gix_protocol/fetch/response/blocking_io.rs
1use std::io;
2
3use gix_transport::{client, Protocol};
4
5use crate::fetch::{
6 response,
7 response::{shallow_update_from_line, Acknowledgement, ShallowUpdate, WantedRef},
8 Response,
9};
10
11fn parse_v2_section<'a, T>(
12 line: &mut String,
13 reader: &mut impl client::ExtendedBufRead<'a>,
14 res: &mut Vec<T>,
15 parse: impl Fn(&str) -> Result<T, response::Error>,
16) -> Result<bool, response::Error> {
17 line.clear();
18 while reader.readline_str(line)? != 0 {
19 res.push(parse(line)?);
20 line.clear();
21 }
22 // End of message, or end of section?
23 Ok(if reader.stopped_at() == Some(client::MessageKind::Delimiter) {
24 // try reading more sections
25 reader.reset(Protocol::V2);
26 false
27 } else {
28 // we are done, there is no pack
29 true
30 })
31}
32
33impl Response {
34 /// Parse a response of the given `version` of the protocol from `reader`.
35 ///
36 /// `client_expects_pack` is only relevant for V1 stateful connections, and if `false`, causes us to stop parsing when seeing `NAK`,
37 /// and if `true` we will keep parsing until we get a pack as the client already signalled to the server that it's done.
38 /// This way of doing things allows us to exploit knowledge about more recent versions of the protocol, which keeps code easier
39 /// and more localized without having to support all the cruft that there is.
40 ///
41 /// `wants_to_negotiate` should be `false` for clones which is when we don't have sent any haves. The reason for this flag to exist
42 /// is to predict how to parse V1 output only, and neither `client_expects_pack` nor `wants_to_negotiate` are relevant for V2.
43 /// This ugliness is in place to avoid having to resort to an [an even more complex ugliness](https://github.com/git/git/blob/9e49351c3060e1fa6e0d2de64505b7becf157f28/fetch-pack.c#L583-L594)
44 /// that `git` has to use to predict how many acks are supposed to be read. We also genuinely hope that this covers it all….
45 pub fn from_line_reader<'a>(
46 version: Protocol,
47 reader: &mut impl client::ExtendedBufRead<'a>,
48 client_expects_pack: bool,
49 wants_to_negotiate: bool,
50 ) -> Result<Response, response::Error> {
51 match version {
52 Protocol::V0 | Protocol::V1 => {
53 let mut line = String::new();
54 let mut acks = Vec::<Acknowledgement>::new();
55 let mut shallows = Vec::<ShallowUpdate>::new();
56 let mut saw_ready = false;
57 let has_pack = 'lines: loop {
58 line.clear();
59 let peeked_line = match reader.peek_data_line() {
60 Some(Ok(Ok(line))) => String::from_utf8_lossy(line),
61 // This special case (hang/block forever) deals with a single NAK being a legitimate EOF sometimes
62 // Note that this might block forever in stateful connections as there it's not really clear
63 // if something will be following or not by just looking at the response. Instead you have to know
64 // [a lot](https://github.com/git/git/blob/9e49351c3060e1fa6e0d2de64505b7becf157f28/fetch-pack.c#L583-L594)
65 // to deal with this correctly.
66 // For now this is acceptable, as V2 can be used as a workaround, which also is the default.
67 Some(Err(err)) if err.kind() == io::ErrorKind::UnexpectedEof => break 'lines false,
68 Some(Err(err)) => return Err(err.into()),
69 Some(Ok(Err(err))) => return Err(err.into()),
70 None => {
71 // maybe we saw a shallow flush packet, let's reset and retry
72 debug_assert_eq!(
73 reader.stopped_at(),
74 Some(client::MessageKind::Flush),
75 "If this isn't a flush packet, we don't know what's going on"
76 );
77 reader.readline_str(&mut line)?;
78 reader.reset(Protocol::V1);
79 match reader.peek_data_line() {
80 Some(Ok(Ok(line))) => String::from_utf8_lossy(line),
81 Some(Err(err)) => return Err(err.into()),
82 Some(Ok(Err(err))) => return Err(err.into()),
83 None => break 'lines false, // EOF
84 }
85 }
86 };
87
88 if Response::parse_v1_ack_or_shallow_or_assume_pack(&mut acks, &mut shallows, &peeked_line) {
89 break 'lines true;
90 }
91 assert_ne!(reader.readline_str(&mut line)?, 0, "consuming a peeked line works");
92 // When the server sends ready, we know there is going to be a pack so no need to stop early.
93 saw_ready |= matches!(acks.last(), Some(Acknowledgement::Ready));
94 if let Some(Acknowledgement::Nak) = acks.last().filter(|_| !client_expects_pack || !saw_ready) {
95 if !wants_to_negotiate {
96 continue;
97 }
98 break 'lines false;
99 }
100 };
101 Ok(Response {
102 acks,
103 shallows,
104 wanted_refs: vec![],
105 has_pack,
106 })
107 }
108 Protocol::V2 => {
109 // NOTE: We only read acknowledgements and scrub to the pack file, until we have use for the other features
110 let mut line = String::new();
111 reader.reset(Protocol::V2);
112 let mut acks = Vec::<Acknowledgement>::new();
113 let mut shallows = Vec::<ShallowUpdate>::new();
114 let mut wanted_refs = Vec::<WantedRef>::new();
115 let has_pack = 'section: loop {
116 line.clear();
117 if reader.readline_str(&mut line)? == 0 {
118 return Err(response::Error::Io(io::Error::new(
119 io::ErrorKind::UnexpectedEof,
120 "Could not read message headline",
121 )));
122 }
123
124 match line.trim_end() {
125 "acknowledgments" => {
126 if parse_v2_section(&mut line, reader, &mut acks, Acknowledgement::from_line)? {
127 break 'section false;
128 }
129 }
130 "shallow-info" => {
131 if parse_v2_section(&mut line, reader, &mut shallows, shallow_update_from_line)? {
132 break 'section false;
133 }
134 }
135 "wanted-refs" => {
136 if parse_v2_section(&mut line, reader, &mut wanted_refs, WantedRef::from_line)? {
137 break 'section false;
138 }
139 }
140 "packfile" => {
141 // what follows is the packfile itself, which can be read with a sideband enabled reader
142 break 'section true;
143 }
144 _ => return Err(response::Error::UnknownSectionHeader { header: line }),
145 }
146 };
147 Ok(Response {
148 acks,
149 shallows,
150 wanted_refs,
151 has_pack,
152 })
153 }
154 }
155 }
156}