Support ifdstream non-blocking mode

1 files changed, 28 insertions, 6 deletions

diff --git a/butl/fdstream b/butl/fdstream
index 49b3d4d..2d7fae5 100644
--- a/butl/fdstream
+++ b/butl/fdstream
@@ -34,11 +34,15 @@ namespace butl
   // - 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 -1 file descriptor is valid and results in the
+  //   creation of an unopened object
   //
   class LIBBUTL_EXPORT fdbuf: public std::basic_streambuf<char>
   {
@@ -46,7 +50,7 @@ namespace butl
     virtual
     ~fdbuf ();
     fdbuf () = default;
-    fdbuf (int fd) {open (fd);}
+    fdbuf (int fd) {if (fd != -1) open (fd);}
 
     fdbuf (const fdbuf&) = delete;
     fdbuf& operator= (const fdbuf&) = delete;
@@ -60,6 +64,9 @@ namespace butl
     bool
     is_open () const {return fd_ != -1;}
 
+    int
+    fd () const {return fd_;}
+
   public:
     using int_type = std::basic_streambuf<char>::int_type;
     using traits_type = std::basic_streambuf<char>::traits_type;
@@ -96,6 +103,7 @@ namespace butl
   private:
     int fd_ = -1;
     char buf_[8192];
+    bool non_blocking_ = false;
   };
 
   // File stream mode.
@@ -109,11 +117,21 @@ namespace butl
   // 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
+    text         = 0x01,
+    binary       = 0x02,
+    skip         = 0x04,
+    blocking     = 0x08,
+    non_blocking = 0x10
   };
 
   inline fdstream_mode operator& (fdstream_mode, fdstream_mode);
@@ -149,6 +167,10 @@ namespace butl
     fdstream_base (int fd): buf_ (fd) {}
     fdstream_base (int, fdstream_mode);
 
+  public:
+    int
+    fd () const {return buf_.fd ();}
+
   protected:
     fdbuf buf_;
   };
@@ -243,7 +265,7 @@ namespace butl
   //
   // throw failed ();
   //
-  class LIBBUTL_EXPORT ifdstream: fdstream_base, public std::istream
+  class LIBBUTL_EXPORT ifdstream: public fdstream_base, public std::istream
   {
   public:
     // Create an unopened object with iostate = badbit | failbit (we cannot
@@ -323,7 +345,7 @@ namespace butl
   // (std::uncaught_exception() == true). This is enforced with assert() in
   // the ofdstream destructor.
   //
-  class LIBBUTL_EXPORT ofdstream: fdstream_base, public std::ostream
+  class LIBBUTL_EXPORT ofdstream: public fdstream_base, public std::ostream
   {
   public:
     // Create an unopened object with iostate = badbit | failbit (we cannot