io.ports: stream-seekable? and stream-length

io.files.windows, io.backend.unix: platform-specific backends for those methods

basis/io/backend/unix/unix.factor

@@ -2,11 +2,12 @@
 ! See http://factorcode.org/license.txt for BSD license.
 USING: alien alien.c-types alien.data alien.syntax generic
 assocs kernel kernel.private math io.ports sequences strings
-sbufs threads unix unix.ffi vectors io.buffers io.backend
+sbufs threads unix unix.ffi unix.stat vectors io.buffers io.backend
 io.encodings math.parser continuations system libc namespaces
 make io.timeouts io.encodings.utf8 destructors
 destructors.private accessors summary combinators locals
-unix.time unix.types fry io.backend.unix.multiplexers ;
+unix.time unix.types fry io.backend.unix.multiplexers
+classes.struct ;
 QUALIFIED: io
 IN: io.backend.unix
 
@@ -57,6 +58,12 @@ M: unix seek-handle ( n seek-type handle -- )
     } case
     [ fd>> swap ] dip [ lseek ] unix-system-call drop ;
 
+M: unix can-seek-handle? ( handle -- ? )
+    fd>> SEEK_CUR 0 lseek -1 = not ;
+M: unix handle-length ( handle -- n/f )
+    fd>> \ stat <struct> [ fstat -1 = not ] keep
+    swap [ st_size>> ] [ drop f ] if ;
+
 SYMBOL: +retry+ ! just try the operation again without blocking
 SYMBOL: +input+
 SYMBOL: +output+

basis/io/files/windows/windows.factor

@@ -151,6 +151,12 @@ M: windows seek-handle ( n seek-type handle -- )
         [ bad-seek-type ]
     } case ;
 
+M: windows can-seek-handle? ( handle -- ? )
+    handle>file-size zero? not ;
+
+M: windows handle-length ( handle -- n/f )
+    handle>file-size [ f ] when-zero ;
+
 : file-error? ( n -- eof? )
     zero? [
         GetLastError {

basis/io/ports/ports.factor

@@ -143,18 +143,21 @@ HOOK: (wait-to-write) io-backend ( port -- )
     dup buffer>> buffer-empty?
     [ drop ] [ dup (wait-to-write) port-flush ] if ;
 
-M: output-port stream-flush ( port -- )
+M: output-port stream-flush
     [ check-disposed ] [ port-flush ] bi ;
 
 HOOK: tell-handle os ( handle -- n )
 
 HOOK: seek-handle os ( n seek-type handle -- )
 
-M: input-port stream-tell ( stream -- n )
+HOOK: can-seek-handle? os ( handle -- ? )
+HOOK: handle-length os ( handle -- n/f )
+
+M: input-port stream-tell
     [ check-disposed ]
     [ [ handle>> tell-handle ] [ buffer>> buffer-length ] bi - ] bi ;
 
-M: output-port stream-tell ( stream -- n )
+M: output-port stream-tell
     [ check-disposed ]
     [ [ handle>> tell-handle ] [ buffer>> buffer-length ] bi + ] bi ;
 
@@ -165,18 +168,28 @@ M: output-port stream-tell ( stream -- n )
     [ n stream stream-tell + seek-absolute ] [ n seek-type ] if
     stream ;
 
-M: input-port stream-seek ( n seek-type stream -- )
+M: input-port stream-seek
     do-seek-relative
     [ check-disposed ]
     [ buffer>> 0 swap buffer-reset ]
     [ handle>> seek-handle ] tri ;
 
-M: output-port stream-seek ( n seek-type stream -- )
+M: output-port stream-seek
     do-seek-relative
     [ check-disposed ]
     [ stream-flush ]
     [ handle>> seek-handle ] tri ;
 
+M: input-port stream-seekable?
+    handle>> can-seek-handle? ;
+M: output-port stream-seekable?
+    handle>> can-seek-handle? ;
+
+M: input-port stream-length
+    handle>> handle-length ;
+M: output-port stream-length
+    handle>> handle-length ;
+
 GENERIC: shutdown ( handle -- )
 
 M: object shutdown drop ;