[pmc] add missing StringHandle methods

Similar to the FileHandle PMC: tell, seek, peek.
Add more error handling to StringHandle->seek (out of bounds)
Add testcase t/pmc/stringhandle_26

Fixes GH #1011

src/io/stringhandle.c

@@ -400,7 +400,10 @@ io_stringhandle_seek(PARROT_INTERP, ARGMOD(PMC *handle), const PIOOFF_T offset,
     INTVAL old_offs;
     STRING *stringhandle;
     INTVAL read_offs = 0;
-    /* TODO: Need more error checking */
+    INTVAL buffer_size;
+    GETATTR_StringHandle_stringhandle(interp, handle, stringhandle);
+    buffer_size = stringhandle->_buflen;
+
     switch (whence) {
         case SEEK_SET:
             /* Absolute seek, start from the beginning of the string */
@@ -420,6 +423,9 @@ io_stringhandle_seek(PARROT_INTERP, ARGMOD(PMC *handle), const PIOOFF_T offset,
             Parrot_ex_throw_from_c_args(interp, NULL, EXCEPTION_PIO_ERROR,
                 "Cannot seek with mode %d", whence);
     }
+    if (read_offs < 0 || read_offs >= buffer_size)
+        Parrot_ex_throw_from_c_args(interp, NULL, EXCEPTION_PIO_ERROR,
+                "seek to %ld out of bounds", read_offs);
     SETATTR_StringHandle_read_offset(interp, handle, read_offs);
     return (PIOOFF_T)read_offs;
 }

src/pmc/stringhandle.pmc

@@ -1,5 +1,5 @@
 /*
-Copyright (C) 2008-2014, Parrot Foundation.
+Copyright (C) 2008-2016, Parrot Foundation.
 
 =head1 NAME
 
@@ -152,7 +152,7 @@ Mark active stringhandle data as live.
 
 =item C<INTVAL get_bool()>
 
-Returns whether the StringHandle has reached the end of the file.
+Returns whether the StringHandle has reached the end of the buffer.
 
 =cut
 
@@ -390,6 +390,61 @@ string data).
         RETURN(INTVAL 0);
     }
 
+/*
+
+=item C<METHOD tell()>
+
+Get the current position in the stream. 2 C<INTVAL>s are returned. The first is
+the position. The second is the position shifted down by 32 bits to handle
+overflows on 32-bit systems.
+
+=cut
+
+*/
+
+    METHOD tell() :no_wb {
+        PIOOFF_T pos;
+        GET_ATTR_read_offset(INTERP, SELF, pos);
+        RETURN(INTVAL pos, INTVAL pos>>32);
+    }
+
+/*
+
+=item C<METHOD seek(INTVAL whence, INTVAL offs, INTVAL offs_overflow)>
+
+Set the position to an offset specified by C<offs> (and optionally
+C<offs_overflow>). C<whence> determines from where in the buffer the
+offset is taken.
+
+ Whence Value      Meaning
+ 0                 Seek from the beginning of the buffer
+ 1                 Seek from the current position
+ 2                 Seek from the end of the buffer
+
+=cut
+
+*/
+
+    METHOD seek(INTVAL whence, INTVAL offs) {
+        IO_VTABLE * vtable;
+        GETATTR_StringHandle_io_vtable(INTERP, SELF, vtable);
+        vtable->seek(INTERP, SELF, offs, whence);
+    }
+
+/*
+
+=item C<METHOD peek()>
+
+Returns the next byte from the stream, but does not remove it.
+
+=cut
+
+*/
+
+    METHOD peek() :no_wb {
+        STRING * const s = Parrot_io_peek(INTERP, SELF);
+        RETURN(STRING* s);
+    }
 
 /*
 

t/pmc/stringhandle.t

@@ -1,12 +1,12 @@
 #!perl
-# Copyright (C) 2006-2010, Parrot Foundation.
+# Copyright (C) 2006-2016, Parrot Foundation.
 
 use strict;
 use warnings;
 use lib qw( . lib ../lib ../../lib );
 
 use Test::More;
-use Parrot::Test tests => 25;
+use Parrot::Test tests => 26;
 
 =head1 NAME
 
@@ -720,6 +720,53 @@ CODE
 ok
 OUTPUT
 
+# GH 1011 FileHandle analog methods
+pir_output_is( <<'CODE', <<"OUTPUT", "seek/tell/peek stringhandle" );
+.sub 'main' :main
+    .local pmc ifh
+    ifh = new ['StringHandle']
+    ifh.'encoding'('utf8')
+    ifh.'open'('README.pod', 'rw')
+    ifh.'puts'('# Copyright (C) 2001-2014, Parrot Foundation.')
+
+    ifh.'seek'(0, 27)
+    $S0 = ifh.'read'(17)
+    if $S0 == 'Parrot Foundation' goto ok_1
+    print 'not '
+    print $S0
+  ok_1:
+    say 'ok 1 - seek 0,28'
+
+    $I0 = ifh.'tell'()
+    if $I0 == 45 goto ok_2
+    print 'not '
+    print $I0
+  ok_2:
+    say 'ok 2 - tell'
+
+    $S0 = ifh.'peek'() # one byte
+    if $S0 == '.' goto ok_3
+    print 'not '
+    print $S0
+  ok_3:
+    say 'ok 3 - peek value'
+
+    $I0 = ifh.'tell'()
+    if $I0 == 45 goto ok_4
+    print 'not '
+    print $I0
+  ok_4:
+    say 'ok 4 - peek does not advance'
+    ifh.'close'()
+.end
+CODE
+ok 1 - seek 0,28
+ok 2 - tell
+ok 3 - peek value
+ok 4 - peek does not advance
+OUTPUT
+
+
 # GH #465
 # L<PDD22/I\/O PMC API/=item get_fd>
 # NOTES: this is going to be platform dependent