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

This reverts commit 18e55fc1e1ec20e8f3166e3059e76c885fc9f8f2.

fix [Bug #19704]
https://bugs.ruby-lang.org/issues/19704
This breaks compatibility for extension libraries. Such changes
need a discussion.

2 files changed, 125 insertions, 43 deletions

diff --git a/include/ruby/internal/core/rfile.h b/include/ruby/internal/core/rfile.h
index 8cf2c4db5b..f8dddde9e5 100644
--- a/include/ruby/internal/core/rfile.h
+++ b/include/ruby/internal/core/rfile.h
@@ -23,10 +23,9 @@
 #include "ruby/internal/core/rbasic.h"
 #include "ruby/internal/cast.h"
 
-/* rb_io is in ruby/io.h and internal/io.h.  The header file has historically
- * not been included into ruby/ruby.h.  We follow that tradition.
- */
-struct rb_io;
+/* rb_io_t is in ruby/io.h.  The header file has historically not been included
+ * into ruby/ruby.h.  We follow that tradition. */
+struct rb_io_t;
 
 /**
  * Ruby's File  and IO.  Ruby's  IO are not  just file descriptors.   They have
@@ -39,7 +38,7 @@ struct RFile {
     struct RBasic basic;
 
     /** IO's specific fields. */
-    struct rb_io *fptr;
+    struct rb_io_t *fptr;
 };
 
 /**
diff --git a/include/ruby/io.h b/include/ruby/io.h
index 881bac03a7..8be83a215c 100644
--- a/include/ruby/io.h
+++ b/include/ruby/io.h
@@ -84,6 +84,29 @@ typedef enum {
     RUBY_IO_PRIORITY = RB_WAITFD_PRI, /**< `IO::PRIORITY` */
 } rb_io_event_t;
 
+/**
+ * IO  buffers.   This  is  an implementation  detail  of  ::rb_io_t::wbuf  and
+ * ::rb_io_t::rbuf.  People don't manipulate it directly.
+ */
+RBIMPL_ATTR_PACKED_STRUCT_UNALIGNED_BEGIN()
+struct rb_io_buffer_t {
+
+    /** Pointer to the underlying memory region, of at least `capa` bytes. */
+    char *ptr;                  /* off + len <= capa */
+
+    /** Offset inside of `ptr`. */
+    int off;
+
+    /** Length of the buffer. */
+    int len;
+
+    /** Designed capacity of the buffer. */
+    int capa;
+} RBIMPL_ATTR_PACKED_STRUCT_UNALIGNED_END();
+
+/** @alias{rb_io_buffer_t} */
+typedef struct rb_io_buffer_t rb_io_buffer_t;
+
 /** Decomposed encoding flags (e.g. `"enc:enc2""`). */
 /*
  * enc  enc2 read action                      write action
@@ -91,7 +114,7 @@ typedef enum {
  * e1   NULL force_encoding(e1)               convert str.encoding to e1
  * e1   e2   convert from e2 to e1            convert str.encoding to e2
  */
-struct rb_io_encoding {
+struct rb_io_enc_t {
     /** Internal encoding. */
     rb_encoding *enc;
     /** External encoding. */
@@ -112,10 +135,103 @@ struct rb_io_encoding {
     VALUE ecopts;
 };
 
-struct rb_io;
-typedef struct rb_io rb_io_t;
+/** Ruby's IO, metadata and buffers. */
+typedef struct rb_io_t {
+
+    /** The IO's Ruby level counterpart. */
+    VALUE self;
+
+    /** stdio ptr for read/write, if available. */
+    FILE *stdio_file;
+
+    /** file descriptor. */
+    int fd;
+
+    /** mode flags: FMODE_XXXs */
+    int mode;
+
+    /** child's pid (for pipes) */
+    rb_pid_t pid;
+
+    /** number of lines read */
+    int lineno;
+
+    /** pathname for file */
+    VALUE pathv;
+
+    /** finalize proc */
+    void (*finalize)(struct rb_io_t*,int);
+
+    /** Write buffer. */
+    rb_io_buffer_t wbuf;
+
+    /**
+     * (Byte)  read   buffer.   Note  also   that  there  is  a   field  called
+     * ::rb_io_t::cbuf, which also concerns read IO.
+     */
+    rb_io_buffer_t rbuf;
+
+    /**
+     * Duplex IO object, if set.
+     *
+     * @see rb_io_set_write_io()
+     */
+    VALUE tied_io_for_writing;
+
+    struct rb_io_enc_t encs; /**< Decomposed encoding flags. */
+
+    /** Encoding converter used when reading from this IO. */
+    rb_econv_t *readconv;
+
+    /**
+     * rb_io_ungetc()  destination.   This  buffer   is  read  before  checking
+     * ::rb_io_t::rbuf
+     */
+    rb_io_buffer_t cbuf;
+
+    /** Encoding converter used when writing to this IO. */
+    rb_econv_t *writeconv;
+
+    /**
+     * This is, when set, an instance  of ::rb_cString which holds the "common"
+     * encoding.   Write  conversion  can  convert strings  twice...   In  case
+     * conversion from encoding  X to encoding Y does not  exist, Ruby finds an
+     * encoding Z that bridges the two, so that X to Z to Y conversion happens.
+     */
+    VALUE writeconv_asciicompat;
+
+    /** Whether ::rb_io_t::writeconv is already set up. */
+    int writeconv_initialized;
 
-typedef struct rb_io_encoding rb_io_enc_t;
+    /**
+     * Value   of    ::rb_io_t::rb_io_enc_t::ecflags   stored    right   before
+     * initialising ::rb_io_t::writeconv.
+     */
+    int writeconv_pre_ecflags;
+
+    /**
+     * Value of ::rb_io_t::rb_io_enc_t::ecopts stored right before initialising
+     * ::rb_io_t::writeconv.
+     */
+    VALUE writeconv_pre_ecopts;
+
+    /**
+     * This is a Ruby  level mutex.  It avoids multiple threads  to write to an
+     * IO at  once; helps  for instance rb_io_puts()  to ensure  newlines right
+     * next to its arguments.
+     *
+     * This of course doesn't help inter-process IO interleaves, though.
+     */
+    VALUE write_lock;
+
+    /**
+     * The timeout associated with this IO when performing blocking operations.
+     */
+    VALUE timeout;
+} rb_io_t;
+
+/** @alias{rb_io_enc_t} */
+typedef struct rb_io_enc_t rb_io_enc_t;
 
 /**
  * @private
@@ -215,16 +331,7 @@ typedef struct rb_io_encoding rb_io_enc_t;
  * Setting this one and #FMODE_BINMODE at the same time is a contradiction.
  */
 #define FMODE_TEXTMODE              0x00001000
-/**
- * This flag means that an IO object is wrapping an "external" file descriptor,
- * which is owned by something outside the Ruby interpreter (usually a C extension).
- * Ruby will not close this file when the IO object is garbage collected.
- * If this flag is set, then IO#autoclose? is false, and vice-versa.
- *
- * This flag was previously called FMODE_PREP internally.
- */
-#define FMODE_EXTERNAL              0x00010000
-
+/* #define FMODE_PREP               0x00010000 */
 /* #define FMODE_SIGNAL_ON_EPIPE    0x00020000 */
 
 /**
@@ -239,18 +346,6 @@ typedef struct rb_io_encoding rb_io_enc_t;
 /** @} */
 
 /**
- * Allocate a new IO object, with the given file descriptor.
- */
-VALUE rb_io_open_descriptor(VALUE klass, int descriptor, int mode, VALUE path, VALUE timeout, struct rb_io_encoding *encoding);
-
-/**
- * Returns whether or not the underlying IO is closed.
- *
- * @return Whether the underlying IO is closed.
- */
-VALUE rb_io_closed_p(VALUE io);
-
-/**
  * Queries the underlying IO pointer.
  *
  * @param[in]   obj              An IO object.
@@ -609,12 +704,6 @@ VALUE rb_io_set_write_io(VALUE io, VALUE w);
 void rb_io_set_nonblock(rb_io_t *fptr);
 
 /**
- * Returns the path for the given IO.
- *
- */
-VALUE rb_io_path(VALUE io);
-
-/**
  * Returns an integer representing the numeric file descriptor for
  * <em>io</em>.
  *
@@ -624,12 +713,6 @@ VALUE rb_io_path(VALUE io);
 int rb_io_descriptor(VALUE io);
 
 /**
- * Get the mode of the IO.
- *
- */
-int rb_io_mode(VALUE io);
-
-/**
  * This function  breaks down the  option hash that `IO#initialize`  takes into
  * components.   This is  an implementation  detail of  rb_io_extract_modeenc()
  * today.  People prefer that API instead.