librsync  2.3.4
tube.c
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1 /*= -*- c-basic-offset: 4; indent-tabs-mode: nil; -*-
2  *
3  * librsync -- dynamic caching and delta update in HTTP
4  *
5  * Copyright (C) 2000, 2001 by Martin Pool <mbp@sourcefrog.net>
6  *
7  * This program is free software; you can redistribute it and/or modify
8  * it under the terms of the GNU Lesser General Public License as published by
9  * the Free Software Foundation; either version 2.1 of the License, or
10  * (at your option) any later version.
11  *
12  * This program is distributed in the hope that it will be useful,
13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15  * GNU Lesser General Public License for more details.
16  *
17  * You should have received a copy of the GNU Lesser General Public License
18  * along with this program; if not, write to the Free Software
19  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
20  */
21 
22  /*=
23  | Where a calculator on the ENIAC is
24  | equpped with 18,000 vaccuum tubes and
25  | weighs 30 tons, computers in the
26  | future may have only 1,000 vaccuum
27  | tubes and perhaps weigh 1 1/2
28  | tons.
29  | -- Popular Mechanics, March 1949
30  */
31 
32 /** \file tube.c
33  * A somewhat elastic but fairly small buffer for data passing through a
34  * stream.
35  *
36  * In most cases the iter can adjust to send just as much data will fit. In
37  * some cases that would be too complicated, because it has to transmit an
38  * integer or something similar. So in that case we stick whatever won't fit
39  * into a small buffer.
40  *
41  * A tube can contain some literal data to go out (typically command bytes),
42  * and also an instruction to copy data from the stream's input or from some
43  * other location. Both literal data and a copy command can be queued at the
44  * same time, but only in that order and at most one of each.
45  *
46  * \todo As an optimization, write it directly to the stream if possible. But
47  * for simplicity don't do that yet.
48  *
49  * \todo I think our current copy code will lock up if the application only
50  * ever calls us with either input or output buffers, and not both. So I guess
51  * in that case we might need to copy into some temporary buffer space, and
52  * then back out again later. */
53 
54 #include "config.h" /* IWYU pragma: keep */
55 #include <assert.h>
56 #include <stdlib.h>
57 #include <string.h>
58 #include "librsync.h"
59 #include "job.h"
60 #include "scoop.h"
61 #include "trace.h"
62 
63 static void rs_tube_catchup_write(rs_job_t *job)
64 {
65  rs_buffers_t *stream = job->stream;
66  size_t len = job->write_len;
67 
68  assert(len > 0);
69  if (len > stream->avail_out)
70  len = stream->avail_out;
71  if (len) {
72  memcpy(stream->next_out, job->write_buf, len);
73  stream->next_out += len;
74  stream->avail_out -= len;
75  job->write_len -= len;
76  if (job->write_len > 0)
77  /* Still something left in the tube, shuffle it to the front. */
78  memmove(job->write_buf, job->write_buf + len, job->write_len);
79  }
80  rs_trace("wrote " FMT_SIZE " bytes from tube, " FMT_SIZE " left to write",
81  len, job->write_len);
82 }
83 
84 /** Catch up on an outstanding copy command.
85  *
86  * Takes data from the scoop and writes as much as will fit to the output, up
87  * to the limit of the outstanding copy. */
88 static void rs_tube_catchup_copy(rs_job_t *job)
89 {
90  assert(job->write_len == 0);
91  assert(job->copy_len > 0);
92  rs_buffers_t *stream = job->stream;
93  size_t copy_len = job->copy_len;
94  size_t avail_in = rs_scoop_avail(job);
95  size_t avail_out = stream->avail_out;
96  size_t len, ilen;
97  void *next;
98 
99  if (copy_len > avail_in)
100  copy_len = avail_in;
101  if (copy_len > avail_out)
102  copy_len = avail_out;
103  len = copy_len;
104  for (next = rs_scoop_iterbuf(job, &len, &ilen); ilen > 0;
105  next = rs_scoop_nextbuf(job, &len, &ilen)) {
106  memcpy(stream->next_out, next, ilen);
107  stream->next_out += ilen;
108  stream->avail_out -= ilen;
109  job->copy_len -= ilen;
110  }
111  rs_trace("copied " FMT_SIZE " bytes from scoop, " FMT_SIZE
112  " left in scoop, " FMT_SIZE " left to copy", copy_len,
113  rs_scoop_avail(job), job->copy_len);
114 }
115 
116 /** Put whatever will fit from the tube into the output of the stream.
117  *
118  * \return RS_DONE if the tube is now empty and ready to accept another
119  * command, RS_BLOCKED if there is still stuff waiting to go out. */
121 {
122  if (job->write_len) {
123  rs_tube_catchup_write(job);
124  if (job->write_len)
125  return RS_BLOCKED;
126  }
127 
128  if (job->copy_len) {
130  if (job->copy_len) {
131  if (rs_scoop_eof(job)) {
132  rs_error("reached end of file while copying data");
133  return RS_INPUT_ENDED;
134  }
135  return RS_BLOCKED;
136  }
137  }
138  return RS_DONE;
139 }
140 
141 /* Check whether there is data in the tube waiting to go out.
142 
143  \return true if the previous command has finished doing all its output. */
144 int rs_tube_is_idle(rs_job_t const *job)
145 {
146  return job->write_len == 0 && job->copy_len == 0;
147 }
148 
149 /** Queue up a request to copy through \p len bytes from the input to the
150  * output of the stream.
151  *
152  * The data is copied from the scoop (if there is anything there) or from the
153  * input, on the next call to rs_tube_write().
154  *
155  * We can only accept this request if there is no copy command already pending.
156  *
157  * \todo Try to do the copy immediately, and return a result. Then, people can
158  * try to continue if possible. Is this really required? Callers can just go
159  * out and back in again after flushing the tube. */
160 void rs_tube_copy(rs_job_t *job, size_t len)
161 {
162  assert(job->copy_len == 0);
163 
164  job->copy_len = len;
165 }
166 
167 /** Push some data into the tube for storage.
168  *
169  * The tube's never supposed to get very big, so this will just pop loudly if
170  * you do that.
171  *
172  * We can't accept write data if there's already a copy command in the tube,
173  * because the write data comes out first. */
174 void rs_tube_write(rs_job_t *job, const void *buf, size_t len)
175 {
176  assert(job->copy_len == 0);
177  assert(len <= sizeof(job->write_buf) - job->write_len);
178 
179  memcpy(job->write_buf + job->write_len, buf, len);
180  job->write_len += len;
181 }
Generic state-machine interface.
Public header for librsync.
rs_result
Return codes from nonblocking rsync operations.
Definition: librsync.h:180
@ RS_DONE
Completed successfully.
Definition: librsync.h:181
@ RS_INPUT_ENDED
Unexpected end of input file, perhaps due to a truncated file or dropped network connection.
Definition: librsync.h:190
@ RS_BLOCKED
Blocked waiting for more data.
Definition: librsync.h:182
Manage librsync streams of IO.
static void * rs_scoop_iterbuf(rs_job_t *job, size_t *len, size_t *ilen)
Iterate through and consume contiguous data buffers in the scoop.
Definition: scoop.h:165
static void * rs_scoop_nextbuf(rs_job_t *job, size_t *len, size_t *ilen)
Get the next iteration of contiguous data buffers from the scoop.
Definition: scoop.h:175
static bool rs_scoop_eof(rs_job_t *job)
Test if the scoop has reached eof.
Definition: scoop.h:100
Description of input and output buffers.
Definition: librsync.h:328
size_t avail_out
Remaining free space at next_out.
Definition: librsync.h:357
char * next_out
Next output byte should be put there.
Definition: librsync.h:351
The contents of this structure are private.
Definition: job.h:47
size_t copy_len
If copy_len is >0, then that much data should be copied through from the input.
Definition: job.h:114
rs_byte_t write_buf[36]
If USED is >0, then buf contains that much write data to be sent out.
Definition: job.h:109
logging functions.
void rs_tube_write(rs_job_t *job, const void *buf, size_t len)
Push some data into the tube for storage.
Definition: tube.c:174
static void rs_tube_catchup_copy(rs_job_t *job)
Catch up on an outstanding copy command.
Definition: tube.c:88
rs_result rs_tube_catchup(rs_job_t *job)
Put whatever will fit from the tube into the output of the stream.
Definition: tube.c:120
void rs_tube_copy(rs_job_t *job, size_t len)
Queue up a request to copy through len bytes from the input to the output of the stream.
Definition: tube.c:160