`flare.http.header_view`

Borrowed header storage.

HeaderMapView[origin] stores headers as (name_start, name_len, value_start, value_len) offsets into a single byte buffer the caller owns (typically ConnHandle.read_buf). Lookups compare against the buffer in place — no per-header String allocation on the read path.

Owned HeaderMap (flare/http/headers.mojo) stays the type of record for response writers (Response.headers) and as the into_owned() target for handlers that need to keep headers alive past one event-loop iteration.

This commit is additive: Request still carries an owned HeaderMap, and _parse_http_request_bytes still allocates. The HeaderMapView -> Request.headers wiring lands with the RequestView[origin] refactor; until then HeaderMapView is a standalone type usable for any byte-range header parsing (WebSocket handshakes, HTTP/2 HEADERS frames, custom protocol layering).

Example:

var raw = "GET / HTTP/1.1

Host: x X-A: 1

".as_bytes() var view = parse_header_view(SpanUInt8, _) assert_equal(view.get("host"), "x") # case-insensitive assert_equal(view.get("X-A"), "1") assert_equal(view.len(), 2) var owned = view.into_owned() # one allocation, copies bytes

The header offsets list itself does allocate (Mojo's List manages its own backing buffer), but each lookup avoids the per-header String copy that HeaderMap.get would have done. For a 12-header request the parse path makes 12 + 12 + 1 String allocations (12 keys, 12 values, one HeaderMap struct internally). The view path makes one List[Int] allocation holding 4 * 12 ints.

Structs

`HeaderMapView`

struct HeaderMapView[origin: Origin[mut=origin.mut]]

Borrowed header collection.

Holds offsets into a caller-owned byte buffer (self.buf) plus a parallel List[Int] of (name_start, name_len, value_start, value_len) quadruples (4 ints per header).

Lookups are case-insensitive ASCII; comparison runs against the underlying buf in place.

The origin parameter ties the view's lifetime to the buffer it borrows from. Mojo's borrow checker prevents the view from outliving the buffer.

Implements Movable

Fields: buf: Span[UInt8, origin]: The byte buffer the view borrows from. Typically ConnHandle.read_buf for the reactor read path; may be any Span[UInt8, ...] for tests / WS handshake / future HTTP/2 HEADERS frame readers.

`init`

def __init__(out self, buf: Span[UInt8, origin])

Empty view bound to buf. Use parse_header_view to populate from raw header bytes.

def __init__(out self, buf: Span[UInt8, origin], var offsets: List[Int])

Populated view. len(offsets) must be a multiple of 4.

`len`

def len(self) -> Int

Number of headers in the view.

`get`

def get(self, name: String) -> StringSpan[origin_of(origin)]

Return the value of the first header named name, case-insensitive. Returns an empty slice if not present.

The returned slice borrows from self.buf; its lifetime is tied to the view's origin. No allocation.

`count`

def count(self, name: String) -> Int

Number of header lines named name, case-insensitive.

`contains`

def contains(self, name: String) -> Bool

True if a header named name is present (case-insensitive).

`into_owned`

def into_owned(self) -> HeaderMap

Materialise an owned HeaderMap by copying each header's bytes out of the borrowed buffer into Strings.

One allocation per header (key + value). Use this only when the handler needs to keep headers alive past the connection's event-loop iteration; the borrowed view itself does not allocate per header.

Functions

`parse_header_view`

def parse_header_view[origin: Origin[mut=origin.mut]](data: Span[UInt8, origin]) -> HeaderMapView[origin]

Parse CRLF-separated header lines into a HeaderMapView.

Expects the request line + \r\n to already be stripped: data should start at the first header line and end at (or after) the empty CRLF that terminates the header block. Stops at the first empty line.

Header values are trimmed of leading / trailing OWS (SP / HTAB) per RFC 7230 §3.2.4. The trim is offset arithmetic on the underlying buffer — no allocation.

Raises Error on malformed lines (missing colon, empty header name).

Args: data: Header bytes (may include CRLF terminators between lines and a trailing empty CRLF).