Make send/receive-pack be closer to doing something interesting

pkt-line.c

@@ -0,0 +1,117 @@
+#include "cache.h"
+#include "pkt-line.h"
+
+/*
+ * Write a packetized stream, where each line is preceded by
+ * its length (including the header) as a 4-byte hex number.
+ * A length of 'zero' means end of stream (and a length of 1-3
+ * would be an error). 
+ *
+ * This is all pretty stupid, but we use this packetized line
+ * format to make a streaming format possible without ever
+ * over-running the read buffers. That way we'll never read
+ * into what might be the pack data (which should go to another
+ * process entirely).
+ *
+ * The writing side could use stdio, but since the reading
+ * side can't, we stay with pure read/write interfaces.
+ */
+static void safe_write(int fd, const void *buf, unsigned n)
+{
+	while (n) {
+		int ret = write(fd, buf, n);
+		if (ret > 0) {
+			buf += ret;
+			n -= ret;
+			continue;
+		}
+		if (!ret)
+			die("write error (disk full?)");
+		if (errno == EAGAIN || errno == EINTR)
+			continue;
+		die("write error (%s)", strerror(errno));
+	}
+}
+
+/*
+ * If we buffered things up above (we don't, but we should),
+ * we'd flush it here
+ */
+void packet_flush(int fd)
+{
+	safe_write(fd, "0000", 4);
+}
+
+#define hex(a) (hexchar[(a) & 15])
+void packet_write(int fd, const char *fmt, ...)
+{
+	static char buffer[1000];
+	static char hexchar[] = "0123456789abcdef";
+	va_list args;
+	unsigned n;
+
+	va_start(args, fmt);
+	n = vsnprintf(buffer + 4, sizeof(buffer) - 4, fmt, args);
+	va_end(args);
+	if (n >= sizeof(buffer)-4)
+		die("protocol error: impossibly long line");
+	n += 4;
+	buffer[0] = hex(n >> 12);
+	buffer[1] = hex(n >> 8);
+	buffer[2] = hex(n >> 4);
+	buffer[3] = hex(n);
+	safe_write(fd, buffer, n);
+}
+
+static void safe_read(int fd, void *buffer, unsigned size)
+{
+	int n = 0;
+
+	while (n < size) {
+		int ret = read(fd, buffer + n, size - n);
+		if (ret < 0) {
+			if (errno == EINTR || errno == EAGAIN)
+				continue;
+			die("read error (%s)", strerror(errno));
+		}
+		if (!ret)
+			die("unexpected EOF");
+		n += ret;
+	}
+}
+
+int packet_read_line(int fd, char *buffer, unsigned size)
+{
+	int n;
+	unsigned len;
+	char linelen[4];
+
+	safe_read(fd, linelen, 4);
+
+	len = 0;
+	for (n = 0; n < 4; n++) {
+		unsigned char c = linelen[n];
+		len <<= 4;
+		if (c >= '0' && c <= '9') {
+			len += c - '0';
+			continue;
+		}
+		if (c >= 'a' && c <= 'f') {
+			len += c - 'a' + 10;
+			continue;
+		}
+		if (c >= 'A' && c <= 'F') {
+			len += c - 'A' + 10;
+			continue;
+		}
+		die("protocol error: bad line length character");
+	}
+	if (!len)
+		return 0;
+	len -= 4;
+	if (len >= size)
+		die("protocol error: bad line length %d", len);
+	safe_read(fd, buffer, len);
+	buffer[len] = 0;
+	return len;
+}