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Add Get_Line function #213

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5e10e79
refactor: extract Populate_Buffer for file input
atalii Jun 9, 2025
37dbc5f
feat: implement Get_Line
atalii Jun 30, 2025
fe46d16
feat: allow Get_Line to keep or ignore terminators
atalii Jun 30, 2025
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206 changes: 162 additions & 44 deletions source/streams/implementation/vss-text_streams-file_input.adb
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Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,7 @@ pragma Ada_2022;
with Ada.Streams;
with Interfaces.C;

with VSS.Characters.Latin;
with VSS.Strings.Character_Iterators;
with VSS.Strings.Conversions;
with VSS.Strings.Formatters.Strings;
Expand Down Expand Up @@ -66,51 +67,11 @@ package body VSS.Text_Streams.File_Input is
Item : out VSS.Characters.Virtual_Character'Base;
Success : in out Boolean) is
begin
if Self.Buffer.Is_Empty then
if Self.Stream = Interfaces.C_Streams.NULL_Stream then
Self.Error := "File is not open";
Item := VSS.Characters.Virtual_Character'Base'Last;
Success := False;

return;
end if;

declare
use type Ada.Streams.Stream_Element_Offset;
use type Interfaces.C_Streams.size_t;

Data : Ada.Streams.Stream_Element_Array (1 .. 128);
Size : Interfaces.C_Streams.size_t;

begin
Size :=
Interfaces.C_Streams.fread
(Data (Data'First)'Address, 0, 1, Data'Length, Self.Stream);

if Size /= 0 then
-- Some data has been read, decode it.

Self.Buffer :=
Self.Decoder.Decode
(Data
(Data'First
.. Data'First
+ Ada.Streams.Stream_Element_Offset (Size) - 1),
False);

elsif Interfaces.C_Streams.feof (Self.Stream) /= 0 then
-- End of file has been reached, let decoder know that no more
-- data available. Decoder will return REPLACEMENT CHARACTER
-- if some data has beed accumulated but can't be decoded.

Self.Buffer :=
Self.Decoder.Decode
(Data (Data'First .. Data'First - 1), True);
Self.Populate_Buffer (Success);

elsif Interfaces.C_Streams.ferror (Self.Stream) /= 0 then
Self.Error := "File IO error";
end if;
end;
if not Success then
Item := VSS.Characters.Virtual_Character'Base'Last;
return;
end if;

if Self.Buffer.Is_Empty then
Expand All @@ -131,6 +92,106 @@ package body VSS.Text_Streams.File_Input is
end if;
end Get;

--------------
-- Get_Line --
--------------

procedure Get_Line
(Self : in out File_Input_Text_Stream'Class;
Line : out VSS.Strings.Virtual_String'Class;
Success : out Boolean;
Terminators : VSS.Strings.Line_Terminator_Set :=
VSS.Strings.New_Line_Function;
Keep_Terminator : Boolean := True)
is

use VSS.Characters.Latin;
use VSS.Strings;

use type VSS.Characters.Virtual_Character;

procedure Terminate_Line;
procedure Read_Char;

Char : VSS.Characters.Virtual_Character;
Line_Staging : Virtual_String'Class := "";

procedure Read_Char is
begin
Get (Self, Char, Success);
if not Success then
return;
end if;

-- Go ahead and refill the buffer in case we need lookahead. Later
-- on, this will disambiguate the cases of an empty buffer or EOF.
if Self.Buffer.Is_Empty then
Self.Populate_Buffer (Success);
if not Success then
return;
end if;
end if;

Line_Staging := Line_Staging & Char; -- GNAT complains about @ here.
end Read_Char;

procedure Terminate_Line
is
LF_Prefix : constant VSS.Strings.Virtual_String := "" & Line_Feed;
begin

-- Only one case can be ambiguous, and that's when both CR ∈
-- Terminators and CRLF ∈ Terminators. Because we only read one
-- character at a time, we'll see Char = CR and at least one byte
-- avaliable to read when facing this case, and we'll go on to
-- check lookahead.
if Char /= Carriage_Return or else
Self.Buffer.Is_Empty or else
not Terminators (CR) or else
not Terminators (CRLF)
then
return;
end if;

if Self.Buffer.Starts_With (LF_Prefix) then
Read_Char;
end if;

end Terminate_Line;

begin

-- We read the line one character at a time, noting and resolving the
-- ambiguity of CRLF and CR both being potentially acceptable line
-- endings by looking ahead when CR portends to end a line on its own.

loop
Read_Char;
exit when not Success;

if Line_Staging.Ends_With (Terminators) then
Terminate_Line;
if Keep_Terminator then
Line := Line_Staging;
end if;

return;
end if;

-- Only always copy the additions over to the output when we've
-- verified that we haven't just read in a terminator.
Line := Line_Staging;

-- Check whether we're at the end of the file. If this is the case,
-- then the buffer will be empty via Read_Char.
if Self.Buffer.Is_Empty then
return;
end if;

end loop;

end Get_Line;

---------------
-- Has_Error --
---------------
Expand Down Expand Up @@ -227,6 +288,63 @@ package body VSS.Text_Streams.File_Input is
end if;
end Open;

---------------------
-- Populate_Buffer --
---------------------

procedure Populate_Buffer
(Self : in out File_Input_Text_Stream;
Success : out Boolean) is
begin
if Self.Buffer.Is_Empty then
if Self.Stream = Interfaces.C_Streams.NULL_Stream then
Self.Error := "File is not open";
Success := False;

return;
end if;

declare
use type Ada.Streams.Stream_Element_Offset;
use type Interfaces.C_Streams.size_t;

Data : Ada.Streams.Stream_Element_Array (1 .. 128);
Size : Interfaces.C_Streams.size_t;

begin
Size :=
Interfaces.C_Streams.fread
(Data (Data'First)'Address, 0, 1, Data'Length, Self.Stream);

if Size /= 0 then
-- Some data has been read, decode it.

Self.Buffer :=
Self.Decoder.Decode
(Data
(Data'First
.. Data'First
+ Ada.Streams.Stream_Element_Offset (Size) - 1),
False);

elsif Interfaces.C_Streams.feof (Self.Stream) /= 0 then
-- End of file has been reached, let decoder know that no more
-- data available. Decoder will return REPLACEMENT CHARACTER
-- if some data has beed accumulated but can't be decoded.

Self.Buffer :=
Self.Decoder.Decode
(Data (Data'First .. Data'First - 1), True);

elsif Interfaces.C_Streams.ferror (Self.Stream) /= 0 then
Self.Error := "File IO error";
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Should Success be set to False here?

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You're probably right, though this is just moved code from what's already in the repo. To be honest, I'm not sure if this is the way it is for a reason that I'm missing, or if it ought to be fixed.

end if;
end;
end if;

Success := True;
end Populate_Buffer;

------------------
-- Set_Encoding --
------------------
Expand Down
12 changes: 12 additions & 0 deletions source/streams/vss-text_streams-file_input.ads
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Original file line number Diff line number Diff line change
Expand Up @@ -33,6 +33,14 @@ package VSS.Text_Streams.File_Input is
-- Sets encoding of the data to be used to load information from the file.
-- Encoding can be set only when file is not open.

procedure Get_Line
(Self : in out File_Input_Text_Stream'Class;
Line : out VSS.Strings.Virtual_String'Class;
Success : out Boolean;
Terminators : VSS.Strings.Line_Terminator_Set :=
VSS.Strings.New_Line_Function;
Keep_Terminator : Boolean := True);

procedure Close (Self : in out File_Input_Text_Stream'Class);
-- Close file.

Expand Down Expand Up @@ -67,4 +75,8 @@ private
overriding function Error_Message
(Self : File_Input_Text_Stream) return VSS.Strings.Virtual_String;

procedure Populate_Buffer
(Self : in out File_Input_Text_Stream;
Success : out Boolean);

end VSS.Text_Streams.File_Input;
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