line: 1, ctx: ctx} // The parser scans data in place; it only reads the buffer, and every
// string it stores in the tree is copied out of it.
p := &parser{src: data, line: 1, ctx: ctx}
return p.parse() return p.parse()
} }
parser.go
+118 -88
View File
@@ -8,6 +8,7 @@ import (
"fmt" "fmt"
"strconv" "strconv"
"strings" "strings"
"unicode/utf8"
) )
// ctxCheckInterval is the number of top-level parser iterations between // ctxCheckInterval is the number of top-level parser iterations between
@@ -16,8 +17,15 @@ import (
const ctxCheckInterval = 64 const ctxCheckInterval = 64
// parser is a recursive-descent TOML parser producing a map[string]any tree. // parser is a recursive-descent TOML parser producing a map[string]any tree.
//
// The scanner works on bytes, not runes: the input is validated UTF-8 before
// the parser runs, every character that drives the grammar (quotes,
// separators, newlines, bare-key characters) is ASCII, and multi-byte runes
// matter only as string content, where they are decoded on the spot. Holding
// the source as []rune instead would cost a conversion pass plus four bytes
// per rune of extra memory before parsing even starts.
type parser struct { type parser struct {
src []rune src []byte
pos int pos int
line int line int
ctx context.Context ctx context.Context
@@ -85,10 +93,10 @@ func (p *parser) checkCtx() error {
func (p *parser) parseTableHeader() error { func (p *parser) parseTableHeader() error {
array := false array := false
p.next() // consume '[' p.pos++ // consume '['
if !p.eof() && p.peek() == '[' { if !p.eof() && p.peek() == '[' {
array = true array = true
p.next() p.pos++
} }
key, err := p.parseKeyPath() key, err := p.parseKeyPath()
@@ -100,12 +108,12 @@ func (p *parser) parseTableHeader() error {
if p.eof() || p.peek() != ']' { if p.eof() || p.peek() != ']' {
return p.errf("expected ']' to close table header") return p.errf("expected ']' to close table header")
} }
p.next() p.pos++
if array { if array {
if p.eof() || p.peek() != ']' { if p.eof() || p.peek() != ']' {
return p.errf("expected ']]' to close array-of-tables header") return p.errf("expected ']]' to close array-of-tables header")
} }
p.next() p.pos++
} }
if array { if array {
@@ -218,7 +226,7 @@ func (p *parser) parseKeyValue() error {
if p.eof() || p.peek() != '=' { if p.eof() || p.peek() != '=' {
return p.errf("expected '=' after key") return p.errf("expected '=' after key")
} }
p.next() p.pos++
p.skipInline() p.skipInline()
val, err := p.parseValue() val, err := p.parseValue()
@@ -227,7 +235,10 @@ func (p *parser) parseKeyValue() error {
} }
dest := p.current dest := p.current
abs := append([]string{}, p.currentPath...) // One allocation covers the current section plus the dotted key; a
// top-level statement reuses it for the leaf.
abs := make([]string, 0, len(p.currentPath)+len(key))
abs = append(abs, p.currentPath...)
for _, k := range key[:len(key)-1] { for _, k := range key[:len(key)-1] {
abs = append(abs, k) abs = append(abs, k)
if p.frozen[pathKey(abs)] { if p.frozen[pathKey(abs)] {
@@ -301,7 +312,7 @@ func (p *parser) parseKeyPath() ([]string, error) {
parts = append(parts, part) parts = append(parts, part)
p.skipInline() p.skipInline()
if !p.eof() && p.peek() == '.' { if !p.eof() && p.peek() == '.' {
p.next() p.pos++
continue continue
} }
break break
@@ -313,7 +324,7 @@ func (p *parser) parseKeyComponent() (string, error) {
if p.eof() { if p.eof() {
return "", p.errf("expected a key") return "", p.errf("expected a key")
} }
switch c := p.peek(); c { switch p.peek() {
case '"': case '"':
if p.lookahead(`"""`) { if p.lookahead(`"""`) {
return "", p.errf("multiline strings are not allowed in keys") return "", p.errf("multiline strings are not allowed in keys")
@@ -330,13 +341,14 @@ func (p *parser) parseKeyComponent() (string, error) {
c := p.peek() c := p.peek()
if (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z') || if (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z') ||
(c >= '0' && c <= '9') || c == '_' || c == '-' { (c >= '0' && c <= '9') || c == '_' || c == '-' {
p.next() p.pos++
continue continue
} }
break break
} }
if p.pos == start { if p.pos == start {
return "", p.errf("invalid key character %q", string(p.peek())) r, _ := utf8.DecodeRune(p.src[p.pos:])
return "", p.errf("invalid key character %q", string(r))
} }
return string(p.src[start:p.pos]), nil return string(p.src[start:p.pos]), nil
} }
@@ -385,7 +397,7 @@ func (p *parser) parseAtom() (any, error) {
// A date may be followed by a space and a time, forming one date-time. // A date may be followed by a space and a time, forming one date-time.
if isDateToken(tok) && !p.eof() && p.peek() == ' ' { if isDateToken(tok) && !p.eof() && p.peek() == ' ' {
if next, ok := p.peekAt(1); ok && next >= '0' && next <= '9' { if next, ok := p.peekAt(1); ok && next >= '0' && next <= '9' {
p.next() // consume the separating space p.pos++ // consume the separating space
timeStart := p.pos timeStart := p.pos
p.scanBareToken() p.scanBareToken()
tok = tok + " " + string(p.src[timeStart:p.pos]) tok = tok + " " + string(p.src[timeStart:p.pos])
@@ -410,7 +422,7 @@ func (p *parser) scanBareToken() {
c == ',' || c == ']' || c == '}' || c == '#' { c == ',' || c == ']' || c == '}' || c == '#' {
return return
} }
p.next() p.pos++
} }
} }
@@ -420,31 +432,32 @@ func (p *parser) parseBasicString() (string, error) {
if p.lookahead(`"""`) { if p.lookahead(`"""`) {
return p.parseMultilineString('"', true) return p.parseMultilineString('"', true)
} }
p.next() // opening quote p.pos++ // opening quote
var b strings.Builder var b strings.Builder
for { for {
if p.eof() { if p.eof() {
return "", p.errf("unterminated string") return "", p.errf("unterminated string")
} }
c := p.next() c := p.peek()
switch c { switch c {
case '"': case '"':
p.pos++
return b.String(), nil return b.String(), nil
case '\n': case '\n':
return "", p.errf("unterminated string") return "", p.errf("unterminated string")
case '\r': case '\r':
return "", p.errf("bare carriage return is not allowed in a string") return "", p.errf("bare carriage return is not allowed in a string")
case '\\': case '\\':
p.pos++
r, err := p.readEscape() r, err := p.readEscape()
if err != nil { if err != nil {
return "", err return "", err
} }
b.WriteRune(r) b.WriteRune(r)
default: default:
if isControlRune(c) { if err := p.writeContentRune(&b); err != nil {
return "", p.errf("control character U+%04X is not allowed in a string", c) return "", err
} }
b.WriteRune(c)
} }
} }
} }
@@ -453,38 +466,58 @@ func (p *parser) parseLiteralString() (string, error) {
if p.lookahead(`'''`) { if p.lookahead(`'''`) {
return p.parseMultilineString('\'', false) return p.parseMultilineString('\'', false)
} }
p.next() // opening quote p.pos++ // opening quote
var b strings.Builder var b strings.Builder
for { for {
if p.eof() { if p.eof() {
return "", p.errf("unterminated literal string") return "", p.errf("unterminated literal string")
} }
c := p.next() c := p.peek()
if c == '\'' { switch c {
case '\'':
p.pos++
return b.String(), nil return b.String(), nil
} case '\n':
if c == '\n' {
return "", p.errf("unterminated literal string") return "", p.errf("unterminated literal string")
} case '\r':
if c == '\r' {
return "", p.errf("bare carriage return is not allowed in a string") return "", p.errf("bare carriage return is not allowed in a string")
default:
if err := p.writeContentRune(&b); err != nil {
return "", err
} }
if isControlRune(c) {
return "", p.errf("control character U+%04X is not allowed in a string", c)
} }
b.WriteRune(c)
} }
} }
func (p *parser) parseMultilineString(quote rune, escapes bool) (string, error) { // writeContentRune appends the rune at the cursor to b and advances past it.
// An ASCII byte, which includes every control character the grammar forbids,
// is checked and written directly; a multi-byte rune is decoded and can never
// be a control character.
func (p *parser) writeContentRune(b *strings.Builder) error {
c := p.peek()
if c < utf8.RuneSelf {
if isControlRune(rune(c)) {
return p.errf("control character U+%04X is not allowed in a string", c)
}
p.pos++
b.WriteByte(c)
return nil
}
r, size := utf8.DecodeRune(p.src[p.pos:])
p.pos += size
b.WriteRune(r)
return nil
}
func (p *parser) parseMultilineString(quote byte, escapes bool) (string, error) {
p.skipN(3) // opening delimiter p.skipN(3) // opening delimiter
// A newline immediately after the opening delimiter is trimmed. // A newline immediately after the opening delimiter is trimmed.
if !p.eof() && p.peek() == '\r' { if !p.eof() && p.peek() == '\r' {
p.next() p.pos++
} }
if !p.eof() && p.peek() == '\n' { if !p.eof() && p.peek() == '\n' {
p.line++ p.line++
p.next() p.pos++
} }
var b strings.Builder var b strings.Builder
@@ -504,31 +537,32 @@ func (p *parser) parseMultilineString(quote rune, escapes bool) (string, error)
return "", p.errf("too many '%c' before the closing delimiter", quote) return "", p.errf("too many '%c' before the closing delimiter", quote)
} }
for range n - 3 { for range n - 3 {
b.WriteRune(quote) b.WriteByte(quote)
} }
p.skipN(n) p.skipN(n)
return b.String(), nil return b.String(), nil
} }
for range n { for range n {
b.WriteRune(quote) b.WriteByte(quote)
p.next() p.pos++
} }
continue continue
} }
c := p.next() c := p.peek()
if c == '\n' { switch {
case c == '\n':
p.line++ p.line++
b.WriteRune(c) p.pos++
continue b.WriteByte(c)
} case c == '\r':
if c == '\r' { if p.pos+1 < len(p.src) && p.src[p.pos+1] == '\n' {
if !p.eof() && p.peek() == '\n' { b.WriteByte(c)
b.WriteRune(c) p.pos++
continue continue
} }
return "", p.errf("bare carriage return is not allowed in a string") return "", p.errf("bare carriage return is not allowed in a string")
} case escapes && c == '\\':
if escapes && c == '\\' { p.pos++
// Line-ending backslash trims the following whitespace/newlines. // Line-ending backslash trims the following whitespace/newlines.
if p.trimLineEndingBackslash() { if p.trimLineEndingBackslash() {
continue continue
@@ -538,12 +572,11 @@ func (p *parser) parseMultilineString(quote rune, escapes bool) (string, error)
return "", err return "", err
} }
b.WriteRune(r) b.WriteRune(r)
continue default:
if err := p.writeContentRune(&b); err != nil {
return "", err
} }
if isControlRune(c) {
return "", p.errf("control character U+%04X is not allowed in a string", c)
} }
b.WriteRune(c)
} }
} }
@@ -555,7 +588,7 @@ func (p *parser) trimLineEndingBackslash() bool {
for !p.eof() { for !p.eof() {
c := p.peek() c := p.peek()
if c == ' ' || c == '\t' || c == '\r' { if c == ' ' || c == '\t' || c == '\r' {
p.next() p.pos++
continue continue
} }
if c == '\n' { if c == '\n' {
@@ -574,11 +607,11 @@ func (p *parser) trimLineEndingBackslash() bool {
c := p.peek() c := p.peek()
if c == '\n' { if c == '\n' {
p.line++ p.line++
p.next() p.pos++
continue continue
} }
if c == ' ' || c == '\t' || c == '\r' { if c == ' ' || c == '\t' || c == '\r' {
p.next() p.pos++
continue continue
} }
break break
@@ -617,7 +650,10 @@ func (p *parser) readEscape() (rune, error) {
case 'U': case 'U':
return p.readUnicode(8) return p.readUnicode(8)
default: default:
return 0, p.errf("invalid escape sequence \\%c", c) // The byte just consumed starts a rune: the backslash before it is a
// boundary, and the input is valid UTF-8.
r, _ := utf8.DecodeRune(p.src[p.pos-1:])
return 0, p.errf("invalid escape sequence \\%c", r)
} }
} }
@@ -640,7 +676,7 @@ func (p *parser) readUnicode(n int) (rune, error) {
// --- arrays and inline tables --------------------------------------------- // --- arrays and inline tables ---------------------------------------------
func (p *parser) parseArray() (any, error) { func (p *parser) parseArray() (any, error) {
p.next() // '[' p.pos++ // '['
arr := []any{} arr := []any{}
for { for {
if err := p.skipNestedSpace(); err != nil { if err := p.skipNestedSpace(); err != nil {
@@ -650,7 +686,7 @@ func (p *parser) parseArray() (any, error) {
return nil, p.errf("unterminated array") return nil, p.errf("unterminated array")
} }
if p.peek() == ']' { if p.peek() == ']' {
p.next() p.pos++
return arr, nil return arr, nil
} }
v, err := p.parseValue() v, err := p.parseValue()
@@ -666,9 +702,9 @@ func (p *parser) parseArray() (any, error) {
} }
switch p.peek() { switch p.peek() {
case ',': case ',':
p.next() p.pos++
case ']': case ']':
p.next() p.pos++
return arr, nil return arr, nil
default: default:
return nil, p.errf("expected ',' or ']' in array") return nil, p.errf("expected ',' or ']' in array")
@@ -677,7 +713,7 @@ func (p *parser) parseArray() (any, error) {
} }
func (p *parser) parseInlineTable() (any, error) { func (p *parser) parseInlineTable() (any, error) {
p.next() // '{' p.pos++ // '{'
tbl := map[string]any{} tbl := map[string]any{}
assigned := map[string]bool{} assigned := map[string]bool{}
// TOML 1.1 lets an inline table span lines: interior whitespace includes // TOML 1.1 lets an inline table span lines: interior whitespace includes
@@ -687,7 +723,7 @@ func (p *parser) parseInlineTable() (any, error) {
return nil, err return nil, err
} }
if !p.eof() && p.peek() == '}' { if !p.eof() && p.peek() == '}' {
p.next() p.pos++
return tbl, nil return tbl, nil
} }
for { for {
@@ -702,7 +738,7 @@ func (p *parser) parseInlineTable() (any, error) {
if p.eof() || p.peek() != '=' { if p.eof() || p.peek() != '=' {
return nil, p.errf("expected '=' in inline table") return nil, p.errf("expected '=' in inline table")
} }
p.next() p.pos++
p.skipInline() p.skipInline()
val, err := p.parseValue() val, err := p.parseValue()
if err != nil { if err != nil {
@@ -745,16 +781,16 @@ func (p *parser) parseInlineTable() (any, error) {
} }
switch p.peek() { switch p.peek() {
case ',': case ',':
p.next() p.pos++
if err := p.skipNestedSpace(); err != nil { if err := p.skipNestedSpace(); err != nil {
return nil, err return nil, err
} }
if !p.eof() && p.peek() == '}' { if !p.eof() && p.peek() == '}' {
p.next() p.pos++
return tbl, nil return tbl, nil
} }
case '}': case '}':
p.next() p.pos++
return tbl, nil return tbl, nil
default: default:
return nil, p.errf("expected ',' or '}' in inline table") return nil, p.errf("expected ',' or '}' in inline table")
@@ -765,12 +801,12 @@ func (p *parser) parseInlineTable() (any, error) {
// --- scanning helpers ------------------------------------------------------ // --- scanning helpers ------------------------------------------------------
func (p *parser) eof() bool { return p.pos >= len(p.src) } func (p *parser) eof() bool { return p.pos >= len(p.src) }
func (p *parser) peek() rune { return p.src[p.pos] } func (p *parser) peek() byte { return p.src[p.pos] }
// peekAt returns the rune at offset n from the current position and whether the // peekAt returns the byte at offset n from the current position and whether the
// offset is within the source. Use it instead of indexing p.src directly when // offset is within the source. Use it instead of indexing p.src directly when
// the offset may sit past the end. // the offset may sit past the end.
func (p *parser) peekAt(n int) (rune, bool) { func (p *parser) peekAt(n int) (byte, bool) {
i := p.pos + n i := p.pos + n
if i < 0 || i >= len(p.src) { if i < 0 || i >= len(p.src) {
return 0, false return 0, false
@@ -778,7 +814,7 @@ func (p *parser) peekAt(n int) (rune, bool) {
return p.src[i], true return p.src[i], true
} }
func (p *parser) next() rune { func (p *parser) next() byte {
c := p.src[p.pos] c := p.src[p.pos]
p.pos++ p.pos++
return c return c
@@ -792,30 +828,23 @@ func (p *parser) skipN(n int) {
func (p *parser) match(word string) bool { func (p *parser) match(word string) bool {
if p.lookahead(word) { if p.lookahead(word) {
p.skipN(len([]rune(word))) p.skipN(len(word))
return true return true
} }
return false return false
} }
// lookahead reports whether s follows the cursor. Every lookahead argument in
// the grammar is ASCII, so comparing bytes is exact.
func (p *parser) lookahead(s string) bool { func (p *parser) lookahead(s string) bool {
r := []rune(s) return p.pos+len(s) <= len(p.src) && string(p.src[p.pos:p.pos+len(s)]) == s
if p.pos+len(r) > len(p.src) {
return false
}
for i, c := range r {
if p.src[p.pos+i] != c {
return false
}
}
return true
} }
// skipInline consumes spaces and tabs only. // skipInline consumes spaces and tabs only.
func (p *parser) skipInline() { func (p *parser) skipInline() {
for !p.eof() { for !p.eof() {
if c := p.peek(); c == ' ' || c == '\t' { if c := p.peek(); c == ' ' || c == '\t' {
p.next() p.pos++
continue continue
} }
break break
@@ -828,14 +857,14 @@ func (p *parser) skipNestedSpace() error {
for !p.eof() { for !p.eof() {
switch p.peek() { switch p.peek() {
case ' ', '\t': case ' ', '\t':
p.next() p.pos++
case '\r': case '\r':
if err := p.expectCRLF(); err != nil { if err := p.expectCRLF(); err != nil {
return err return err
} }
case '\n': case '\n':
p.line++ p.line++
p.next() p.pos++
case '#': case '#':
if err := p.skipComment(); err != nil { if err := p.skipComment(); err != nil {
return err return err
@@ -852,14 +881,14 @@ func (p *parser) skipBlank() error {
for !p.eof() { for !p.eof() {
switch p.peek() { switch p.peek() {
case ' ', '\t': case ' ', '\t':
p.next() p.pos++
case '\r': case '\r':
if err := p.expectCRLF(); err != nil { if err := p.expectCRLF(); err != nil {
return err return err
} }
case '\n': case '\n':
p.line++ p.line++
p.next() p.pos++
case '#': case '#':
if err := p.skipComment(); err != nil { if err := p.skipComment(); err != nil {
return err return err
@@ -872,7 +901,7 @@ func (p *parser) skipBlank() error {
} }
func (p *parser) skipComment() error { func (p *parser) skipComment() error {
p.next() // consume '#' p.pos++ // consume '#'
for !p.eof() { for !p.eof() {
c := p.peek() c := p.peek()
switch { switch {
@@ -884,11 +913,11 @@ func (p *parser) skipComment() error {
} }
return p.errf("bare carriage return is not allowed") return p.errf("bare carriage return is not allowed")
case c == '\t': case c == '\t':
p.next() p.pos++
case c < 0x20 || c == 0x7f: case c < 0x20 || c == 0x7f:
return p.errf("control character U+%04X is not allowed in a comment", c) return p.errf("control character U+%04X is not allowed in a comment", c)
default: default:
p.next() p.pos++
} }
} }
return nil return nil
@@ -898,7 +927,7 @@ func (p *parser) skipComment() error {
// line feed; a bare CR is invalid. // line feed; a bare CR is invalid.
func (p *parser) expectCRLF() error { func (p *parser) expectCRLF() error {
if p.pos+1 < len(p.src) && p.src[p.pos+1] == '\n' { if p.pos+1 < len(p.src) && p.src[p.pos+1] == '\n' {
p.next() // consume CR; the LF is handled by the caller p.pos++ // consume CR; the LF is handled by the caller
return nil return nil
} }
return p.errf("bare carriage return is not allowed") return p.errf("bare carriage return is not allowed")
@@ -929,10 +958,11 @@ func (p *parser) expectLineEnd() error {
} }
if p.peek() == '\n' { if p.peek() == '\n' {
p.line++ p.line++
p.next() p.pos++
return nil return nil
} }
return p.errf("unexpected %q after value", string(p.peek())) r, _ := utf8.DecodeRune(p.src[p.pos:])
return p.errf("unexpected %q after value", string(r))
} }
func (p *parser) errf(format string, args ...any) error { func (p *parser) errf(format string, args ...any) error {