fish-shell/src/io.h

#ifndef FISH_IO_H
#define FISH_IO_H

#include <stdarg.h>
#include <unistd.h>

#include <cstdint>
#include <cwchar>
#include <future>
#include <memory>
#include <string>
#include <utility>
#include <vector>

#include "common.h"
#include "fds.h"
#include "global_safety.h"
#include "redirection.h"

using std::shared_ptr;

class job_group_t;

/// separated_buffer_t represents a buffer of output from commands, prepared to be turned into a
/// variable. For example, command substitutions output into one of these. Most commands just
/// produce a stream of bytes, and those get stored directly. However other commands produce
/// explicitly separated output, in particular `string` like `string collect` and `string split0`.
/// The buffer tracks a sequence of elements. Some elements are explicitly separated and should not
/// be further split; other elements have inferred separation and may be split by IFS (or not,
/// depending on its value).
enum class separation_type_t {
    inferred,    // this element should be further separated by IFS
    explicitly,  // this element is explicitly separated and should not be further split
};

/// A separated_buffer_t contains a list of elements, some of which may be separated explicitly and
/// others which must be separated further by the user (e.g. via IFS).
class separated_buffer_t : noncopyable_t {
   public:
    struct element_t {
        std::string contents;
        separation_type_t separation;

        element_t(std::string contents, separation_type_t sep)
            : contents(std::move(contents)), separation(sep) {}

        bool is_explicitly_separated() const { return separation == separation_type_t::explicitly; }
    };

    /// We not be copied but may be moved.
    /// Note this leaves the moved-from value in a bogus state until clear() is called on it.
    separated_buffer_t(separated_buffer_t &&) = default;
    separated_buffer_t &operator=(separated_buffer_t &&) = default;

    /// Construct a separated_buffer_t with the given buffer limit \p limit, or 0 for no limit.
    separated_buffer_t(size_t limit) : buffer_limit_(limit) {}

    /// \return the buffer limit size, or 0 for no limit.
    size_t limit() const { return buffer_limit_; }

    /// \return the contents size.
    size_t size() const { return contents_size_; }

    /// \return whether the output has been discarded.
    bool discarded() const { return discard_; }

    /// Serialize the contents to a single string, where explicitly separated elements have a
    /// newline appended.
    std::string newline_serialized() const {
        std::string result;
        result.reserve(size());
        for (const auto &elem : elements_) {
            result.append(elem.contents);
            if (elem.is_explicitly_separated()) {
                result.push_back('\n');
            }
        }
        return result;
    }

    /// \return the list of elements.
    const std::vector<element_t> &elements() const { return elements_; }

    /// Append a string \p str of a given length \p len, with separation type \p sep.
    void append(const char *str, size_t len, separation_type_t sep = separation_type_t::inferred) {
        if (!try_add_size(len)) return;
        // Try merging with the last element.
        if (sep == separation_type_t::inferred && last_inferred()) {
            elements_.back().contents.append(str, len);
        } else {
            elements_.emplace_back(std::string(str, len), sep);
        }
    }

    /// Append a string \p str with separation type \p sep.
    void append(std::string &&str, separation_type_t sep = separation_type_t::inferred) {
        if (!try_add_size(str.size())) return;
        // Try merging with the last element.
        if (sep == separation_type_t::inferred && last_inferred()) {
            elements_.back().contents.append(str);
        } else {
            elements_.emplace_back(std::move(str), sep);
        }
    }

    /// Remove all elements and unset the discard flag.
    void clear() {
        elements_.clear();
        contents_size_ = 0;
        discard_ = false;
    }

   private:
    /// \return true if our last element has an inferred separation type.
    bool last_inferred() const {
        return !elements_.empty() && !elements_.back().is_explicitly_separated();
    }

    /// If our last element has an inferred separation, return a pointer to it; else nullptr.
    /// This is useful for appending one inferred separation to another.
    element_t *last_if_inferred() {
        if (!elements_.empty() && !elements_.back().is_explicitly_separated()) {
            return &elements_.back();
        }
        return nullptr;
    }

    /// Mark that we are about to add the given size \p delta to the buffer. \return true if we
    /// succeed, false if we exceed buffer_limit.
    bool try_add_size(size_t delta) {
        if (discard_) return false;
        size_t proposed_size = contents_size_ + delta;
        if ((proposed_size < delta) || (buffer_limit_ > 0 && proposed_size > buffer_limit_)) {
            clear();
            discard_ = true;
            return false;
        }
        contents_size_ = proposed_size;
        return true;
    }

    /// Limit on how much data we'll buffer. Zero means no limit.
    size_t buffer_limit_;

    /// Current size of all contents.
    size_t contents_size_{0};

    /// List of buffer elements.
    std::vector<element_t> elements_;

    /// True if we're discarding input because our buffer_limit has been exceeded.
    bool discard_{false};
};

/// Describes what type of IO operation an io_data_t represents.
enum class io_mode_t { file, pipe, fd, close, bufferfill };

/// Represents an FD redirection.
class io_data_t : noncopyable_t, nonmovable_t {
   protected:
    io_data_t(io_mode_t m, int fd, int source_fd) : io_mode(m), fd(fd), source_fd(source_fd) {}

   public:
    /// Type of redirect.
    const io_mode_t io_mode;

    /// FD to redirect.
    const int fd;

    /// Source fd. This is dup2'd to fd, or if it is -1, then fd is closed.
    /// That is, we call dup2(source_fd, fd).
    const int source_fd;

    virtual void print() const = 0;
    virtual ~io_data_t() = 0;
};

class io_close_t final : public io_data_t {
   public:
    explicit io_close_t(int f) : io_data_t(io_mode_t::close, f, -1) {}

    void print() const override;
    ~io_close_t() override;
};

class io_fd_t final : public io_data_t {
   public:
    void print() const override;

    ~io_fd_t() override;

    /// fd to redirect specified fd to. For example, in 2>&1, source_fd is 1, and io_data_t::fd
    /// is 2.
    io_fd_t(int f, int source_fd) : io_data_t(io_mode_t::fd, f, source_fd) {}
};

/// Represents a redirection to or from an opened file.
class io_file_t final : public io_data_t {
   public:
    void print() const override;

    io_file_t(int fd, autoclose_fd_t file)
        : io_data_t(io_mode_t::file, fd, file.fd()), file_fd_(std::move(file)) {
        // Invalid file redirections are replaced with a closed fd, so the following
        // assertion isn't guaranteed to pass:
        // assert(file_fd_.valid() && "File is not valid");
    }

    ~io_file_t() override;

   private:
    // The fd for the file which we are writing to or reading from.
    autoclose_fd_t file_fd_;
};

/// Represents (one end) of a pipe.
class io_pipe_t final : public io_data_t {
    // The pipe's fd. Conceptually this is dup2'd to io_data_t::fd.
    autoclose_fd_t pipe_fd_;

    /// Whether this is an input pipe. This is used only for informational purposes.
    const bool is_input_;

   public:
    void print() const override;

    io_pipe_t(int fd, bool is_input, autoclose_fd_t pipe_fd)
        : io_data_t(io_mode_t::pipe, fd, pipe_fd.fd()),
          pipe_fd_(std::move(pipe_fd)),
          is_input_(is_input) {
        assert(pipe_fd_.valid() && "Pipe is not valid");
    }

    ~io_pipe_t() override;
};

class io_buffer_t;

/// Represents filling an io_buffer_t. Very similar to io_pipe_t.
class io_bufferfill_t final : public io_data_t {
    /// Write end. The other end is connected to an io_buffer_t.
    const autoclose_fd_t write_fd_;

    /// The receiving buffer.
    const std::shared_ptr<io_buffer_t> buffer_;

   public:
    void print() const override;

    // The ctor is public to support make_shared() in the static create function below.
    // Do not invoke this directly.
    io_bufferfill_t(int target, autoclose_fd_t write_fd, std::shared_ptr<io_buffer_t> buffer)
        : io_data_t(io_mode_t::bufferfill, target, write_fd.fd()),
          write_fd_(std::move(write_fd)),
          buffer_(std::move(buffer)) {
        assert(write_fd_.valid() && "fd is not valid");
    }

    ~io_bufferfill_t() override;

    std::shared_ptr<io_buffer_t> buffer() const { return buffer_; }

    /// Create an io_bufferfill_t which, when written from, fills a buffer with the contents.
    /// \returns nullptr on failure, e.g. too many open fds.
    ///
    /// \param target the fd which this will be dup2'd to - typically stdout.
    static shared_ptr<io_bufferfill_t> create(size_t buffer_limit = 0, int target = STDOUT_FILENO);

    /// Reset the receiver (possibly closing the write end of the pipe), and complete the fillthread
    /// of the buffer. \return the buffer.
    static separated_buffer_t finish(std::shared_ptr<io_bufferfill_t> &&filler);
};

/// An io_buffer_t is a buffer which can populate itself by reading from an fd.
/// It is not an io_data_t.
class io_buffer_t {
   public:
    explicit io_buffer_t(size_t limit) : buffer_(limit) {}

    ~io_buffer_t();

    /// Append a string to the buffer.
    void append(std::string &&str, separation_type_t type = separation_type_t::inferred) {
        buffer_.acquire()->append(std::move(str), type);
    }

    /// \return true if output was discarded due to exceeding the read limit.
    bool discarded() { return buffer_.acquire()->discarded(); }

   private:
    /// Read some, filling the buffer. The buffer is passed in to enforce that the append lock is
    /// held. \return positive on success, 0 if closed, -1 on error (in which case errno will be
    /// set).
    ssize_t read_once(int fd, acquired_lock<separated_buffer_t> &buff);

    /// Begin the fill operation, reading from the given fd in the background.
    void begin_filling(autoclose_fd_t readfd);

    /// End the background fillthread operation, and return the buffer, transferring ownership.
    separated_buffer_t complete_background_fillthread_and_take_buffer();

    /// Helper to return whether the fillthread is running.
    bool fillthread_running() const { return fill_waiter_.get() != nullptr; }

    /// Buffer storing what we have read.
    owning_lock<separated_buffer_t> buffer_;

    /// Atomic flag indicating our fillthread should shut down.
    relaxed_atomic_bool_t shutdown_fillthread_{false};

    /// A promise, allowing synchronization with the background fill operation.
    /// The operation has a reference to this as well, and fulfills this promise when it exits.
    std::shared_ptr<std::promise<void>> fill_waiter_{};

    /// The item id of our background fillthread fd monitor item.
    uint64_t item_id_{0};

    friend io_bufferfill_t;
};

using io_data_ref_t = std::shared_ptr<const io_data_t>;

class io_chain_t : public std::vector<io_data_ref_t> {
   public:
    using std::vector<io_data_ref_t>::vector;
    // user-declared ctor to allow const init. Do not default this, it will break the build.
    io_chain_t() {}

    void remove(const io_data_ref_t &element);
    void push_back(io_data_ref_t element);
    void append(const io_chain_t &chain);

    /// \return the last io redirection in the chain for the specified file descriptor, or nullptr
    /// if none.
    io_data_ref_t io_for_fd(int fd) const;

    /// Attempt to resolve a list of redirection specs to IOs, appending to 'this'.
    /// \return true on success, false on error, in which case an error will have been printed.
    bool append_from_specs(const redirection_spec_list_t &specs, const wcstring &pwd);

    /// Output debugging information to stderr.
    void print() const;
};

/// Base class representing the output that a builtin can generate.
/// This has various subclasses depending on the ultimate output destination.
class output_stream_t : noncopyable_t, nonmovable_t {
   public:
    /// Required override point. The output stream receives a string \p s with \p amt chars.
    virtual void append(const wchar_t *s, size_t amt) = 0;

    /// \return any internally buffered contents.
    /// This is only implemented for a string_output_stream; others flush data to their underlying
    /// receiver (fd, or separated buffer) immediately and so will return an empty string here.
    virtual const wcstring &contents() const;

    /// Flush any unwritten data to the underlying device, and return an error code.
    /// A 0 code indicates success. The base implementation returns 0.
    virtual int flush_and_check_error();

    /// An optional override point. This is for explicit separation.
    /// \param want_newline this is true if the output item should be ended with a newline. This
    /// is only relevant if we are printing the output to a stream,
    virtual void append_with_separation(const wchar_t *s, size_t len, separation_type_t type,
                                        bool want_newline = true);

    /// The following are all convenience overrides.
    void append_with_separation(const wcstring &s, separation_type_t type,
                                bool want_newline = true) {
        append_with_separation(s.data(), s.size(), type, want_newline);
    }

    /// Append a string.
    void append(const wcstring &s) { append(s.data(), s.size()); }
    void append(const wchar_t *s) { append(s, std::wcslen(s)); }

    /// Append a char.
    void append(wchar_t s) { append(&s, 1); }
    void push_back(wchar_t c) { append(c); }

    // Append data from a narrow buffer, widening it.
    void append_narrow_buffer(const separated_buffer_t &buffer);

    /// Append a format string.
    void append_format(const wchar_t *format, ...) {
        va_list va;
        va_start(va, format);
        append_formatv(format, va);
        va_end(va);
    }

    void append_formatv(const wchar_t *format, va_list va) { append(vformat_string(format, va)); }

    output_stream_t() = default;
    virtual ~output_stream_t() = default;
};

/// A null output stream which ignores all writes.
class null_output_stream_t final : public output_stream_t {
    virtual void append(const wchar_t *s, size_t amt) override;
};

/// An output stream for builtins which outputs to an fd.
/// Note the fd may be something like stdout; there is no ownership implied here.
class fd_output_stream_t final : public output_stream_t {
   public:
    /// Construct from a file descriptor, which must be nonegative.
    explicit fd_output_stream_t(int fd) : fd_(fd) { assert(fd_ >= 0 && "Invalid fd"); }

    int flush_and_check_error() override;

    void append(const wchar_t *s, size_t amt) override;

   private:
    /// The file descriptor to write to.
    const int fd_;

    /// Whether we have received an error.
    bool errored_{false};
};

/// A simple output stream which buffers into a wcstring.
class string_output_stream_t final : public output_stream_t {
   public:
    string_output_stream_t() = default;
    void append(const wchar_t *s, size_t amt) override;

    /// \return the wcstring containing the output.
    const wcstring &contents() const override;

   private:
    wcstring contents_;
};

/// An output stream for builtins which writes into a separated buffer.
class buffered_output_stream_t final : public output_stream_t {
   public:
    explicit buffered_output_stream_t(std::shared_ptr<io_buffer_t> buffer)
        : buffer_(std::move(buffer)) {
        assert(buffer_ && "Buffer must not be null");
    }

    void append(const wchar_t *s, size_t amt) override;
    void append_with_separation(const wchar_t *s, size_t len, separation_type_t type,
                                bool want_newline) override;
    int flush_and_check_error() override;

   private:
    /// The buffer we are filling.
    std::shared_ptr<io_buffer_t> buffer_;
};

struct io_streams_t : noncopyable_t {
    // Streams for out and err.
    output_stream_t &out;
    output_stream_t &err;

    // fd representing stdin. This is not closed by the destructor.
    // Note: if stdin is explicitly closed by `<&-` then this is -1!
    int stdin_fd{-1};

    // Whether stdin is "directly redirected," meaning it is the recipient of a pipe (foo | cmd) or
    // direct redirection (cmd < foo.txt). An "indirect redirection" would be e.g.
    //    begin ; cmd ; end < foo.txt
    // If stdin is closed (cmd <&-) this is false.
    bool stdin_is_directly_redirected{false};

    // Indicates whether stdout and stderr are specifically piped.
    // If this is set, then the is_redirected flags must also be set.
    bool out_is_piped{false};
    bool err_is_piped{false};

    // Indicates whether stdout and stderr are at all redirected (e.g. to a file or piped).
    bool out_is_redirected{false};
    bool err_is_redirected{false};

    // Actual IO redirections. This is only used by the source builtin. Unowned.
    const io_chain_t *io_chain{nullptr};

    // The job group of the job, if any. This enables builtins which run more code like eval() to
    // share pgid.
    // FIXME: this is awkwardly placed.
    std::shared_ptr<job_group_t> job_group{};

    io_streams_t(output_stream_t &out, output_stream_t &err) : out(out), err(err) {}
};

#endif