Description
Map explicit field occurrences to stable canonical-name ordering and within-name ordinals without serializing or reordering a request.
HTTP field names are case-insensitive, while values follow each field’s own grammar. Repeated occurrences sometimes form lists but cannot always be combined. Quoted values, optional spaces/tabs and quality weights need their own treatment; the tools here use explicit field records or a stated text subset.1
Map explicit field occurrences to stable canonical-name ordering and within-name ordinals without serializing or reordering a request.
When to use this tool
Use this tool to map explicit field occurrences to stable canonical-name ordering and within-name ordinals without serializing or reordering a request.
How to use the tool and how it works
- Enter headersJson using the field definitions below. For JSON text, serialize the explicit records in the shown shape.
- Run the operation. Correct input errors before interpreting an output.
- Read result.canonicalOrder, result.occurrenceOrdinals. Use the ordering, boundary rules and absence conditions described below.
Return stable indexes sorting names case-insensitively and, for every original occurrence, the number of earlier occurrences of that same normalized name.2
| Input field | Meaning and units | Accepted input |
|---|---|---|
| headersJson | JSON text encoding array of {name: string, value: string}. Keep the record keys and value types shown in the decoded example below. | Text, at most 8,192 UTF-16 code units; the operation’s grammar also applies. |
These are the decoded structures used in the example’s JSON text fields. Supply the corresponding serialized JSON strings as input.
{
"headersJson": [
{
"name": "X-A",
"value": "one"
},
{
"name": "x-a",
"value": "two"
},
{
"name": "Set-Cookie",
"value": "a=1"
}
]
}| Output field | Interpretation |
|---|---|
| result | Object containing the named fields below. |
| result.canonicalOrder | Original indexes in stable case-insensitive name sort order. |
| result.occurrenceOrdinals | Zero-based repetition number of each original normalized header name. |
{
"input": {
"headersJson": "[{\"name\":\"X-A\",\"value\":\"one\"},{\"name\":\"x-a\",\"value\":\"two\"},{\"name\":\"Set-Cookie\",\"value\":\"a=1\"}]"
},
"output": {
"result": {
"canonicalOrder": [
2,
0,
1
],
"occurrenceOrdinals": [
0,
1,
0
]
}
}
}Limitations and assumptions
- The tool returns a mapping without rewriting headers or recommending a universal canonical order.
- Explicit header records have name and value strings. Names must use token syntax; supported value code units are tab or 32–255 excluding DEL. Byte budgets use that single-byte representation, not UTF-8 or HTTP/2 compression.
- Every declared top-level input field is required and unexpected fields are rejected. Ordinary strings are limited to 8,192 UTF-16 code units and lists to 128 entries, with tighter operation-specific bounds where stated. JSON text has bounded nesting and node counts.
- Numeric outputs must be finite and no larger in absolute magnitude than the safe-integer limit; operations returning exact large integers use decimal text. Positions are zero-based and spans end exclusively unless the operation explicitly states a different convention.
Alternative or Complementary methods
Choose field-specific parsing and combination rules rather than applying one policy to every header. Preserve occurrence order and use a full HTTP implementation for message framing and protocol-level decisions.
References
-
RFC 9110: HTTP Semantics — RFC Editor
-
Tool behavior and example: HTTP Header Occurrence Order Map — tool.io
Similar or alternative tools
- HTTP Header Occurrence Byte Budget
Budget HTTP/1 field section octets under literal name-colon-space-value-CRLF serialization plus final CRLF; Latin-1 octets, not HTTP/2 compression or UTF-8.
- HTTP Header Occurrence Case Collisions
Audit HTTP field-name spelling collisions separately from repeated identical spellings; validates token names and Latin-1 field-value octets.