Content-Length

The Content-Length header indicates the size of the message body in bytes. Its grammar is strict: Content-Length = 1*DIGIT. Any deviation — non-numeric characters, plus signs, leading zeros, negative values, overflow — can cause parsers to disagree on body boundaries.

Key Rules

Grammar: 1*DIGIT means one or more ASCII digits (0-9). No signs, no spaces, no hex.

“If a message is received without Transfer-Encoding and with an invalid Content-Length header field, then the message framing is invalid and the recipient MUST treat it as an unrecoverable error...” — RFC 9112 Section 6.3

Tests

CL-NON-NUMERIC

Non-numeric Content-Length value.

CL-PLUS-SIGN

Content-Length with a + prefix.

NO-CL-IN-204

Content-Length forbidden in 204 responses.