HTTP Header Outer Whitespace Span Map

Description

Map leading/core/trailing HTTP optional whitespace spans, recognizing SP and HTAB only and preserving raw UTF-16 coordinates.

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 leading/core/trailing HTTP optional whitespace spans, recognizing SP and HTAB only and preserving raw UTF-16 coordinates.

When to use this tool

Use this tool to map leading/core/trailing HTTP optional whitespace spans, recognizing SP and HTAB only and preserving raw UTF-16 coordinates.

How to use the tool and how it works

Enter value using the field definitions below.
Run the operation. Correct input errors before interpreting an output.
Read result.leading, result.value, result.trailing. Use the ordering, boundary rules and absence conditions described below.

Scan only spaces and horizontal tabs at the beginning and end and return half-open leading, value and trailing spans.^[2]

Input field	Meaning and units	Accepted input
value	Field-value text under the stated supported character and splitting rules.	Text, at most 8,192 UTF-16 code units; the operation’s grammar also applies.

Output field	Interpretation
result	Object containing the named fields below.
result.leading	Half-open leading space/tab span.
result.value	Half-open retained-value span in the OWS operation, or unchanged field text after the first colon.
result.trailing	Half-open trailing space/tab span.

json

{
  "input": {
    "value": " \ta \t"
  },
  "output": {
    "result": {
      "leading": [
        0,
        2
      ],
      "value": [
        2,
        3
      ],
      "trailing": [
        3,
        5
      ]
    }
  }
}

Limitations and assumptions

Offsets count UTF-16 code units; interior whitespace is not collapsed or validated.
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 Outer Whitespace Span Map — tool.io

Similar or alternative tools

HTTP Header Occurrence Order Map
Map explicit field occurrences to stable canonical-name ordering and within-name ordinals without serializing or reordering a request.
HTTP Header Quoted Token Source Map
Map complete HTTP quoted-string source spans and decoded quoted-pair values; token contents are Latin-1/HTAB and unclosed escapes/strings reject.