view rust/chg/src/locator.rs @ 48981:f3aafd785e65

filemerge: add support for partial conflict resolution by external tool

A common class of merge conflicts is in imports/#includes/etc. It's
relatively easy to write a tool that can resolve these conflicts,
perhaps by naively just unioning the statements and leaving any
cleanup to other tools to do later [1]. Such specialized tools cannot
generally resolve all conflicts in a file, of course. Let's therefore
call them "partial merge tools". Note that the internal simplemerge
algorithm is such a partial merge tool - one that only resolves
trivial "conflicts" where one side is unchanged or both sides change
in the same way.

One can also imagine having smarter language-aware partial tools that
merge the AST. It may be useful for such tools to interactively let
the user resolve any conflicts it can't resolve itself. However,
having the option of implementing it as a partial merge tool means
that the developer doesn't *need* to create a UI for it. Instead, the
user can resolve any remaining conflicts with their regular merge tool
(e.g. `:merge3` or `meld).

We don't currently have a way to let the user define such partial
merge tools. That's what this patch addresses. It lets the user
configure partial merge tools to run. Each tool can be configured to
run only on files matching certain patterns (e.g. "*.py"). The tool
takes three inputs (local, base, other) and resolves conflicts by
updating these in place. For example, let's say the inputs are these:


base:
```
import sys

def main():
  print('Hello')
```

local:
```
import os
import sys

def main():
  print('Hi')
```

other:
```
import re
import sys

def main():
  print('Howdy')
```

A partial merge tool could now resolve the conflicting imports by
replacing the import statements in *all* files by the following
snippet, while leaving the remainder of the files unchanged.

```
import os
import re
import sys
```

As a result, simplemerge and any regular merge tool that runs after
the partial merge tool(s) will consider the imports to be
non-conflicting and will only present the conflict in `main()` to the
user.

Differential Revision: https://phab.mercurial-scm.org/D12356

// Copyright 2011, 2018 Yuya Nishihara <[e-mail]>
//
// This software may be used and distributed according to the terms of the
// GNU General Public License version 2 or any later version.

//! Utility for locating command-server process.

use log::debug;
use std::env;
use std::ffi::{OsStr, OsString};
use std::fs::{self, DirBuilder};
use std::io;
use std::os::unix::ffi::{OsStrExt, OsStringExt};
use std::os::unix::fs::{DirBuilderExt, MetadataExt};
use std::path::{Path, PathBuf};
use std::process::{self, Child, Command};
use std::time::{Duration, Instant};
use tokio::time;

use crate::clientext::ChgClient;
use crate::message::{Instruction, ServerSpec};
use crate::procutil;

const REQUIRED_SERVER_CAPABILITIES: &[&str] = &[
    "attachio",
    "chdir",
    "runcommand",
    "setenv",
    "setumask2",
    "validate",
];

/// Helper to connect to and spawn a server process.
#[derive(Clone, Debug)]
pub struct Locator {
    hg_command: OsString,
    hg_early_args: Vec<OsString>,
    current_dir: PathBuf,
    env_vars: Vec<(OsString, OsString)>,
    process_id: u32,
    base_sock_path: PathBuf,
    redirect_sock_path: Option<PathBuf>,
    timeout: Duration,
}

impl Locator {
    /// Creates locator capturing the current process environment.
    ///
    /// If no `$CHGSOCKNAME` is specified, the socket directory will be
    /// created as necessary.
    pub fn prepare_from_env() -> io::Result<Locator> {
        Ok(Locator {
            hg_command: default_hg_command(),
            hg_early_args: Vec::new(),
            current_dir: env::current_dir()?,
            env_vars: env::vars_os().collect(),
            process_id: process::id(),
            base_sock_path: prepare_server_socket_path()?,
            redirect_sock_path: None,
            timeout: default_timeout(),
        })
    }

    /// Temporary socket path for this client process.
    fn temp_sock_path(&self) -> PathBuf {
        let src = self.base_sock_path.as_os_str().as_bytes();
        let mut buf = Vec::with_capacity(src.len() + 6); // "{src}.{pid}".len()
        buf.extend_from_slice(src);
        buf.extend_from_slice(format!(".{}", self.process_id).as_bytes());
        OsString::from_vec(buf).into()
    }

    /// Specifies the arguments to be passed to the server at start.
    pub fn set_early_args(
        &mut self,
        args: impl IntoIterator<Item = impl AsRef<OsStr>>,
    ) {
        self.hg_early_args =
            args.into_iter().map(|a| a.as_ref().to_owned()).collect();
    }

    /// Connects to the server.
    ///
    /// The server process will be spawned if not running.
    pub async fn connect(&mut self) -> io::Result<ChgClient> {
        for _cnt in 0..10 {
            let mut client = self.try_connect().await?;
            let instructions = client.validate(&self.hg_early_args).await?;
            let reconnect = self.run_instructions(&instructions)?;
            if !reconnect {
                return Ok(client);
            }
        }

        let msg = format!(
            concat!(
                "too many redirections.\n",
                "Please make sure {:?} is not a wrapper which ",
                "changes sensitive environment variables ",
                "before executing hg. If you have to use a ",
                "wrapper, wrap chg instead of hg.",
            ),
            self.hg_command
        );
        Err(io::Error::new(io::ErrorKind::Other, msg))
    }

    /// Runs instructions received from the server.
    ///
    /// Returns true if the client should try connecting to the other server.
    fn run_instructions(
        &mut self,
        instructions: &[Instruction],
    ) -> io::Result<bool> {
        let mut reconnect = false;
        for inst in instructions {
            debug!("instruction: {:?}", inst);
            match inst {
                Instruction::Exit(_) => {
                    // Just returns the current connection to run the
                    // unparsable command and report the error
                    return Ok(false);
                }
                Instruction::Reconnect => {
                    reconnect = true;
                }
                Instruction::Redirect(path) => {
                    if path.parent() != self.base_sock_path.parent() {
                        let msg = format!(
                            "insecure redirect instruction from server: {}",
                            path.display()
                        );
                        return Err(io::Error::new(
                            io::ErrorKind::InvalidData,
                            msg,
                        ));
                    }
                    self.redirect_sock_path = Some(path.to_owned());
                    reconnect = true;
                }
                Instruction::Unlink(path) => {
                    if path.parent() != self.base_sock_path.parent() {
                        let msg = format!(
                            "insecure unlink instruction from server: {}",
                            path.display()
                        );
                        return Err(io::Error::new(
                            io::ErrorKind::InvalidData,
                            msg,
                        ));
                    }
                    fs::remove_file(path).unwrap_or(()); // may race
                }
            }
        }

        Ok(reconnect)
    }

    /// Tries to connect to the existing server, or spawns new if not running.
    async fn try_connect(&mut self) -> io::Result<ChgClient> {
        let sock_path = self
            .redirect_sock_path
            .as_ref()
            .unwrap_or(&self.base_sock_path)
            .clone();
        debug!("try connect to {}", sock_path.display());
        let mut client = match ChgClient::connect(sock_path).await {
            Ok(client) => client,
            Err(_) => {
                // Prevent us from being re-connected to the outdated
                // master server: We were told by the server to redirect
                // to redirect_sock_path, which didn't work. We do not
                // want to connect to the same master server again
                // because it would probably tell us the same thing.
                if self.redirect_sock_path.is_some() {
                    fs::remove_file(&self.base_sock_path).unwrap_or(());
                    // may race
                }
                self.spawn_connect().await?
            }
        };
        check_server_capabilities(client.server_spec())?;
        // It's purely optional, and the server might not support this command.
        if client.server_spec().capabilities.contains("setprocname") {
            client
                .set_process_name(format!("chg[worker/{}]", self.process_id))
                .await?;
        }
        client.set_current_dir(&self.current_dir).await?;
        client
            .set_env_vars_os(self.env_vars.iter().cloned())
            .await?;
        Ok(client)
    }

    /// Spawns new server process and connects to it.
    ///
    /// The server will be spawned at the current working directory, then
    /// chdir to "/", so that the server will load configs from the target
    /// repository.
    async fn spawn_connect(&mut self) -> io::Result<ChgClient> {
        let sock_path = self.temp_sock_path();
        debug!("start cmdserver at {}", sock_path.display());
        let server = Command::new(&self.hg_command)
            .arg("serve")
            .arg("--cmdserver")
            .arg("chgunix")
            .arg("--address")
            .arg(&sock_path)
            .arg("--daemon-postexec")
            .arg("chdir:/")
            .args(&self.hg_early_args)
            .current_dir(&self.current_dir)
            .env_clear()
            .envs(self.env_vars.iter().cloned())
            .env("CHGINTERNALMARK", "")
            .spawn()?;
        let client = self.connect_spawned(server, &sock_path).await?;
        debug!(
            "rename {} to {}",
            sock_path.display(),
            self.base_sock_path.display()
        );
        fs::rename(&sock_path, &self.base_sock_path)?;
        Ok(client)
    }

    /// Tries to connect to the just spawned server repeatedly until timeout
    /// exceeded.
    async fn connect_spawned(
        &mut self,
        mut server: Child,
        sock_path: &Path,
    ) -> io::Result<ChgClient> {
        debug!("try connect to {} repeatedly", sock_path.display());
        // waits for either connection established or server failed to start
        let start_time = Instant::now();
        while start_time.elapsed() < self.timeout {
            if let Ok(client) = ChgClient::connect(&sock_path).await {
                // server handle is dropped here, but the detached process
                // will continue running in background
                return Ok(client);
            }

            if let Some(st) = server.try_wait()? {
                return Err(io::Error::new(
                    io::ErrorKind::Other,
                    format!("server exited too early: {}", st),
                ));
            }

            // try again with slight delay
            time::delay_for(Duration::from_millis(10)).await;
        }

        Err(io::Error::new(
            io::ErrorKind::TimedOut,
            "timed out while connecting to server",
        ))
    }
}

/// Determines the server socket to connect to.
///
/// If no `$CHGSOCKNAME` is specified, the socket directory will be created
/// as necessary.
fn prepare_server_socket_path() -> io::Result<PathBuf> {
    if let Some(s) = env::var_os("CHGSOCKNAME") {
        Ok(PathBuf::from(s))
    } else {
        let mut path = default_server_socket_dir();
        create_secure_dir(&path)?;
        path.push("server");
        Ok(path)
    }
}

/// Determines the default server socket path as follows.
///
/// 1. `$XDG_RUNTIME_DIR/chg`
/// 2. `$TMPDIR/chg$UID`
/// 3. `/tmp/chg$UID`
pub fn default_server_socket_dir() -> PathBuf {
    // XDG_RUNTIME_DIR should be ignored if it has an insufficient permission.
    // https://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html
    if let Some(Ok(s)) = env::var_os("XDG_RUNTIME_DIR").map(check_secure_dir) {
        let mut path = PathBuf::from(s);
        path.push("chg");
        path
    } else {
        let mut path = env::temp_dir();
        path.push(format!("chg{}", procutil::get_effective_uid()));
        path
    }
}

/// Determines the default hg command.
pub fn default_hg_command() -> OsString {
    // TODO: maybe allow embedding the path at compile time (or load from hgrc)
    env::var_os("CHGHG")
        .or(env::var_os("HG"))
        .unwrap_or(OsStr::new("hg").to_owned())
}

fn default_timeout() -> Duration {
    let secs = env::var("CHGTIMEOUT")
        .ok()
        .and_then(|s| s.parse().ok())
        .unwrap_or(60);
    Duration::from_secs(secs)
}

/// Creates a directory which the other users cannot access to.
///
/// If the directory already exists, tests its permission.
fn create_secure_dir(path: impl AsRef<Path>) -> io::Result<()> {
    DirBuilder::new()
        .mode(0o700)
        .create(path.as_ref())
        .or_else(|err| {
            if err.kind() == io::ErrorKind::AlreadyExists {
                check_secure_dir(path).map(|_| ())
            } else {
                Err(err)
            }
        })
}

fn check_secure_dir<P>(path: P) -> io::Result<P>
where
    P: AsRef<Path>,
{
    let a = fs::symlink_metadata(path.as_ref())?;
    if a.is_dir()
        && a.uid() == procutil::get_effective_uid()
        && (a.mode() & 0o777) == 0o700
    {
        Ok(path)
    } else {
        Err(io::Error::new(io::ErrorKind::Other, "insecure directory"))
    }
}

fn check_server_capabilities(spec: &ServerSpec) -> io::Result<()> {
    let unsupported: Vec<_> = REQUIRED_SERVER_CAPABILITIES
        .iter()
        .cloned()
        .filter(|&s| !spec.capabilities.contains(s))
        .collect();
    if unsupported.is_empty() {
        Ok(())
    } else {
        let msg = format!(
            "insufficient server capabilities: {}",
            unsupported.join(", ")
        );
        Err(io::Error::new(io::ErrorKind::Other, msg))
    }
}

/// Collects arguments which need to be passed to the server at start.
pub fn collect_early_args(
    args: impl IntoIterator<Item = impl AsRef<OsStr>>,
) -> Vec<OsString> {
    let mut args_iter = args.into_iter();
    let mut early_args = Vec::new();
    while let Some(arg) = args_iter.next() {
        let argb = arg.as_ref().as_bytes();
        if argb == b"--" {
            break;
        } else if argb.starts_with(b"--") {
            let mut split = argb[2..].splitn(2, |&c| c == b'=');
            match split.next().unwrap() {
                b"traceback" => {
                    if split.next().is_none() {
                        early_args.push(arg.as_ref().to_owned());
                    }
                }
                b"config" | b"cwd" | b"repo" | b"repository" => {
                    if split.next().is_some() {
                        // --<flag>=<val>
                        early_args.push(arg.as_ref().to_owned());
                    } else {
                        // --<flag> <val>
                        args_iter.next().map(|val| {
                            early_args.push(arg.as_ref().to_owned());
                            early_args.push(val.as_ref().to_owned());
                        });
                    }
                }
                _ => {}
            }
        } else if argb.starts_with(b"-R") {
            if argb.len() > 2 {
                // -R<val>
                early_args.push(arg.as_ref().to_owned());
            } else {
                // -R <val>
                args_iter.next().map(|val| {
                    early_args.push(arg.as_ref().to_owned());
                    early_args.push(val.as_ref().to_owned());
                });
            }
        }
    }

    early_args
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn collect_early_args_some() {
        assert!(collect_early_args(&[] as &[&OsStr]).is_empty());
        assert!(collect_early_args(&["log"]).is_empty());
        assert_eq!(
            collect_early_args(&["log", "-Ra", "foo"]),
            os_string_vec_from(&[b"-Ra"])
        );
        assert_eq!(
            collect_early_args(&["log", "-R", "repo", "", "--traceback", "a"]),
            os_string_vec_from(&[b"-R", b"repo", b"--traceback"])
        );
        assert_eq!(
            collect_early_args(&["log", "--config", "diff.git=1", "-q"]),
            os_string_vec_from(&[b"--config", b"diff.git=1"])
        );
        assert_eq!(
            collect_early_args(&["--cwd=..", "--repository", "r", "log"]),
            os_string_vec_from(&[b"--cwd=..", b"--repository", b"r"])
        );
        assert_eq!(
            collect_early_args(&["log", "--repo=r", "--repos", "a"]),
            os_string_vec_from(&[b"--repo=r"])
        );
    }

    #[test]
    fn collect_early_args_orphaned() {
        assert!(collect_early_args(&["log", "-R"]).is_empty());
        assert!(collect_early_args(&["log", "--config"]).is_empty());
    }

    #[test]
    fn collect_early_args_unwanted_value() {
        assert!(collect_early_args(&["log", "--traceback="]).is_empty());
    }

    fn os_string_vec_from(v: &[&[u8]]) -> Vec<OsString> {
        v.iter().map(|s| OsStr::from_bytes(s).to_owned()).collect()
    }
}