Hide most of the implementation of `struct rb_io`. (#6511)

* Add rb_io_path and rb_io_open_descriptor.

* Use rb_io_open_descriptor to create PTY objects

* Rename FMODE_PREP -> FMODE_EXTERNAL and expose it

FMODE_PREP I believe refers to the concept of a "pre-prepared" file, but
FMODE_EXTERNAL is clearer about what the file descriptor represents and
aligns with language in the IO::Buffer module.

* Ensure that rb_io_open_descriptor closes the FD if it fails

If FMODE_EXTERNAL is not set, then it's guaranteed that Ruby will be
responsible for closing your file, eventually, if you pass it to
rb_io_open_descriptor, even if it raises an exception.

* Rename IS_EXTERNAL_FD -> RUBY_IO_EXTERNAL_P

* Expose `rb_io_closed_p`.

* Add `rb_io_mode` to get IO mode.

---------

Co-authored-by: KJ Tsanaktsidis <[email protected]>

4 files changed, 27 insertions, 33 deletions

diff --git a/ext/objspace/depend b/ext/objspace/depend
index 91ae569d67..3cdfaffa66 100644
--- a/ext/objspace/depend
+++ b/ext/objspace/depend
@@ -580,6 +580,7 @@ objspace_dump.o: $(top_srcdir)/internal/compilers.h
 objspace_dump.o: $(top_srcdir)/internal/gc.h
 objspace_dump.o: $(top_srcdir)/internal/hash.h
 objspace_dump.o: $(top_srcdir)/internal/imemo.h
+objspace_dump.o: $(top_srcdir)/internal/io.h
 objspace_dump.o: $(top_srcdir)/internal/sanitizers.h
 objspace_dump.o: $(top_srcdir)/internal/serial.h
 objspace_dump.o: $(top_srcdir)/internal/static_assert.h
diff --git a/ext/objspace/objspace_dump.c b/ext/objspace/objspace_dump.c
index d8a11083d6..39584e03b8 100644
--- a/ext/objspace/objspace_dump.c
+++ b/ext/objspace/objspace_dump.c
@@ -18,6 +18,7 @@
 #include "internal/class.h"
 #include "internal/gc.h"
 #include "internal/hash.h"
+#include "internal/io.h"
 #include "internal/string.h"
 #include "internal/sanitizers.h"
 #include "symbol.h"
diff --git a/ext/pty/pty.c b/ext/pty/pty.c
index acec33f9bf..0aca10bfa0 100644
--- a/ext/pty/pty.c
+++ b/ext/pty/pty.c
@@ -448,8 +448,10 @@ pty_close_pty(VALUE assoc)
 
     for (i = 0; i < 2; i++) {
         io = rb_ary_entry(assoc, i);
-        if (RB_TYPE_P(io, T_FILE) && 0 <= RFILE(io)->fptr->fd)
+        if (RB_TYPE_P(io, T_FILE)) {
+            /* it's OK to call rb_io_close again even if it's already closed */
             rb_io_close(io);
+        }
     }
     return Qnil;
 }
@@ -499,28 +501,21 @@ pty_open(VALUE klass)
 {
     int master_fd, slave_fd;
     char slavename[DEVICELEN];
-    VALUE master_io, slave_file;
-    rb_io_t *master_fptr, *slave_fptr;
-    VALUE assoc;
 
     getDevice(&master_fd, &slave_fd, slavename, 1);
 
-    master_io = rb_obj_alloc(rb_cIO);
-    MakeOpenFile(master_io, master_fptr);
-    master_fptr->mode = FMODE_READWRITE | FMODE_SYNC | FMODE_DUPLEX;
-    master_fptr->fd = master_fd;
-    master_fptr->pathv = rb_obj_freeze(rb_sprintf("masterpty:%s", slavename));
+    VALUE master_path = rb_obj_freeze(rb_sprintf("masterpty:%s", slavename));
+    VALUE master_io = rb_io_open_descriptor(rb_cIO, master_fd, FMODE_READWRITE | FMODE_SYNC | FMODE_DUPLEX, master_path, RUBY_IO_TIMEOUT_DEFAULT, NULL);
+
+    VALUE slave_path = rb_obj_freeze(rb_str_new_cstr(slavename));
+    VALUE slave_file = rb_io_open_descriptor(rb_cFile, slave_fd, FMODE_READWRITE | FMODE_SYNC | FMODE_DUPLEX | FMODE_TTY, slave_path, RUBY_IO_TIMEOUT_DEFAULT, NULL);
 
-    slave_file = rb_obj_alloc(rb_cFile);
-    MakeOpenFile(slave_file, slave_fptr);
-    slave_fptr->mode = FMODE_READWRITE | FMODE_SYNC | FMODE_DUPLEX | FMODE_TTY;
-    slave_fptr->fd = slave_fd;
-    slave_fptr->pathv = rb_obj_freeze(rb_str_new_cstr(slavename));
+    VALUE assoc = rb_assoc_new(master_io, slave_file);
 
-    assoc = rb_assoc_new(master_io, slave_file);
     if (rb_block_given_p()) {
         return rb_ensure(rb_yield, assoc, pty_close_pty, assoc);
     }
+
     return assoc;
 }
 
@@ -577,30 +572,27 @@ pty_getpty(int argc, VALUE *argv, VALUE self)
 {
     VALUE res;
     struct pty_info info;
-    rb_io_t *wfptr,*rfptr;
-    VALUE rport = rb_obj_alloc(rb_cFile);
-    VALUE wport = rb_obj_alloc(rb_cFile);
     char SlaveName[DEVICELEN];
 
-    MakeOpenFile(rport, rfptr);
-    MakeOpenFile(wport, wfptr);
-
     establishShell(argc, argv, &info, SlaveName);
 
-    rfptr->mode = rb_io_modestr_fmode("r");
-    rfptr->fd = info.fd;
-    rfptr->pathv = rb_obj_freeze(rb_str_new_cstr(SlaveName));
+    VALUE pty_path = rb_obj_freeze(rb_str_new_cstr(SlaveName));
+    VALUE rport = rb_io_open_descriptor(
+        rb_cFile, info.fd, FMODE_READABLE, pty_path, RUBY_IO_TIMEOUT_DEFAULT, NULL
+    );
 
-    wfptr->mode = rb_io_modestr_fmode("w") | FMODE_SYNC;
-    wfptr->fd = rb_cloexec_dup(info.fd);
-    if (wfptr->fd == -1)
+    int wpty_fd = rb_cloexec_dup(info.fd);
+    if (wpty_fd == -1) {
         rb_sys_fail("dup()");
-    rb_update_max_fd(wfptr->fd);
-    wfptr->pathv = rfptr->pathv;
+    }
+    VALUE wport = rb_io_open_descriptor(
+        rb_cFile, wpty_fd, FMODE_WRITABLE | FMODE_TRUNC | FMODE_CREATE | FMODE_SYNC,
+        pty_path, RUBY_IO_TIMEOUT_DEFAULT, NULL
+    );
 
     res = rb_ary_new2(3);
-    rb_ary_store(res,0,(VALUE)rport);
-    rb_ary_store(res,1,(VALUE)wport);
+    rb_ary_store(res, 0, rport);
+    rb_ary_store(res, 1, wport);
     rb_ary_store(res,2,PIDT2NUM(info.child_pid));
 
     if (rb_block_given_p()) {
diff --git a/ext/stringio/stringio.c b/ext/stringio/stringio.c
index e69afc31f1..cb9dbece1c 100644
--- a/ext/stringio/stringio.c
+++ b/ext/stringio/stringio.c
@@ -276,7 +276,7 @@ strio_init(int argc, VALUE *argv, struct StringIO *ptr, VALUE self)
 {
     VALUE string, vmode, opt;
     int oflags;
-    struct rb_io_enc_t convconfig;
+    struct rb_io_encoding convconfig;
 
     argc = rb_scan_args(argc, argv, "02:", &string, &vmode, &opt);
     rb_io_extract_modeenc(&vmode, 0, opt, &oflags, &ptr->flags, &convconfig);
@@ -1743,7 +1743,7 @@ strio_set_encoding(int argc, VALUE *argv, VALUE self)
     else {
 	enc = rb_find_encoding(ext_enc);
 	if (!enc) {
-	    struct rb_io_enc_t convconfig;
+	    struct rb_io_encoding convconfig;
 	    int oflags, fmode;
 	    VALUE vmode = rb_str_append(rb_str_new_cstr("r:"), ext_enc);
 	    rb_io_extract_modeenc(&vmode, 0, Qnil, &oflags, &fmode, &convconfig);