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>

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();
+}