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![Jeff King](/assets/img/avatar_default.png)
This shows a trace of all packets coming in or out of a given program. This can help with debugging object negotiation or other protocol issues. To keep the code changes simple, we operate at the lowest level, meaning we don't necessarily understand what's in the packets. The one exception is a packet starting with "PACK", which causes us to skip that packet and turn off tracing (since the gigantic pack data will not be interesting to read, at least not in the trace format). We show both written and read packets. In the local case, this may mean you will see packets twice (written by the sender and read by the receiver). However, for cases where the other end is remote, this allows you to see the full conversation. Packet tracing can be enabled with GIT_TRACE_PACKET=<foo>, where <foo> takes the same arguments as GIT_TRACE. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
223 lines
4.5 KiB
C
223 lines
4.5 KiB
C
#include "cache.h"
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#include "pkt-line.h"
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const char *packet_trace_prefix = "git";
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static const char trace_key[] = "GIT_TRACE_PACKET";
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void packet_trace_identity(const char *prog)
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{
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packet_trace_prefix = xstrdup(prog);
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}
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static void packet_trace(const char *buf, unsigned int len, int write)
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{
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int i;
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struct strbuf out;
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if (!trace_want(trace_key))
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return;
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/* +32 is just a guess for header + quoting */
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strbuf_init(&out, len+32);
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strbuf_addf(&out, "packet: %12s%c ",
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packet_trace_prefix, write ? '>' : '<');
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if ((len >= 4 && !prefixcmp(buf, "PACK")) ||
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(len >= 5 && !prefixcmp(buf+1, "PACK"))) {
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strbuf_addstr(&out, "PACK ...");
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unsetenv(trace_key);
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}
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else {
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/* XXX we should really handle printable utf8 */
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for (i = 0; i < len; i++) {
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/* suppress newlines */
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if (buf[i] == '\n')
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continue;
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if (buf[i] >= 0x20 && buf[i] <= 0x7e)
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strbuf_addch(&out, buf[i]);
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else
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strbuf_addf(&out, "\\%o", buf[i]);
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}
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}
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strbuf_addch(&out, '\n');
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trace_strbuf(trace_key, &out);
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strbuf_release(&out);
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}
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/*
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* Write a packetized stream, where each line is preceded by
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* its length (including the header) as a 4-byte hex number.
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* A length of 'zero' means end of stream (and a length of 1-3
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* would be an error).
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*
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* This is all pretty stupid, but we use this packetized line
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* format to make a streaming format possible without ever
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* over-running the read buffers. That way we'll never read
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* into what might be the pack data (which should go to another
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* process entirely).
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*
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* The writing side could use stdio, but since the reading
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* side can't, we stay with pure read/write interfaces.
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*/
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ssize_t safe_write(int fd, const void *buf, ssize_t n)
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{
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ssize_t nn = n;
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while (n) {
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int ret = xwrite(fd, buf, n);
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if (ret > 0) {
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buf = (char *) buf + ret;
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n -= ret;
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continue;
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}
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if (!ret)
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die("write error (disk full?)");
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die_errno("write error");
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}
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return nn;
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}
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/*
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* If we buffered things up above (we don't, but we should),
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* we'd flush it here
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*/
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void packet_flush(int fd)
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{
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packet_trace("0000", 4, 1);
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safe_write(fd, "0000", 4);
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}
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void packet_buf_flush(struct strbuf *buf)
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{
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packet_trace("0000", 4, 1);
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strbuf_add(buf, "0000", 4);
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}
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#define hex(a) (hexchar[(a) & 15])
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static char buffer[1000];
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static unsigned format_packet(const char *fmt, va_list args)
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{
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static char hexchar[] = "0123456789abcdef";
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unsigned n;
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n = vsnprintf(buffer + 4, sizeof(buffer) - 4, fmt, args);
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if (n >= sizeof(buffer)-4)
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die("protocol error: impossibly long line");
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n += 4;
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buffer[0] = hex(n >> 12);
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buffer[1] = hex(n >> 8);
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buffer[2] = hex(n >> 4);
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buffer[3] = hex(n);
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packet_trace(buffer+4, n-4, 1);
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return n;
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}
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void packet_write(int fd, const char *fmt, ...)
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{
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va_list args;
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unsigned n;
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va_start(args, fmt);
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n = format_packet(fmt, args);
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va_end(args);
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safe_write(fd, buffer, n);
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}
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void packet_buf_write(struct strbuf *buf, const char *fmt, ...)
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{
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va_list args;
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unsigned n;
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va_start(args, fmt);
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n = format_packet(fmt, args);
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va_end(args);
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strbuf_add(buf, buffer, n);
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}
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static void safe_read(int fd, void *buffer, unsigned size)
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{
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ssize_t ret = read_in_full(fd, buffer, size);
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if (ret < 0)
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die_errno("read error");
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else if (ret < size)
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die("The remote end hung up unexpectedly");
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}
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static int packet_length(const char *linelen)
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{
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int n;
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int len = 0;
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for (n = 0; n < 4; n++) {
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unsigned char c = linelen[n];
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len <<= 4;
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if (c >= '0' && c <= '9') {
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len += c - '0';
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continue;
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}
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if (c >= 'a' && c <= 'f') {
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len += c - 'a' + 10;
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continue;
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}
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if (c >= 'A' && c <= 'F') {
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len += c - 'A' + 10;
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continue;
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}
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return -1;
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}
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return len;
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}
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int packet_read_line(int fd, char *buffer, unsigned size)
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{
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int len;
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char linelen[4];
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safe_read(fd, linelen, 4);
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len = packet_length(linelen);
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if (len < 0)
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die("protocol error: bad line length character: %.4s", linelen);
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if (!len) {
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packet_trace("0000", 4, 0);
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return 0;
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}
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len -= 4;
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if (len >= size)
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die("protocol error: bad line length %d", len);
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safe_read(fd, buffer, len);
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buffer[len] = 0;
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packet_trace(buffer, len, 0);
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return len;
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}
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int packet_get_line(struct strbuf *out,
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char **src_buf, size_t *src_len)
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{
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int len;
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if (*src_len < 4)
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return -1;
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len = packet_length(*src_buf);
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if (len < 0)
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return -1;
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if (!len) {
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*src_buf += 4;
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*src_len -= 4;
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packet_trace("0000", 4, 0);
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return 0;
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}
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if (*src_len < len)
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return -2;
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*src_buf += 4;
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*src_len -= 4;
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len -= 4;
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strbuf_add(out, *src_buf, len);
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*src_buf += len;
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*src_len -= len;
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packet_trace(out->buf, out->len, 0);
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return len;
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}
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