perliol.1

视频监控网络部分的协议ddns,的模块的实现代码,请大家大胆指正.

needed a mechanism to allow data to be translated between perl's
internal encoding (conceptually at least Unicode as \s-1UTF\-8\s0), and the
\&\*(L"native\*(R" format used by the system. This is provided by the
\&\*(L":encoding(xxxx)\*(R" layer which typically sits above the buffering layer.
.IP "\(bu" 4
A layer can be added that does \*(L"\en\*(R" to \s-1CRLF\s0 translation. This layer
can be used on any platform, not just those that normally do such
things.
.Sh "Per-instance flag bits"
.IX Subsection "Per-instance flag bits"
The generic flag bits are a hybrid of \f(CW\*(C`O_XXXXX\*(C'\fR style flags deduced
from the mode string passed to \f(CW\*(C`PerlIO_open()\*(C'\fR, and state bits for
typical buffer layers.
.IP "\s-1PERLIO_F_EOF\s0" 4
.IX Item "PERLIO_F_EOF"
End of file.
.IP "\s-1PERLIO_F_CANWRITE\s0" 4
.IX Item "PERLIO_F_CANWRITE"
Writes are permitted, i.e. opened as \*(L"w\*(R" or \*(L"r+\*(R" or \*(L"a\*(R", etc.
.IP "\s-1PERLIO_F_CANREAD\s0" 4
.IX Item "PERLIO_F_CANREAD"
Reads are permitted i.e. opened \*(L"r\*(R" or \*(L"w+\*(R" (or even \*(L"a+\*(R" \- ick).
.IP "\s-1PERLIO_F_ERROR\s0" 4
.IX Item "PERLIO_F_ERROR"
An error has occurred (for \f(CW\*(C`PerlIO_error()\*(C'\fR).
.IP "\s-1PERLIO_F_TRUNCATE\s0" 4
.IX Item "PERLIO_F_TRUNCATE"
Truncate file suggested by open mode.
.IP "\s-1PERLIO_F_APPEND\s0" 4
.IX Item "PERLIO_F_APPEND"
All writes should be appends.
.IP "\s-1PERLIO_F_CRLF\s0" 4
.IX Item "PERLIO_F_CRLF"
Layer is performing Win32\-like \*(L"\en\*(R" mapped to \s-1CR\s0,LF for output and \s-1CR\s0,LF
mapped to \*(L"\en\*(R" for input. Normally the provided \*(L"crlf\*(R" layer is the only
layer that need bother about this. \f(CW\*(C`PerlIO_binmode()\*(C'\fR will mess with this
flag rather than add/remove layers if the \f(CW\*(C`PERLIO_K_CANCRLF\*(C'\fR bit is set
for the layers class.
.IP "\s-1PERLIO_F_UTF8\s0" 4
.IX Item "PERLIO_F_UTF8"
Data written to this layer should be \s-1UTF\-8\s0 encoded; data provided
by this layer should be considered \s-1UTF\-8\s0 encoded. Can be set on any layer
by \*(L":utf8\*(R" dummy layer. Also set on \*(L":encoding\*(R" layer.
.IP "\s-1PERLIO_F_UNBUF\s0" 4
.IX Item "PERLIO_F_UNBUF"
Layer is unbuffered \- i.e. write to next layer down should occur for
each write to this layer.
.IP "\s-1PERLIO_F_WRBUF\s0" 4
.IX Item "PERLIO_F_WRBUF"
The buffer for this layer currently holds data written to it but not sent
to next layer.
.IP "\s-1PERLIO_F_RDBUF\s0" 4
.IX Item "PERLIO_F_RDBUF"
The buffer for this layer currently holds unconsumed data read from
layer below.
.IP "\s-1PERLIO_F_LINEBUF\s0" 4
.IX Item "PERLIO_F_LINEBUF"
Layer is line buffered. Write data should be passed to next layer down
whenever a \*(L"\en\*(R" is seen. Any data beyond the \*(L"\en\*(R" should then be
processed.
.IP "\s-1PERLIO_F_TEMP\s0" 4
.IX Item "PERLIO_F_TEMP"
File has been \f(CW\*(C`unlink()\*(C'\fRed, or should be deleted on \f(CW\*(C`close()\*(C'\fR.
.IP "\s-1PERLIO_F_OPEN\s0" 4
.IX Item "PERLIO_F_OPEN"
Handle is open.
.IP "\s-1PERLIO_F_FASTGETS\s0" 4
.IX Item "PERLIO_F_FASTGETS"
This instance of this layer supports the "fast \f(CW\*(C`gets\*(C'\fR" interface.
Normally set based on \f(CW\*(C`PERLIO_K_FASTGETS\*(C'\fR 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 \*(L"pending\*(R" layer needs to do this when
it is pushed above a layer which does not support the interface.
(Perl's \f(CW\*(C`sv_gets()\*(C'\fR does not expect the streams fast \f(CW\*(C`gets\*(C'\fR behaviour
to change during one \*(L"get\*(R".)
.Sh "Methods in Detail"
.IX Subsection "Methods in Detail"
.IP "fsize" 4
.IX Item "fsize"
.Vb 1
\&        Size_t fsize;
.Ve
.Sp
Size of the function table. This is compared against the value PerlIO
code \*(L"knows\*(R" as a compatibility check. Future versions \fImay\fR be able
to tolerate layers compiled against an old version of the headers.
.IP "name" 4
.IX Item "name"
.Vb 1
\&        char * name;
.Ve
.Sp
The name of the layer whose \fIopen()\fR method Perl should invoke on
\&\fIopen()\fR.  For example if the layer is called \s-1APR\s0, you will call:
.Sp
.Vb 1
\&  open $fh, ">:APR", ...
.Ve
.Sp
and Perl knows that it has to invoke the \fIPerlIOAPR_open()\fR method
implemented by the \s-1APR\s0 layer.
.IP "size" 4
.IX Item "size"
.Vb 1
\&        Size_t size;
.Ve
.Sp
The size of the per-instance data structure, e.g.:
.Sp
.Vb 1
\&  sizeof(PerlIOAPR)
.Ve
.Sp
If this field is zero then \f(CW\*(C`PerlIO_pushed\*(C'\fR 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 \f(CW\*(C`PerlIOl\*(C'\fR,
\&\f(CW\*(C`PerlIO_pushed\*(C'\fR 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.)
.IP "kind" 4
.IX Item "kind"
.Vb 1
\&        IV kind;
.Ve
.RS 4
.IP "\(bu" 4
\&\s-1PERLIO_K_BUFFERED\s0
.Sp
The layer is buffered.
.IP "\(bu" 4
\&\s-1PERLIO_K_RAW\s0
.Sp
The layer is acceptable to have in a binmode(\s-1FH\s0) stack \- i.e. it does not
(or will configure itself not to) transform bytes passing through it.
.IP "\(bu" 4
\&\s-1PERLIO_K_CANCRLF\s0
.Sp
Layer can translate between \*(L"\en\*(R" and \s-1CRLF\s0 line ends.
.IP "\(bu" 4
\&\s-1PERLIO_K_FASTGETS\s0
.Sp
Layer allows buffer snooping.
.IP "\(bu" 4
\&\s-1PERLIO_K_MULTIARG\s0
.Sp
Used when the layer's \fIopen()\fR accepts more arguments than usual. The
extra arguments should come not before the \f(CW\*(C`MODE\*(C'\fR argument. When this
flag is used it's up to the layer to validate the args.
.RE
.RS 4
.RE
.IP "Pushed" 4
.IX Item "Pushed"
.Vb 1
\&        IV      (*Pushed)(pTHX_ PerlIO *f,const char *mode, SV *arg);
.Ve
.Sp
The only absolutely mandatory method. Called when the layer is pushed
onto the stack.  The \f(CW\*(C`mode\*(C'\fR argument may be \s-1NULL\s0 if this occurs
post-open. The \f(CW\*(C`arg\*(C'\fR will be non\-\f(CW\*(C`NULL\*(C'\fR if an argument string was
passed. In most cases this should call \f(CW\*(C`PerlIOBase_pushed()\*(C'\fR to
convert \f(CW\*(C`mode\*(C'\fR into the appropriate \f(CW\*(C`PERLIO_F_XXXXX\*(C'\fR 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 \f(CW\*(C`Getarg()\*(C'\fR (it could perhaps \f(CW\*(C`Perl_warn\*(C'\fR that the argument
was un-expected).
.Sp
Returns 0 on success. On failure returns \-1 and should set errno.
.IP "Popped" 4
.IX Item "Popped"
.Vb 1
\&        IV      (*Popped)(pTHX_ PerlIO *f);
.Ve
.Sp
Called when the layer is popped from the stack. A layer will normally
be popped after \f(CW\*(C`Close()\*(C'\fR is called. But a layer can be popped
without being closed if the program is dynamically managing layers on
the stream. In such cases \f(CW\*(C`Popped()\*(C'\fR should free any resources
(buffers, translation tables, ...) not held directly in the layer's
struct.  It should also \f(CW\*(C`Unread()\*(C'\fR 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.
.Sp
Returns 0 on success and failure.  If \f(CW\*(C`Popped()\*(C'\fR returns \fItrue\fR then
\&\fIperlio.c\fR 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 \fIfalse\fR.
.IP "Open" 4
.IX Item "Open"
.Vb 1
\&        PerlIO *        (*Open)(...);
.Ve
.Sp
The \f(CW\*(C`Open()\*(C'\fR method has lots of arguments because it combines the
functions of perl's \f(CW\*(C`open\*(C'\fR, \f(CW\*(C`PerlIO_open\*(C'\fR, perl's \f(CW\*(C`sysopen\*(C'\fR,
\&\f(CW\*(C`PerlIO_fdopen\*(C'\fR and \f(CW\*(C`PerlIO_reopen\*(C'\fR.  The full prototype is as
follows:
.Sp
.Vb 6
\& PerlIO *       (*Open)(pTHX_ PerlIO_funcs *tab,
\&                        AV *layers, IV n,
\&                        const char *mode,
\&                        int fd, int imode, int perm,
\&                        PerlIO *old,
\&                        int narg, SV **args);
.Ve
.Sp
Open should (perhaps indirectly) call \f(CW\*(C`PerlIO_allocate()\*(C'\fR to allocate
a slot in the table and associate it with the layers information for
the opened file, by calling \f(CW\*(C`PerlIO_push\*(C'\fR.  The \fIlayers\fR \s-1AV\s0 is an
array of all the layers destined for the \f(CW\*(C`PerlIO *\*(C'\fR, and any
arguments passed to them, \fIn\fR is the index into that array of the
layer being called. The macro \f(CW\*(C`PerlIOArg\*(C'\fR will return a (possibly
\&\f(CW\*(C`NULL\*(C'\fR) \s-1SV\s0 * for the argument passed to the layer.
.Sp
The \fImode\fR string is an "\f(CW\*(C`fopen()\*(C'\fR\-like" string which would match
the regular expression \f(CW\*(C`/^[I#]?[rwa]\e+?[bt]?$/\*(C'\fR.
.Sp
The \f(CW\*(AqI\*(Aq\fR prefix is used during creation of \f(CW\*(C`stdin\*(C'\fR..\f(CW\*(C`stderr\*(C'\fR via
special \f(CW\*(C`PerlIO_fdopen\*(C'\fR calls; the \f(CW\*(Aq#\*(Aq\fR prefix means that this is
\&\f(CW\*(C`sysopen\*(C'\fR and that \fIimode\fR and \fIperm\fR should be passed to
\&\f(CW\*(C`PerlLIO_open3\*(C'\fR; \f(CW\*(Aqr\*(Aq\fR means \fBr\fRead, \f(CW\*(Aqw\*(Aq\fR means \fBw\fRrite and
\&\f(CW\*(Aqa\*(Aq\fR means \fBa\fRppend. The \f(CW\*(Aq+\*(Aq\fR suffix means that both reading and
writing/appending are permitted.  The \f(CW\*(Aqb\*(Aq\fR suffix means file should
be binary, and \f(CW\*(Aqt\*(Aq\fR means it is text. (Almost all layers should do
the \s-1IO\s0 in binary mode, and ignore the b/t bits. The \f(CW\*(C`:crlf\*(C'\fR layer
should be pushed to handle the distinction.)
.Sp
If \fIold\fR is not \f(CW\*(C`NULL\*(C'\fR then this is a \f(CW\*(C`PerlIO_reopen\*(C'\fR. Perl itself
does not use this (yet?) and semantics are a little vague.
.Sp
If \fIfd\fR not negative then it is the numeric file descriptor \fIfd\fR,
which will be open in a manner compatible with the supplied mode
string, the call is thus equivalent to \f(CW\*(C`PerlIO_fdopen\*(C'\fR. In this case
\&\fInargs\fR will be zero.
.Sp
If \fInargs\fR is greater than zero then it gives the number of arguments
passed to \f(CW\*(C`open\*(C'\fR, otherwise it will be 1 if for example
\&\f(CW\*(C`PerlIO_open\*(C'\fR was called.  In simple cases SvPV_nolen(*args) is the
pathname to open.
.Sp
Having said all that translation-only layers do not need to provide
\&\f(CW\*(C`Open()\*(C'\fR at all, but rather leave the opening to a lower level layer
and wait to be \*(L"pushed\*(R".  If a layer does provide \f(CW\*(C`Open()\*(C'\fR it should
normally call the \f(CW\*(C`Open()\*(C'\fR method of next layer down (if any) and
then push itself on top if that succeeds.
.Sp
If \f(CW\*(C`PerlIO_push\*(C'\fR was performed and open has failed, it must
\&\f(CW\*(C`PerlIO_pop\*(C'\fR itself, since if it's not, the layer won't be removed
and may cause bad problems.
.Sp
Returns \f(CW\*(C`NULL\*(C'\fR on failure.
.IP "Binmode" 4
.IX Item "Binmode"
.Vb 1
\&        IV        (*Binmode)(pTHX_ PerlIO *f);
.Ve
.Sp
Optional. Used when \f(CW\*(C`:raw\*(C'\fR layer is pushed (explicitly or as a result
of binmode(\s-1FH\s0)). 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 \f(CW\*(C`binmode\*(C'\fR will fail with layer
still on the stack.
.IP "Getarg" 4
.IX Item "Getarg"
.Vb 2
\&        SV *      (*Getarg)(pTHX_ PerlIO *f,
\&                            CLONE_PARAMS *param, int flags);
.Ve
.Sp
Optional. If present should return an \s-1SV\s0 * representing the string
argument passed to the layer when it was
pushed. e.g. \*(L":encoding(ascii)\*(R" would return an SvPV with value
\&\*(L"ascii\*(R". (\fIparam\fR and \fIflags\fR arguments can be ignored in most
cases)
.Sp
\&\f(CW\*(C`Dup\*(C'\fR uses \f(CW\*(C`Getarg\*(C'\fR to retrieve the argument originally passed to
\&\f(CW\*(C`Pushed\*(C'\fR, so you must implement this function if your layer has an
extra argument to \f(CW\*(C`Pushed\*(C'\fR and will ever be \f(CW\*(C`Dup\*(C'\fRed.
.IP "Fileno" 4
.IX Item "Fileno"
.Vb 1
\&        IV        (*Fileno)(pTHX_ PerlIO *f);
.Ve
.Sp
Returns the Unix/Posix numeric file descriptor for the handle. Normally
\&\f(CW\*(C`PerlIOBase_fileno()\*(C'\fR (which just asks next layer down) will suffice
for this.
.Sp
Returns \-1 on error, which is considered to include the case where the
layer cannot provide such a file descriptor.
.IP "Dup" 4
.IX Item "Dup"
.Vb 2
\&        PerlIO * (*Dup)(pTHX_ PerlIO *f, PerlIO *o,
\&                        CLONE_PARAMS *param, int flags);
.Ve
.Sp
\&\s-1XXX:\s0 Needs more docs.
.Sp
Used as part of the \*(L"clone\*(R" process when a thread is spawned (in which
case param will be non-NULL) and when a stream is being duplicated via
\&'&' in the \f(CW\*(C`open\*(C'\fR.
.Sp
Similar to \f(CW\*(C`Open\*(C'\fR, returns PerlIO* on success, \f(CW\*(C`NULL\*(C'\fR on failure.
.IP "Read" 4
.IX Item "Read"
.Vb 1
\&        SSize_t (*Read)(pTHX_ PerlIO *f, void *vbuf, Size_t count);
.Ve
.Sp
Basic read operation.
.Sp
Typically will call \f(CW\*(C`Fill\*(C'\fR and manipulate pointers (possibly via the
\&\s-1API\s0).  \f(CW\*(C`PerlIOBuf_read()\*(C'\fR may be suitable for derived classes which
provide \*(L"fast gets\*(R" methods.
.Sp
Returns actual bytes read, or \-1 on an error.
.IP "Unread" 4
.IX Item "Unread"
.Vb 2
\&        SSize_t (*Unread)(pTHX_ PerlIO *f,
\&                          const void *vbuf, Size_t count);
.Ve
.Sp
A superset of stdio's \f(CW\*(C`ungetc()\*(C'\fR. Should arrange for future reads to
see the bytes in \f(CW\*(C`vbuf\*(C'\fR. If there is no obviously better implementation
then \f(CW\*(C`PerlIOBase_unread()\*(C'\fR provides the function by pushing a \*(L"fake\*(R"
\&\*(L"pending\*(R" layer above the calling layer.
.Sp
Returns the number of unread chars.
.IP "Write" 4
.IX Item "Write"
.Vb 1
\&        SSize_t (*Write)(PerlIO *f, const void *vbuf, Size_t count);
.Ve
.Sp
Basic write operation.
.Sp
Returns bytes written or \-1 on an error.
.IP "Seek" 4
.IX Item "Seek"
.Vb 1
\&        IV      (*Seek)(pTHX_ PerlIO *f, Off_t offset, int whence);
.Ve
.Sp
Position the file pointer. Should normally call its own \f(CW\*(C`Flush\*(C'\fR
method and then the \f(CW\*(C`Seek\*(C'\fR method of next layer down.
.Sp
Returns 0 on success, \-1 on failure.
.IP "Tell" 4
.IX Item "Tell"
.Vb 1
\&        Off_t   (*Tell)(pTHX_ PerlIO *f);
.Ve
.Sp
Return the file pointer. May be based on layers cached concept of
position to avoid overhead.
.Sp
Returns \-1 on failure to get the file pointer.
.IP "Close" 4
.IX Item "Close"
.Vb 1
\&        IV      (*Close)(pTHX_ PerlIO *f);
.Ve
.Sp
Close the stream. Should normally call \f(CW\*(C`PerlIOBase_close()\*(C'\fR to flush
itself and close layers below, and then deallocate any data structures
(buffers, translation tables, ...) not  held directly in the data
structure.
.Sp
Returns 0 on success, \-1 on failure.
.IP "Flush" 4
.IX Item "Flush"
.Vb 1
\&        IV      (*Flush)(pTHX_ PerlIO *f);
.Ve
.Sp
Should make stream's state consistent with layers below. That is, any
buffered write data should be written, and file position of lower layers