Add stream helper library

This library provides thread-unsafe fgets()- and fread()-like
functions where the caller does not have to supply a buffer.  It
maintains a couple of static buffers and provides an API to use
them.

[rr: allow input from files other than stdin]
[jn: with tests, documentation, and error handling improvements]

Signed-off-by: David Barr <david.barr@cordelta.com>
Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

7 files changed, 274 insertions, 2 deletions

diff --git a/.gitignore b/.gitignore
index 9f109db88e..8c0512e03b 100644
--- a/.gitignore
+++ b/.gitignore
@@ -166,6 +166,7 @@
 /test-dump-cache-tree
 /test-genrandom
 /test-index-version
+/test-line-buffer
 /test-match-trees
 /test-obj-pool
 /test-parse-options
diff --git a/Makefile b/Makefile
index 9cb83e1b3e..ea7fc8795d 100644
--- a/Makefile
+++ b/Makefile
@@ -408,6 +408,7 @@ TEST_PROGRAMS_NEED_X += test-date
 TEST_PROGRAMS_NEED_X += test-delta
 TEST_PROGRAMS_NEED_X += test-dump-cache-tree
 TEST_PROGRAMS_NEED_X += test-genrandom
+TEST_PROGRAMS_NEED_X += test-line-buffer
 TEST_PROGRAMS_NEED_X += test-match-trees
 TEST_PROGRAMS_NEED_X += test-obj-pool
 TEST_PROGRAMS_NEED_X += test-parse-options
@@ -1743,7 +1744,7 @@ ifndef NO_CURL
 endif
 XDIFF_OBJS = xdiff/xdiffi.o xdiff/xprepare.o xdiff/xutils.o xdiff/xemit.o \
 	xdiff/xmerge.o xdiff/xpatience.o
-VCSSVN_OBJS = vcs-svn/string_pool.o
+VCSSVN_OBJS = vcs-svn/string_pool.o vcs-svn/line_buffer.o
 OBJECTS := $(GIT_OBJS) $(XDIFF_OBJS) $(VCSSVN_OBJS)
 
 dep_files := $(foreach f,$(OBJECTS),$(dir $f).depend/$(notdir $f).d)
@@ -1868,7 +1869,8 @@ xdiff-interface.o $(XDIFF_OBJS): \
 	xdiff/xutils.h xdiff/xprepare.h xdiff/xdiffi.h xdiff/xemit.h
 
 $(VCSSVN_OBJS): \
-	vcs-svn/obj_pool.h vcs-svn/trp.h vcs-svn/string_pool.h
+	vcs-svn/obj_pool.h vcs-svn/trp.h vcs-svn/string_pool.h \
+	vcs-svn/line_buffer.h
 endif
 
 exec_cmd.s exec_cmd.o: EXTRA_CPPFLAGS = \
@@ -2017,6 +2019,8 @@ test-date$X: date.o ctype.o
 
 test-delta$X: diff-delta.o patch-delta.o
 
+test-line-buffer$X: vcs-svn/lib.a
+
 test-parse-options$X: parse-options.o
 
 test-string-pool$X: vcs-svn/lib.a
diff --git a/t/t0080-vcs-svn.sh b/t/t0080-vcs-svn.sh
index 99a314b080..d3225ada68 100755
--- a/t/t0080-vcs-svn.sh
+++ b/t/t0080-vcs-svn.sh
@@ -76,6 +76,60 @@ test_expect_success 'obj pool: high-water mark' '
 	test_cmp expected actual
 '
 
+test_expect_success 'line buffer' '
+	echo HELLO >expected1 &&
+	printf "%s\n" "" HELLO >expected2 &&
+	echo >expected3 &&
+	printf "%s\n" "" Q | q_to_nul >expected4 &&
+	printf "%s\n" foo "" >expected5 &&
+	printf "%s\n" "" foo >expected6 &&
+
+	test-line-buffer <<-\EOF >actual1 &&
+	5
+	HELLO
+	EOF
+
+	test-line-buffer <<-\EOF >actual2 &&
+	0
+
+	5
+	HELLO
+	EOF
+
+	q_to_nul <<-\EOF |
+	1
+	Q
+	EOF
+	test-line-buffer >actual3 &&
+
+	q_to_nul <<-\EOF |
+	0
+
+	1
+	Q
+	EOF
+	test-line-buffer >actual4 &&
+
+	test-line-buffer <<-\EOF >actual5 &&
+	5
+	foo
+	EOF
+
+	test-line-buffer <<-\EOF >actual6 &&
+	0
+
+	5
+	foo
+	EOF
+
+	test_cmp expected1 actual1 &&
+	test_cmp expected2 actual2 &&
+	test_cmp expected3 actual3 &&
+	test_cmp expected4 actual4 &&
+	test_cmp expected5 actual5 &&
+	test_cmp expected6 actual6
+'
+
 test_expect_success 'string pool' '
 	echo a does not equal b >expected.differ &&
 	echo a equals a >expected.match &&
diff --git a/test-line-buffer.c b/test-line-buffer.c
new file mode 100644
index 0000000000..c11bf7f967
--- /dev/null
+++ b/test-line-buffer.c
@@ -0,0 +1,46 @@
+/*
+ * test-line-buffer.c: code to exercise the svn importer's input helper
+ *
+ * Input format:
+ *	number NL
+ *	(number bytes) NL
+ *	number NL
+ *	...
+ */
+
+#include "git-compat-util.h"
+#include "vcs-svn/line_buffer.h"
+
+static uint32_t strtouint32(const char *s)
+{
+	char *end;
+	uintmax_t n = strtoumax(s, &end, 10);
+	if (*s == '\0' || *end != '\0')
+		die("invalid count: %s", s);
+	return (uint32_t) n;
+}
+
+int main(int argc, char *argv[])
+{
+	char *s;
+
+	if (argc != 1)
+		usage("test-line-buffer < input.txt");
+	if (buffer_init(NULL))
+		die_errno("open error");
+	while ((s = buffer_read_line())) {
+		s = buffer_read_string(strtouint32(s));
+		fputs(s, stdout);
+		fputc('\n', stdout);
+		buffer_skip_bytes(1);
+		if (!(s = buffer_read_line()))
+			break;
+		buffer_copy_bytes(strtouint32(s) + 1);
+	}
+	if (buffer_deinit())
+		die("input error");
+	if (ferror(stdout))
+		die("output error");
+	buffer_reset();
+	return 0;
+}
diff --git a/vcs-svn/line_buffer.c b/vcs-svn/line_buffer.c
new file mode 100644
index 0000000000..1543567093
--- /dev/null
+++ b/vcs-svn/line_buffer.c
@@ -0,0 +1,97 @@
+/*
+ * Licensed under a two-clause BSD-style license.
+ * See LICENSE for details.
+ */
+
+#include "git-compat-util.h"
+#include "line_buffer.h"
+#include "obj_pool.h"
+
+#define LINE_BUFFER_LEN 10000
+#define COPY_BUFFER_LEN 4096
+
+/* Create memory pool for char sequence of known length */
+obj_pool_gen(blob, char, 4096)
+
+static char line_buffer[LINE_BUFFER_LEN];
+static char byte_buffer[COPY_BUFFER_LEN];
+static FILE *infile;
+
+int buffer_init(const char *filename)
+{
+	infile = filename ? fopen(filename, "r") : stdin;
+	if (!infile)
+		return -1;
+	return 0;
+}
+
+int buffer_deinit(void)
+{
+	int err;
+	if (infile == stdin)
+		return ferror(infile);
+	err = ferror(infile);
+	err |= fclose(infile);
+	return err;
+}
+
+/* Read a line without trailing newline. */
+char *buffer_read_line(void)
+{
+	char *end;
+	if (!fgets(line_buffer, sizeof(line_buffer), infile))
+		/* Error or data exhausted. */
+		return NULL;
+	end = line_buffer + strlen(line_buffer);
+	if (end[-1] == '\n')
+		end[-1] = '\0';
+	else if (feof(infile))
+		; /* No newline at end of file.  That's fine. */
+	else
+		/*
+		 * Line was too long.
+		 * There is probably a saner way to deal with this,
+		 * but for now let's return an error.
+		 */
+		return NULL;
+	return line_buffer;
+}
+
+char *buffer_read_string(uint32_t len)
+{
+	char *s;
+	blob_free(blob_pool.size);
+	s = blob_pointer(blob_alloc(len + 1));
+	s[fread(s, 1, len, infile)] = '\0';
+	return ferror(infile) ? NULL : s;
+}
+
+void buffer_copy_bytes(uint32_t len)
+{
+	uint32_t in;
+	while (len > 0 && !feof(infile) && !ferror(infile)) {
+		in = len < COPY_BUFFER_LEN ? len : COPY_BUFFER_LEN;
+		in = fread(byte_buffer, 1, in, infile);
+		len -= in;
+		fwrite(byte_buffer, 1, in, stdout);
+		if (ferror(stdout)) {
+			buffer_skip_bytes(len);
+			return;
+		}
+	}
+}
+
+void buffer_skip_bytes(uint32_t len)
+{
+	uint32_t in;
+	while (len > 0 && !feof(infile) && !ferror(infile)) {
+		in = len < COPY_BUFFER_LEN ? len : COPY_BUFFER_LEN;
+		in = fread(byte_buffer, 1, in, infile);
+		len -= in;
+	}
+}
+
+void buffer_reset(void)
+{
+	blob_reset();
+}
diff --git a/vcs-svn/line_buffer.h b/vcs-svn/line_buffer.h
new file mode 100644
index 0000000000..9c78ae11a1
--- /dev/null
+++ b/vcs-svn/line_buffer.h
@@ -0,0 +1,12 @@
+#ifndef LINE_BUFFER_H_
+#define LINE_BUFFER_H_
+
+int buffer_init(const char *filename);
+int buffer_deinit(void);
+char *buffer_read_line(void);
+char *buffer_read_string(uint32_t len);
+void buffer_copy_bytes(uint32_t len);
+void buffer_skip_bytes(uint32_t len);
+void buffer_reset(void);
+
+#endif
diff --git a/vcs-svn/line_buffer.txt b/vcs-svn/line_buffer.txt
new file mode 100644
index 0000000000..8906fb1f50
--- /dev/null
+++ b/vcs-svn/line_buffer.txt
@@ -0,0 +1,58 @@
+line_buffer API
+===============
+
+The line_buffer library provides a convenient interface for
+mostly-line-oriented input.
+
+Each line is not permitted to exceed 10000 bytes.  The provided
+functions are not thread-safe or async-signal-safe, and like
+`fgets()`, they generally do not function correctly if interrupted
+by a signal without SA_RESTART set.
+
+Calling sequence
+----------------
+
+The calling program:
+
+ - specifies a file to read with `buffer_init`
+ - processes input with `buffer_read_line`, `buffer_read_string`,
+   `buffer_skip_bytes`, and `buffer_copy_bytes`
+ - closes the file with `buffer_deinit`, perhaps to start over and
+   read another file.
+
+Before exiting, the caller can use `buffer_reset` to deallocate
+resources for the benefit of profiling tools.
+
+Functions
+---------
+
+`buffer_init`::
+	Open the named file for input.  If filename is NULL,
+	start reading from stdin.  On failure, returns -1 (with
+	errno indicating the nature of the failure).
+
+`buffer_deinit`::
+	Stop reading from the current file (closing it unless
+	it was stdin).  Returns nonzero if `fclose` fails or
+	the error indicator was set.
+
+`buffer_read_line`::
+	Read a line and strip off the trailing newline.
+	On failure or end of file, returns NULL.
+
+`buffer_read_string`::
+	Read `len` characters of input or up to the end of the
+	file, whichever comes first.  Returns NULL on error.
+	Returns whatever characters were read (possibly "")
+	for end of file.
+
+`buffer_copy_bytes`::
+	Read `len` bytes of input and dump them to the standard output
+	stream.  Returns early for error or end of file.
+
+`buffer_skip_bytes`::
+	Discards `len` bytes from the input stream (stopping early
+	if necessary because of an error or eof).
+
+`buffer_reset`::
+	Deallocates non-static buffers.