* libguile/ports-internal.h (struct scm_port_internal): Add new members
'at_stream_start_for_bom_read' and 'at_stream_start_for_bom_write'.
(SCM_UNICODE_BOM): New macro.
(scm_i_port_iconv_descriptors): Add 'mode' parameter to prototype.
* libguile/ports.c (scm_new_port_table_entry): Initialize
'at_stream_start_for_bom_read' and 'at_stream_start_for_bom_write'.
(get_iconv_codepoint): Pass new 'mode' parameter to
'scm_i_port_iconv_descriptors'.
(get_codepoint): After reading a codepoint at stream start, record
that we're no longer at stream start, and consume a BOM where
appropriate.
(scm_seek): Set the stream start flags according to the new position.
(looking_at_bytes): New static function.
(scm_utf8_bom, scm_utf16be_bom, scm_utf16le_bom, scm_utf32be_bom,
scm_utf32le_bom): New static const arrays.
(decide_utf16_encoding, decide_utf32_encoding): New static functions.
(scm_i_port_iconv_descriptors): Add new 'mode' parameter. If the
specified encoding is UTF-16 or UTF-32, make that precise by deciding
what byte order to use, and construct iconv descriptors based on the
precise encoding.
(scm_i_set_port_encoding_x): Record that we are now at stream start.
Do not open the new iconv descriptors immediately; let them be
initialized lazily.
* libguile/print.c (display_string_using_iconv): Record that we're no
longer at stream start. Write a BOM if appropriate.
* doc/ref/api-io.texi (BOM Handling): New node.
* test-suite/tests/ports.test ("set-port-encoding!, wrong encoding"):
Adapt test to cope with the fact that 'set-port-encoding!' does not
immediately open the iconv descriptors.
(bv-read-test): New procedure.
("unicode byte-order marks (BOMs)"): New test prefix.
* libguile/ports-internal.h (struct scm_port_internal): Add 'alist'
member.
* libguile/ports.c (scm_i_port_alist, scm_i_set_port_alist_x): New
internal functions.
(scm_i_port_weak_hash): Update comment: the hash table is no longer
used to store the port's alist.
(scm_new_port_table_entry): Initialize 'alist'. Store SCM_BOOL_F in
the port weak hash, not SCM_EOL.
* libguile/ports.h (scm_i_port_alist, scm_i_set_port_alist_x): Add
protoypes.
* libguile/read.c (set_port_read_option, init_read_options): Access the
port's alist via 'scm_i_port_alist' and 'scm_i_set_port_alist_x'.
Based on 6c98257f2e by Andy Wingo.
* libguile/ports-internal.h (struct scm_port_internal): Add a flag
for the port encoding mode: UTF8 or iconv. The iconv descriptors
are now in a separate structure so that we can avoid attaching
finalizers to the ports themselves in the future.
(enum scm_port_encoding_mode): New enum.
(struct scm_iconv_descriptors): New struct.
(scm_i_port_iconv_descriptors): Add prototype.
* libguile/ports.c (finalize_port): Don't close iconv descriptors here.
(scm_new_port_table_entry): Adapt to the iconv descriptors being
moved. Initialize 'encoding_mode'.
(scm_i_remove_port): Adapt to call 'close_iconv_descriptors'.
(close_iconv_descriptors): New static function.
(get_iconv_codepoint): Use 'scm_i_port_iconv_descriptors'.
(get_codepoint): Check the port 'encoding_mode'.
(finalize_iconv_descriptors, open_iconv_descriptors,
close_iconv_descriptors, scm_i_port_iconv_descriptors): New static
functions.
(scm_i_set_port_encoding_x): Adapt to iconv descriptors being moved
to separate structure, to set the 'encoding_mode' flag, and to use
'open_iconv_descriptors' and 'close_iconv_descriptors'.
* libguile/print.c (display_string_using_iconv): Use
'scm_i_port_iconv_descriptors'.
(display_string): Use 'encoding_mode' flag.
* libguile/ports-internal.h: New file.
* libguile/Makefile.am (noinst_HEADERS): Add ports-internal.h.
* libguile/ports.h (scm_t_port): Add a comment mentioning that the
'input_cd' and 'output_cd' fields of the public structure are no
longer what they seem to be.
* libguile/ports.c: Include ports-internal.h.
(finalize_port, scm_i_remove_port, get_iconv_codepoint, get_codepoint,
scm_i_set_port_encoding_x): Access 'input_cd' and 'output_cd' via the
new internal port structure.
(scm_new_port_table_entry): Allocate and initialize the internal port
structure.
* libguile/print.c: Include ports-internal.h.
(display_string_using_iconv, display_string): Access 'input_cd' and
'output_cd' via 'internal' pointer.
