+/* Read a hunk of data from FD, up until a terminator. The hunk is
+ limited by whatever the TERMINATOR callback chooses as its
+ terminator. For example, if terminator stops at newline, the hunk
+ will consist of a line of data; if terminator stops at two
+ newlines, it can be used to read the head of an HTTP response.
+ Upon determining the boundary, the function returns the data (up to
+ the terminator) in malloc-allocated storage.
+
+ In case of read error, NULL is returned. In case of EOF and no
+ data read, NULL is returned and errno set to 0. In case of having
+ read some data, but encountering EOF before seeing the terminator,
+ the data that has been read is returned, but it will (obviously)
+ not contain the terminator.
+
+ The TERMINATOR function is called with three arguments: the
+ beginning of the data read so far, the beginning of the current
+ block of peeked-at data, and the length of the current block.
+ Depending on its needs, the function is free to choose whether to
+ analyze all data or just the newly arrived data. If TERMINATOR
+ returns NULL, it means that the terminator has not been seen.
+ Otherwise it should return a pointer to the charactre immediately
+ following the terminator.
+
+ The idea is to be able to read a line of input, or otherwise a hunk
+ of text, such as the head of an HTTP request, without crossing the
+ boundary, so that the next call to fd_read etc. reads the data
+ after the hunk. To achieve that, this function does the following:
+
+ 1. Peek at incoming data.
+
+ 2. Determine whether the peeked data, along with the previously
+ read data, includes the terminator.
+
+ 2a. If yes, read the data until the end of the terminator, and
+ exit.
+
+ 2b. If no, read the peeked data and goto 1.
+
+ The function is careful to assume as little as possible about the
+ implementation of peeking. For example, every peek is followed by
+ a read. If the read returns a different amount of data, the
+ process is retried until all data arrives safely.
+
+ SIZEHINT is the buffer size sufficient to hold all the data in the
+ typical case (it is used as the initial buffer size). MAXSIZE is
+ the maximum amount of memory this function is allowed to allocate,
+ or 0 if no upper limit is to be enforced.
+
+ This function should be used as a building block for other
+ functions -- see fd_read_line as a simple example. */
+
+char *
+fd_read_hunk (int fd, hunk_terminator_t terminator, long sizehint, long maxsize)
+{
+ long bufsize = sizehint;
+ char *hunk = xmalloc (bufsize);
+ int tail = 0; /* tail position in HUNK */
+
+ assert (maxsize >= bufsize);
+
+ while (1)
+ {
+ const char *end;
+ int pklen, rdlen, remain;
+
+ /* First, peek at the available data. */
+
+ pklen = fd_peek (fd, hunk + tail, bufsize - 1 - tail, -1);
+ if (pklen < 0)
+ {
+ xfree (hunk);
+ return NULL;
+ }
+ end = terminator (hunk, hunk + tail, pklen);
+ if (end)
+ {
+ /* The data contains the terminator: we'll drain the data up
+ to the end of the terminator. */
+ remain = end - (hunk + tail);
+ assert (remain >= 0);
+ if (remain == 0)
+ {
+ /* No more data needs to be read. */
+ hunk[tail] = '\0';
+ return hunk;
+ }
+ if (bufsize - 1 < tail + remain)
+ {
+ bufsize = tail + remain + 1;
+ hunk = xrealloc (hunk, bufsize);
+ }
+ }
+ else
+ /* No terminator: simply read the data we know is (or should
+ be) available. */
+ remain = pklen;
+
+ /* Now, read the data. Note that we make no assumptions about
+ how much data we'll get. (Some TCP stacks are notorious for
+ read returning less data than the previous MSG_PEEK.) */
+
+ rdlen = fd_read (fd, hunk + tail, remain, 0);
+ if (rdlen < 0)
+ {
+ xfree_null (hunk);
+ return NULL;
+ }
+ tail += rdlen;
+ hunk[tail] = '\0';
+
+ if (rdlen == 0)
+ {
+ if (tail == 0)
+ {
+ /* EOF without anything having been read */
+ xfree (hunk);
+ errno = 0;
+ return NULL;
+ }
+ else
+ /* EOF seen: return the data we've read. */
+ return hunk;
+ }
+ if (end && rdlen == remain)
+ /* The terminator was seen and the remaining data drained --
+ we got what we came for. */
+ return hunk;
+
+ /* Keep looping until all the data arrives. */
+
+ if (tail == bufsize - 1)
+ {
+ /* Double the buffer size, but refuse to allocate more than
+ MAXSIZE bytes. */
+ if (maxsize && bufsize >= maxsize)
+ {
+ xfree (hunk);
+ errno = ENOMEM;
+ return NULL;
+ }
+ bufsize <<= 1;
+ if (maxsize && bufsize > maxsize)
+ bufsize = maxsize;
+ hunk = xrealloc (hunk, bufsize);
+ }
+ }
+}
+
+static const char *
+line_terminator (const char *start, const char *peeked, int peeklen)
+{
+ const char *p = memchr (peeked, '\n', peeklen);
+ if (p)
+ /* p+1 because the line must include '\n' */
+ return p + 1;
+ return NULL;
+}
+
+/* The maximum size of the single line we agree to accept. This is
+ not meant to impose an arbitrary limit, but to protect the user
+ from Wget slurping up available memory upon encountering malicious
+ or buggy server output. Define it to 0 to remove the limit. */
+#define FD_READ_LINE_MAX 4096
+
+/* Read one line from FD and return it. The line is allocated using
+ malloc, but is never larger than FD_READ_LINE_MAX.
+
+ If an error occurs, or if no data can be read, NULL is returned.
+ In the former case errno indicates the error condition, and in the
+ latter case, errno is NULL. */
+