vcs-svn: add binary-safe read function

buffer_read_string works well for non line-oriented input except for
one problem: it does not tell the caller how many bytes were actually
written.  This means that unless one is very careful about checking
for errors (and eof) the calling program cannot tell the difference
between the string "foo" followed by an early end of file and the
string "foo\0bar\0baz".

So introduce a variant that reports the length, too, a thinner wrapper
around strbuf_fread.  Its result is written to a strbuf so the caller
does not need to keep track of the number of bytes read.

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>

t/t0081-line-buffer.sh

@@ -151,6 +151,15 @@ test_expect_success 'skip, copy null byte' '
 	test_cmp expect actual
 '
 
+test_expect_success 'read null byte' '
+	echo ">QhelloQ" | q_to_nul >expect &&
+	q_to_nul <<-\EOF | test-line-buffer >actual &&
+	binary 8
+	QhelloQ
+	EOF
+	test_cmp expect actual
+'
+
 test_expect_success 'long reads are truncated' '
 	echo foo >expect &&
 	test-line-buffer <<-\EOF >actual &&
@@ -171,4 +180,13 @@ test_expect_success 'long copies are truncated' '
 	test_cmp expect actual
 '
 
+test_expect_success 'long binary reads are truncated' '
+	echo ">foo" >expect &&
+	test-line-buffer <<-\EOF >actual &&
+	binary 5
+	foo
+	EOF
+	test_cmp expect actual
+'
+
 test_done

test-line-buffer.c

@@ -3,6 +3,7 @@
  */
 
 #include "git-compat-util.h"
+#include "strbuf.h"
 #include "vcs-svn/line_buffer.h"
 
 static uint32_t strtouint32(const char *s)
@@ -17,6 +18,15 @@ static uint32_t strtouint32(const char *s)
 static void handle_command(const char *command, const char *arg, struct line_buffer *buf)
 {
 	switch (*command) {
+	case 'b':
+		if (!prefixcmp(command, "binary ")) {
+			struct strbuf sb = STRBUF_INIT;
+			strbuf_addch(&sb, '>');
+			buffer_read_binary(buf, &sb, strtouint32(arg));
+			fwrite(sb.buf, 1, sb.len, stdout);
+			strbuf_release(&sb);
+			return;
+		}
 	case 'c':
 		if (!prefixcmp(command, "copy ")) {
 			buffer_copy_bytes(buf, strtouint32(arg));

vcs-svn/line_buffer.c

@@ -56,6 +56,12 @@ char *buffer_read_string(struct line_buffer *buf, uint32_t len)
 	return ferror(buf->infile) ? NULL : buf->blob_buffer.buf;
 }
 
+void buffer_read_binary(struct line_buffer *buf,
+				struct strbuf *sb, uint32_t size)
+{
+	strbuf_fread(sb, size, buf->infile);
+}
+
 void buffer_copy_bytes(struct line_buffer *buf, uint32_t len)
 {
 	char byte_buffer[COPY_BUFFER_LEN];

vcs-svn/line_buffer.h

@@ -16,6 +16,7 @@ int buffer_init(struct line_buffer *buf, const char *filename);
 int buffer_deinit(struct line_buffer *buf);
 char *buffer_read_line(struct line_buffer *buf);
 char *buffer_read_string(struct line_buffer *buf, uint32_t len);
+void buffer_read_binary(struct line_buffer *buf, struct strbuf *sb, uint32_t len);
 void buffer_copy_bytes(struct line_buffer *buf, uint32_t len);
 void buffer_skip_bytes(struct line_buffer *buf, uint32_t len);
 void buffer_reset(struct line_buffer *buf);