add fgetline(3) implementation

Makefile

@@ -6,7 +6,8 @@ LIBIFUPDOWN_SRC = \
 	libifupdown/list.c \
 	libifupdown/dict.c \
 	libifupdown/interface.c \
-	libifupdown/interface-file.c
+	libifupdown/interface-file.c \
+	libifupdown/fgetline.c
 
 LIBIFUPDOWN_OBJ = ${LIBIFUPDOWN_SRC:.c=.o}
 LIBIFUPDOWN_LIB = libifupdown.a

libifupdown/fgetline.c

@@ -0,0 +1,123 @@
+/*
+ * libifupdown/fgetline.c
+ * Purpose: portable fgetline(3)
+ *
+ * Copyright (c) 2020 Ariadne Conill <ariadne@dereferenced.org>
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * This software is provided 'as is' and without any warranty, express or
+ * implied.  In no event shall the authors be liable for any damages arising
+ * from the use of this software.
+ */
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdio.h>
+#include "libifupdown/fgetline.h"
+
+char *
+lif_fgetline(char *line, size_t size, FILE *stream)
+{
+	char *s = line;
+	char *end = line + size - 2;
+	bool quoted = false;
+	int c = '\0', c2;
+
+	if (s == NULL)
+		return NULL;
+
+	while (s < end && (c = getc(stream)) != EOF)
+	{
+		if (c == '\\' && !quoted)
+		{
+			quoted = true;
+			continue;
+		}
+		else if (c == '#')
+		{
+			if (!quoted) {
+				/* Skip the rest of the line */
+				do {
+					c = getc(stream);
+				} while (c != '\n' && c != EOF);
+				*s++ = c;
+				break;
+			}
+			quoted = false;
+			continue;
+		}
+		else if (c == '\n')
+		{
+			if (quoted)
+			{
+				/* Trim spaces */
+				do {
+					c2 = getc(stream);
+				} while (c2 == '\t' || c2 == ' ');
+
+				ungetc(c2, stream);
+
+				quoted = false;
+				continue;
+			}
+			else
+			{
+				*s++ = c;
+			}
+
+			break;
+		}
+		else if (c == '\r')
+		{
+			*s++ = '\n';
+
+			if ((c2 = getc(stream)) == '\n')
+			{
+				if (quoted)
+				{
+					quoted = false;
+					continue;
+				}
+
+				break;
+			}
+
+			ungetc(c2, stream);
+
+			if (quoted)
+			{
+				quoted = false;
+				continue;
+			}
+
+			break;
+		}
+		else
+		{
+			if (quoted) {
+				*s++ = '\\';
+				quoted = false;
+			}
+			*s++ = c;
+		}
+
+	}
+
+	if (c == EOF && (s == line || ferror(stream)))
+		return NULL;
+
+	*s = '\0';
+
+	/* Remove newline character. */
+	if (s > line && *(--s) == '\n') {
+		*s = '\0';
+
+		if (s > line && *(--s) == '\r')
+			*s = '\0';
+	}
+
+	return line;
+}

libifupdown/fgetline.h

@@ -0,0 +1,25 @@
+/*
+ * libifupdown/fgetline.h
+ * Purpose: portable fgetline(3)
+ *
+ * Copyright (c) 2020 Ariadne Conill <ariadne@dereferenced.org>
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * This software is provided 'as is' and without any warranty, express or
+ * implied.  In no event shall the authors be liable for any damages arising
+ * from the use of this software.
+ */
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdio.h>
+
+#ifndef LIBIFUPDOWN_FGETLINE_H__GUARD
+#define LIBIFUPDOWN_FGETLINE_H__GUARD
+
+extern char *lif_fgetline(char *line, size_t size, FILE *stream);
+
+#endif

libifupdown/libifupdown.h

@@ -20,5 +20,6 @@
 #include "libifupdown/dict.h"
 #include "libifupdown/interface.h"
 #include "libifupdown/interface-file.h"
+#include "libifupdown/fgetline.h"
 
 #endif