Module: Mailmate::HeaderReader

Extended by:
HeaderReader
Included in:
HeaderReader
Defined in:
lib/mailmate/header_reader.rb

Overview

Read just the header block of an ‘.eml` file. Pulls in a small amount of the file from disk (up to ~64 KB), stops at the first blank line that separates headers from body, and extracts named header values.

Cheap relative to ‘Mail.read` — no MIME parsing, no body decode — when all the caller wants is `Message-ID` or `From` from a known `.eml` path.

Stateless utility surface, so it’s a module (cf. AppleScriptDriver, which is a class because it carries per-invocation state).

Constant Summary collapse

DEFAULT_MAX_BYTES = 
65_536
CHUNK_SIZE = 
4_096

Instance Method Summary collapse

Instance Method Details

#header(path, name, max_bytes: DEFAULT_MAX_BYTES) ⇒ Object

Extract a named header’s value from a path. Case-insensitive. Handles RFC 5322 §2.2.3 header folding — a value continued on subsequent lines with leading whitespace is unfolded into a single line (CRLF + WSP collapsed to a single space). Returns nil if the header isn’t present in the first ‘max_bytes` of the file.



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# File 'lib/mailmate/header_reader.rb', line 49

def header(path, name, max_bytes: DEFAULT_MAX_BYTES)
  block = read_block(path, max_bytes: max_bytes)
  # Match the header name at start of line, then the rest of that line and
  # any subsequent continuation lines (lines beginning with WSP).
  pattern = /^#{Regexp.escape(name)}:[\t ]*(.*(?:\r?\n[\t ].*)*)/i
  match = block.match(pattern)
  return nil unless match
  unfold(match[1])
end

#message_id(path) ⇒ Object

Convenience for the Message-ID specifically. Strips the surrounding angle brackets if present, returning the bare ID suitable for building a ‘mid:` URL via Mailmate::MidUrl.for.



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# File 'lib/mailmate/header_reader.rb', line 68

def message_id(path)
  val = header(path, "Message-ID")
  return nil if val.nil?
  val.match(/<([^>]+)>/)&.captures&.first || val
end

#read_block(path, max_bytes: DEFAULT_MAX_BYTES) ⇒ Object

Returns the raw bytes of the header block, capped at ‘max_bytes`. Truncates at the first blank line (the header/body separator) so callers looking for “To:” or similar don’t accidentally match a ‘To:` line that appears in the body.



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# File 'lib/mailmate/header_reader.rb', line 25

def read_block(path, max_bytes: DEFAULT_MAX_BYTES)
  header_bytes = +""
  File.open(path, "rb") do |f|
    while (chunk = f.read(CHUNK_SIZE))
      header_bytes << chunk
      break if header_bytes.index("\r\n\r\n") || header_bytes.index("\n\n")
      break if header_bytes.bytesize > max_bytes
    end
  end

  if (i = header_bytes.index("\r\n\r\n"))
    header_bytes[0, i]
  elsif (i = header_bytes.index("\n\n"))
    header_bytes[0, i]
  else
    header_bytes
  end
end

#unfold(raw) ⇒ Object

Collapse CRLF + WSP runs into a single space (RFC 5322 §2.2.3 “unfolding”). Trailing whitespace is stripped.



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# File 'lib/mailmate/header_reader.rb', line 61

def unfold(raw)
  raw.gsub(/\r?\n[\t ]+/, " ").strip
end