名前

perliol - C API for Perl's implementation of IO in Layers.

perliol - IO 層の Perl 実装への C API

概要

    /* Defining a layer ... */
    #include <perliol.h>

説明

This document describes the behavior and implementation of the PerlIO abstraction described in perlapio when USE_PERLIO is defined (and USE_SFIO is not).

この文書は、USE_PERLIO が定義されている(そして USE_SFIO が 定義されていない)場合に perlapio で記述されている PerlIO 抽象化の 振る舞いと実装について記述しています。

歴史と背景

The PerlIO abstraction was introduced in perl5.003_02 but languished as just an abstraction until perl5.7.0. However during that time a number of perl extensions switched to using it, so the API is mostly fixed to maintain (source) compatibility.

PerlIO 抽象化は was introduced in perl5.003_02 but languished as just an abstraction until perl5.7.0. However during that time a number of perl extensions switched to using it, so the API is mostly fixed to maintain (source) compatibility. (TBT)

The aim of the implementation is to provide the PerlIO API in a flexible and platform neutral manner. It is also a trial of an "Object Oriented C, with vtables" approach which may be applied to Perl 6.

The aim of the implementation is to provide the PerlIO API in a flexible and platform neutral manner. It is also a trial of an "Object Oriented C, with vtables" approach which may be applied to Perl 6. (TBT)

基本構造

PerlIO is a stack of layers.

PerlIO は層のスタックです。

The low levels of the stack work with the low-level operating system calls (file descriptors in C) getting bytes in and out, the higher layers of the stack buffer, filter, and otherwise manipulate the I/O, and return characters (or bytes) to Perl. Terms above and below are used to refer to the relative positioning of the stack layers.

The low levels of the stack work with the low-level operating system calls (file descriptors in C) getting bytes in and out, the higher layers of the stack buffer, filter, and otherwise manipulate the I/O, and return characters (or bytes) to Perl. Terms above and below are used to refer to the relative positioning of the stack layers. (TBT)

A layer contains a "vtable", the table of I/O operations (at C level a table of function pointers), and status flags. The functions in the vtable implement operations like "open", "read", and "write".

A layer contains a "vtable", the table of I/O operations (at C level a table of function pointers), and status flags. The functions in the vtable implement operations like "open", "read", and "write". (TBT)

When I/O, for example "read", is requested, the request goes from Perl first down the stack using "read" functions of each layer, then at the bottom the input is requested from the operating system services, then the result is returned up the stack, finally being interpreted as Perl data.

When I/O, for example "read", is requested, the request goes from Perl first down the stack using "read" functions of each layer, then at the bottom the input is requested from the operating system services, then the result is returned up the stack, finally being interpreted as Perl data. (TBT)

The requests do not necessarily go always all the way down to the operating system: that's where PerlIO buffering comes into play.

The requests do not necessarily go always all the way down to the operating system: that's where PerlIO buffering comes into play. (TBT)

When you do an open() and specify extra PerlIO layers to be deployed, the layers you specify are "pushed" on top of the already existing default stack. One way to see it is that "operating system is on the left" and "Perl is on the right".

When you do an open() and specify extra PerlIO layers to be deployed, the layers you specify are "pushed" on top of the already existing default stack. One way to see it is that "operating system is on the left" and "Perl is on the right". (TBT)

What exact layers are in this default stack depends on a lot of things: your operating system, Perl version, Perl compile time configuration, and Perl runtime configuration. See PerlIO, "PERLIO" in perlrun, and open for more information.

What exact layers are in this default stack depends on a lot of things: your operating system, Perl version, Perl compile time configuration, and Perl runtime configuration. See PerlIO, "PERLIO" in perlrun, and open for more information. (TBT)

binmode() operates similarly to open(): by default the specified layers are pushed on top of the existing stack.

binmode() operates similarly to open(): by default the specified layers are pushed on top of the existing stack. (TBT)

However, note that even as the specified layers are "pushed on top" for open() and binmode(), this doesn't mean that the effects are limited to the "top": PerlIO layers can be very 'active' and inspect and affect layers also deeper in the stack. As an example there is a layer called "raw" which repeatedly "pops" layers until it reaches the first layer that has declared itself capable of handling binary data. The "pushed" layers are processed in left-to-right order.

However, note that even as the specified layers are "pushed on top" for open() and binmode(), this doesn't mean that the effects are limited to the "top": PerlIO layers can be very 'active' and inspect and affect layers also deeper in the stack. As an example there is a layer called "raw" which repeatedly "pops" layers until it reaches the first layer that has declared itself capable of handling binary data. The "pushed" layers are processed in left-to-right order. (TBT)

sysopen() operates (unsurprisingly) at a lower level in the stack than open(). For example in UNIX or UNIX-like systems sysopen() operates directly at the level of file descriptors: in the terms of PerlIO layers, it uses only the "unix" layer, which is a rather thin wrapper on top of the UNIX file descriptors.

sysopen() operates (unsurprisingly) at a lower level in the stack than open(). For example in UNIX or UNIX-like systems sysopen() operates directly at the level of file descriptors: in the terms of PerlIO layers, it uses only the "unix" layer, which is a rather thin wrapper on top of the UNIX file descriptors. (TBT)

層とディシプリン

Initial discussion of the ability to modify IO streams behaviour used the term "discipline" for the entities which were added. This came (I believe) from the use of the term in "sfio", which in turn borrowed it from "line disciplines" on Unix terminals. However, this document (and the C code) uses the term "layer".

Initial discussion of the ability to modify IO streams behaviour used the term "discipline" for the entities which were added. This came (I believe) from the use of the term in "sfio", which in turn borrowed it from "line disciplines" on Unix terminals. However, this document (and the C code) uses the term "layer". (TBT)

This is, I hope, a natural term given the implementation, and should avoid connotations that are inherent in earlier uses of "discipline" for things which are rather different.

This is, I hope, a natural term given the implementation, and should avoid connotations that are inherent in earlier uses of "discipline" for things which are rather different. (TBT)

データ構造体

The basic data structure is a PerlIOl:

基本データ構造体は PerlIOl です:

        typedef struct _PerlIO PerlIOl;
        typedef struct _PerlIO_funcs PerlIO_funcs;
        typedef PerlIOl *PerlIO;

        struct _PerlIO
        {
         PerlIOl *      next;       /* Lower layer */
         PerlIO_funcs * tab;        /* Functions for this layer */
         IV             flags;      /* Various flags for state */
        };

A PerlIOl * is a pointer to the struct, and the application level PerlIO * is a pointer to a PerlIOl * - i.e. a pointer to a pointer to the struct. This allows the application level PerlIO * to remain constant while the actual PerlIOl * underneath changes. (Compare perl's SV * which remains constant while its sv_any field changes as the scalar's type changes.) An IO stream is then in general represented as a pointer to this linked-list of "layers".

A PerlIOl * is a pointer to the struct, and the application level PerlIO * is a pointer to a PerlIOl * - i.e. a pointer to a pointer to the struct. This allows the application level PerlIO * to remain constant while the actual PerlIOl * underneath changes. (Compare perl's SV * which remains constant while its sv_any field changes as the scalar's type changes.) An IO stream is then in general represented as a pointer to this linked-list of "layers". (TBT)

It should be noted that because of the double indirection in a PerlIO *, a &(perlio->next) "is" a PerlIO *, and so to some degree at least one layer can use the "standard" API on the next layer down.

It should be noted that because of the double indirection in a PerlIO *, a &(perlio->next) "is" a PerlIO *, and so to some degree at least one layer can use the "standard" API on the next layer down. (TBT)

A "layer" is composed of two parts:

一つの「層」は二つの部分から構成されます:

  1. The functions and attributes of the "layer class".

    「層クラス」の関数と属性。

  2. The per-instance data for a particular handle.

    特定のハンドルのためのインスタンス単位のデータ。

関数と属性

The functions and attributes are accessed via the "tab" (for table) member of PerlIOl. The functions (methods of the layer "class") are fixed, and are defined by the PerlIO_funcs type. They are broadly the same as the public PerlIO_xxxxx functions:

The functions and attributes are accessed via the "tab" (for table) member of PerlIOl. The functions (methods of the layer "class") are fixed, and are defined by the PerlIO_funcs type. They are broadly the same as the public PerlIO_xxxxx functions: (TBT)

  struct _PerlIO_funcs
  {
   Size_t               fsize;
   char *               name;
   Size_t               size;
   IV           kind;
   IV           (*Pushed)(pTHX_ PerlIO *f,const char *mode,SV *arg, PerlIO_funcs *tab);
   IV           (*Popped)(pTHX_ PerlIO *f);
   PerlIO *     (*Open)(pTHX_ PerlIO_funcs *tab,
                        PerlIO_list_t *layers, IV n,
                        const char *mode,
                        int fd, int imode, int perm,
                        PerlIO *old,
                        int narg, SV **args);
   IV           (*Binmode)(pTHX_ PerlIO *f);
   SV *         (*Getarg)(pTHX_ PerlIO *f, CLONE_PARAMS *param, int flags)
   IV           (*Fileno)(pTHX_ PerlIO *f);
   PerlIO *     (*Dup)(pTHX_ PerlIO *f, PerlIO *o, CLONE_PARAMS *param, int flags)
   /* Unix-like functions - cf sfio line disciplines */
   SSize_t      (*Read)(pTHX_ PerlIO *f, void *vbuf, Size_t count);
   SSize_t      (*Unread)(pTHX_ PerlIO *f, const void *vbuf, Size_t count);
   SSize_t      (*Write)(pTHX_ PerlIO *f, const void *vbuf, Size_t count);
   IV           (*Seek)(pTHX_ PerlIO *f, Off_t offset, int whence);
   Off_t        (*Tell)(pTHX_ PerlIO *f);
   IV           (*Close)(pTHX_ PerlIO *f);
   /* Stdio-like buffered IO functions */
   IV           (*Flush)(pTHX_ PerlIO *f);
   IV           (*Fill)(pTHX_ PerlIO *f);
   IV           (*Eof)(pTHX_ PerlIO *f);
   IV           (*Error)(pTHX_ PerlIO *f);
   void         (*Clearerr)(pTHX_ PerlIO *f);
   void         (*Setlinebuf)(pTHX_ PerlIO *f);
   /* Perl's snooping functions */
   STDCHAR *    (*Get_base)(pTHX_ PerlIO *f);
   Size_t       (*Get_bufsiz)(pTHX_ PerlIO *f);
   STDCHAR *    (*Get_ptr)(pTHX_ PerlIO *f);
   SSize_t      (*Get_cnt)(pTHX_ PerlIO *f);
   void         (*Set_ptrcnt)(pTHX_ PerlIO *f,STDCHAR *ptr,SSize_t cnt);
  };

The first few members of the struct give a function table size for compatibility check "name" for the layer, the size to malloc for the per-instance data, and some flags which are attributes of the class as whole (such as whether it is a buffering layer), then follow the functions which fall into four basic groups:

The first few members of the struct give a function table size for compatibility check "name" for the layer, the size to malloc for the per-instance data, and some flags which are attributes of the class as whole (such as whether it is a buffering layer), then follow the functions which fall into four basic groups: (TBT)

  1. Opening and setup functions

    オープンと設定のための関数

  2. Basic IO operations

    基本 IO 操作

  3. Stdio class buffering options.

    Stdio クラスバッファリングオプション。

  4. Functions to support Perl's traditional "fast" access to the buffer.

    Perl の伝統的なバッファへの「高速」アクセスに対応する関数。

A layer does not have to implement all the functions, but the whole table has to be present. Unimplemented slots can be NULL (which will result in an error when called) or can be filled in with stubs to "inherit" behaviour from a "base class". This "inheritance" is fixed for all instances of the layer, but as the layer chooses which stubs to populate the table, limited "multiple inheritance" is possible.

A layer does not have to implement all the functions, but the whole table has to be present. Unimplemented slots can be NULL (which will result in an error when called) or can be filled in with stubs to "inherit" behaviour from a "base class". This "inheritance" is fixed for all instances of the layer, but as the layer chooses which stubs to populate the table, limited "multiple inheritance" is possible. (TBT)

インスタンス単位のデータ

The per-instance data are held in memory beyond the basic PerlIOl struct, by making a PerlIOl the first member of the layer's struct thus:

The per-instance data are held in memory beyond the basic PerlIOl struct, by making a PerlIOl the first member of the layer's struct thus: (TBT)

        typedef struct
        {
         struct _PerlIO base;       /* Base "class" info */
         STDCHAR *      buf;        /* Start of buffer */
         STDCHAR *      end;        /* End of valid part of buffer */
         STDCHAR *      ptr;        /* Current position in buffer */
         Off_t          posn;       /* Offset of buf into the file */
         Size_t         bufsiz;     /* Real size of buffer */
         IV             oneword;    /* Emergency buffer */
        } PerlIOBuf;

In this way (as for perl's scalars) a pointer to a PerlIOBuf can be treated as a pointer to a PerlIOl.

In this way (as for perl's scalars) a pointer to a PerlIOBuf can be treated as a pointer to a PerlIOl. (TBT)

実行中の層

                table           perlio          unix
            |           |
            +-----------+    +----------+    +--------+
   PerlIO ->|           |--->|  next    |--->|  NULL  |
            +-----------+    +----------+    +--------+
            |           |    |  buffer  |    |   fd   |
            +-----------+    |          |    +--------+
            |           |    +----------+

The above attempts to show how the layer scheme works in a simple case. The application's PerlIO * points to an entry in the table(s) representing open (allocated) handles. For example the first three slots in the table correspond to stdin,stdout and stderr. The table in turn points to the current "top" layer for the handle - in this case an instance of the generic buffering layer "perlio". That layer in turn points to the next layer down - in this case the low-level "unix" layer.

The above attempts to show how the layer scheme works in a simple case. The application's PerlIO * points to an entry in the table(s) representing open (allocated) handles. For example the first three slots in the table correspond to stdin,stdout and stderr. The table in turn points to the current "top" layer for the handle - in this case an instance of the generic buffering layer "perlio". That layer in turn points to the next layer down - in this case the low-level "unix" layer. (TBT)

The above is roughly equivalent to a "stdio" buffered stream, but with much more flexibility:

The above is roughly equivalent to a "stdio" buffered stream, but with much more flexibility: (TBT)

  • If Unix level read/write/lseek is not appropriate for (say) sockets then the "unix" layer can be replaced (at open time or even dynamically) with a "socket" layer.

    If Unix level read/write/lseek is not appropriate for (say) sockets then the "unix" layer can be replaced (at open time or even dynamically) with a "socket" layer. (TBT)

  • Different handles can have different buffering schemes. The "top" layer could be the "mmap" layer if reading disk files was quicker using mmap than read. An "unbuffered" stream can be implemented simply by not having a buffer layer.

    Different handles can have different buffering schemes. The "top" layer could be the "mmap" layer if reading disk files was quicker using mmap than read. An "unbuffered" stream can be implemented simply by not having a buffer layer. (TBT)

  • Extra layers can be inserted to process the data as it flows through. This was the driving need for including the scheme in perl 5.7.0+ - we needed a mechanism to allow data to be translated between perl's internal encoding (conceptually at least Unicode as UTF-8), and the "native" format used by the system. This is provided by the ":encoding(xxxx)" layer which typically sits above the buffering layer.

    Extra layers can be inserted to process the data as it flows through. This was the driving need for including the scheme in perl 5.7.0+ - we needed a mechanism to allow data to be translated between perl's internal encoding (conceptually at least Unicode as UTF-8), and the "native" format used by the system. This is provided by the ":encoding(xxxx)" layer which typically sits above the buffering layer. (TBT)

  • A layer can be added that does "\n" to CRLF translation. This layer can be used on any platform, not just those that normally do such things.

    A layer can be added that does "\n" to CRLF translation. This layer can be used on any platform, not just those that normally do such things. (TBT)

インスタンス単位のフラグビット

The generic flag bits are a hybrid of O_XXXXX style flags deduced from the mode string passed to PerlIO_open(), and state bits for typical buffer layers.

The generic flag bits are a hybrid of O_XXXXX style flags deduced from the mode string passed to PerlIO_open(), and state bits for typical buffer layers. (TBT)

PERLIO_F_EOF

End of file.

ファイルの末尾。

PERLIO_F_CANWRITE

Writes are permitted, i.e. opened as "w" or "r+" or "a", etc.

書き込みが許可されている; つまり "w", "r+", "a" などとして開かれている。

PERLIO_F_CANREAD

Reads are permitted i.e. opened "r" or "w+" (or even "a+" - ick).

読み込みが許可されている; "r", "w+" (または "a+" 的) として開かれている。

PERLIO_F_ERROR

An error has occurred (for PerlIO_error()).

(PerlIO_error() のための) エラーが発生した。

PERLIO_F_TRUNCATE

Truncate file suggested by open mode.

オープンモードで提案されたファイルを切り詰める。

PERLIO_F_APPEND

All writes should be appends.

全ての書き込みは追記される。

PERLIO_F_CRLF

Layer is performing Win32-like "\n" mapped to CR,LF for output and CR,LF mapped to "\n" for input. Normally the provided "crlf" layer is the only layer that need bother about this. PerlIO_binmode() will mess with this flag rather than add/remove layers if the PERLIO_K_CANCRLF bit is set for the layers class.

Layer is performing Win32-like "\n" mapped to CR,LF for output and CR,LF mapped to "\n" for input. Normally the provided "crlf" layer is the only layer that need bother about this. PerlIO_binmode() will mess with this flag rather than add/remove layers if the PERLIO_K_CANCRLF bit is set for the layers class. (TBT)

PERLIO_F_UTF8

Data written to this layer should be UTF-8 encoded; data provided by this layer should be considered UTF-8 encoded. Can be set on any layer by ":utf8" dummy layer. Also set on ":encoding" layer.

Data written to this layer should be UTF-8 encoded; data provided by this layer should be considered UTF-8 encoded. Can be set on any layer by ":utf8" dummy layer. Also set on ":encoding" layer. (TBT)

PERLIO_F_UNBUF

Layer is unbuffered - i.e. write to next layer down should occur for each write to this layer.

Layer is unbuffered - i.e. write to next layer down should occur for each write to this layer. (TBT)

PERLIO_F_WRBUF

The buffer for this layer currently holds data written to it but not sent to next layer.

The buffer for this layer currently holds data written to it but not sent to next layer. (TBT)

PERLIO_F_RDBUF

The buffer for this layer currently holds unconsumed data read from layer below.

The buffer for this layer currently holds unconsumed data read from layer below. (TBT)

PERLIO_F_LINEBUF

Layer is line buffered. Write data should be passed to next layer down whenever a "\n" is seen. Any data beyond the "\n" should then be processed.

Layer is line buffered. Write data should be passed to next layer down whenever a "\n" is seen. Any data beyond the "\n" should then be processed. (TBT)

PERLIO_F_TEMP

File has been unlink()ed, or should be deleted on close().

ファイルが unlink() されている、または close() で削除されるべき。

PERLIO_F_OPEN

Handle is open.

ハンドルが開いている。

PERLIO_F_FASTGETS

This instance of this layer supports the "fast gets" interface. Normally set based on PERLIO_K_FASTGETS for the class and by the existence of the function(s) in the table. However a class that normally provides that interface may need to avoid it on a particular instance. The "pending" layer needs to do this when it is pushed above a layer which does not support the interface. (Perl's sv_gets() does not expect the streams fast gets behaviour to change during one "get".)

This instance of this layer supports the "fast gets" interface. Normally set based on PERLIO_K_FASTGETS for the class and by the existence of the function(s) in the table. However a class that normally provides that interface may need to avoid it on a particular instance. The "pending" layer needs to do this when it is pushed above a layer which does not support the interface. (Perl's sv_gets() does not expect the streams fast gets behaviour to change during one "get".) (TBT)

メソッドの詳細

fsize
        Size_t fsize;

Size of the function table. This is compared against the value PerlIO code "knows" as a compatibility check. Future versions may be able to tolerate layers compiled against an old version of the headers.

Size of the function table. This is compared against the value PerlIO code "knows" as a compatibility check. Future versions may be able to tolerate layers compiled against an old version of the headers. (TBT)

name
        char * name;

The name of the layer whose open() method Perl should invoke on open(). For example if the layer is called APR, you will call:

The name of the layer whose open() method Perl should invoke on open(). For example if the layer is called APR, you will call: (TBT)

  open $fh, ">:APR", ...

and Perl knows that it has to invoke the PerlIOAPR_open() method implemented by the APR layer.

and Perl knows that it has to invoke the PerlIOAPR_open() method implemented by the APR layer. (TBT)

size
        Size_t size;

The size of the per-instance data structure, e.g.:

インスタンス単位のデータ構造体のサイズ; つまり:

  sizeof(PerlIOAPR)

If this field is zero then PerlIO_pushed does not malloc anything and assumes layer's Pushed function will do any required layer stack manipulation - used to avoid malloc/free overhead for dummy layers. If the field is non-zero it must be at least the size of PerlIOl, PerlIO_pushed will allocate memory for the layer's data structures and link new layer onto the stream's stack. (If the layer's Pushed method returns an error indication the layer is popped again.)

If this field is zero then PerlIO_pushed does not malloc anything and assumes layer's Pushed function will do any required layer stack manipulation - used to avoid malloc/free overhead for dummy layers. If the field is non-zero it must be at least the size of PerlIOl, PerlIO_pushed will allocate memory for the layer's data structures and link new layer onto the stream's stack. (If the layer's Pushed method returns an error indication the layer is popped again.) (TBT)

kind
        IV kind;
  • PERLIO_K_BUFFERED

    The layer is buffered.

    層がバッファリングされている。

  • PERLIO_K_RAW

    The layer is acceptable to have in a binmode(FH) stack - i.e. it does not (or will configure itself not to) transform bytes passing through it.

    The layer is acceptable to have in a binmode(FH) stack - i.e. it does not (or will configure itself not to) transform bytes passing through it. (TBT)

  • PERLIO_K_CANCRLF

    Layer can translate between "\n" and CRLF line ends.

    層は "\n" と CRLF 行末を変換できる。

  • PERLIO_K_FASTGETS

    Layer allows buffer snooping.

    層はバッファを覗くことを許可している。

  • PERLIO_K_MULTIARG

    Used when the layer's open() accepts more arguments than usual. The extra arguments should come not before the MODE argument. When this flag is used it's up to the layer to validate the args.

    Used when the layer's open() accepts more arguments than usual. The extra arguments should come not before the MODE argument. When this flag is used it's up to the layer to validate the args. (TBT)

Pushed
        IV      (*Pushed)(pTHX_ PerlIO *f,const char *mode, SV *arg);

The only absolutely mandatory method. Called when the layer is pushed onto the stack. The mode argument may be NULL if this occurs post-open. The arg will be non-NULL if an argument string was passed. In most cases this should call PerlIOBase_pushed() to convert mode into the appropriate PERLIO_F_XXXXX flags in addition to any actions the layer itself takes. If a layer is not expecting an argument it need neither save the one passed to it, nor provide Getarg() (it could perhaps Perl_warn that the argument was un-expected).

The only absolutely mandatory method. Called when the layer is pushed onto the stack. The mode argument may be NULL if this occurs post-open. The arg will be non-NULL if an argument string was passed. In most cases this should call PerlIOBase_pushed() to convert mode into the appropriate PERLIO_F_XXXXX flags in addition to any actions the layer itself takes. If a layer is not expecting an argument it need neither save the one passed to it, nor provide Getarg() (it could perhaps Perl_warn that the argument was un-expected). (TBT)

Returns 0 on success. On failure returns -1 and should set errno.

成功時は 0 を返します。 失敗時には -1 を返して errno が設定されます。

Popped
        IV      (*Popped)(pTHX_ PerlIO *f);

Called when the layer is popped from the stack. A layer will normally be popped after Close() is called. But a layer can be popped without being closed if the program is dynamically managing layers on the stream. In such cases Popped() should free any resources (buffers, translation tables, ...) not held directly in the layer's struct. It should also Unread() any unconsumed data that has been read and buffered from the layer below back to that layer, so that it can be re-provided to what ever is now above.

Called when the layer is popped from the stack. A layer will normally be popped after Close() is called. But a layer can be popped without being closed if the program is dynamically managing layers on the stream. In such cases Popped() should free any resources (buffers, translation tables, ...) not held directly in the layer's struct. It should also Unread() any unconsumed data that has been read and buffered from the layer below back to that layer, so that it can be re-provided to what ever is now above. (TBT)

Returns 0 on success and failure. If Popped() returns true then perlio.c assumes that either the layer has popped itself, or the layer is super special and needs to be retained for other reasons. In most cases it should return false.

Returns 0 on success and failure. If Popped() returns true then perlio.c assumes that either the layer has popped itself, or the layer is super special and needs to be retained for other reasons. In most cases it should return false. (TBT)

Open
        PerlIO *        (*Open)(...);

The Open() method has lots of arguments because it combines the functions of perl's open, PerlIO_open, perl's sysopen, PerlIO_fdopen and PerlIO_reopen. The full prototype is as follows:

The Open() method has lots of arguments because it combines the functions of perl's open, PerlIO_open, perl's sysopen, PerlIO_fdopen and PerlIO_reopen. The full prototype is as follows: (TBT)

 PerlIO *       (*Open)(pTHX_ PerlIO_funcs *tab,
                        PerlIO_list_t *layers, IV n,
                        const char *mode,
                        int fd, int imode, int perm,
                        PerlIO *old,
                        int narg, SV **args);

Open should (perhaps indirectly) call PerlIO_allocate() to allocate a slot in the table and associate it with the layers information for the opened file, by calling PerlIO_push. The layers is an array of all the layers destined for the PerlIO *, and any arguments passed to them, n is the index into that array of the layer being called. The macro PerlIOArg will return a (possibly NULL) SV * for the argument passed to the layer.

Open should (perhaps indirectly) call PerlIO_allocate() to allocate a slot in the table and associate it with the layers information for the opened file, by calling PerlIO_push. The layers is an array of all the layers destined for the PerlIO *, and any arguments passed to them, n is the index into that array of the layer being called. The macro PerlIOArg will return a (possibly NULL) SV * for the argument passed to the layer. (TBT)

The mode string is an "fopen()-like" string which would match the regular expression /^[I#]?[rwa]\+?[bt]?$/.

The mode string is an "fopen()-like" string which would match the regular expression /^[I#]?[rwa]\+?[bt]?$/. (TBT)

The 'I' prefix is used during creation of stdin..stderr via special PerlIO_fdopen calls; the '#' prefix means that this is sysopen and that imode and perm should be passed to PerlLIO_open3; 'r' means read, 'w' means write and 'a' means append. The '+' suffix means that both reading and writing/appending are permitted. The 'b' suffix means file should be binary, and 't' means it is text. (Almost all layers should do the IO in binary mode, and ignore the b/t bits. The :crlf layer should be pushed to handle the distinction.)

The 'I' prefix is used during creation of stdin..stderr via special PerlIO_fdopen calls; the '#' prefix means that this is sysopen and that imode and perm should be passed to PerlLIO_open3; 'r' means read, 'w' means write and 'a' means append. The '+' suffix means that both reading and writing/appending are permitted. The 'b' suffix means file should be binary, and 't' means it is text. (Almost all layers should do the IO in binary mode, and ignore the b/t bits. The :crlf layer should be pushed to handle the distinction.) (TBT)

If old is not NULL then this is a PerlIO_reopen. Perl itself does not use this (yet?) and semantics are a little vague.

If old is not NULL then this is a PerlIO_reopen. Perl itself does not use this (yet?) and semantics are a little vague. (TBT)

If fd not negative then it is the numeric file descriptor fd, which will be open in a manner compatible with the supplied mode string, the call is thus equivalent to PerlIO_fdopen. In this case nargs will be zero.

If fd not negative then it is the numeric file descriptor fd, which will be open in a manner compatible with the supplied mode string, the call is thus equivalent to PerlIO_fdopen. In this case nargs will be zero. (TBT)

If nargs is greater than zero then it gives the number of arguments passed to open, otherwise it will be 1 if for example PerlIO_open was called. In simple cases SvPV_nolen(*args) is the pathname to open.

If nargs is greater than zero then it gives the number of arguments passed to open, otherwise it will be 1 if for example PerlIO_open was called. In simple cases SvPV_nolen(*args) is the pathname to open. (TBT)

Having said all that translation-only layers do not need to provide Open() at all, but rather leave the opening to a lower level layer and wait to be "pushed". If a layer does provide Open() it should normally call the Open() method of next layer down (if any) and then push itself on top if that succeeds.

Having said all that translation-only layers do not need to provide Open() at all, but rather leave the opening to a lower level layer and wait to be "pushed". If a layer does provide Open() it should normally call the Open() method of next layer down (if any) and then push itself on top if that succeeds. (TBT)

If PerlIO_push was performed and open has failed, it must PerlIO_pop itself, since if it's not, the layer won't be removed and may cause bad problems.

If PerlIO_push was performed and open has failed, it must PerlIO_pop itself, since if it's not, the layer won't be removed and may cause bad problems. (TBT)

Returns NULL on failure.

失敗時には NULL を返します。

Binmode
        IV        (*Binmode)(pTHX_ PerlIO *f);

Optional. Used when :raw layer is pushed (explicitly or as a result of binmode(FH)). If not present layer will be popped. If present should configure layer as binary (or pop itself) and return 0. If it returns -1 for error binmode will fail with layer still on the stack.

Optional. Used when :raw layer is pushed (explicitly or as a result of binmode(FH)). If not present layer will be popped. If present should configure layer as binary (or pop itself) and return 0. If it returns -1 for error binmode will fail with layer still on the stack. (TBT)

Getarg
        SV *      (*Getarg)(pTHX_ PerlIO *f,
                            CLONE_PARAMS *param, int flags);

Optional. If present should return an SV * representing the string argument passed to the layer when it was pushed. e.g. ":encoding(ascii)" would return an SvPV with value "ascii". (param and flags arguments can be ignored in most cases)

Optional. If present should return an SV * representing the string argument passed to the layer when it was pushed. e.g. ":encoding(ascii)" would return an SvPV with value "ascii". (param and flags arguments can be ignored in most cases) (TBT)

Dup uses Getarg to retrieve the argument originally passed to Pushed, so you must implement this function if your layer has an extra argument to Pushed and will ever be Duped.

Dup uses Getarg to retrieve the argument originally passed to Pushed, so you must implement this function if your layer has an extra argument to Pushed and will ever be Duped. (TBT)

Fileno
        IV        (*Fileno)(pTHX_ PerlIO *f);

Returns the Unix/Posix numeric file descriptor for the handle. Normally PerlIOBase_fileno() (which just asks next layer down) will suffice for this.

Returns the Unix/Posix numeric file descriptor for the handle. Normally PerlIOBase_fileno() (which just asks next layer down) will suffice for this. (TBT)

Returns -1 on error, which is considered to include the case where the layer cannot provide such a file descriptor.

Returns -1 on error, which is considered to include the case where the layer cannot provide such a file descriptor. (TBT)

Dup
        PerlIO * (*Dup)(pTHX_ PerlIO *f, PerlIO *o,
                        CLONE_PARAMS *param, int flags);

XXX: Needs more docs.

XXX: もっと文書が必要です。

Used as part of the "clone" process when a thread is spawned (in which case param will be non-NULL) and when a stream is being duplicated via '&' in the open.

Used as part of the "clone" process when a thread is spawned (in which case param will be non-NULL) and when a stream is being duplicated via '&' in the open. (TBT)

Similar to Open, returns PerlIO* on success, NULL on failure.

Open と同様ですが、正常時には PerlIO* を返し、失敗時には NULL を 返します。

Read
        SSize_t (*Read)(pTHX_ PerlIO *f, void *vbuf, Size_t count);

Basic read operation.

基本読み込み操作です。

Typically will call Fill and manipulate pointers (possibly via the API). PerlIOBuf_read() may be suitable for derived classes which provide "fast gets" methods.

Typically will call Fill and manipulate pointers (possibly via the API). PerlIOBuf_read() may be suitable for derived classes which provide "fast gets" methods. (TBT)

Returns actual bytes read, or -1 on an error.

実際に読み込まれたバイト数か、エラー時には -1 を返します。

Unread
        SSize_t (*Unread)(pTHX_ PerlIO *f,
                          const void *vbuf, Size_t count);

A superset of stdio's ungetc(). Should arrange for future reads to see the bytes in vbuf. If there is no obviously better implementation then PerlIOBase_unread() provides the function by pushing a "fake" "pending" layer above the calling layer.

A superset of stdio's ungetc(). Should arrange for future reads to see the bytes in vbuf. If there is no obviously better implementation then PerlIOBase_unread() provides the function by pushing a "fake" "pending" layer above the calling layer. (TBT)

Returns the number of unread chars.

まだ読み込んでいない文字の数を返します。

Write
        SSize_t (*Write)(PerlIO *f, const void *vbuf, Size_t count);

Basic write operation.

基本書き込み操作です。

Returns bytes written or -1 on an error.

書き込まれたバイト数か、エラー時には -1 を返します。

Seek
        IV      (*Seek)(pTHX_ PerlIO *f, Off_t offset, int whence);

Position the file pointer. Should normally call its own Flush method and then the Seek method of next layer down.

Position the file pointer. Should normally call its own Flush method and then the Seek method of next layer down. (TBT)

Returns 0 on success, -1 on failure.

成功時には 0 を、失敗時には -1 を返します。

Tell
        Off_t   (*Tell)(pTHX_ PerlIO *f);

Return the file pointer. May be based on layers cached concept of position to avoid overhead.

Return the file pointer. May be based on layers cached concept of position to avoid overhead. (TBT)

Returns -1 on failure to get the file pointer.

ファイルポインタヲ得るのに失敗した場合は -1 を返します。

Close
        IV      (*Close)(pTHX_ PerlIO *f);

Close the stream. Should normally call PerlIOBase_close() to flush itself and close layers below, and then deallocate any data structures (buffers, translation tables, ...) not held directly in the data structure.

Close the stream. Should normally call PerlIOBase_close() to flush itself and close layers below, and then deallocate any data structures (buffers, translation tables, ...) not held directly in the data structure. (TBT)

Returns 0 on success, -1 on failure.

成功時には 0 を、失敗時には -1 を返します。

Flush
        IV      (*Flush)(pTHX_ PerlIO *f);

Should make stream's state consistent with layers below. That is, any buffered write data should be written, and file position of lower layers adjusted for data read from below but not actually consumed. (Should perhaps Unread() such data to the lower layer.)

Should make stream's state consistent with layers below. That is, any buffered write data should be written, and file position of lower layers adjusted for data read from below but not actually consumed. (Should perhaps Unread() such data to the lower layer.) (TBT)

Returns 0 on success, -1 on failure.

成功時には 0 を、失敗時には -1 を返します。

Fill
        IV      (*Fill)(pTHX_ PerlIO *f);

The buffer for this layer should be filled (for read) from layer below. When you "subclass" PerlIOBuf layer, you want to use its _read method and to supply your own fill method, which fills the PerlIOBuf's buffer.

The buffer for this layer should be filled (for read) from layer below. When you "subclass" PerlIOBuf layer, you want to use its _read method and to supply your own fill method, which fills the PerlIOBuf's buffer. (TBT)

Returns 0 on success, -1 on failure.

成功時には 0 を、失敗時には -1 を返します。

Eof
        IV      (*Eof)(pTHX_ PerlIO *f);

Return end-of-file indicator. PerlIOBase_eof() is normally sufficient.

ファイル終端指示子を返します。 普通は PerlIOBase_eof() で十分です。

Returns 0 on end-of-file, 1 if not end-of-file, -1 on error.

ファイル末尾では 0 を、ファイル末尾でなければ 1 を、エラー時には -1 を 返します。

Error
        IV      (*Error)(pTHX_ PerlIO *f);

Return error indicator. PerlIOBase_error() is normally sufficient.

エラー指示子を返します。 普通は PerlIOBase_error() で十分です。

Returns 1 if there is an error (usually when PERLIO_F_ERROR is set, 0 otherwise.

エラー (普通は PERLIO_F_ERROR がセットされている) の場合は 1、 さもなければ 0 を返します。

Clearerr
        void    (*Clearerr)(pTHX_ PerlIO *f);

Clear end-of-file and error indicators. Should call PerlIOBase_clearerr() to set the PERLIO_F_XXXXX flags, which may suffice.

Clear end-of-file and error indicators. Should call PerlIOBase_clearerr() to set the PERLIO_F_XXXXX flags, which may suffice. (TBT)

Setlinebuf
        void    (*Setlinebuf)(pTHX_ PerlIO *f);

Mark the stream as line buffered. PerlIOBase_setlinebuf() sets the PERLIO_F_LINEBUF flag and is normally sufficient.

Mark the stream as line buffered. PerlIOBase_setlinebuf() sets the PERLIO_F_LINEBUF flag and is normally sufficient. (TBT)

Get_base
        STDCHAR *       (*Get_base)(pTHX_ PerlIO *f);

Allocate (if not already done so) the read buffer for this layer and return pointer to it. Return NULL on failure.

Allocate (if not already done so) the read buffer for this layer and return pointer to it. Return NULL on failure. (TBT)

Get_bufsiz
        Size_t  (*Get_bufsiz)(pTHX_ PerlIO *f);

Return the number of bytes that last Fill() put in the buffer.

直前の Fill() がバッファに設定したバイト数を返します。

Get_ptr
        STDCHAR *       (*Get_ptr)(pTHX_ PerlIO *f);

Return the current read pointer relative to this layer's buffer.

現在の層のバッファに関連する現在の読み込みポインタを返します。

Get_cnt
        SSize_t (*Get_cnt)(pTHX_ PerlIO *f);

Return the number of bytes left to be read in the current buffer.

現在のバッファで読み込まれるために残っているバイト数を返します。

Set_ptrcnt
        void    (*Set_ptrcnt)(pTHX_ PerlIO *f,
                              STDCHAR *ptr, SSize_t cnt);

Adjust the read pointer and count of bytes to match ptr and/or cnt. The application (or layer above) must ensure they are consistent. (Checking is allowed by the paranoid.)

Adjust the read pointer and count of bytes to match ptr and/or cnt. The application (or layer above) must ensure they are consistent. (Checking is allowed by the paranoid.) (TBT)

ユーティリティ

To ask for the next layer down use PerlIONext(PerlIO *f).

次の層を調べるには PerlIONext(PerlIO *f) を使います。

To check that a PerlIO* is valid use PerlIOValid(PerlIO *f). (All this does is really just to check that the pointer is non-NULL and that the pointer behind that is non-NULL.)

To check that a PerlIO* is valid use PerlIOValid(PerlIO *f). (All this does is really just to check that the pointer is non-NULL and that the pointer behind that is non-NULL.) (TBT)

PerlIOBase(PerlIO *f) returns the "Base" pointer, or in other words, the PerlIOl* pointer.

PerlIOBase(PerlIO *f) returns the "Base" pointer, or in other words, the PerlIOl* pointer. (TBT)

PerlIOSelf(PerlIO* f, type) return the PerlIOBase cast to a type.

PerlIOSelf(PerlIO* f, type) は PerlIOBase cast to a type. (TBT)

Perl_PerlIO_or_Base(PerlIO* f, callback, base, failure, args) either calls the callback from the functions of the layer f (just by the name of the IO function, like "Read") with the args, or if there is no such callback, calls the base version of the callback with the same args, or if the f is invalid, set errno to EBADF and return failure.

Perl_PerlIO_or_Base(PerlIO* f, callback, base, failure, args) either calls the callback from the functions of the layer f (just by the name of the IO function, like "Read") with the args, or if there is no such callback, calls the base version of the callback with the same args, or if the f is invalid, set errno to EBADF and return failure. (TBT)

Perl_PerlIO_or_fail(PerlIO* f, callback, failure, args) either calls the callback of the functions of the layer f with the args, or if there is no such callback, set errno to EINVAL. Or if the f is invalid, set errno to EBADF and return failure.

Perl_PerlIO_or_fail(PerlIO* f, callback, failure, args) either calls the callback of the functions of the layer f with the args, or if there is no such callback, set errno to EINVAL. Or if the f is invalid, set errno to EBADF and return failure. (TBT)

Perl_PerlIO_or_Base_void(PerlIO* f, callback, base, args) either calls the callback of the functions of the layer f with the args, or if there is no such callback, calls the base version of the callback with the same args, or if the f is invalid, set errno to EBADF.

Perl_PerlIO_or_Base_void(PerlIO* f, callback, base, args) either calls the callback of the functions of the layer f with the args, or if there is no such callback, calls the base version of the callback with the same args, or if the f is invalid, set errno to EBADF. (TBT)

Perl_PerlIO_or_fail_void(PerlIO* f, callback, args) either calls the callback of the functions of the layer f with the args, or if there is no such callback, set errno to EINVAL. Or if the f is invalid, set errno to EBADF.

Perl_PerlIO_or_fail_void(PerlIO* f, callback, args) either calls the callback of the functions of the layer f with the args, or if there is no such callback, set errno to EINVAL. Or if the f is invalid, set errno to EBADF. (TBT)

PerlIO 層の実装

If you find the implementation document unclear or not sufficient, look at the existing PerlIO layer implementations, which include:

If you find the implementation document unclear or not sufficient, look at the existing PerlIO layer implementations, which include: (TBT)

  • C implementations

    The perlio.c and perliol.h in the Perl core implement the "unix", "perlio", "stdio", "crlf", "utf8", "byte", "raw", "pending" layers, and also the "mmap" and "win32" layers if applicable. (The "win32" is currently unfinished and unused, to see what is used instead in Win32, see "Querying the layers of filehandles" in PerlIO .)

    The perlio.c and perliol.h in the Perl core implement the "unix", "perlio", "stdio", "crlf", "utf8", "byte", "raw", "pending" layers, and also the "mmap" and "win32" layers if applicable. (The "win32" is currently unfinished and unused, to see what is used instead in Win32, see "Querying the layers of filehandles" in PerlIO .) (TBT)

    PerlIO::encoding, PerlIO::scalar, PerlIO::via in the Perl core.

    Perl コアの PerlIO::encoding, PerlIO::scalar, PerlIO::via。

    PerlIO::gzip and APR::PerlIO (mod_perl 2.0) on CPAN.

    CPAN の PerlIO::gzip と APR::PerlIO (mod_perl 2.0)。

  • Perl implementations

    PerlIO::via::QuotedPrint in the Perl core and PerlIO::via::* on CPAN.

    Perl コアの PerlIO::via::QuotedPrint と CPAN の PerlIO::via::*。

If you are creating a PerlIO layer, you may want to be lazy, in other words, implement only the methods that interest you. The other methods you can either replace with the "blank" methods

If you are creating a PerlIO layer, you may want to be lazy, in other words, implement only the methods that interest you. The other methods you can either replace with the "blank" methods (TBT)

    PerlIOBase_noop_ok
    PerlIOBase_noop_fail

(which do nothing, and return zero and -1, respectively) or for certain methods you may assume a default behaviour by using a NULL method. The Open method looks for help in the 'parent' layer. The following table summarizes the behaviour:

(which do nothing, and return zero and -1, respectively) or for certain methods you may assume a default behaviour by using a NULL method. The Open method looks for help in the 'parent' layer. The following table summarizes the behaviour: (TBT)

    method      behaviour with NULL

    Clearerr    PerlIOBase_clearerr
    Close       PerlIOBase_close
    Dup         PerlIOBase_dup
    Eof         PerlIOBase_eof
    Error       PerlIOBase_error
    Fileno      PerlIOBase_fileno
    Fill        FAILURE
    Flush       SUCCESS
    Getarg      SUCCESS
    Get_base    FAILURE
    Get_bufsiz  FAILURE
    Get_cnt     FAILURE
    Get_ptr     FAILURE
    Open        INHERITED
    Popped      SUCCESS
    Pushed      SUCCESS
    Read        PerlIOBase_read
    Seek        FAILURE
    Set_cnt     FAILURE
    Set_ptrcnt  FAILURE
    Setlinebuf  PerlIOBase_setlinebuf
    Tell        FAILURE
    Unread      PerlIOBase_unread
    Write       FAILURE

 FAILURE        Set errno (to EINVAL in UNIXish, to LIB$_INVARG in VMS) and
                return -1 (for numeric return values) or NULL (for pointers)
 INHERITED      Inherited from the layer below
 SUCCESS        Return 0 (for numeric return values) or a pointer 

コア層

The file perlio.c provides the following layers:

ファイル perlio.c は以下の層を提供します:

"unix"

A basic non-buffered layer which calls Unix/POSIX read(), write(), lseek(), close(). No buffering. Even on platforms that distinguish between O_TEXT and O_BINARY this layer is always O_BINARY.

A basic non-buffered layer which calls Unix/POSIX read(), write(), lseek(), close(). No buffering. Even on platforms that distinguish between O_TEXT and O_BINARY this layer is always O_BINARY. (TBT)

"perlio"

A very complete generic buffering layer which provides the whole of PerlIO API. It is also intended to be used as a "base class" for other layers. (For example its Read() method is implemented in terms of the Get_cnt()/Get_ptr()/Set_ptrcnt() methods).

A very complete generic buffering layer which provides the whole of PerlIO API. It is also intended to be used as a "base class" for other layers. (For example its Read() method is implemented in terms of the Get_cnt()/Get_ptr()/Set_ptrcnt() methods). (TBT)

"perlio" over "unix" provides a complete replacement for stdio as seen via PerlIO API. This is the default for USE_PERLIO when system's stdio does not permit perl's "fast gets" access, and which do not distinguish between O_TEXT and O_BINARY.

"perlio" over "unix" provides a complete replacement for stdio as seen via PerlIO API. This is the default for USE_PERLIO when system's stdio does not permit perl's "fast gets" access, and which do not distinguish between O_TEXT and O_BINARY. (TBT)

"stdio"

A layer which provides the PerlIO API via the layer scheme, but implements it by calling system's stdio. This is (currently) the default if system's stdio provides sufficient access to allow perl's "fast gets" access and which do not distinguish between O_TEXT and O_BINARY.

A layer which provides the PerlIO API via the layer scheme, but implements it by calling system's stdio. This is (currently) the default if system's stdio provides sufficient access to allow perl's "fast gets" access and which do not distinguish between O_TEXT and O_BINARY. (TBT)

"crlf"

A layer derived using "perlio" as a base class. It provides Win32-like "\n" to CR,LF translation. Can either be applied above "perlio" or serve as the buffer layer itself. "crlf" over "unix" is the default if system distinguishes between O_TEXT and O_BINARY opens. (At some point "unix" will be replaced by a "native" Win32 IO layer on that platform, as Win32's read/write layer has various drawbacks.) The "crlf" layer is a reasonable model for a layer which transforms data in some way.

A layer derived using "perlio" as a base class. It provides Win32-like "\n" to CR,LF translation. Can either be applied above "perlio" or serve as the buffer layer itself. "crlf" over "unix" is the default if system distinguishes between O_TEXT and O_BINARY opens. (At some point "unix" will be replaced by a "native" Win32 IO layer on that platform, as Win32's read/write layer has various drawbacks.) The "crlf" layer is a reasonable model for a layer which transforms data in some way. (TBT)

"mmap"

If Configure detects mmap() functions this layer is provided (with "perlio" as a "base") which does "read" operations by mmap()ing the file. Performance improvement is marginal on modern systems, so it is mainly there as a proof of concept. It is likely to be unbundled from the core at some point. The "mmap" layer is a reasonable model for a minimalist "derived" layer.

If Configure detects mmap() functions this layer is provided (with "perlio" as a "base") which does "read" operations by mmap()ing the file. Performance improvement is marginal on modern systems, so it is mainly there as a proof of concept. It is likely to be unbundled from the core at some point. The "mmap" layer is a reasonable model for a minimalist "derived" layer. (TBT)

"pending"

An "internal" derivative of "perlio" which can be used to provide Unread() function for layers which have no buffer or cannot be bothered. (Basically this layer's Fill() pops itself off the stack and so resumes reading from layer below.)

An "internal" derivative of "perlio" which can be used to provide Unread() function for layers which have no buffer or cannot be bothered. (Basically this layer's Fill() pops itself off the stack and so resumes reading from layer below.) (TBT)

"raw"

A dummy layer which never exists on the layer stack. Instead when "pushed" it actually pops the stack removing itself, it then calls Binmode function table entry on all the layers in the stack - normally this (via PerlIOBase_binmode) removes any layers which do not have PERLIO_K_RAW bit set. Layers can modify that behaviour by defining their own Binmode entry.

A dummy layer which never exists on the layer stack. Instead when "pushed" it actually pops the stack removing itself, it then calls Binmode function table entry on all the layers in the stack - normally this (via PerlIOBase_binmode) removes any layers which do not have PERLIO_K_RAW bit set. Layers can modify that behaviour by defining their own Binmode entry. (TBT)

"utf8"

Another dummy layer. When pushed it pops itself and sets the PERLIO_F_UTF8 flag on the layer which was (and now is once more) the top of the stack.

Another dummy layer. When pushed it pops itself and sets the PERLIO_F_UTF8 flag on the layer which was (and now is once more) the top of the stack. (TBT)

In addition perlio.c also provides a number of PerlIOBase_xxxx() functions which are intended to be used in the table slots of classes which do not need to do anything special for a particular method.

In addition perlio.c also provides a number of PerlIOBase_xxxx() functions which are intended to be used in the table slots of classes which do not need to do anything special for a particular method. (TBT)

エクステンション層

Layers can made available by extension modules. When an unknown layer is encountered the PerlIO code will perform the equivalent of :

Layers can made available by extension modules. When an unknown layer is encountered the PerlIO code will perform the equivalent of : (TBT)

   use PerlIO 'layer';

Where layer is the unknown layer. PerlIO.pm will then attempt to:

layer が不明な層とします。 PerlIO.pm は以下を試します:

   require PerlIO::layer;

If after that process the layer is still not defined then the open will fail.

If after that process the layer is still not defined then the open will fail. (TBT)

The following extension layers are bundled with perl:

以下のエクステンション層は perl に組み込まれています:

":encoding"
   use Encoding;

makes this layer available, although PerlIO.pm "knows" where to find it. It is an example of a layer which takes an argument as it is called thus:

makes this layer available, although PerlIO.pm "knows" where to find it. It is an example of a layer which takes an argument as it is called thus: (TBT)

   open( $fh, "<:encoding(iso-8859-7)", $pathname );
":scalar"

Provides support for reading data from and writing data to a scalar.

スカラに対するデータの読み書き対応を提供します。

   open( $fh, "+<:scalar", \$scalar );

When a handle is so opened, then reads get bytes from the string value of $scalar, and writes change the value. In both cases the position in $scalar starts as zero but can be altered via seek, and determined via tell.

When a handle is so opened, then reads get bytes from the string value of $scalar, and writes change the value. In both cases the position in $scalar starts as zero but can be altered via seek, and determined via tell. (TBT)

Please note that this layer is implied when calling open() thus:

open() を呼び出すときにこの層が暗示されていることにどうか注意してください; 従って:

   open( $fh, "+<", \$scalar );
":via"

Provided to allow layers to be implemented as Perl code. For instance:

Perl コードとして実装された層を使えるようにします。 例えば:

   use PerlIO::via::StripHTML;
   open( my $fh, "<:via(StripHTML)", "index.html" );

See PerlIO::via for details.

詳しくは PerlIO::via を参照してください。

TODO

Things that need to be done to improve this document.

この文書を改良するために行われる必要のあることです。

  • Explain how to make a valid fh without going through open()(i.e. apply a layer). For example if the file is not opened through perl, but we want to get back a fh, like it was opened by Perl.

    How PerlIO_apply_layera fits in, where its docs, was it made public?

    Currently the example could be something like this:

      PerlIO *foo_to_PerlIO(pTHX_ char *mode, ...)
      {
          char *mode; /* "w", "r", etc */
          const char *layers = ":APR"; /* the layer name */
          PerlIO *f = PerlIO_allocate(aTHX);
          if (!f) {
              return NULL;
          }
    
          PerlIO_apply_layers(aTHX_ f, mode, layers);
    
          if (f) {
              PerlIOAPR *st = PerlIOSelf(f, PerlIOAPR);
              /* fill in the st struct, as in _open() */
              st->file = file;
              PerlIOBase(f)->flags |= PERLIO_F_OPEN;
    
              return f;
          }
          return NULL;
      }
  • fix/add the documentation in places marked as XXX.

  • The handling of errors by the layer is not specified. e.g. when $! should be set explicitly, when the error handling should be just delegated to the top layer.

    Probably give some hints on using SETERRNO() or pointers to where they can be found.

  • I think it would help to give some concrete examples to make it easier to understand the API. Of course I agree that the API has to be concise, but since there is no second document that is more of a guide, I think that it'd make it easier to start with the doc which is an API, but has examples in it in places where things are unclear, to a person who is not a PerlIO guru (yet).