Description
Add start and length to obtain endExclusive.
A wire-format length may count headers, payload, padding, or only part of an enclosing message. Offsets and exclusive ends must use a clearly stated byte convention.
Add start and length to obtain endExclusive.
When to use this tool
Use DNS Resource Record Rdata Span when you need a field-level byte count or boundary check.
How to use the tool and how it works
- Enter start, length, messageLength. Use the units and conventions below.
- Run the tool. Correct any format, range, or cross-field input error before interpreting the output.
- Read endExclusive, fits. Inspect fits before interpreting the associated values.
Add start and length to obtain endExclusive. Set fits when that end is at most messageLength.1
| Input field | Meaning and units | Accepted input |
|---|---|---|
| start | Start | Required. Safe integer; minimum 0. |
| length | Length | Required. Safe integer; minimum 0; maximum 65535. |
| messageLength | Message Length | Required. Safe integer; minimum 0. |
| Output field | Interpretation | Returned shape |
|---|---|---|
| endExclusive | End boundary excluded from the represented span. | Required. Safe integer. |
| fits | Fits | Required. Boolean. |
json
{
"input": {
"start": 40,
"length": 4,
"messageLength": 100
},
"output": {
"endExclusive": 44,
"fits": true
}
}Limitations and assumptions
- All positions are byte offsets; record contents and DNS compression references are not parsed.
- Inputs must satisfy both the field types and the cross-field conditions above. Invalid input causes an error; a successful false flag or documented placeholder is a different result.
- Numeric calculations use binary floating point unless exact decimal-integer arithmetic is explicitly stated. No hidden measurement tolerance or decimal rounding is added; nonfinite or out-of-contract results are rejected. Numeric signed-zero results are exported as zero.
Alternative or Complementary methods
Compare the computed span with the actual captured buffer and validate its contents separately.
References
Similar or alternative tools
- DNS Opcode Header Bit Extractor
Extract bits 11-14 of headerWord as opcode and its top bit as response.
- Network: DNS Rcode Low High Field Join
Combine the eight-bit extendedRcode and four-bit headerRcode as 16 × extendedRcode + headerRcode.