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package binary
import (
"bytes"
"fmt"
"io"
"github.com/tetratelabs/wazero/api"
"github.com/tetratelabs/wazero/internal/leb128"
"github.com/tetratelabs/wazero/internal/wasm"
)
// dataSegmentPrefix represents three types of data segments.
//
// https://www.w3.org/TR/2022/WD-wasm-core-2-20220419/binary/modules.html#data-section
type dataSegmentPrefix = uint32
const (
// dataSegmentPrefixActive is the prefix for the version 1.0 compatible data segment, which is classified as "active" in 2.0.
dataSegmentPrefixActive dataSegmentPrefix = 0x0
// dataSegmentPrefixPassive prefixes the "passive" data segment as in version 2.0 specification.
dataSegmentPrefixPassive dataSegmentPrefix = 0x1
// dataSegmentPrefixActiveWithMemoryIndex is the active prefix with memory index encoded which is defined for futur use as of 2.0.
dataSegmentPrefixActiveWithMemoryIndex dataSegmentPrefix = 0x2
)
func decodeDataSegment(r *bytes.Reader, enabledFeatures api.CoreFeatures, ret *wasm.DataSegment) (err error) {
dataSegmentPrefx, _, err := leb128.DecodeUint32(r)
if err != nil {
err = fmt.Errorf("read data segment prefix: %w", err)
return
}
if dataSegmentPrefx != dataSegmentPrefixActive {
if err = enabledFeatures.RequireEnabled(api.CoreFeatureBulkMemoryOperations); err != nil {
err = fmt.Errorf("non-zero prefix for data segment is invalid as %w", err)
return
}
}
switch dataSegmentPrefx {
case dataSegmentPrefixActive,
dataSegmentPrefixActiveWithMemoryIndex:
// Active data segment as in
// https://www.w3.org/TR/2022/WD-wasm-core-2-20220419/binary/modules.html#data-section
if dataSegmentPrefx == 0x2 {
d, _, err := leb128.DecodeUint32(r)
if err != nil {
return fmt.Errorf("read memory index: %v", err)
} else if d != 0 {
return fmt.Errorf("memory index must be zero but was %d", d)
}
}
err = decodeConstantExpression(r, enabledFeatures, &ret.OffsetExpression)
if err != nil {
return fmt.Errorf("read offset expression: %v", err)
}
case dataSegmentPrefixPassive:
// Passive data segment doesn't need const expr nor memory index encoded.
// https://www.w3.org/TR/2022/WD-wasm-core-2-20220419/binary/modules.html#data-section
ret.Passive = true
default:
err = fmt.Errorf("invalid data segment prefix: 0x%x", dataSegmentPrefx)
return
}
vs, _, err := leb128.DecodeUint32(r)
if err != nil {
err = fmt.Errorf("get the size of vector: %v", err)
return
}
ret.Init = make([]byte, vs)
if _, err = io.ReadFull(r, ret.Init); err != nil {
err = fmt.Errorf("read bytes for init: %v", err)
}
return
}
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