Streaming means that outputs are produced as soon as possible. With the
`foreach` syntax one can write programs which reduce portions of the
streaming parse of a large input (reduce into proper JSON values, for
example), and discard the rest, processing incrementally.
This:
$ jq -c --stream .
should produce the same output as this:
$ jq -c '. as $dot | path(..) as $p | $dot | getpath($p) | [$p,.]'
The output of `jq --stream .` should be a sequence of`[[<path>],<leaf>]`
and `[[<path>]]` values. The latter indicate that the array/object at
that path ended.
Scalars and empty arrays and objects are leaf values for this purpose.
For example, a truncated input produces a path as soon as possible, then
later the error:
$ printf '[0,\n'|./jq -c --stream .
[[0],0]
parse error: Unfinished JSON term at EOF at line 3, column 0
$
If the caller is at EOF and has no more bytes to feed the parser, how is
the parser to be told about the EOF condition? A small fix to allow
zero-length buffers in jv_parser_set_buf() fixes this problem (it also
makes it easier to deal with async I/O: feed the parser whatever is
available, including nothing).
This reverts commit 77936a594d.
There are too many odd bugs in this mode, and it turns out to be a bad
idea anyways. Instead, in the future a better option will be to pursue
alternative parsers, such as:
- streaming parser that outputs only when a new leaf value is added or
an array/object is opened/closed; options here include whether to
include a path in each output;
- parsers for binary JSON encodings (there's a variety of them).
Then one might run jq with a streaming parser and use `reduce` to
coalesce inputs from some depth down (instead of from one level down as
the reverted commit had intended).
Besides, a fully streaming parser is desirable in some cases, therefore
we should have such a thing as an option.
I've explored modifying the current parser to support a streaming
option, but it only makes the code very difficult to follow, which is
one reason that alternate parsers makes sense. At any rate, this is all
for the future. For now there's no streaming of individual texts, just
text sequences.
