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

[git.git] / pkt-line.c

diff --git a/pkt-line.c b/pkt-line.c
new file mode 100644 (file)
index 0000000..6947304
--- /dev/null
+++ b/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;
+}