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Diffstat (limited to 'libbutl/fdstream.hxx')
| -rw-r--r-- | libbutl/fdstream.hxx | 643 |
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diff --git a/libbutl/fdstream.hxx b/libbutl/fdstream.hxx new file mode 100644 index 0000000..e1f5790 --- /dev/null +++ b/libbutl/fdstream.hxx @@ -0,0 +1,643 @@ +// file : libbutl/fdstream.hxx -*- C++ -*- +// copyright : Copyright (c) 2014-2017 Code Synthesis Ltd +// license : MIT; see accompanying LICENSE file + +#ifndef LIBBUTL_FDSTREAM_HXX +#define LIBBUTL_FDSTREAM_HXX + +#include <string> +#include <istream> +#include <ostream> +#include <utility> // move() +#include <cstdint> // uint16_t + +#include <libbutl/export.hxx> + +#include <libbutl/path.hxx> +#include <libbutl/filesystem.hxx> // permissions + +namespace butl +{ + // RAII type for file descriptors. Note that failure to close the descriptor + // is silently ignored by both the destructor and reset(). + // + // The descriptor can be negative. Such a descriptor is treated as unopened + // and is not closed. + // + struct nullfd_t {constexpr explicit nullfd_t (int) {}}; + constexpr const nullfd_t nullfd (-1); + + class LIBBUTL_EXPORT auto_fd + { + public: + auto_fd (nullfd_t = nullfd) noexcept: fd_ (-1) {} + + explicit + auto_fd (int fd) noexcept: fd_ (fd) {} + + auto_fd (auto_fd&& fd) noexcept: fd_ (fd.release ()) {} + auto_fd& operator= (auto_fd&&) noexcept; + + auto_fd (const auto_fd&) = delete; + auto_fd& operator= (const auto_fd&) = delete; + + ~auto_fd () noexcept; + + int + get () const noexcept {return fd_;} + + void + reset (int fd = -1) noexcept; + + int + release () noexcept + { + int r (fd_); + fd_ = -1; + return r; + } + + // Close an open file descriptor. Throw ios::failure on the underlying OS + // error. Reset the descriptor to -1 whether the exception is thrown or + // not. + // + void + close (); + + private: + int fd_; + }; + + // An [io]fstream that can be initialized with a file descriptor in addition + // to a file name and that also by default enables exceptions on badbit and + // failbit. So instead of a dance like this: + // + // ifstream ifs; + // ifs.exceptions (ifstream::badbit | ifstream::failbit); + // ifs.open (path.string ()); + // + // You can simply do: + // + // ifdstream ifs (path); + // + // Notes and limitations: + // + // - char only + // - input or output but not both + // - no support for put back + // - non-blocking file descriptor is supported only by showmanyc() function + // and only on POSIX + // - throws ios::failure in case of open()/read()/write()/close() errors + // - exception mask has at least badbit + // - after catching an exception caused by badbit the stream is no longer + // used + // - not movable, though can be easily supported + // - passing to constructor auto_fd with a negative file descriptor is valid + // and results in the creation of an unopened object + // + class LIBBUTL_EXPORT fdbuf: public std::basic_streambuf<char> + { + public: + fdbuf () = default; + fdbuf (auto_fd&&); + + // Before we invented auto_fd into fdstreams we keept fdbuf opened on + // faulty close attempt. Now fdbuf is always closed by close() function. + // This semantics change seems to be the right one as there is no reason to + // expect fdclose() to succeed after it has already failed once. + // + void + close () {fd_.close ();} + + auto_fd + release (); + + void + open (auto_fd&&); + + bool + is_open () const {return fd_.get () >= 0;} + + int + fd () const {return fd_.get ();} + + public: + using int_type = std::basic_streambuf<char>::int_type; + using traits_type = std::basic_streambuf<char>::traits_type; + + // basic_streambuf input interface. + // + public: + virtual std::streamsize + showmanyc (); + + virtual int_type + underflow (); + + private: + bool + load (); + + // basic_streambuf output interface. + // + public: + virtual int_type + overflow (int_type); + + virtual int + sync (); + + virtual std::streamsize + xsputn (const char_type*, std::streamsize); + + private: + bool + save (); + + private: + auto_fd fd_; + char buf_[8192]; + bool non_blocking_ = false; + }; + + // File stream mode. + // + // The text/binary flags have the same semantics as those in std::fstream. + // Specifically, this is a noop for POSIX systems where the two modes are + // the same. On Windows, when reading in the text mode the sequence of 0xD, + // 0xA characters is translated into the single OxA character and 0x1A is + // interpreted as EOF. When writing in the text mode the OxA character is + // translated into the 0xD, 0xA sequence. + // + // The skip flag instructs the stream to skip to the end before closing the + // file descriptor. This is primarily useful when working with pipes where + // you may want not to "offend" the other end by closing your end before + // reading all the data. + // + // The blocking/non_blocking flags determine whether the IO operation should + // block or return control if currently there is no data to read or no room + // to write. Only the istream::readsome() function supports the semantics of + // non-blocking operations. We also only support this on POSIX (Windows does + // not provide means for the non-blocking reading from a file descriptor so + // these flags are noop there). IO stream operations other than readsome() + // are illegal for non_blocking mode and result in the badbit being set. + // + enum class fdstream_mode: std::uint16_t + { + text = 0x01, + binary = 0x02, + skip = 0x04, + blocking = 0x08, + non_blocking = 0x10 + }; + + inline fdstream_mode operator& (fdstream_mode, fdstream_mode); + inline fdstream_mode operator| (fdstream_mode, fdstream_mode); + inline fdstream_mode operator&= (fdstream_mode&, fdstream_mode); + inline fdstream_mode operator|= (fdstream_mode&, fdstream_mode); + + // Extended (compared to ios::openmode) file open flags. + // + enum class fdopen_mode: std::uint16_t + { + in = 0x01, // Open for reading. + out = 0x02, // Open for writing. + append = 0x04, // Seek to the end of file before each write. + truncate = 0x08, // Discard the file contents on open. + create = 0x10, // Create a file if not exists. + exclusive = 0x20, // Fail if the file exists and the create flag is set. + binary = 0x40, // Set binary translation mode. + at_end = 0x80, // Seek to the end of stream immediately after open. + + none = 0 // Usefull when build the mode incrementally. + }; + + inline fdopen_mode operator& (fdopen_mode, fdopen_mode); + inline fdopen_mode operator| (fdopen_mode, fdopen_mode); + inline fdopen_mode operator&= (fdopen_mode&, fdopen_mode); + inline fdopen_mode operator|= (fdopen_mode&, fdopen_mode); + + class LIBBUTL_EXPORT fdstream_base + { + protected: + fdstream_base () = default; + fdstream_base (auto_fd&& fd): buf_ (std::move (fd)) {} + fdstream_base (auto_fd&&, fdstream_mode); + + public: + int + fd () const {return buf_.fd ();} + + protected: + fdbuf buf_; + }; + + // iofdstream constructors and open() functions that take openmode as an + // argument mimic the corresponding iofstream functions in terms of the + // openmode mask interpretation. They throw std::invalid_argument for an + // invalid combination of flags (as per the standard). Note that the in and + // out flags are always added implicitly for ifdstream and ofdstream, + // respectively. + // + // iofdstream constructors and open() functions that take fdopen_mode as an + // argument interpret the mask literally just ignoring some flags which are + // meaningless in the absense of others (read more on that in the comment + // for fdopen()). Note that the in and out flags are always added implicitly + // for ifdstream and ofdstream, respectively. + // + // iofdstream constructors and open() functions that take file path as a + // const std::string& or const char* may throw the invalid_path exception. + // + // Passing auto_fd with a negative file descriptor is valid and results in + // the creation of an unopened object. + // + // Also note that open() and close() functions can be successfully called + // for an opened and unopened objects respectively. That is in contrast with + // iofstream that sets failbit in such cases. + // + + // Note that ifdstream destructor will close an open file descriptor but + // will ignore any errors. To detect such errors, call close() explicitly. + // + // This is a sample usage of iofdstreams with process. Note that here it is + // expected that the child process reads from STDIN first and writes to + // STDOUT afterwards. + // + // try + // { + // process pr (args, -1, -1); + // + // try + // { + // // In case of exception, skip and close input after output. + // // + // ifdstream is (move (pr.in_ofd), fdstream_mode::skip); + // ofdstream os (move (pr.out_fd)); + // + // // Write. + // + // os.close (); // Don't block the other end. + // + // // Read. + // + // is.close (); // Skip till end and close. + // + // if (pr.wait ()) + // { + // return ...; // Good. + // } + // + // // Non-zero exit, diagnostics presumably issued, fall through. + // } + // catch (const failure&) + // { + // // IO failure, child exit status doesn't matter. Just wait for the + // // process completion and fall through. + // // + // // Note that this is optional if the process_error handler simply + // // falls through since process destructor will wait (but will ignore + // // any errors). + // // + // pr.wait (); + // } + // + // error << .... ; + // + // // Fall through. + // } + // catch (const process_error& e) + // { + // error << ... << e; + // + // if (e.child ()) + // exit (1); + // + // // Fall through. + // } + // + // throw failed (); + // + class LIBBUTL_EXPORT ifdstream: public fdstream_base, public std::istream + { + public: + // Create an unopened object. + // + explicit + ifdstream (iostate e = badbit | failbit); + + explicit + ifdstream (auto_fd&&, iostate e = badbit | failbit); + ifdstream (auto_fd&&, fdstream_mode m, iostate e = badbit | failbit); + + explicit + ifdstream (const char*, + openmode = in, + iostate e = badbit | failbit); + + explicit + ifdstream (const std::string&, + openmode = in, + iostate e = badbit | failbit); + + explicit + ifdstream (const path&, + openmode = in, + iostate e = badbit | failbit); + + ifdstream (const char*, + fdopen_mode, + iostate e = badbit | failbit); + + ifdstream (const std::string&, + fdopen_mode, + iostate e = badbit | failbit); + + ifdstream (const path&, + fdopen_mode, + iostate e = badbit | failbit); + + ~ifdstream () override; + + void + open (const char*, openmode = in); + + void + open (const std::string&, openmode = in); + + void + open (const path&, openmode = in); + + void + open (const char*, fdopen_mode); + + void + open (const std::string&, fdopen_mode); + + void + open (const path&, fdopen_mode); + + void + open (auto_fd&& fd) {buf_.open (std::move (fd)); clear ();} + + void close (); + auto_fd release (); // Note: no skipping. + bool is_open () const {return buf_.is_open ();} + + private: + bool skip_ = false; + }; + + // Note that ofdstream requires that you explicitly call close() before + // destroying it. Or, more specifically, the ofdstream object should not be + // in the opened state by the time its destructor is called, unless it is in + // the "not good" state (good() == false) or the destructor is being called + // during the stack unwinding due to an exception being thrown + // (std::uncaught_exception() == true). This is enforced with assert() in + // the ofdstream destructor. + // + class LIBBUTL_EXPORT ofdstream: public fdstream_base, public std::ostream + { + public: + // Create an unopened object. + // + explicit + ofdstream (iostate e = badbit | failbit); + + explicit + ofdstream (auto_fd&&, iostate e = badbit | failbit); + ofdstream (auto_fd&&, fdstream_mode m, iostate e = badbit | failbit); + + explicit + ofdstream (const char*, + openmode = out, + iostate e = badbit | failbit); + + explicit + ofdstream (const std::string&, + openmode = out, + iostate e = badbit | failbit); + + explicit + ofdstream (const path&, + openmode = out, + iostate e = badbit | failbit); + + ofdstream (const char*, + fdopen_mode, + iostate e = badbit | failbit); + + ofdstream (const std::string&, + fdopen_mode, + iostate e = badbit | failbit); + + ofdstream (const path&, + fdopen_mode, + iostate e = badbit | failbit); + + ~ofdstream () override; + + void + open (const char*, openmode = out); + + void + open (const std::string&, openmode = out); + + void + open (const path&, openmode = out); + + void + open (const char*, fdopen_mode); + + void + open (const std::string&, fdopen_mode); + + void + open (const path&, fdopen_mode); + + void + open (auto_fd&& fd) {buf_.open (std::move (fd)); clear ();} + + void close () {if (is_open ()) flush (); buf_.close ();} + auto_fd release (); + bool is_open () const {return buf_.is_open ();} + }; + + // The std::getline() replacement that provides a workaround for libstdc++'s + // ios::failure ABI fiasco (#66145) by throwing ios::failure, as it is + // defined at libbutl build time (new ABI on recent distributions) rather + // than libstdc++ build time (still old ABI on most distributions). + // + // Notes: + // + // - This relies of ADL so if the stream is used via the std::istream + // interface, then std::getline() will still be used. To put it another + // way, this is "the best we can do" until GCC folks get their act + // together. + // + // - The fail and eof bits may be left cleared in the stream exception mask + // when the function throws because of badbit. + // + LIBBUTL_EXPORT ifdstream& + getline (ifdstream&, std::string&, char delim = '\n'); + + // Open a file returning an auto_fd that holds its file descriptor on + // success and throwing ios::failure otherwise. + // + // The mode argument should have at least one of the in or out flags set. + // The append and truncate flags are meaningless in the absense of the out + // flag and are ignored without it. The exclusive flag is meaningless in the + // absense of the create flag and is ignored without it. Note also that if + // the exclusive flag is specified then a dangling symbolic link is treated + // as an existing file. + // + // The permissions argument is taken into account only if the file is + // created. Note also that permissions can be adjusted while being set in a + // way specific for the OS. On POSIX systems they are modified with the + // process' umask, so effective permissions are permissions & ~umask. On + // Windows permissions other than ru and wu are unlikelly to have effect. + // + // Also note that on POSIX the FD_CLOEXEC flag is set for the file descriptor + // to prevent its leakage into child processes. On Windows, for the same + // purpose, the _O_NOINHERIT flag is set. Note that the process class, that + // passes such a descriptor to the child, makes it inheritable for a while. + // + LIBBUTL_EXPORT auto_fd + fdopen (const char*, + fdopen_mode, + permissions = permissions::ru | permissions::wu | + permissions::rg | permissions::wg | + permissions::ro | permissions::wo); + + LIBBUTL_EXPORT auto_fd + fdopen (const std::string&, + fdopen_mode, + permissions = permissions::ru | permissions::wu | + permissions::rg | permissions::wg | + permissions::ro | permissions::wo); + + LIBBUTL_EXPORT auto_fd + fdopen (const path&, + fdopen_mode, + permissions = permissions::ru | permissions::wu | + permissions::rg | permissions::wg | + permissions::ro | permissions::wo); + + // Duplicate an open file descriptor. Throw ios::failure on the underlying + // OS error. + // + // Note that on POSIX the FD_CLOEXEC flag is set for the new descriptor if it + // is present for the source one. That's in contrast to POSIX dup() that + // doesn't copy file descriptor flags. Also note that duplicating descriptor + // and setting the flag is not an atomic operation generally, but it is in + // regards to child process spawning (to prevent file descriptor leakage into + // a child process). + // + // Note that on Windows the _O_NOINHERIT flag is set for the new descriptor + // if it is present for the source one. That's in contrast to Windows _dup() + // that doesn't copy the flag. Also note that duplicating descriptor and + // setting the flag is not an atomic operation generally, but it is in + // regards to child process spawning (to prevent file descriptor leakage into + // a child process). + // + LIBBUTL_EXPORT auto_fd + fddup (int fd); + + // Set the translation mode for the file descriptor. Throw invalid_argument + // for an invalid combination of flags. Return the previous mode on success, + // throw ios::failure otherwise. + // + // The text and binary flags are mutually exclusive on Windows. Due to + // implementation details at least one of them should be specified. On POSIX + // system the two modes are the same and so no check is performed. + // + // The blocking and non-blocking flags are mutually exclusive on POSIX + // system. Non-blocking mode is not supported on Windows and so the blocking + // mode is assumed regardless of the flags. + // + LIBBUTL_EXPORT fdstream_mode + fdmode (int, fdstream_mode); + + // Convenience functions for setting the translation mode for standard + // streams. + // + LIBBUTL_EXPORT fdstream_mode stdin_fdmode (fdstream_mode); + LIBBUTL_EXPORT fdstream_mode stdout_fdmode (fdstream_mode); + LIBBUTL_EXPORT fdstream_mode stderr_fdmode (fdstream_mode); + + // Low-level, nothrow file descriptor API. + // + + // Close the file descriptor. Return true on success, set errno and return + // false otherwise. + // + LIBBUTL_EXPORT bool + fdclose (int) noexcept; + + // Open the null device (e.g., /dev/null) that discards all data written to + // it and provides no data for read operations (i.e., yelds EOF on read). + // Return an auto_fd that holds its file descriptor on success and throwing + // ios::failure otherwise. + // + // On Windows the null device is NUL and writing anything substantial to it + // (like redirecting a process' output) is extremely slow, as in, an order + // of magnitude slower than writing to disk. If you are using the descriptor + // yourself this can be mitigated by setting the binary mode (already done + // by fdopen()) and using a buffer of around 64K. However, sometimes you + // have no control of how the descriptor will be used. For instance, it can + // be used to redirect a child's stdout and the way the child sets up its + // stdout is out of your control (on Windows). For such cases, there is an + // emulation via a temporary file. Mostly it functions as a proper null + // device with the file automatically removed once the descriptor is + // closed. One difference, however, would be if you were to both write to + // and read from the descriptor. + // + // Note that on POSIX the FD_CLOEXEC flag is set for the file descriptor to + // prevent its leakage into child processes. On Windows, for the same + // purpose, the _O_NOINHERIT flag is set. + // +#ifndef _WIN32 + LIBBUTL_EXPORT auto_fd + fdnull () noexcept; +#else + LIBBUTL_EXPORT auto_fd + fdnull (bool temp = false) noexcept; +#endif + + struct fdpipe + { + auto_fd in; + auto_fd out; + + void + close () + { + in.close (); + out.close (); + } + }; + + // Create a pipe. Throw ios::failure on the underlying OS error. By default + // both ends of the pipe are opened in the text mode. Pass the binary flag + // to instead open them in the binary mode. Passing a mode other than none + // or binary is illegal. + // + // Note that on Windows both ends of the created pipe are not inheritable. + // In particular, the process class that uses fdpipe underneath makes the + // appropriate end (the one being passed to the child) inheritable. + // + // Note that on POSIX the FD_CLOEXEC flag is set for both ends, so they get + // automatically closed by the child process to prevent undesired behaviors + // (such as child deadlock on read from a pipe due to the write-end leakage + // into the child process). Opening a pipe and setting the flag is not an + // atomic operation generally, but it is in regards to child process spawning + // (to prevent file descriptor leakage into child processes spawned from + // other threads). Also note that you don't need to reset the flag for a pipe + // end being passed to the process class ctor. + // + LIBBUTL_EXPORT fdpipe + fdopen_pipe (fdopen_mode = fdopen_mode::none); +} + +#include <libbutl/fdstream.ixx> + +#endif // LIBBUTL_FDSTREAM_HXX |