use std::borrow::Cow;
use std::num::NonZeroU32;
use std::collections::HashSet;
use anyhow::{anyhow, bail, Result};
use imap_codec::imap_types::core::{AString, IString, NonEmptyVec};
use imap_codec::imap_types::fetch::{
Section as FetchSection, Part as FetchPart
};
use eml_codec::{
header, part::AnyPart,
};
pub enum BodySection<'a> {
Full(Cow<'a, [u8]>),
Slice {
body: Cow<'a, [u8]>,
origin_octet: u32,
},
}
/// Logic for BODY[<section>]<<partial>>
/// Works in 3 times:
/// 1. Find the section (RootMime::subset)
/// 2. Apply the extraction logic (SelectedMime::extract), like TEXT, HEADERS, etc.
/// 3. Keep only the given subset provided by partial
pub fn body_ext<'a>(
part: &'a AnyPart<'a>,
section: &Option<FetchSection>,
partial: &Option<(u32, NonZeroU32)>
) -> Result<Cow<'a, [u8]>> {
let root_mime = RootMime(part);
let (extractor, path) = SubsettedSection::from(section);
let selected_mime = root_mime.subset(path);
unimplemented!();
}
/// RootMime
///
/// Example of message sections:
///
/// ```
/// HEADER ([RFC-2822] header of the message)
/// TEXT ([RFC-2822] text body of the message) MULTIPART/MIXED
/// 1 TEXT/PLAIN
/// 2 APPLICATION/OCTET-STREAM
/// 3 MESSAGE/RFC822
/// 3.HEADER ([RFC-2822] header of the message)
/// 3.TEXT ([RFC-2822] text body of the message) MULTIPART/MIXED
/// 3.1 TEXT/PLAIN
/// 3.2 APPLICATION/OCTET-STREAM
/// 4 MULTIPART/MIXED
/// 4.1 IMAGE/GIF
/// 4.1.MIME ([MIME-IMB] header for the IMAGE/GIF)
/// 4.2 MESSAGE/RFC822
/// 4.2.HEADER ([RFC-2822] header of the message)
/// 4.2.TEXT ([RFC-2822] text body of the message) MULTIPART/MIXED
/// 4.2.1 TEXT/PLAIN
/// 4.2.2 MULTIPART/ALTERNATIVE
/// 4.2.2.1 TEXT/PLAIN
/// 4.2.2.2 TEXT/RICHTEXT
/// ```
struct RootMime<'a>(&'a AnyPart<'a>);
impl<'a> RootMime<'a> {
/// A MIME object is a tree of elements.
/// The path indicates which element must be picked.
/// This function returns the picked element as the new view
fn subset(&self, path: Option<&FetchPart>) -> Result<SelectedMime> {
match path {
None => Ok(SelectedMime(self.0)),
Some(v) => self.rec_subset(v.0.as_ref()),
}
}
fn rec_subset(self, path: &[NonZeroU32]) -> Result<SelectedMime> {
if path.is_empty() {
Ok(SelectedMime(self.0))
} else {
match self.0 {
AnyPart::Mult(x) => {
let next = Self(x.children
.get(path[0].get() as usize - 1)
.ok_or(anyhow!("Unable to resolve subpath {:?}, current multipart has only {} elements", path, x.children.len()))?);
next.rec_subset(&path[1..])
},
AnyPart::Msg(x) => {
let next = Self(x.child.as_ref());
next.rec_subset(path)
},
_ => bail!("You tried to access a subpart on an atomic part (text or binary). Unresolved subpath {:?}", path),
}
}
}
}
//----------------------------------------------------------
/// A FetchSection must be handled in 2 times:
/// - First we must extract the MIME part
/// - Then we must process it as desired
/// The given struct mixes both work, so
/// we separate this work here.
enum SubsettedSection<'a> {
Part,
Header,
HeaderFields(&'a NonEmptyVec<AString<'a>>),
HeaderFieldsNot(&'a NonEmptyVec<AString<'a>>),
Text,
Mime,
}
impl<'a> SubsettedSection<'a> {
fn from(section: &'a Option<FetchSection>) -> (Self, Option<&'a FetchPart>) {
match section {
Some(FetchSection::Text(maybe_part)) => (Self::Text, maybe_part.as_ref()),
Some(FetchSection::Header(maybe_part)) => (Self::Header, maybe_part.as_ref()),
Some(FetchSection::HeaderFields(maybe_part, fields)) => (Self::HeaderFields(fields), maybe_part.as_ref()),
Some(FetchSection::HeaderFieldsNot(maybe_part, fields)) => (Self::HeaderFieldsNot(fields), maybe_part.as_ref()),
Some(FetchSection::Text(maybe_part)) => (Self::Text, maybe_part.as_ref()),
Some(FetchSection::Mime(part)) => (Self::Mime, Some(part)),
Some(FetchSection::Part(part)) => (Self::Part, Some(part)),
None => (Self::Part, None),
}
}
}
struct SelectedMime<'a>(&'a AnyPart<'a>);
impl<'a> SelectedMime<'a> {
/// The subsetted fetch section basically tells us the
/// extraction logic to apply on our selected MIME.
/// This function acts as a router for these logic.
fn extract(&self, extractor: &SubsettedSection) -> Result<ExtractedFull<'a>> {
match extractor {
SubsettedSection::Text => self.text(),
SubsettedSection::Header => self.header(),
SubsettedSection::HeaderFields(fields) => self.header_fields(fields, false),
SubsettedSection::HeaderFieldsNot(fields) => self.header_fields(fields, true),
SubsettedSection::Part => self.part(),
SubsettedSection::Mime => self.mime(),
}
}
fn mime(&self) -> Result<ExtractedFull<'a>> {
let bytes = match &self.0 {
AnyPart::Txt(p) => p.mime.fields.raw,
AnyPart::Bin(p) => p.mime.fields.raw,
AnyPart::Msg(p) => p.child.mime().raw,
AnyPart::Mult(p) => p.mime.fields.raw,
};
Ok(ExtractedFull(bytes.to_vec().into()))
}
fn part(&self) -> Result<ExtractedFull<'a>> {
let bytes = match &self.0 {
AnyPart::Txt(p) => p.body,
AnyPart::Bin(p) => p.body,
AnyPart::Msg(p) => p.raw_part,
AnyPart::Mult(_) => bail!("Multipart part has no body"),
};
Ok(ExtractedFull(bytes.to_vec().into()))
}
/// The [...] HEADER.FIELDS, and HEADER.FIELDS.NOT part
/// specifiers refer to the [RFC-2822] header of the message or of
/// an encapsulated [MIME-IMT] MESSAGE/RFC822 message.
/// HEADER.FIELDS and HEADER.FIELDS.NOT are followed by a list of
/// field-name (as defined in [RFC-2822]) names, and return a
/// subset of the header. The subset returned by HEADER.FIELDS
/// contains only those header fields with a field-name that
/// matches one of the names in the list; similarly, the subset
/// returned by HEADER.FIELDS.NOT contains only the header fields
/// with a non-matching field-name. The field-matching is
/// case-insensitive but otherwise exact.
fn header_fields(&self, fields: &'a NonEmptyVec<AString<'a>>, invert: bool) -> Result<ExtractedFull<'a>> {
// Build a lowercase ascii hashset with the fields to fetch
let index = fields
.as_ref()
.iter()
.map(|x| match x {
AString::Atom(a) => a.inner().as_bytes(),
AString::String(IString::Literal(l)) => l.as_ref(),
AString::String(IString::Quoted(q)) => q.inner().as_bytes(),
}.to_ascii_lowercase())
.collect::<HashSet<_>>();
// Extract MIME headers
let mime = match &self.0 {
AnyPart::Msg(msg) => msg.child.mime(),
other => other.mime(),
};
// Filter our MIME headers based on the field index
// 1. Keep only the correctly formatted headers
// 2. Keep only based on the index presence or absence
// 3. Reduce as a byte vector
let buffer = mime.kv.iter()
.filter_map(|field| match field {
header::Field::Good(header::Kv2(k, v)) => Some((k, v)),
_ => None,
})
.filter(|(k, _)| index.contains(&k.to_ascii_lowercase()) ^ invert)
.fold(vec![], |mut acc, (k, v)| {
acc.extend(*k);
acc.extend(b": ");
acc.extend(*v);
acc.extend(b"\r\n");
acc
});
Ok(ExtractedFull(buffer.into()))
}
/// The HEADER [...] part specifiers refer to the [RFC-2822] header of the message or of
/// an encapsulated [MIME-IMT] MESSAGE/RFC822 message.
/// ```raw
/// HEADER ([RFC-2822] header of the message)
/// ```
fn header(&self) -> Result<ExtractedFull<'a>> {
let msg = self.0.as_message().ok_or(anyhow!("Selected part must be a message/rfc822"))?;
Ok(ExtractedFull(msg.raw_headers.into()))
}
/// The TEXT part specifier refers to the text body of the message, omitting the [RFC-2822] header.
fn text(&self) -> Result<ExtractedFull<'a>> {
let msg = self.0.as_message().ok_or(anyhow!("Selected part must be a message/rfc822"))?;
Ok(ExtractedFull(msg.raw_body.into()))
}
}
// ---------------------------
struct ExtractedFull<'a>(Cow<'a, [u8]>);
impl<'a> ExtractedFull<'a> {
/// It is possible to fetch a substring of the designated text.
/// This is done by appending an open angle bracket ("<"), the
/// octet position of the first desired octet, a period, the
/// maximum number of octets desired, and a close angle bracket
/// (">") to the part specifier. If the starting octet is beyond
/// the end of the text, an empty string is returned.
///
/// Any partial fetch that attempts to read beyond the end of the
/// text is truncated as appropriate. A partial fetch that starts
/// at octet 0 is returned as a partial fetch, even if this
/// truncation happened.
///
/// Note: This means that BODY[]<0.2048> of a 1500-octet message
/// will return BODY[]<0> with a literal of size 1500, not
/// BODY[].
///
/// Note: A substring fetch of a HEADER.FIELDS or
/// HEADER.FIELDS.NOT part specifier is calculated after
/// subsetting the header.
fn to_body_section(&self, partial: &'_ Option<(u32, NonZeroU32)>) -> BodySection<'a> {
match partial {
Some((begin, len)) => self.partialize(*begin, *len),
None => BodySection::Full(self.0),
}
}
fn partialize(&self, begin: u32, len: NonZeroU32) -> BodySection<'a> {
// Asked range is starting after the end of the content,
// returning an empty buffer
if begin as usize > self.0.len() {
return BodySection::Slice {
body: Cow::Borrowed(&[][..]),
origin_octet: begin,
}
}
// Asked range is ending after the end of the content,
// slice only the beginning of the buffer
if (begin + len.get()) as usize >= self.0.len() {
return BodySection::Slice {
body: Cow::Borrowed(&self.0[begin as usize..]),
origin_octet: begin,
}
}
// Range is included inside the considered content,
// this is the "happy case"
BodySection::Slice {
body: Cow::Borrowed(&self.0[begin as usize..(begin + len.get()) as usize]),
origin_octet: begin,
}
}
}
