erec: Review erec_print()

A new requirement to erec for the upcoming JSON support is printing
records with file input descriptors without open stream. The approach is
to treat 'name' field as file name, open it, extract the offending line
and close it again.

Further changes to libnftables input parsing routines though have shown
that the whole concept of file pointer reuse in erec is tedious and not
worth keeping:

* Closed files are to be supported as well, so there needs to be
  fallback code for opening the file anyway.

* When input descriptor is duplicated from parser state into an error
  record, the file pointer is copied as well. Therefore care has to be
  taken to not free the parser state before any error records have been
  printed. This is the only point where old and duplicated input
  descriptors are connected.

Therefore drop struct input_descriptor's 'fp' field and just always open
the file by name. This way also the old stream offset doesn't have to be
restored after reading.

While being at it, this patch fixes two other (potential) problems:

* If the offending line from input contains tabs, add them at the right
  position in the marker buffer as well to avoid misalignment.

* The input file may not be seekable (/dev/stdin for instance), so skip
  printing of offending line and markers if it couldn't be read
  properly.

Signed-off-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

3 files changed, 44 insertions, 42 deletions

diff --git a/include/nftables.h b/include/nftables.h
index 75134def..5f2da8b0 100644
--- a/include/nftables.h
+++ b/include/nftables.h
@@ -114,10 +114,7 @@ struct input_descriptor {
 	struct location			location;
 	enum input_descriptor_types	type;
 	const char			*name;
-	union {
-		const char		*data;
-		FILE			*fp;
-	};
+	const char			*data;
 	unsigned int			lineno;
 	unsigned int			column;
 	off_t				token_offset;
diff --git a/src/erec.c b/src/erec.c
index 226c51f5..617c04ad 100644
--- a/src/erec.c
+++ b/src/erec.c
@@ -118,16 +118,12 @@ void erec_print(struct output_ctx *octx, const struct error_record *erec,
 {
 	const struct location *loc = erec->locations, *iloc;
 	const struct input_descriptor *indesc = loc->indesc, *tmp;
-	const char *line = NULL; /* silence gcc */
+	const char *line = NULL;
 	char buf[1024] = {};
 	char *pbuf = NULL;
 	unsigned int i, end;
+	FILE *f;
 	int l;
-	off_t orig_offset = 0;
-	FILE *f = octx->error_fp;
-
-	if (!f)
-		return;
 
 	switch (indesc->type) {
 	case INDESC_BUFFER:
@@ -136,13 +132,16 @@ void erec_print(struct output_ctx *octx, const struct error_record *erec,
 		*strchrnul(line, '\n') = '\0';
 		break;
 	case INDESC_FILE:
-		orig_offset = ftell(indesc->fp);
-		if (orig_offset >= 0 &&
-		    !fseek(indesc->fp, loc->line_offset, SEEK_SET) &&
-		    fread(buf, 1, sizeof(buf) - 1, indesc->fp) > 0 &&
-		    !fseek(indesc->fp, orig_offset, SEEK_SET))
+		f = fopen(indesc->name, "r");
+		if (!f)
+			break;
+
+		if (!fseek(f, loc->line_offset, SEEK_SET) &&
+		    fread(buf, 1, sizeof(buf) - 1, f) > 0) {
 			*strchrnul(buf, '\n') = '\0';
-		line = buf;
+			line = buf;
+		}
+		fclose(f);
 		break;
 	case INDESC_INTERNAL:
 	case INDESC_NETLINK:
@@ -151,6 +150,8 @@ void erec_print(struct output_ctx *octx, const struct error_record *erec,
 		BUG("invalid input descriptor type %u\n", indesc->type);
 	}
 
+	f = octx->error_fp;
+
 	if (indesc->type == INDESC_NETLINK) {
 		fprintf(f, "%s: ", indesc->name);
 		if (error_record_names[erec->type])
@@ -160,32 +161,34 @@ void erec_print(struct output_ctx *octx, const struct error_record *erec,
 			loc = &erec->locations[l];
 			netlink_dump_expr(loc->nle, f, debug_mask);
 		}
-		fprintf(f, "\n");
-	} else {
-		if (indesc->location.indesc != NULL) {
-			const char *prefix = "In file included from";
-			iloc = &indesc->location;
-			for (tmp = iloc->indesc;
-			     tmp != NULL && tmp->type != INDESC_INTERNAL;
-			     tmp = iloc->indesc) {
-				fprintf(f, "%s %s:%u:%u-%u:\n", prefix,
-					tmp->name,
-					iloc->first_line, iloc->first_column,
-					iloc->last_column);
-				prefix = "                 from";
-				iloc = &tmp->location;
-			}
+		fprintf(f, "\n\n");
+		return;
+	}
+
+	if (indesc->location.indesc != NULL) {
+		const char *prefix = "In file included from";
+		iloc = &indesc->location;
+		for (tmp = iloc->indesc;
+		     tmp != NULL && tmp->type != INDESC_INTERNAL;
+		     tmp = iloc->indesc) {
+			fprintf(f, "%s %s:%u:%u-%u:\n", prefix,
+				tmp->name,
+				iloc->first_line, iloc->first_column,
+				iloc->last_column);
+			prefix = "                 from";
+			iloc = &tmp->location;
 		}
-		if (indesc->name != NULL)
-			fprintf(f, "%s:%u:%u-%u: ", indesc->name,
-				loc->first_line, loc->first_column,
-				loc->last_column);
-		if (error_record_names[erec->type])
-			fprintf(f, "%s: ", error_record_names[erec->type]);
-		fprintf(f, "%s\n", erec->msg);
+	}
+	if (indesc->name != NULL)
+		fprintf(f, "%s:%u:%u-%u: ", indesc->name,
+			loc->first_line, loc->first_column,
+			loc->last_column);
+	if (error_record_names[erec->type])
+		fprintf(f, "%s: ", error_record_names[erec->type]);
+	fprintf(f, "%s\n", erec->msg);
 
-		if (indesc->type != INDESC_INTERNAL)
-			fprintf(f, "%s\n", line);
+	if (line) {
+		fprintf(f, "%s\n", line);
 
 		end = 0;
 		for (l = erec->num_locations - 1; l >= 0; l--) {
@@ -194,6 +197,10 @@ void erec_print(struct output_ctx *octx, const struct error_record *erec,
 		}
 		pbuf = xmalloc(end + 1);
 		memset(pbuf, ' ', end + 1);
+		for (i = 0; i < end && line[i]; i++) {
+			if (line[i] == '\t')
+				pbuf[i] = '\t';
+		}
 		for (l = erec->num_locations - 1; l >= 0; l--) {
 			loc = &erec->locations[l];
 			for (i = loc->first_column ? loc->first_column - 1 : 0;
diff --git a/src/scanner.l b/src/scanner.l
index d908a8fe..ba60ec17 100644
--- a/src/scanner.l
+++ b/src/scanner.l
@@ -662,7 +662,6 @@ static struct error_record *scanner_push_file(void *scanner, const char *filenam
 		state->indesc->location = *loc;
 	state->indesc->type	= INDESC_FILE;
 	state->indesc->name	= xstrdup(filename);
-	state->indesc->fp	= f;
 	init_pos(state);
 	return NULL;
 }
@@ -891,7 +890,6 @@ void scanner_destroy(void *scanner)
 		if (inpdesc && inpdesc->name) {
 			xfree(inpdesc->name);
 			inpdesc->name = NULL;
-			fclose(inpdesc->fp);
 		}
 		yypop_buffer_state(scanner);
 	} while (state->indesc_idx--);