Skip to content

Latest commit

 

History

History
48 lines (38 loc) · 1.72 KB

IMF.md

File metadata and controls

48 lines (38 loc) · 1.72 KB
Raw

Notes on the Internet Message Format (RFC 5322)

2: An Overview

  • Lines end CRLF
  • The message format is the header block and then, optionally, the body
  • A line MUST not be more than 1000 characters total long and SHOULD NOT be more than 80 (lest it "disastrously wrap")

Header Fields

  • In the format <field name>:<field body>.
  • The field name must be ASCII 33-126, excluding the colon
  • A field body may be 32-126 and horizontal tab (ASCII 9).
  • A field body MUST NOT include CRLF unless used in folding and unfolding

Unstructured Header Field Bodies

  • A field body that is simply a string with no further processing done
  • Can still be folding/unfolding

Structured Header Field Bodies

  • Specific tokens described in sections 3, 4
  • May still be folded/unfolded where appropriate.

Long Header Fields

  • Folding whitespace (so that's what it is) is when you have to break a line, because it's too long, so you CRLF and start the next line with whitespace to indicate it is part of the previous line.
  • Unfolding is removing any CRLF immediately followed by whitespace
  • Unfolded lines are not subject to line length restrictions

The Message Body

  • Simply lines of US-ASCII but...
  • CR and LF MUST appear together as CRLF. They MUST NOT appear independently
  • Same line length restrictions as mentioned in 2

3: Legal Syntax

  • Tokens starting with obs- refer to obsolete syntax described in 4. You MUST be able to parse these but MUST NOT generate them.

ABNF Things

From 5234

SP    = %x20      ; A space character
HTAB  = %x09      ; A tab character
WSP   = SP / HTAB ; White space
VCHAR = %x21-7E   ; Visibile, printable, ASCII
  • Escaping characters
quoted-pair = ("\" (VCHAR / WSP)) / obs-qp